Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jfca.2023.105627

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Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.chroma.2023.464247

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acsomega.2c08138

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Pleiades Publishing Ltd  

DOI： 10.1134/s1061934823010033

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Other Link： https://link.springer.com/article/10.1134/S1061934823010033/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Academy of Science of South Africa  

A simple, fast, low-cost and sensitive microfluidic paper-based analytical device (u-PADs) integrated with the co-precipitation enrichment procedure was developed to analyse Ni(II) in tap and mineral water samples. The impacting factors, including pH, centrifugation (5 min at 4000 rpm), and amounts of reagents were optimized. The limit of detection of 0.009 mg L-1 and linear range of 0.03-2.00 mg L-1 were achieved with good intra- and inter-day precision (4.7 and 5.6% RSD, respectively). The recovery tests were conducted by spiking tap and mineral water samples and analyzed using the u-PADs after co-precipitation enrichment. The results obtained by the proposed method were validated by inductively coupled plasma-optical emission spectrometry (ICP-OES). The recoveries of the present method and ICP-OES were ranged from 92.4-106.8% and 92.9-97.2%, respectively. The two sets of (u-PADs and ICP-OES) results were in good agreement, as a paired t-test indicated no significant differences. The proposed method could be utilized for analyzing trace levels of Ni(II) in water samples in developing countries where the availability of conventional analytical instruments are significant problems.

DOI： 10.17159/0379-4350/2023/v77a01

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Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s44211-022-00207-2

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Other Link： https://link.springer.com/article/10.1007/s44211-022-00207-2/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)  

A microfluidic paper-based analytical device (µ-PAD) is a promising new technology platform for the development of extremely low-cost sensing devices. However, it has low sensitivity that might not enable to measure maximum allowable concentration of various pollutants in the environment. In this study, a dispersive liquid-liquid microextraction (DLLME) was developed as a preconcentration method to enhance the sensitivity of the µ-PAD for trace analysis of selected pesticides. Four critical parameters (volume of n-hexane and acetone, extraction time, NaCl amount) that affect the efficiency of DLLME have been optimized using response surface methodology. An acceptable mean recovery of 79-97% and 83-93% was observed at 1 µg L-1 and 5 µg L-1 fortification level, respectively, with very good repeatability (2.2-6.01% RSD) and reproducibility (5.60-10.41% RSD). Very high enrichment factors ranging from 317 to 1471 were obtained. The limits of detection for the studied analytes were in the range of 0.18-0.41 µg L-1 which is much lower than the WHO limits of 5-50 µg L-1 for similar category of analytes. Therefore, by coupling DLLME with µ-PAD, a sensitivity that allows to detect environmental threat and also that surpassed most of the previous reports have been achieved in this study. This implies that the preconcentration step has a paramount contribution to address the sensitivity problem associated with µ-PAD.

DOI： 10.1007/s44211-022-00167-7

PubMed

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Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

A paper-based device (PAD) capable of colorimetric detection was developed to determine the presence of glutamate in various food samples. The PAD employs an enzymatic reaction with glutamate followed by an oxidation reaction with N-benzoyl leucomethylene blue (BLMB) in the presence of horseradish peroxidase. The designed PAD consists of a sample introduction zone connected to a channel that transports a sample solution to three detection zones. The detection zones contain pre-deposited reagents: glutamate oxidase, horseradish peroxidase, BLMB, a phosphate buffer, and poly(acrylic acid). The PAD is perpendicularly immersed into a sample solution and bent at a right angle using a 3D-printed holder to allow the sample to simultaneously flow into three different detection zones. When the PAD is immersed into a sample containing glutamate, glutamate oxidase produces hydrogen peroxide, which changes the pale blue color of BLMB to a deep blue color in the presence of horseradish peroxidase. Under the optimum conditions, the calibration curve between the logarithm of the glutamate concentrations and the color intensity was linear within a range of from 5 × 10-6 mol L-1 to 10-2 and with a correlation coefficient of 0.994. Using this system, the PAD successfully determined glutamate in soup stocks, sauces, snacks, and tomato juice without the need of complicated sample pretreatment. These results agreed with those of a commercially available glutamate assay kit, which was employed as a certification method (tstat = 1.95, tcrit = 2.57). The developed PAD is simple, easy to fabricate, portable, and could be used outside of equipped laboratories to determine the presence of glutamate in food samples.

DOI： 10.1016/j.microc.2022.107513

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Language：English   Publishing type：Research paper (scientific journal)  

Microfluidic paper-based analytical devices (μ-PADs) are a new technology platform for the development of extremely low-cost sensing applications. In this study, μ-PADs has been developed for quantitative determination of carbamate pesticides. Key experimental parameters including concentration and volume of acetylcholinesterase, acetylthiocholine iodide and 5,5'-dithiobis-(2-nitrobenzoic acid), incubation time and image capturing time were systematically optimized. Under optimal conditions, the method showed wide range of linearity (0.25-16 mg/L), repeatability (4%-5% RSD) and intermediate precision (7%-10% RSD). Limit of detection was observed to be 0.4, 0.24 and 0.46 mg/L for carbaryl, carbosulfan and furathiocarb, respectively. An acceptable mean recovery (87% to 94%) was observed for the three pesticides at 1 mg/L fortification level. The results reveal that the developed method requires minimal reagents, simple and is easy to handle. It can be used for the quantification of carbamate pesticides in resource limited laboratories without the need for the conventional analytical instruments.

DOI： 10.1007/s00128-022-03533-3

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We developed an organic solvent-compatible paper-based analytical device (PAD) for the quantitative analysis of indole, which is an indicator of shrimp freshness. Although indole is insoluble in water, ethyl acetate is a suitable solvent to dissolve and extract indole from shrimp. The PADs are fabricated using a cutting method that allows the use of an organic solvent because no hydrophobic barrier is needed to form fluidic channels. Ehrlich's reagent consists of 4-(dimethylamino)benzaldehyde and p-dimethylaminobenzaldehyde and was deposited onto the reaction zone of the PAD followed by lamination to prevent evaporation of the ethyl acetate. Samples are introduced into the PAD via immersion in organic sample solutions. When the PAD is immersed into an indole solution of ethyl acetate in a closed bottle, the sample solution penetrates the channel of the PAD and successively flows into the detection zone to form a hydrophilic colored product. The PADs provide a linear relationship between the logarithm of the indole concentration and the color intensity within a range of 1.0-20 ppm with correlation coefficients of r2 > 0.99. The limits of detection and quantification are 0.36 and 0.71 ppm, respectively. Relative standard deviations for both the intraday (n = 2) and interday (n = 3) precision were less than 2.5%. In the indole analysis of shrimp, the PADs separated the interfering orange-colored astaxanthin in the extract from the colored product of indole via the paper chromatographic principle. We used the PADs to investigate the degradation of shrimp, and the results showed a rapid increase in the indole level after 7 days. High-performance liquid chromatography verified the accuracy of the PADs by showing good agreement with the obtained indole levels.

DOI： 10.1021/acssensors.2c00300

PubMed

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Horseradish peroxidase (HRP) is an enzyme that is frequently employed in various assays because HRP catalyzes the oxidation reactions of chromogenic and fluorogenic compounds to produce chromophores and fluorophores, respectively. The results of this study show that N-benzoyl leucomethylene blue (BLMB) is an excellent substrate for enzyme assay using HRP. In the presence of hydrogen peroxide (H2O2), HRP catalyzed an oxidation reaction of BLMB that produced methylene blue with a deep blue color. Thus, absorption spectrophotometry and capillary electrophoresis-laser-induced fluorometry (CE-LIF) could be used to easily determine the produced methylene blue. Under the optimum conditions, absorption spectrophotometry showed a linear calibration curve that ranged from 25 to 500 µg mL-1. The reaction conditions were also applicable to CE-LIF, showing a linear range of from 25 to 500 µg mL-1 with limits of detection and quantification at 2 and 6 µg mL-1, respectively.

DOI： 10.1007/s44211-022-00078-7

PubMed

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The present study focused on improving sensitivity to trace levels of Cu(II) by subjecting microfluidic paper-based analytical devices (μ-PADs) to a preconcentration process via coprecipitation using aluminum hydroxide. The experimental conditions were optimized for the pH of the coprecipitation, centrifugation, and amounts of reagents that were deposited onto µ-PADs for the Cu(II) assay. The resultant limit of detection reached as low as 0.003 mg L-1 with a linear range of 0.01-2.00 mg L-1. The relative standard deviations for intra- and inter-day precision were 3.2 and 4.6%, respectively (n = 9). Spiked water samples were analyzed using the μ-PADs after coprecipitation preconcentration. The results were verified by comparing them with those of inductively coupled plasma-optical emission spectrometry (ICP-OES). Recoveries ranged from 97.1 to 104% and from 98.7 to 105% using the present method and ICP-OES, respectively. These results suggest that the simple, highly sensitive, and inexpensive proposed method would be helpful for analyzing trace levels of Cu(II) in water samples in poorly equipped laboratories.

DOI： 10.2116/analsci.21P215

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Here we describe a methodology for the determination of paraquat and diquat using a newly developed portable photometer equipped with two colors of paired light emitter detector diodes (PEDD). The colorimetric measurements employed in this work include the redox reactions between 1) dithiothreitol and diquat to produce the red color characteristic of a diquat radical and 2) between sodium dithionite and either diquat or paraquat that results in the green and blue colors of diquat and paraquat radicals, respectively. The addition of sodium dithionite or dithiothreitol in a solid-state provides reproducible absorbance of the radicals, prevents decomposition of the reagents in a solution, and simplifies handling of the reagents. The diquat radical produced by dithiothreitol (λmax = 495 nm) was successfully detected by using a pair of blue LEDs with a maximum emission wavelength at 472 nm while the radicals of paraquat (λmax = 603 nm) and diquat (λmax = 771 nm) reduced by sodium dithionite were measured by a pair of orange LEDs with a maximum emission wavelength of 609 nm. The proposed method consists of measuring diquat radicals at 472 nm, estimating the absorbance of diquat radicals at 609 nm, and subtracting the estimated absorbance of diquat radicals from the total absorbance at 609 nm to determine paraquat radicals. The developed method yielded examples of excellent linear regression (r2) of more than 0.99 in three calibration curves of the radicals measured at 472 nm for diquat radicals and measured at 609 nm for both diquat and paraquat radicals. The intra-day (n = 3) and inter-day (n = 3) precision of three calibration curves were less than or equal to 5%. By comparison with the standard method of high-performance liquid chromatography, the reliability of the proposed method was proven via the analysis of paraquat and diquat radicals in a commercially available herbicide.

DOI： 10.1016/j.microc.2021.106777

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER HEIDELBERG  

Speciation of chromium (Cr) was demonstrated using microfluidic paper-based analytical devices (mu-PADs) that permit the colorimetric determination of hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)) via online oxidation. The mu-PADs consist of left and right channels that allow the simultaneous measurements of Cr(VI) and total Cr based on the colorimetric reaction of Cr(VI) with 1,5-diphenylcarbazide (DPC). For the determination of Cr(VI), a sample solution was directly reacted with DPC in the left channels whereas total Cr was determined in the right channels, which permitted online oxidation in the pretreatment zone containing cerium (IV) (Ce(IV)) followed by a colorimetric reaction with DPC. We found that the online oxidation of Cr(III) proceeded 100% whereas Ce(IV) inhibited the reaction of Cr(VI) with DPC. Therefore, speciation can be achieved by measuring the Cr(VI) and total Cr in the left and right channels followed by the subtraction of Cr(VI) from total Cr. The limits of detection and quantification were 0.008 and 0.02 mg L-1 for Cr(VI) and 0.07 and 0.1 mg L-1 for Cr(III) or total Cr, respectively. The linear dynamic ranges were 0.02-100 mg L-1 and 0.1-60 mg L-1 for Cr(VI) and Cr(III), respectively. The RSDs were less than 7.5%. The results obtained using mu-PADs were in good agreement with those obtained via ICP-OES with recoveries of 92-108% for Cr(III) and 108-110% for Cr (VI) using mu-PADs, and 106-110% for total Cr using ICP-OES. Thus, the mu-PADs could potentially be utilized for the speciation of chromium in developing countries where environmental pollution and the availability of sophisticated instruments are significant problems.

DOI： 10.1007/s00216-021-03274-y

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society for Analytical Chemistry  

DOI： 10.2116/analsci.20p325

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Seventeen inorganic and organic anions, that normally are insufficiently separated via ion chromatography, were completely separated by the addition of an organic solvent to a solution of BGE combined with an adjustment of the apparent pH via CE in combination with indirect UV absorbance detection. Methanol, ethanol, and acetonitrile were examined for their utility in manipulating the selective separation of anions. Methanol and acetonitrile were better modifiers than ethanol at enhancing the resolution of anions comigrating in an aqueous solution of BGE. Methanol was selected as the modifier that provided the largest separation window that could achieve a complete separation of the target analytes. Via the use of methanol, manipulation of the selectivity between inorganic anions and that between inorganic and organic anions was enhanced, but the separation between organic anions remained difficult when only methanol was used. By varying the apparent pH of the BGE in the presence of 10% v/v methanol, however, the separation selectivity between organic anions was substantially improved. Eventually, 7 inorganic and 10 organic anions were simultaneously separated using BGE at a pH of 6.3 in the presence of 10% v/v methanol.

DOI： 10.1002/elps.202100014

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Extracellular vesicles (EVs) exist in biological fluids such as blood, urine, and cerebrospinal fluid, and these have shown promise for use as biomarkers of cancers. Conventional methods for determination of EVs include direct detection via enzyme-linked immunosorbent assay and detection of their membrane proteins via western blotting. These techniques, however, have individual shortcomings in terms of the need for large sample consumption, processes that are time-consuming, and a lack of the capacity for quantification. In this study, we developed a method to determine the EV membrane protein, CD63, by coupling capillary electrophoresis immunoassay with laser-induced fluorescence (CEIA-LIF). In this process, the EVs were isolated from a culture medium and were subsequently reacted with a fluorescently labeled anti-CD63 antibody to form a CD63 complex localized on the surface of EVs. After removing the EVs containing the CD63 immune complex by centrifugation, the supernatant containing the free fluorescent antibody was injected into a capillary to serve as a sample. A decrease in the peak area of the free fluorescent antibody became apparent when the amount of EVs was increased while that of the fluorescent antibody remained constant. The peak areas were decreased proportionally against the increased amounts of EVs. The concentration of the CD63 could then be estimated based on the slope of the linear relationship. This study is the first to quantify CD63 immobilized on EVs via CEIA-LIF, which is a novel method with the potential to determine membrane proteins localized on the surface of EVs. (c) 2020 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2020.461513

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This work describes a methodology that can be used to achieve on-site analysis of paraquat in water samples by using a miniaturized portable photometer consisting of a couple of light-emitting diodes (LEDs). Paraquat produces a colored radical via a redox reaction with sodium dithionite, which is unstable against oxygen in solution. The steps taken to stabilize the reagent solution included control of the pH and the addition of organic solvents, but the most effective was the formation of an oil layer. Together, these steps stabilized the reagent solution for two days. An increase in the duration of reagent stability, however, is necessary in order to transport the reagent for on-site applications in remote locales. For the time being, an excess amount of solid sodium dithionite can be added directly to sample solutions because the unreacted dithionite shows no influence on absorbance of the paraquat radical. Orange LEDs with a maximum emission wavelength of 609 nm were employed in the portable photometer to measure the absorbance of paraquat radical produced by a redox reaction that has an absorption maximum of 603 nm. The developed photometer showed excellent performance with a linear range of from 2.0 mg L-1 to 40.0 mg L-1 and a linear regression (r(2) = 1). The limits of detection and quantification were 0.5 mg L-1 and 1.5 mg L-1, respectively, intra-day precision (n = 3) and inter-day precision (n = 5) were both less than 5%, and accuracy based on the percentage of sample recovery ranged from 89 +/- 0 to 105 +/- 0% (n = 3). The proposed method was applied to the analysis of paraquat in water samples taken from rice fields. The results showed no paraquat in all thirteen samples, which could have been due to strong adsorption of paraquat by soil particles and/or to complications with the sampling conditions. To confirm the adsorption onto soil of paraquat contained in water, we constructed an artificial rice field where water containing paraquat was impounded above the soil layer. The results showed that paraquat in water gradually decreased within three days and could be measured in the soil on the fourth day. These results were confirmed by HPLC analysis, which underscores the utility of this portable photometer for the on-site monitoring of paraquat in water samples. (C) 2020 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.aca.2020.08.051

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Language：English   Publisher：ELSEVIER  

The pretreatment of carbonaceous material in double refractory gold ores (DRGO) is necessary to decrease pregrobbing of gold and maximize gold recovery. DRGO contains of carbonaceous matter and gold grains encapsulated in sulfide minerals, which typically results in very poor gold recovery. However, there is growing interest in DRGO because some estimates show that it makes up about a third of the total available gold for production by mining. This can be achieved by chemical and biological techniques, however, the chemical techniques like flotation, surface passivation and chemical oxidation have received more extensive study and either have to be retooled or modified to be applied to the carbonaceous matter in the DRGO. In comparison, the biological techniques are relatively unknown with significant gaps in the knowledge about the bio-treatment mechanism, byproducts and avenues for scaling up like bioreactor design. This study reviews the enzymatic pretreatment of DRGO to facilitate gold recovery and minimize reagent consumption. It focuses on the potential for application of oxidative enzymes like lignin peroxidase, manganese peroxidase and laccase to pretreat carbonaceous matter in DRGO with or without an additional step of sulfide oxidation and addresses characterization of byproducts of the enzymatic decomposition. Further, potential bioreactor configurations for the enzymatic decomposition without direct contact of ore with microorganisms are considered, both in terms of understanding the mechanisms within the pretreatment and in terms of application.

DOI： 10.1016/j.hydromet.2020.105434

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Exosomes are expected to be biomarkers of cancer since they contain information about the cells that excrete them. In this study we developed a method to count the exosomes secreted from cancer cells in a culture medium without the need for isolation and/or preconcentration. This detection system consists of a square capillary on which a laser beam is focused in a sheet shape via the use of two cylindrical lenses. A fluorescently labeled anti-CD63 antibody is used to mark the exosomes that are then flowed into the square capillary. In this study, individual exosomes were observed on a trajectory when passing through the laser beam sheet and were counted for 10 min at a constant flow velocity. The total analysis time was less than 1.5 h including the steps required to remove large particles and allow reaction with the antibody. The results for two samples prepared with and without the isolation of exosomes showed a loss of exosomes in the isolation step. We also determined the number of the exosomes secreted by the cells to a culture medium during cultivation. As expected, the total number of exosomes in a culture medium increased with an increase in the cultivation time, and the number of exosomes released every 12 h either remained constant or showed no more than a slight increase for as long as 72 h. It was unclear whether the number exosomes was dependent on the cell population at confluences of 10-60%. (C) 2020 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.aca.2020.04.052

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Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

We demonstrated the utility of optical pressure in the manipulation of oil droplets and vesicles in the field of analytical chemistry. In order to realize chemical analysis in a limited small space, a method to capture and coalesce two oil droplets was developed using two laser beams. Three types of stabilizers for the formation of oil droplets were explored to achieve the coalescence of two droplets whereas polyethylene glycol (PEG) was the most suitable one among them. When using the oil droplets with PEG, the increase in temperature of the medium induced successful coalescence of two droplets. We also developed a method to collect liposomes, which are a model of artificial extracellular vesicles, using optical pressure. It was found that the collection efficiency was significantly improved by adding gold nanoparticles into the solution. This effect is due to thermal convection induced by the optical absorption of gold nanoparticles in solution and an enhancement of the optical pressure caused by binding between the vesicles and the gold nanoparticles. It was also elucidated that the binding was strongly related to the electrostatic interaction in addition to the hydrophobic interaction. Based on these findings, we achieved the collection of nanometer-sized vesicles and exosomes released by cells by optical pressure.

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A simple, small and inexpensive photometer that uses a pair of light-emitting diodes (LEDs) and a simple operational amplifier was developed for investigating thiocyanate levels in saliva obtained from smokers and nonsmokers. The photometer is based on paired emitter-detector diodes (PEDDs), and the entire system can be purchased for less than a hundred US dollars. The PEDD-based photometer can measure the transmittance of a solution in a 1-cm disposable polystyrene cuvette using only rechargeable dry-cell batteries, which makes it suitable for analysis outside of equipped laboratories. The metal complex formation between Fe (III) and thiocyanate ions in an acidic condition permits colorimetric detection of thiocyanate ions using LEDs emitting at 465 nm, because the complex shows maximum absorption at 457 nm. The developed photometer exhibits excellent performance with linearity ranging from 0.05 mmol L-1 to 0.75 mmol L-1 and a correlation coefficient (r(2)) > 0.999. The limits of detection and quantification were 0.01 mmol L-1 and 0.05 mmol L-1, respectively. Both intra-and inter-day precision were obtained with relative standard deviations (RSD) of less than 1% in the determination of thiocyanate. The proposed method is simple, facile, and sensitive enough to investigate the levels of thiocyanate in the saliva samples of smokers and non-smokers with centrifugation being the only special treatment for samples. The results showed that the concentrations of thiocyanate were approximately 5-fold higher in smokers than in non-smokers.

DOI： 10.1016/j.talanta.2019.06.024

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER  

In this study, we developed and compared three different methods for chromium speciation in water samples using microfluidic paper-based analytical devices (mu PADs). In all methods, detection was based on the complexation reaction of Cr(VI) with diphenylcarbazide on the mu PADs. Cr(III) ions were oxidized to Cr(VI) by Ce(IV) prior to colorimetric detection on the RADs. In the first method, oxidization of Cr(III) to Cr(VI) in the solution containing both trivalent and hexavalent chromium was performed using a batch procedure to obtain total chromium. A dual electromembrane extraction (DEME) technique for simultaneous preconcentration and extraction of chromium species and a single electromembrane extraction (SEME) for preconcentration and extraction of Cr(VI)/total chromium [quantified as Cr(VI) content after oxidation of Cr(III) ions to Cr(VI)] were used in the second and third methods, respectively. The electromembrane extraction was based on the electrokinetic migration of cationic Cr(III) and anionic Cr(VI) toward the cathode and anode, respectively, into the two different hollow fibres. Octanol-1 and bis(2-ethylhexyl) phosphate (DEHP) in octanol-1 (0.7% v/v) were the most suitable supported liquid membranes for extraction of Cr(VI) and Cr(III), respectively. Among these methods, SEME showed the lowest limits of detection for both analytes.Under optimized conditions, linear calibrations were obtained for Cr(III) from 3 to 30 mu g L-1 and for Cr(VI) from 3 to 70 mu g L-1. The detection limits were 1.0 mu g L-1 and 0.7 mu g L-1 for Cr(III) and Cr(VI), respectively. Our developed method was applied to analyse water samples spiked with different concentrations of Cr(III) and Cr(VI) at the parts-per-billion (ppb) level. The statistical evaluation showed that the proposed method agreed well with the validation method, i.e., inductively coupled plasma atomic emission spectroscopy (ICP-AES). (C) 2019 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.aca.2019.08.002

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Reagent-deposited pieces of paper were characterized by the use of a compact conductometer, a compact pH sensor, and a conventional spectrophotometer to assess their suitability for use as reagent containers. The pieces of paper were fabricated by wax printing to form a limited hydrophilic area to which a consistent volume of an aqueous reagent could be added. The pieces of paper without the reagent increased the conductivity of water gradually because of the release of sodium salts, whereas pH of NaOH decreased because of the acidity of the functional groups in the paper. Three reagents, sulfamic acid as an acid, Na2CO3 as a base, and BaCl2 as a metal salt, were deposited on the pieces of paper to evaluate their ability to release from the pieces of paper. Sulfamic acid and Na2CO3 were released in quantities of 58 and 73% into water after 420 s, whereas 100% of BaCl2 was released after 480 s. The conductometric titrations of NaOH, HCl, and Na2SO4, and the spectrophotometry of Fe2+ were examined using the pieces of paper that contained sulfamic acid, Na2CO3, BaCl2, and 1,10-phenanthroline. Titrations using the pieces of paper suggested that the reagents were quantitatively released into the titrant, which resulted in a linear relationship between the endpoints and the equivalent points. In 120 s of soaking time, 60-70% of the reagents were released. The spectrophotometric measurements of Fe2+ indicated that when an excess amount of the reagents was deposited onto the pieces of paper, they nonetheless sufficiently fulfilled the role of a reagent container.

DOI： 10.1021/acsomega.9b02226

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Stabilizing reagents that can be deposited onto paper is an important issue for researchers who depend on paper-based analytical devices (PADs), because long-term stability of the devices is essential in pointof-care testing. Here, we found that poly(vinyl alcohol) (PVA) would stabilize hydrogen peroxide placed on a paper substrate following exposure to air. Horseradish peroxidase was employed as a sample in colorimetric measurements of PADs after hydrogen peroxide and 3,3',5,5'-tetramethylbenzidine were deposited as substrates in an enzymatic reaction. The addition of PVA to hydrogen peroxide significantly suppressed its degradation. Concentrations of PVA that ranged from 0.5 to 2%, increased the duration of the stability of hydrogen peroxide, and the results for a PVA concentration of 1% approximated those of 2% PVA. Storage of the PADs at 4 degrees C in a refrigerator extended the stability of the hydrogen peroxide containing 2% PVA by as much as 30 days. The stability of hydrogen peroxide without PVA was degraded after one day under room temperature.

DOI： 10.1038/s41598-019-49393-6

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

To determine the total acidity in freshly squeezed fruit juice, we miniaturized the potentiometric titrations and achieved better accuracy compared with titrations from a conventional pH probe. The improvement was the result of a higher jump in pH at the endpoint due to a reduction in the dilutions of both the titrand and titrant. A conventional pH probe requires more than 50 mL of titrand, which can lead to a 25000-fold dilution of the titrant when adding the titrant at 2 mu L intervals. Conversely, when the volume of the titrand can be reduced to 1 mL, the dilution is only 500-fold, which results in a higher jump in pH at the endpoint. The concentration of the titrant, NaOH, was optimized by titrating sample solutions containing 25 and 50 mM of citric acid. The addition of 5 M NaOH in intervals of 2 mu L led to a more accurate endpoint for both 25 and 50 mM citric acid solutions. Miniaturization of the titration process is advantageous in terms of portability, accuracy, and in requiring less consumption of a sample, thereby simplifying the process of repeat measurements that are helpful in evaluating the precision of analytical results. Practical samples of squeezed fruit juices were titrated via three methods that showed no significant differences: classic titrimetry with an indicator, conventional potentiometry, and miniaturized potentiometry. This process would be effective for use in the field and in developing countries. Practical Application The total acidity of fruits and fruit juices is an important indicator of quality and is generally expressed in terms of the citric acid content. However, a standard potentiometric titration requires a large sample volume, which makes it difficult to assess dispersion of the acidity for individual fruits. The results of this study indicate that the use of miniaturized potentiometric titration could benefit food chemistry in many developing countries in addition to opening new fields of food chemistry such as on-site quality control of citrus fruit and evaluation of variations in quality.

DOI： 10.1111/1750-3841.14721

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC  

Here we found that gold nanoparticles (AuNPs) enhance the optical force acting on vesicles prepared from phospholipids via hydrophobic and electrostatic interactions. A laser beam was introduced into a cuvette filled with a suspension of vesicles and it accelerated them in its propagation direction via a scattering force. The addition of the AuNPs exponentially increased the velocity of the vesicles as their concentration increased, but polystyrene particles had no significant impact on velocity in the presence of AuNPs. To elucidate the mechanism of the increased velocity, the surface charges in the vesicles and the AuNPs were controlled; the surface charges of the vesicles were varied via the use of anionic, cationic and neutral phospholipids, whereas AuNPs with positive and negative charges were synthesized by coating with citrate ion and 4-dimethylaminopyridine, respectively. All vesicles increased the velocity at different degrees depending on the surface charge. The vesicles were accelerated more efficiently when their charges were opposite those of the AuNPs. These results suggested that hydrophobic and electrostatic interactions between the vesicles and the AuNPs enhanced the optical force. By accounting for the binding constant between the vesicles and the AuNPs, we proposed a model for the relationship between the concentration of the AuNPs and the velocity of the vesicles. Consequently, the increased velocity of the vesicles was attributed to the light scattering that was enhanced when AuNPs were adsorbed onto the vesicles.

DOI： 10.1098/rsos.190293

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Laser-induced fluorometry (LIF) has achieved the detection of single molecules, which ranks it among the most sensitive of detection techniques, whereas capillary electrophoresis (CE) is known as a powerful separation method with resolution that is beyond the reach of many other types of chromatography. Therefore, a coupling of LIF with CE has established an unrivaled analytical technique in terms of sensitivity and resolution. CE-LIF has demonstrated excellent performance in bioanalytical chemistry for the high-resolution separation and highly sensitive detection of DNAs, proteins, and small bioactive molecules. This review describes the CE-LIF methods developed by the author's group that include indirect and direct detection using diode lasers, post-column derivatization, and Hadamard transformation, as well as applications to the binding assays of specific DNA immunoassays of proteins and to the determination of anticancer drugs.

DOI： 10.1002/tcr.201800051

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A novel detection scheme using chromatographic retention was proposed for paper-based analytical devices (PADs). Using a wax printer and an ink-jet printer, the PADs consisted of a straight-flow channel, a circular sample zone, and a band of brilliant green (BG) printed at the connection between the sample zone and the flow channel. When a constant volume of a sample solution was applied to the sample zone, the BG band formed a colored bar along the flow channel that marked the adsorption and desorption of the paper substrate according to the principles of chromatography. If the sample solution contained an anionic complex of boric acid with chromotropic acid, the anionic complex enhanced desorption of the BG from the paper substrate via the formation of an ion-pair with the BG, which resulted in an elongated colored bar. Fundamental equations for the retention behavior of the BG on the PADs were derived using a model based on chromatographic principles and ion-pairing formation. A retardation factor, R-f, was correlated with the concentration of boric acid contained in the sample solutions. To enhance the adsorption of the BG, 2,2,6,6-tetramethylpiperidine 1-oxyl was used to oxidize the paper substrate. The oxidized paper substrate shortened the colored bar of a blank solution and formed a clear boundary for the color. When the analytical conditions were optimized for pH and the concentration of chromotropic acid, the PAD permitted the measurement of boric acid for a concentration ranging from 0.3 to 3 mM. The proposed model was validated when the fitting curve was calculated using the derived equations, which resulted in good agreement with the experimental data.

DOI： 10.1039/c8ay02298d

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Authorship：Corresponding author   Language：English   Publisher：TAYLOR & FRANCIS INC  

Microfluidic paper-based analytical devices (mu PADs) have attracted much attention over the past decade because they offer clinicians the ability to deliver point-of-care testing and onsite analysis. Many of the advantages of mu PADs, however, are limited to work in a laboratory setting due to the difficulties of processing data when using electronic devices in the field. This review focuses on the use of mu PADs that have the potential to work without batteries or with only small and portable devices such as smartphones, timers, or miniaturized detectors. The mu PADs that can be operated without batteries are, in general, those that allow the visual judgment of analyte concentrations via readouts that are measured in time, distance, count, or text. Conversely, a smartphone works as a camera to permit the capture and processing of an image that digitizes the color intensity produced by the reaction of an analyte with a colorimetric reagent. Miniaturized detectors for electrochemical, fluorometric, chemiluminescence, and electrochemiluminescence methods are also discussed, although some of them require the use of a laptop computer for operation and data processing.

DOI： 10.1080/05704928.2018.1457045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Hydrophobic effect was utilized to self-assemble gold nanoparticles into oligomer structures, or plasmonic dimers, trimers, and so on. Langmuir-Blodgett film of n-octadecanamine was prepared on a glass substrate. Citrate-stabilized gold nanoparticles were adsorbed onto the film, resulting hydrophobic point decoration. The gold nanoparticles with the point decoration were removed from the substrate and self-assembled into plasmonic dimers in ethanol. The products were observed by an atomic force microscope, where not only dimers but also trimers and other aggregates were found. The yield of the plasmonic dimer was similar to 13% without any purifications. We measured the scattering spectrum of the single plasmonic dimer, exhibiting the optical anisotropy. (C) 2018 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.57.120311

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A simple and highly sensitive procedure based on the combination of hollow fiber membrane liquid phase microextraction and a microfluidic paper-based analytical device (mu PAD) was developed for pre-concentration and determination of hexavalent chromium in water samples. The hexavalent chromium was pre-concentrated using the HF-LPME technique via ion exchange or a coupled transport process through a supported ionic liquid (Aliquat 336) prior to colorimetric detection with diphenylcarbazide on the mu PAD. The violet colour could be seen by the naked eye. Images from the mu PADs were scanned using a commercial desktop scanner at 600 dpi resolution. ImageJ software was used for quantitative analysis by measuring the intensity values at green colour channel since it gave the best sensitivity among the RGB colour. Under optimal conditions, the calibration curve was linear in the range 10-90 mu gL(-1), with a limit of detection of 3 mu g L-1. The developed method was successfully applied to determine the level of hexavalent chromium spiked into natural water samples at the parts-per-billion (ppb) level, and the results were in good agreement with those obtained using inductively coupled plasma atomic emission spectroscopy (ICP-AES). The developed method was able to improve the detection limit of the conventional mu PAD, and was expected to be used for the effective analysis of hexavalent chromium in natural water.

DOI： 10.1016/j.talanta.2018.07.056

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We describe a process for collecting micro- and nanovesicles on a glass substrate using the optical pressure of a laser beam. The laser beam was focused on a glass substrate that sandwiched a solution containing vesicles prepared using a phospholipid. The optical pressure generated at the surface of the vesicles pulled them into the center of the beam where they formed an aggregate on the glass surface. The vesicles prepared with a buffer solution were successfully collected via adsorption onto the glass surface, whereas the vesicles prepared with pure water exhibited no such tendency. The time required to collect a certain amount of vesicles was inversely proportional to their concentration. To enhance the collection efficiency, we added gold nanoparticles to the vesicle solution. The addition of gold nanoparticles into the solution reduced the collection time to one-tenth of that without it, and this was attributed to thermal mixing promoted by the heat generated by the absorption from the gold nanoparticles in the solution, as well as to an enhancement of light scattering induced by the gold nanoparticles. The optical collection of vesicles coupled with gold nanoparticles shows a promise for the collection of trace amounts of extracellular vesicles in biological fluids.

DOI： 10.1021/acsomega.8b00033

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

The implementation of continuous flow in paper-based analytical devices (PADs) was challenging because of the large volume introduction that was created; but this allowed for the development of novel types of PADs for preconcentration, separation, and sensitive detection. In this study, pump-free continuous flow was applied to a distance-based PAD for the determination of iron ions. Continuous flow enabled the introduction of a volume that exceeded what was necessary to fill the hydrophilic channel of a PAD. Thus, this continuous-flow method significantly improved both the limits of detection (LOD) and the limits of quantification (LOQ) for a distance-based PAD by increasing the sample volume that could be introduced into the PAD. The values for LOD and LOQ were 20 and 26 ppb, respectively, which were more than 150-times lower than that obtained using a small sample volume (50 mu L), and were comparable to those of inductively coupled plasma-atomic emission spectrometry. The continuous-flow technique was applicable to the determination of iron ions at levels of several tens of ppb in natural water without preconcentration.

DOI： 10.2116/analsci.34.65

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Language：English   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We developed a method to collect micro- and nano-vesicles on a glass substrate using the optical pressure of a laser beam. The laser beam was focused on the glass substrate which sandwiches a suspension containing micro- or nano-sized vesicles prepared by a phospholipid. The optical pressure generated at the interface of the medium and the vesicles accelerated the vesicles to form aggregates on the glass surface. Two types of glass substrates, hydrophilic and aminated ones, showed no difference in the adsorption property of the vesicles. Time to be required for collecting a certain amount of the vesicles was inversely proportional to the concentration of the vesicles. To enhance the collection efficiency, gold nanoparticles were added to the suspension of the vesicles. We found that gold nanoparticles reduced the collection time as short as 1/10-times.

DOI： 10.1117/12.2317724

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society for Analytical Chemistry  

DOI： 10.2116/analsci.34.5

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Here, we developed an enzyme assay of manganese peroxidase (MnP) by capillary electrophoresis using an in-capillary reaction and applied it to a simultaneous assay of MnP and lignin peroxidase (LiP). The enzyme activity of MnP was determined from the peak area corresponding to Mn(III)-malonate produced by the plug-plug reaction between MnP and Mn(II) in a separation capillary. A background electrolyte containing 250 mM malonate buffer (pH 4.5) and 5 mM cetyltrimethylammonium bromide was employed for the separation of Mn(III)-malonate from MnP at-10 kV after a plug-plug reaction for 5 min. Although the assay permitted the determination of purified MnP, we found that both LiP and MnP have similar activities against their substrates, that is, LiP catalyzed the oxidation reaction of Mn(II) as well as MnP, whereas MnP catalyzed the oxidation reaction of veratryl alcohol which was the substrate used in the LiP assay developed previously. Thus, we proposed a method to discriminate MnP from LiP based on the difference in the activities of these enzymes to each substrate. Amounts of MnP and LiP in a mixture were successfully evaluated by the proposed method.

DOI： 10.1021/acsomega.7b00998

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Coalescence of oil droplets in an oil-in-water (O/W) emulsion was achieved with heating and optical trapping. Three types of O/W emulsions were prepared by adding a mixture of butanol and n-decane to an aqueous solution containing a cationic surfactant (cetyltrimethylammonium bromide, CTAB), an anionic surfactant (sodium dodecyl sulfate, SDS), or a neutral hydrophilic polymer (polyethylene glycol, PEG) as an emulsifier. Two oil droplets in the emulsions were randomly trapped in a square capillary tube by two laser beams in order to induce coalescence. Coalescence of the droplets could not be achieved at room temperature (25 degrees C) regardless of the type of emulsifier. Conversely, the droplets prepared with PEG coalesced at a temperature higher than 30 degrees C, although the droplets with ionic surfactants CTAB and SDS did not coalesce even at the elevated temperature due to their electrostatic repulsion. The size of the resultant coalesced droplet was consistent with that calculated from the size of the two droplets of oil, which indicated successful coalescence of the two droplets. We also found that the time required for the coalescence could be correlated with the temperature using an Arrhenius plot.

DOI： 10.2116/analsci.33.709

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Carbonaceous matter in refractory gold ore is known to be one of the primary causes of gold recovery loss. Model experiments were conducted to simulate the bio-modification of carbonaceous matter using powdered activated carbon (PAC) as a surrogate and cell-free spent medium (CFSM) of Phanerochaete chrysosporium. The CFSM was used because of the lignin peroxidase and manganese peroxidase secreted by the microbe during its incubation. In the present work, an investigation was conducted to determine the physical and chemical alterations in PAC after enzymatic treatment and its effect on Au(CN)(2)(-) uptake. Characterization of the solid residues of PAC by C-13 NMR and N-2 adsorption after bio-modification revealed that the treatment had decomposed poly-aromatic carbons into aliphatic carbons and also reduced the specific surface area from 1430 m(2)/g to 697 m(2)/g in 14 days. As a result, Au(CN)(2)(-) uptake decreased from 100% (0.048 mmol/g) to 43% within 12 h primarily due to the enzyme treatment and adsorption of CFSM components. It further decreased to 26% due to surface passivation by bio-chemicals derived from CFSM and/or decomposed aliphatic hydrocarbons from aromatic carbons between 7 days and 14 days. These findings may contribute to efforts to decrease preg-robbing in hydrometallurgical processing of refractory gold ores. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.hydromet.2016.08.003

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Trans Tech Publications Ltd  

The bio-treatment of double refractory gold ores (DRGO) to reduce preg-robbing needs to account for the heterogeneity of the ore so as to acquire a much more complete picture of the system. To this end, the effects of ferrous ion additives on the degradation of powdered activated carbon (PAC) by cell-free spent medium (CFSM) was studied. Au(CN)2- adsorption and Raman spectrometric results suggest that the ferrous salt could have possibly reacted with some biogenic hydrogen peroxide to aid in the degradation of PAC. The bio-treatment produced mixed solid residues containing some partially degraded aromatic compounds which were soluble in alkaline solutions. Ultimately, biodegradation of PAC using CFSM in the presence of 50 µM FeSO4.7H2 O for 7 days followed by washing with 3 mM NaOH reduced Au(CN)2- uptake by 80%.

DOI： 10.4028/www.scientific.net/SSP.262.43

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We developed microfluidic paper-based analytical devices (mu PADs) for the chelate titrations of Ca2+ and Mg2+ in natural water. The mu PAD consisted of ten reaction zones and ten detection zones connected through narrow channels to a sample zone located at the center. Buffer solutions with a pH of 10 or 13 were applied to all surfaces of the channels and zones. Different amounts of ethylenediaminetetraacetic acid (EDTA) were added to the reaction zones and a consistent amount of a metal indicator (Eriochrome Black T or Calcon) was added to the detection zones. The total concentrations of Ca2+ and Mg2+ (total hardness) in the water were measured using a mu PAD containing a buffer solution with a pH of 10, whereas only Ca2+ was titrated using a mu PAD prepared with a potassium hydroxide solution with a pH of 13. The mu PADs permitted the determination of Ca2+ and Mg2+ in mineral water, river water, and seawater samples within only a few minutes using only the naked eye-no need of instruments. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.aca.2016.04.019

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Here we describe the application of an in-capillary enzyme assay using micellar electrokinetic chromatography (MEKC) in the determination of enzyme activity in a crude culture medium containing lignin peroxidase released from Phanerochaete chrysosporium (P. chrysosporium). The method consists of a plug-plug reaction between lignin peroxidase and its substrate, veratryl alcohol, the separation of the product, veratraldehyde, from the other components including the enzyme and the culture medium, and the determination of the enzyme activity from the peak area of veratraldehyde produced by the plug-plug reaction. This method is more sensitive than conventional spectrophotometry since the background originates from the enzyme and the culture medium can be removed via MEKC separation. Veratraldehyde was separated at-10 kV in a background electrolyte containing 50mM tartrate buffer (pH 2.5) and 50 mM sodium dodecyl sulfate (SDS) after a plug-plug reaction in the capillary for 5 min. The calibration curve of veratraldehyde was linear up to 4pmol (500 mu M) with a limit to quantification of 0.026 pmol (3.211 mu M) (SN = 10). The activity of lignin peroxidase was directly measured from the peak area of veratraldehyde. The activity of lignin peroxidase released from P. chrysosporium into the medium for 7 days was successfully determined to be 3.40 UL-1. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2016.02.062

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Microfluidic paper-based analytical devices (mu PADs) were used to detect the iron ion content in the water of a natural hot spring in order to assess the applicability of this process to the environmental analysis of natural water. The mu PADs were fabricated using a wax printer after the addition of hydroxylamine into the detection reservoirs to reduce Fe3+ to Fe2+, 1,10-phenanthroline for the forming of a complex, and poly(acrylic acid) for ion-pair formation with an acetate buffer (pH 4.7). The calibration curve of Fe3+ showed a linearity that ranged from 100 to 1000 ppm in the semi-log plot whereas the color intensity was proportional to the concentration of Fe3+ and ranged from 40 to 350 ppm. The calibration curve represented the daily fluctuation in successive experiments during four days, which indicated that a calibration curve must be constructed for each day. When freshly prepared mu PADs were compared with stored ones, no significant difference was found. The mu PADs were applied to the determination of Fe3+ in a sample of water from a natural hot spring. Both the accuracy and the precision of the mu PAD method were evaluated by comparisons with the results obtained via conventional spectrophotometry. The results of the mu PADs were in good agreement with, but less precise than, those obtained via conventional spectrophotometry. Consequently, the mu PADs offer advantages that include rapid and miniaturized operation, although the precision was poorer than that of conventional spectrophotometry.

DOI： 10.2116/analsci.32.31

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

A miniaturized detection system for chemiluminescence that is generated on a microfluidic paper-based analytical device (mu PAD) was developed using optical fibers and was applied to the determination of Cr(III). The mPAD was fabricated by wax printing and consisted of 6 separate channels in a parallel alignment. Each channel was composed of an injection zone for a reagent solution, a reaction zone, and a waste zone. The mu PAD was placed on a plastic holder equipped with 6 optical fibers to collect chemiluminescence (CL). The other ends of the optical fibers were bundled and introduced into a small photomultiplier tube module to obtain the CL signals. The CL reaction was based on luminol oxidation by hydrogen peroxide in the presence of Cr(III), which catalyzed the reaction in an alkaline medium. The reaction conditions, including the use of an enhancer and a masking agent, were optimized to obtain high sensitivity and selectivity. Under the optimal conditions, a linear range was obtained at 0.05 to 1.00 ppm with a detection limit of 0.02 ppm. The analysis time was less than 1 min per one mu PAD in order to obtain 6 measurements of differing concentrations with a precision of < 6.5%. This method was successfully applied to the determination of Cr(III) spiked into natural water samples at the sub-ppm range.

DOI： 10.1039/c6ay00954a

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Language：English   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Capillary electrophoresis (CE) coupled with laser-induced fluorescence (LIF) is a powerful method for the trace analysis of cellular components. This review presents a summary of topics for the direct analysis of anthracyclines and multidrug resistance proteins in cancerous cells. A micellar electrokinetic chromatography (MEKC) method that does not use organic solvents, and hence prevents the precipitation of proteins in cellular samples, was shown to be a reliable method for the determination of several anthracyclines including the epimeric doxorubicin and epirubicin. A fast CE-based immunoassay for investigating transporter multidrug resistance associated protein (MRP1) was also developed for routine or explorative analysis of the levels of transporter proteins in cancerous cells. A combination of the developed MEKC-LIF method and the CE immunoassay (CEIA) method has permitted the analysis of anthracyclines and MRP1 in a cell line to show the relationship between the levels of MRP1 and amount of anthracyclines in cancerous cells.

DOI： 10.2116/analsci.31.1121

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Language：English   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Capillary electrophoresis (CE) coupled with laser-induced fluorescence (LIF) is a powerful method for the trace analysis of cellular components. This review presents a summary of topics for the direct analysis of anthracyclines and multidrug resistance proteins in cancerous cells. A micellar electrokinetic chromatography (MEKC) method that does not use organic solvents, and hence prevents the precipitation of proteins in cellular samples, was shown to be a reliable method for the determination of several anthracyclines including the epimeric doxorubicin and epirubicin. A fast CE-based immunoassay for investigating transporter multidrug resistance associated protein (MRP1) was also developed for routine or explorative analysis of the levels of transporter proteins in cancerous cells. A combination of the developed MEKC-LIF method and the CE immunoassay (CEIA) method has permitted the analysis of anthracyclines and MRP1 in a cell line to show the relationship between the levels of MRP1 and amount of anthracyclines in cancerous cells.

DOI： 10.2116/analsci.31.1121

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：OSA - The Optical Society  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Rapid and simple acid-base titration was accomplished using a novel microfluidic paper-based analytical device (mu PAD). The mu PAD was fabricated by wax printing and consisted of ten reservoirs for reaction and detection. The reaction reservoirs contained various amounts of a primary standard substance, potassium hydrogen phthalate (KHPth), whereas a constant amount of phenolphthalein was added to all the detection reservoirs. A sample solution containing NaOH was dropped onto the center of the mu PAD and was allowed to spread to the reaction reservoirs where the KHPth neutralized it. When the amount of NaOH exceeded that of the KHPth in the reaction reservoirs, unneutralized hydroxide ion penetrated the detection reservoirs, resulting in a color reaction from the phenolphthalein. Therefore, the number of the detection reservoirs with no color change determined the concentration of the NaOH in the sample solution. The titration was completed within 1 min by visually determining the end point, which required neither instrumentation nor software. The volumes of the KHPth and phenolphthalein solutions added to the corresponding reservoirs were optimized to obtain reproducible and accurate results for the concentration of NaOH. The mu PADs determined the concentration of NaOH at orders of magnitude ranging from 0.01 to 1 M. An acid sample, HCl, was also determined using Na2CO3 as a primary standard substance instead of KHPth. Furthermore, the mu PAD was applicable to the titrations of nitric acid, sulfuric acid, acetic acid, and ammonia solutions. The mu PADs were stable for more than 1 month when stored in darkness at room temperature, although this was reduced to only 5 days under daylight conditions. The analysis of acidic hot spring water was also demonstrated in the field using the mu PAD, and the results agreed well with those obtained by classic acid-base titration.

DOI： 10.1021/ac5039384

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

A computer-controlled system, included a sequential injection system and an electrochemical detector, was developed for the determination of mercury(II) ion (Hg2+) concentrations. The screen-printed carbon electrode (SPCE), a well-known low-cost electrode, was modified by overlaying in situ with a gold film (Au-SPCE). Square wave anodic stripping voltammetry (SWASV) using the Au-SPCE was performed with a two-step deposition potential of an initial -0.5 V vs Ag/AgCl for the preparation of the gold film and then a deposition potential of +0.2 V vs Ag/AgCl for the preconcentration of mercury. An on-line medium exchange method was included in the injection step to reduce the effect of chloride ions, whilst a solid phase extraction cartridge was used to remove interference for copper(II) ions. The flow pattern of the sequentially injected solutions with the synchronized two-step deposition potentials did not significantly affect the detection of Hg2+. Square wave parameters of a 4 mV step potential, 150 Hz frequency and 30 mV amplitude gave an optimal Hg2+ detection sensitivity with a limit of detection of 0.22 mu g L-1 (sample volume of 0.9 mL) without any significant interference effect. This method was successfully applied to determine Hg2+ concentrations in real water samples, including in the chloride-rich samples of sea water and table salt, with very good accuracy (recovery in the range of 96.0-101%). (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jelechem.2014.05.026

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The thermoacidophilic iron-oxidizing archaeon Acidianus brierleyi is a microorganism that could be useful in the removal of inorganic As from wastewater, because it simultaneously oxidizes As(III) and Fe(II) to As(V) and Fe(III) in an acidic culture medium, resulting in the immobilization of As(V) as FeAsO4. To investigate the oxidation mechanism, speciation of the As species in both the cells and its culture media is an important issue. Here we describe the successive determination of As(III), As(V), and total As in A. brierleyi and its culture medium via a facile method based on inductively coupled plasma-optical emission spectroscopy (ICP-OES) with a flow injection pretreatment system using a mini-column packed with an anion-exchange resin. The flow-injection pretreatment system consisted of a syringe pump, a selection valve, and a switching valve, which were controlled by a personal computer. Sample solutions with the pH adjusted to 5 were flowed into the mini-column to retain the anionic As(V), whereas As(III) was introduced into ICP-OES with no adsorption on the mini-column due to its electrically neutral form. An acidic solution (I M HNO3) was then flowed into the mini-column to elute As(V) followed by ICP-OES measurement. The same sample was also subjected to ICP-OES without being passed through the mini-column in order to determine the total amounts of As(III) and As(V). The method was verified by comparing the results of the total As with the sum of As(III) and As(V). The calibration curves showed good linearity with limits of detection of 158, 86, and 211 ppb for As(III), As(V), and total As, respectively. The method was successfully applicable to the determination of the As species contained in the pellets of A. brierleyi and their culture media. The results suggested that the oxidation of As(III) was influenced by the presence of Fe(II) in the culture medium, i.e., Fe(II) enhanced the oxidation of As(III) in A. brierleyi. In addition, we found that no soluble As species was contained in the cell pellets and more than 60% of the As(III) in the culture medium was oxidized by A. brierleyi after a 6-day incubation. (c) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.talanta.2014.01.057

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An automated method has been developed for determining the concentration of inorganic arsenic. The technique uses sequential injection/anodic stripping voltammetry with a long-lasting gold-modified screen-printed carbon electrode. The long-lasting gold electrode was electrochemically deposited onto a screen-printed carbon electrode at a potential of -0.5 V vs. Ag/AgCl in a supporting electrolyte solution of 1 M hydrochloric acid. Under optimal conditions and the applied potentials, the electrode demonstrated that it can be used for a long time without a renewal process. The linear range for the determination of arsenic(III) was 1-100 mu g L-1, and the limit of detection (LOD) in standard solutions was as low as 0.03 mu g L-1 for a deposition time of 120 s and sample volume of 1 mL. This method was used to determine the concentration of arsenic(III) in water samples with satisfactory results. The LOD in real samples was found to be 0.5 mu g L-1. In addition, speciation between arsenic(III) and arsenic(V) has been achieved with the proposed method using deposition potentials of -0.5 V and -1.5 V for the determination of the arsenic(III) concentration and the total arsenic concentration, respectively; the results were acceptable. The proposed method is an automated system that offers a less expensive alternative for determining trace amounts of inorganic arsenic. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.talanta.2013.08.030

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

Here, we report a novel method consisting of capillary electrophoretic separation followed by two-color LIF detection with postcolumn derivatization. The method can be used to discriminate glycoproteins in a protein mixture containing both glycosylated and unglycosylated proteins. The detector permitted simultaneous measurements of two electropherograms obtained by 450 nm (diode laser) and 532 nm (Nd:YAG laser) lasers excited native proteins following postcolumn derivatization with naphthalene-2,3-dicarboxaldehyde and concanavalin A (Con A) labeled with tetramethylrhodamine (rhodamine-labeled Con A), respectively. So, a protein can be assigned as glycosylated if it shows a peak at the same migration time in both electropherograms. According to the proposed principle, in a single run we discriminated a glycosylated protein (thyroglobulin) from an unglycosylated protein (albumin) in the presence of rhodamine-labeled Con A. Because the methodology permits the simultaneous detection of native proteins and their complexes with a fluorescently labeled probe, it should have broad applicability to binding assays.

DOI： 10.1002/elps.201300149

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An acid dissociation constant of tetrabromophenolphthalein ethyl ester (TBPE) was determined through the measurement of electrophoretic mobility by capillary zone electrophoresis (CZE). Although TBPE is degradable in acidic pH region and it gradually degraded at pH conditions around and below its pK(a) values in the time scale of the CZE measurement, equilibrium species of interest were detected as a peak-shaped signal with tailing of the degraded species. Changes in electrophoretic mobility of the equilibrium species of TBPE were analyzed at its detectable pH range in the presence of phenol red as a mobility standard. An acid dissociation constant of 3.47 +/- 0.06 (pK(a), I = 0.01, 25 degrees C, standard error) was determined for TBPE.

DOI： 10.2116/analsci.29.547

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Hydro gel formed by 5'-guanosine monophosphate (GMP) in the presence of a potassium ion is expected to exhibit interesting selectivity in capillary electrophoretic separations. Here, we estimated the conditional association constants between the hydro gel (G-gel) and aromatic compounds by capillary electrophoresis in order to investigate the separation selectivity that is induced by the G-gel. Several aromatic compounds were separated in a solution containing GMP and potassium ion at different concentrations. The association constants were calculated by correlating the electrophoretic mobilities of the analytes obtained experimentally using a concentration of G-gel. During semi-quantitative estimation, naphthalene derivatives had larger association constants (K-ass = 10.3-16.8) compared with those of benzene derivatives (K-ass = 3.91-5.31), which means that the binding sites of G-gel match better to a naphthalene ring than to a benzene ring. A hydrophobic interaction was also found when the association constants for alkyl resorcinol were compared with those of different hydrocarbon chains. The association constants of nucleobases and tryptophan ranged from 6.05 to 12.6, which approximated the intermediate values between benzene and naphthalene derivatives. Consequently, the selective interaction between G-gel and aromatic compounds was classified as one of three types: (1) an intercalation into stacked planar GMP tetramers; (2) a hydrophobic interaction with a long alkyl chain; or, (3) a small contribution of steric hindrance and/or hydrogen bonding with functional groups such as amino and hydroxyl groups. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2013.02.090

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Herein, we report a novel method for the determination of polyamines in a sample extracted from Arabidopsis thaliana by capillary electrophoresis (CE) using salicylaldehyde-5-sulfonate (SAS) as a derivatizing reagent. An aldehyde group of SAS forms a Schiff base with amino groups of aliphatic polyamines, resulting in an anionic species with an absorption band in the ultraviolet region. The derivatization method was straightforward since the derivatives were formed by mixing a sample with the derivatizing reagent at a neutral pH. In addition, the negative charges induced by SAS led to a high resolution with a short analysis time. This method permitted the separation of five polyamines, which play important roles in plants. However, further improvement in sensitivity was needed for the determination of the polyamines in plant samples. Therefore, the CE method was coupled with solid-phase extraction (SPE) using an ion-pairing formation with sodium dodecyl benzene sulfonate. The SPE method improved the concentration limits of detection to sub-mu M levels, which corresponded with a 10-fold enhancement. The calibration curves for cadaverine, putrescine, and spermidine were linear with concentrations that ranged from 1 to 20 mu M and correlation coefficients (R-2) were greater than 0.998. The proposed method was applied to the determination of spermidine in a plant sample, Arabidopsis thaliana.

DOI： 10.1039/c3ay26360f

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Here, we report the detection of native amino acids using a sheath-flow electrochemical detector with a working electrode made of copper wire. A separation capillary that was inserted into a platinum tube in the detector acted as a grounded electrode for electrophoresis and as a flow channel for sheath liquid. Sheath liquid flowed outside the capillary to support the transport of the separated analytes to the working electrode for electrochemical detection. The copper wire electrode was aligned at the outlet of the capillary in a wall-jet configuration. Amino acids injected into the capillary were separated following elution from the end of the capillary and detection by the copper electrode. Three kinds of copper electrodes with different diameters50, 125, and 300 mu mwere examined to investigate the effect of the electrode diameter on sensitivity. The peak widths of the analytes were independent of the diameter of the working electrode, while the 300-mu m electrode led to a decrease in the signal-to-noise ratio compared with the 50- and 125-mu m electrodes, which showed no significant difference. The flow rate of the sheath liquid was also varied to optimize the detection conditions. The limits of detection for amino acids ranged from 4.4 to 27 mu M under optimal conditions.

DOI： 10.1002/elps.201200059

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Polyacrylamide gel electrophoresis (PAGE) is used frequently for isolation and purification of DNA fragments. In the present study, DNA fragments extracted from polyacrylamide gels showed significant band broadening in capillary electrophoresis (CE). A pHY300PLK (a shuttle vector functioning in Escherichia coli and Bacillus subtilis) marker, which contained nine fragments ranging from 80 to 4870?bp, was separated by PAGE, and each fragment was isolated by phenol/chloroform extraction and ethanol precipitation. After extraction from the polyacrylamide gel, the peaks of the isolated DNA fragments exhibited band broadening in CE, where a linear poly(ethylene oxide) was used as a sieving matrix. The theoretical plate numbers of the DNA fragments contained in the pHY300PLK marker were >106 for all the fragments before extraction. However, the DNA fragments extracted from the polyacrylamide gel showed decreased theoretical plate numbers (520 times smaller). The degradation of the theoretical plate number was significant for middle sizes of the DNA fragments ranging from 489 to 1360?bp, whereas the largest and smallest fragments (80 and 4870?bp) had no obvious influence. The band broadening was attributed to contamination of the DNA fragments by polyacrylamide fibers during the separation and extraction process.

DOI： 10.1002/jssc.201100909

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Cell membrane transporter-proteins have been partly implicated in lowering the accumulation of drugs in cancer cells, leading to multidrug resistance (MDR). Two cancer cell lines, A549 and RDES, were continuously exposed to subclinical concentration (250 nM) of anthracyclines and micellar electrokinetic chromatography was used to investigate their in vitro accumulation after treatment with inhibitors of membrane transporter-proteins. The four anthracylines [doxorubicin (DOX), epirubicin (EPI), daunorubicin (DNR), and idarubicin (IDA)] were separated within a short analysis time of less than 15 min in borate buffer (80 mM, pH 9.22) containing sodium taurodeoxycholate (35 mM), 2-hydroxypropyl-.-cyclodextrin (3.5% wt/v), and sodium dodecylsulfate (20 mM). Laser-induced fluorescence was used for detection of the anthracyclines. Three inhibitors, verapamil, cyclosporine A and probenecid, were examined by adding each inhibitor independently or two inhibitors simultaneously to the culture medium. It was found that independent use of each inhibitor leads to more efficient accumulation than combined use of verapamil and probenecid. In addition, the results show that effect of inhibitors on the accumulation of anthracyclines depended on type of cell: in RDES, inhibitors enhanced accumulation of all four anthracyclines, while in A549, inhibitors showed different accumulation behavior for each anthracycline. Generally higher accumulation of anthracyclines was observed in RDES cells than A549, as evidenced by dead cells (7-16%) after 24 h of continuous exposure to subclinical concentration. Copyright (C) 2011 John Wiley & Sons, Ltd.

DOI： 10.1002/bmc.1589

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The adenosine triphosphate (ATP) binding-cassette (ABC) transporters are a superfamily of cellular proteins that have been partly implicated as a cause of multidrug resistance (MDR) in cancer cells. The ABC superfamily consists of P-glycoprotein, multidrug resistance-associated proteins (MRP) and breast cancer-related proteins, of which MRP is of particular interest because of its ability to efflux a broader range of substrates. Since MRP1 is the most prominent member of the MRP family, a simple technique is needed for its quantification. We developed a simple, fast (total analysis time of 3 h) capillary electrophoresis immunoassay (CEIA) for the quantification of MRP1 in cancer cells. MRP1 antibody was labeled with fluorescein isothiocyanate. The labeled antibody was incubated with the cell lysate for a fixed interval (1 h), after which the cell lysate mixture was directly injected into the capillary to separate the complex of MRP1 and its antibody from free antibody. The noncompetitive CEIA method had a limit of detection of 0.2 nM and a good linear range (1.7-14.9 x 10(4) cells), and was fairly reproducible (RSD < 10%). The results showed that two cell lines. A549 and RDES, expressed MRP1 in the absence of doxorubicin (DOX), with A549 registering a higher expression. Compared to DOX-free cancer cells, there was an acceleration of MRP1 expression during the 12 h-exposure to DOX, after which the level of expression remained nearly constant as the intracellular accumulation of DOX decreased. The results obtained in this work indicate that the developed CEIA method is useful for relative quantification of MRPs in cancer cells. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2011.04.046

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Previously, we have demonstrated postcolumn derivatization of proteins separated by capillary sieving electrophoresis (CSE), in which naphthalene-2,3-dicarbaldehyde was employed as a fluorogenic labeling reagent. Standard proteins separated by CSE were reacted with naphthalene-2,3-dicarbaldehyde in the presence of 2-mercaptoethanol (2-ME) which plays a role of a reducing agent in the derivatization reaction. To improve the sensitivity, we attempted the use of ethanethiol instead of 2-ME. Ethanethiol showed 1.4- to 4.5-fold lower limits of detection for proteins than 2-ME. Furthermore, we found that 8-aminopyrene-1,3,6-trisulfonate (APTS) is a good marker for relative electrophoretic mobilities of proteins in CSE. Since APTS is a fluorescent and trivalent anion, it generates strong fluorescence and migrates faster than any of the proteins. Therefore, we employed APTS as a marker to obtain the relative electrophoretic mobilities of proteins. The present method was applied to the analyses of proteins in biological samples. Human Ewing's family tumor cell line 'RDES' was used as a sample. The cultured cells were lysed with a buffer containing Tris-HCl, NaCl, sodium dodecyl sulfate, and 2-ME. After denaturation, the lysate was directly introduced into the capillary. Several peaks, which would correspond to proteins with molecular mass ranging from 10 to 93 kDa, were found in the cell lysate. In addition, we measured a milk sample by the CSE with postcolumn derivatization. The electropherogram showed five major peaks which corresponded to alpha-lactalbumin, beta-lactoglobulin, kappa-casein, bovine serum albumin, and mixture of alpha- and beta-casein.

DOI： 10.1002/elps.201000488

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A Hadamard transform-gas chromatography/mass spectrometry (HT-GC/MS) technique was employed for the online detection of ethanol or toluene in exhaled breath after drinking or smoking, respectively. Exhaled breath samples, collected from volunteers, were directly injected into the GC inlet by a Hadamard-injector without any pretreatment. In the case of breath from a drinker, using a conventional single injection, a small ion peak (corresponding to similar to 0.1 ng of ethanol), the intensity of which was approximately equal to or less than the limit of detection. When the HT technique was applied, the signal-to-noise (S/N) ratio was dramatically improved. Furthermore, in the case of breath from a smoker, using conventional injection, a weak ion peak (corresponding to similar to 0.7 pg of toluene) was marginally detected. However, the HT technique led to an improvement in the S/N ratio, with the peak corresponding to the limit of detection. In both cases, the HT technique permitted specific components in exhaled breath to be determined, without the need for any extraction procedures. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2010.06.034

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Anthracyclines are chemotherapeutic drugs that are broadly used in the treatment of various types of solid cancers and leukemia. Herein, we report on a novel analytical method for intracellular accumulation of anthracyclines using MEKC/LIF detection. An aqueous separation system permitted the injection of cell lysates directly into the capillary. The MEKC migrating solution was made up of borate buffer at pH 9.22 containing sodium taurodeoxycholate, (2-hydroxypropyl)-gamma-CD, and SDS. The anthracyclines, Doxorubicin (DOX) and epirubicin (EPI) were detected by LIF using a Nd:YAG laser (532 nm) or an argon ion laser (488 nm) for excitation. Two cell lines, human humerus tumor cells (RDES) and human lung tumor cells (A549), were treated with a mixture of the two anthracyclines for fixed periods of time, and then intracellular concentrations were determined by injecting cell lysates directly. Recovery values of 96.0-100.8% were obtained for DOX and EPI. Reproducibility quantified by RSD was less than 3.9% intraday and 6.7% interday at concentrations ranging between 50 and 500 nM. The uptake of EPI was found to be slightly less than that of DOX for A549, but higher levels of EPI were observed in RDES. Intracellular accumulation of anthracyclines was greater in RDES than in A549, but both types of cells excreted anthracyclines after 12 h. These results indicate that MEKC with an aqueous medium is useful for investigating intracellular uptake and accumulation of drugs, since cell lysates can be used directly with no pretreatment such as deproteination or solvent extraction of analytes.

DOI： 10.1002/elps.200900659

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The technique of Hadamard transform was successfully coupled with GC/nonresonant multiphoton ionization/TOFMS, for the first time. 1,4-Dichlorobenzene and the fourth harmonic generation (266 nm) of a Nd:YAG laser were employed as a model sample and an ionization laser, respectively. A Hadamard-injector coupled with a capillary-based supersonic jet nozzle (capillary-injector) was also developed in this study. The Hadamard-injector was used to obtain the chromatogram, which was encoded by successive sample introduction based on Hadamard codes, and the capillary-injector was used for injection of GC-elutes into TOFMS. Compared with a conventional single injection method, the S/N ratios were substantially improved after inverse Hadamard transformation of the encoded chromatogram. Under optimized conditions, when Hadamard matrices of 103 and 255 were used, the S/N ratios of the signals for 1,4-dichlorobenzene (concentration level, 4 mu g/1 mL ACN) were substantially improved to 4.1- and 6.6-fold, respectively, and those improvements are in good agreement with those obtained by theory (5.1- and 8.0-fold).

DOI： 10.1002/jssc.200900662

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A novel Hadamard transform-gas chromatography/mass spectrometry (HT-GC/MS) system equipped with on-line sample collection systems is described. A Hadamard-injector was successfully designed and then coupled with an on-line adsorption/desorption system for detecting volatile organic compounds (VOCs) and a supercritical fluid extraction (SFE) system, respectively, by HT-GC/MS. Six VOCs and three pesticides were used as model compounds. In the former case, an activated-charcoal trap was used to trap VOCs from the indoor air. After 10 L of indoor air had passed through the trap, the condensed components were heated and simultaneously injected into the GC column through the Hadamard-injector, based on Hadamard codes. In a second experiment, a sample of rice was spiked with three types of pesticides and the sample then extracted using a commercially available supercritical fluid extractor. After extraction, the extracted components were transferred to a holding tank and simultaneously injected into the GC column also using the Hadamard-injector. The findings show that, in both cases, the combination of on-line sample collection methods and the use of the Hadamard transform resulted in improved sensitivity and detection. Compared to the single injection used in most GC/MS systems, the signal-to-noise (S/N) ratios were substantially improved after inverse Hadamard transformation of the encoded chromatogram. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2009.12.007

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DOI： 10.1002/9780470530191.ch17

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The separation methods for proteins with high resolution and sensitivity are absolutely important in the field of biological sciences Capillary sieving electrophoresis (CSE) is an excellent separation technique for DNA and proteins with high resolution, while LIF permits the most sensitive detection in CSE. Therefore, proteins have to be labeled with fluorescent or fluorogenic reagent to produce fluorescent derivatives. Both precolumn and oncolumn derivatization have been employed for the labeling of proteins in CSE. However, there is no report on the postcolumn derivatization due to the limitation in the use of a standard migration buffer, despite it being a promising method for sensitive detection of proteins. Here, we show a novel postcolumn derivatization method for protein separation by CSE, using a tertiary amine as a buffer component in the running buffer. Tris, which is commonly used as a base in CSE separation buffers, was substituted by tertiary amines, 2-(diethylamino) ethanol and triethanolamine. A buffer solution containing 2-(diethylamino)ethanol or triethanolamine can be used for the CSE separation followed by the postcolumn derivatization. of proteins, since both reagents are unreactive toward a fluorogenic labeling reagent, naphthalene-2,3-dicarbaldehyde. Thus, LIF detection using the postcolumn derivatization. permits significant reduction in the LOD (by a factor of 2.4-28) of proteins, compared with conventional absorbance detection.

DOI： 10.1002/elps.200900314

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Hadamard transform electrophoresis combined with laser-induced fluorescence (LIF) detection on a microchip was demonstrated. A compact, diode-pumped neodymium-doped yttrium aluminum garnet laser was employed as the light source for LIF detection. The analytical conditions were optimized using rhodamine B as the analyte. Under optimal conditions, the signal-to-noise ratio (S/N) of the analyte was improved by a factor of 7.5 by means of Hadamard transformation based on a 255-order cyclic S matrix. Additionally, the relationship between fluorescence intensity and analyte concentration was linear with a correlation coefficient of 0.993 in the inverse Hadamard transformed data at the concentration range from 25 to 100 pM. The results indicate that the present method is applicable to quantitative analysis at the concentration lower than the concentration limit of detection in a conventional method. The concentration limit of detection was similar to 25 pM (the relative standard deviation of the peak height was 5.2%). The present technique was successfully applied to the separation of a mixture containing 1.9 nM phenylalanine and 1.9 nM glutamic acid labeled with rhodamine B isothiocyanate. The S/Ns of the analyte peaks were improved up to similar to 10 in the inverse Hadamard transformed data derived from a 127-order cyclic S matrix, while neither peak was lower than the limit of detection (S/N < 3) in conventional microchip electrophoresis by a single injection.

DOI： 10.1063/1.3116121

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DOI： 10.1093/chromsci/46.8.712

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Successful application of the Hadamard transform (HI) technique to gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS) is described. Novel sample injection devices were developed to achieve multiple sample injections in both GC and LC instruments. Air pressure was controlled by an electromagnetic valve in GC, while a syringe pump and Tee connector were employed for the injection device in LC. Two well-known, abused drugs, 3,4-methylenedioxy-N-methylamphetamine (MDMA) and N,N-dimethyltryptamine (DMT), were employed as model samples. Both of the injection devices permitted precise successive injections, resulting in clearly modulated chromatograms encoded by Hadamard matrices. After inverse Hadamard transformation of the encoded chromatogram, the signal-to-noise (S/N) ratios of the signals were substantially improved compared with those expected from theoretical values. ne S/N ratios were enhanced similar to 10-fold in HT-GC/MS and 6.8 in HT-LC/MS, using the matrices of 1023 and 511, respectively. The HT-GC/MS was successfully applied to the determination of MDMA in the urine sample of a suspect.

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This study investigated a novel postcolumn reactor for fluorescence detection in CE. A laser-drilled capillary, with an aperture made by laser ablation, was used for mixing derivatization reagents with the analytes separated by CZE. The derivatization reagents, o-phthaldialdehyde (OPA), and 2-mercaptoethanol, were introduced into the capillary through the aperture and reacted with the analytes after CZE separation. High voltages were applied to both the inlet reservoir and the reservoir filled with the derivatization reagents. Thus, the flow rate of the derivatization reagents was controlled by the electric potential that was applied to the reservoir of the derivatization reagents. A UV light-emitting diode was used as an excitation light source for the fluorescence detection of OPA derivatives. A commercially available tee connector was compared with the laser-drilled capillary. The results implied that the dead volume of the laser-drilled capillary was less than that of the tee connector since the laser-drilled capillary suppressed band broadening more efficiently. The LODs for amino acids were determined to be similar to 5 mu M. The method was applied to the determination of amino acids in a Japanese beverage.

DOI： 10.1002/elps.200700274

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Laser-induced fluorescence detection using diode lasers as excitation light sources has been applied to the highly sensitive analysis of polyaromatic hydrocarbons, amino acids, DNA, and proteins. Diode lasers emitting at the near-infrared to red region were employed for direct and indirect fluorescence detections. In addition, to enhance the sensitivity in capillary electrophoresis, Hadamard transform capillary electrophoresis has been developed. The method includes multiple injection, followed by an inverse Hadamard transformation. Optically gated injection, electrokinetic injection using a microchip, and electrokinetic injection using a laser-fabricated capillary have been developed for achieving multiple sample injection. These methods have permitted multiple sample injection in capillary electrophoresis. The results obtained by Hadamard transform capillary electrophoresis showed a significant improvement in the S/N.

DOI： 10.2116/bunsekikagaku.56.841

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The on-column capture of a specific protein using magnetic beads was applied to SDS-CGE. In a preliminary study, an immunological reaction in the presence of SDS, using a batch method, was attempted. Carbonic anhydrase (CA), alpha-lactalbumin (LA), and HSA were denatured by heating in the presence of SDS and 2-mercaptoethanol, and then reacted with anti-CA that had been immobilized on magnetic beads. Not only native CA, but also the denatured CA reacted with anti-CA, even in the presence of SDS. Therefore, the on-column capture of denatured CA separated by SDS-CGE was attempted using a two-point detection technique. A mixture of proteins, containing LA, CA, and HSA, were separated by SDS-CGE according to their M-Gamma. The CA was then specifically captured on anti-CA-immobilized magnetic beads, which were packed between two detection windows in the capillary column, during the electrophoresis. The results show that the technique leads to information similar to that obtained by Western blotting, i.e., a protein can be identified by its M-Gamma and reaction with its antibody.

DOI： 10.1002/elps.200600726

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The Hadamard transform (HT) technique, which permits the S/N in CE to be improved, was applied to MEKC. Multiple sample injection of fluorescent analytes according to a Hadamard code sequence was performed using an optically gated sample injection technique, in which a sample plug was produced based on photodegradation by irradiation with an intense laser beam. The capillary and reservoirs were filled with a sample solution containing buffer components and SDS as a pseudostationary phase. A preliminary study confirmed that fluorescein ion could be photobleached in the presence of SIDS. The optically gated sample injection technique was then applied to multiple sample injection, based on a Hadamard matrix. The S/N in the electropherogram obtained by HT-MEKC was improved substantially compared to that obtained by a single injection method. When the technique was applied to the separation of several amino acids labeled with FITC, the S/N ratio for each amino acid was enhanced, without any evidence of degradation in separation resolution. Moreover, HT-MEKC was applied to the analysis of amino acids contained in a Japanese beverage, resulting in improved S/Ns for the amino acids.

DOI： 10.1002/elps.200600183

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A method for capturing specific molecules separated by CE has been explored. To demonstrate on-column capture of migrating analyte molecules, two detection windows were fabricated on a capillary. Magnetic beads containing immobilized molecules that react with the specific molecules under study were placed between the detection windows in the capillary using magnets. Molecules in a sample solution injected into the capillary were separated and detected at the first detection window. After passing through the first detection window, the separated molecules encountered the magnetic beads, where the specific analyte was captured. As a result, the peak area for those analyte molecules decreased or disappeared completely at the second detection window. Rabbit IgG and carbonic anhydrase were employed to demonstrate on-column capture of a specific molecule. For rabbit IgG, magnetic beads containing the immobilized antibody (anti-rabbit IgG),were used. Rabbit IgG molecules were captured on the magnetic beads during CE migration. Furthermore, the capture of carbonic anhydrase was demonstrated by the reaction between magnetic beads (containing immobilized anti-rabbit IgG) and anti-carbonic anhydrase (rabbit IgG), before the beads were packed in the capillary. After packing the magnetic beads in the capillary, a mixture of two proteins was injected into the capillary. Two proteins were detected at the first detection window, while the peak corresponding to carbonic anhydrase disappeared at the second detection window. The results show that using an appropriate antibody, the present technique would be applicable to any proteins.

DOI： 10.1002/elps.200500936

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A hydrophilic polymer, poly(vinylpyrrolidone) (PVP), was employed for suppressing the electroosmotic flow (EOF). A capillary was filled with aqueous PVP solution for coating the capillary wall with PVP; the PVP solution was then replaced by a migration buffer solution containing no PVP. Three types of PVP with different molecular weights were examined. The EOF was suppressed more effectively as the molecular weight of PVP increased. The EOF in the coated capillary was similar to 10-fold smaller than that of a bare capillary and was constant in the pH range of 6-8. The suppressed EOF was stable even when no PVP was added to the migration buffer. However, the EOF increased significantly when sodium dodecyl sulfate was added into the migration buffer. The method was applied for determining the electrophoretic mobilities of inorganic anions that have negative electrophoretic mobilities larger than the electroosmotic mobility of the bare capillary. A novel method for determining the electrophoretic mobilities was proposed based on the linear relationship between electric current and electrophoretic mobility. The electrophoretic mobility was proportional to the electric current. Therefore, the intercept of the regression equation represents the electrophoretic mobility at room temperature. The electrophoretic mobilities were in good agreement with the absolute electrophoretic mobilities. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2005.08.062

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Hadamard transform capillary electrophoresis (HTCE) based on electrokinetic injection allows laser-induced fluorescence detection using a small laser, namely the laser-diode-pumped YAG laser, as an excitation source. A small hole is fabricated at the center of a capillary by laser ablation; this hole functions as an inlet port for a sample solution. Therefore, the sample solution can be introduced electrophoretically into the capillary through the small hole. Multiple sample injection is accomplished by introducing a buffer solution from the end of the capillary and the sample solution through the hole. Both solutions are injected using two sets of high-voltage power supplies and migrate toward the opposite end of the capillary. A fluorescent analyte, rhodamine B, is successfully detected in the case of both single and multiple injection according to the Hadamard sequence code. By transforming the data encoded by the Hadamard matrix, the decoded data showed an increase in the signal-to-noise (S/N) ratio by a factor of 9.8. In the case of the sample containing two amino acids labeled with rhodamine B isothiocyanate (RBITC), although the concentration of every component including free RBITC is lower than the concentration limit of detection obtained by single injection, a substantial improvement in the sensitivity is achieved and all components are identified by the Hadamard transform technique. (c) 2005 Elsevier B.V. All fights reserved.

DOI： 10.1016/j.aca.2005.06.068

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An on-column immunological reaction was employed to achieve simple and rapid analysis in an immunoassay based on capillary electrophoresis using semiconductor laser-induced fluorescence detection. Human serum albumin (HSA) labeled with sulfoindocyanine succinimidyl ester (Cy5), a fluorescent compound with an absorption maximum at 649 urn, was used as a fluorescent probe for the immunoassay. In a binding assay, with anti-HSA as the analyte molecule, Cy5-HSA was injected in a capillary column followed by the injection of anti-HSA so as to form individual zones. By applying a potential, the anti-HSA reacted with Cy5-HSA at the boundary between Cy5-HSA and anti-HSA zones, since anti-HSA has a higher electrophoretic mobility than Cy5-HSA. Furthermore, the on-column method enhances the sensitivity by injecting a large volume of the sample. Free Cy5-HSA and its immunocomplex with anti-HSA were separated with less degradation in resolution than that predicted from the injection time of anti-HSA, even when the injection time for anti-HSA was increased. The ratio of the peak area of the complex to that of the total Cy5-HSA (free Cy5-HSA and the complex) increased in proportion to the injection time of anti-HSA. As a result, the detection limit was improved up to eight-fold (the concentration detection limit, 0.007 mg mL(-1)), for an injection time of 240 s, compared to that obtained using an off-column sample preparation. Furthermore, the on-column reaction method was applicable to an immunoassay to determine native HSA, in which native HSA and Cy5-HSA react with anti-HSA stepwise. The detection limit in the stepwise reaction immunoassay was 0.005 mg mL(-1), which is 14 times lower than that in an off-column method, with the analysis time less than 10 min as the result of increasing the injection time of native HSA. In addition, the present on-column immunoassay was applied to the sample containing a high concentration of salts for investigating the effect of salts in the sample solution. (C) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2005.01.037

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A novel method for the on-column sample stacking of proteins is described. The strategy takes advantage of interactions between protein molecules and sodium dodecyl sulfate (SDS) monomers. A long plug of a protein sample (either acidic or basic) is injected into a capillary filled with a background electrolyte (BGE) containing SDS. When a potential is applied, the proteins interact with SDS monomers in the BGE to form protein-SDS complexes that migrate more slowly than the corresponding uncomplexed protein, resulting in protein stacking. Both acidic and basic proteins migrate at an almost identical electrophoretic velocity after stacking, which indicates that the protein-SDS complexes formed in the BGE zone have a similar charge/mass ratio. The mechanism of stacking was investigated using a sample consisting of a basic protein, lysozyme, and a small molecule, methylene blue. The findings clearly show that two interactions with SDS occur, a stepwise binding interaction between protein molecules and SDS monomers and an interaction in which the small molecules enter into micelles formed by SDS molecules. The method was also applied to the detection of a protein labeled with a fluorescent labeling reagent at trace levels. The labeled protein was detected even under labeling conditions where the labeling efficiency was too low to detect by short-plug injection.

DOI： 10.2116/analsci.21.37

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Methods with a high sensitivity and high separation efficiency are goals in analytical separation techniques. On-line sample concentration techniques in capillary electrophoresis (CE) separations have rapidly grown in popularity over the past few years because they achieve this goal. This review describes the methodology and theory associated with a number of different techniques, including electrokinetic and chromatographic methods. For small molecules, several on-line concentration methods based on velocity gradient techniques are described, in which the electrophoretic velocities of the analyte molecules are manipulated by field amplification, sweeping, and isotachophoretic migration, resulting in the on-line concentration of the analyte zones. In addition, the on-line concentration methods for macromolecules are described, since the techniques used for macromolecules (DNAs and proteins), are different from those for small molecules, with respect to either mechanism or methodology. Recent studies relating to this topic are also discussed, including electrophoretic and chromatographic techniques on capillary or microchip.

DOI： 10.1002/elps.200406172

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A novel injection device for applying absorption spectrometty to Hadamard transform (HT) capillary electrophoresis is described. A small hole, at the center part of the capillary, functions as an inlet port for the sample. The hole is immersed in a sample solution and the end of the capillary that is usually employed for sample introduction is immersed in a buffer solution. An ultraviolet absorption detector is placed between the sample injection port and the other end of the capillary filled with a buffer solution. A high potential is continuously applied between the injection port and the end of the capillary, which allows the sample solution to be introduced into the separation capillary. By application of a higher potential modulated according to a Hadamard code between both ends of the capillary, the buffer solution is injected into the separation capillary. In some preliminary experiments, this injection device was utilized to introduce a single sample segment into a capillary. As expected, a single peak was observed in the electropherogram for a sample containing a single component. This device was then employed for multiple sample injection in HT capillary electrophoresis. An 8-fold improvement in the S/N ratio was observed when the HT technique was used, in which a 255-order of a Hadamard matrix was used, as expected from theory. The present approach was also utilized for the sensitive detection of a sample comprised of multiple components.

DOI： 10.1021/ac035366j

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A concentration detection limit of 100 fM was achieved for the fluorescein ion by improving the experimental setup used for Hadamard transform capillary electrophoresis. Two argon-ion lasers, a gating laser for sample injection and a probe laser for the excitation of analyte molecules, were employed for the efficient photodegradation of analyte molecules in laser-induced fluorescence detection using an optically gated sample-injection method. In addition, a dichroic mirror, located in the pathway of the probe laser was used to exclude the other lines of the argon-ion laser. Using a Hadamard matrix on the order of 2046, the concentration limit of detection for fluorescein ion was determined to be 100 fM at S/N = 3, in which the average number of molecules in a single injection volume was calculated to be 27. The influences of the output power in both the gating and probe lasers on the sensitivity are also discussed.

DOI： 10.2116/analsci.19.1659

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Hadamard transform capillary electrophoresis, which is a sensitive detection method using multiple sample injection, was applied to the separation of glutamic acid enantiomers labeled with fluorescein isothiocyanate (FITC). A capillary was filled with a sample solution containing FITC-labeled D,L-glutamic acids, cyclodextrin, and buffer components. The sample was injected by an optically gated sample injection method, in which an intense laser beam was focused onto the capillary to convert fluorescent analyte ions to nonfluorescent ones by photodegradation. To form analyte plug, a shutter placed in the pathway of the laser beam was closed for a constant time period. In the presence of cyclodextrin, enatiomers of FITC-labeled glutamic acid could be injected by the optically gated sample injection method. Two cyclodextrins, beta- and gamma-cyclodextrins, were employed as chiral selectors in the capillary electrophoretic separations. For the separation of FITC-labeled glutamic acid enantiomers, gamma-cyclodextrin shows a better resolution than P-cyclodextrin. The optimum concentration of gamma-cyclodextrin was found to be 10 mM. Multiple sample injection was accomplished by closing or opening the shutter according to a sequence based on a Hadamard matrix. When the resulting electropherogram was transformed by the inverse Hadamard matrix, The S/N ratio in the transformed result was enhanced with no degradation in the resolution, compared to that in the electropherogram obtained by a single injection method. As a result, Hadamard transform capillary electrophoresis allows a significant improvement in the SIN ratios for FITC-labeled glutamic acid enantionters. Therefore, the present method will be applicable to the separation and sensitive detection of enantiomers labeled with FITC.

DOI： 10.2116/bunsekikagaku.52.1193

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A novel diffractive optical element was constructed by means of gel electrophoresis. Five capillaries were filled with a methylene blue solution and inserted into a slab gel. An electrical potential was then applied to the slab gel. Methylene Blue in the capillaries underwent electrophoretic migration, forming clear blue bands in the gel. The bands functioned as a transmission grating, and diffracted a laser beam. The intensity of the diffracted light increased with increasing the concentration of methylene blue.

DOI： 10.2116/analsci.19.795

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The application of a Hadamard transform technique to microchip electrophoresis is described. The sample is electrokinetically injected into a separation channel and is then detected by diode laser-induced fluorometry. The sample and buffer solutions are introduced into the channel by controlling the high voltages applied to the solutions, according to a code determined by a Hadamard matrix. The S/N ratio of the signal in the electropherogram can be improved by a factor of 5 in comparison with that obtained by a conventional single-injection method, although an 8-fold improvement is theoretically predicted when a 255-order matrix is used.

DOI： 10.1021/ac026330e

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The degree of labeling, i.e., dye/protein ratio (DIP) is important for characterizing properties of dye labeling with proteins. A method for the determination of this ratio between a fluorescent cyanine dye and bovine serum albumin (BSA), based on the separation of the labeling mixture using micellar electrokinetic chromatography with diode laser-induced fluorescence detection, is described. Two methods for the determination of DIP were examined in this study. In these methods, a hydrolysis product and impurities, which are usually unfavorable compounds that are best excluded for protein analysis, were utilized to determine the amounts of dye bound to BSA. One is a direct method in which a ratio of the peak area of BSA to the total peak area of all the products produced in the labeling reaction was used for determining the average number of dye molecules bound to a single BSA molecule. The other is an indirect determination, which is based on diminution of all peak areas related to the products except for the labeled BSA. These methods were directly compared by means of a spectrophotometric method. The experimental results show that the indirect method is both reliable and sensitive. Therefore, DIP values can be determined at trace levels using the indirect method.

DOI： 10.1002/1522-2683(200208)23:15<2465::AID-ELPS2465>3.0.CO;2-G

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When a labeling reagent is used, in the determination of proteins by capillary electrophoresis with laser-induced fluorescence detection, the multiple labeling of proteins frequently occurs, which can degrade the separation efficiency. In order to understand the influence of the multiple labeling of proteins on separation efficiency, the band broadening caused by a labeling reaction between bovine serum albumin (BSA) and a cyanine fluorescent dye (Cy5) was investigated using micellar electrokinetic chromatography in conjunction with diode laser-induced fluorometry. With the aid of an internal standard, methylene blue, the height equivalent to the theoretical plate (HETP) ratio of BSA to methylene blue was used as an indicator for band broadening under optimum separation conditions. Labeling conditions, including reaction buffer pH, reaction time, and initial concentration of Cy5 to bovine serum albumin, were found to influence the HETP ratio. The separation efficiency for the labeled protein was degraded by experimental conditions employed in the labeling, which indicates an increase in the heterogeneity of the final products. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0021-9673(02)00357-6

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Hadamard transform capillary electrophoresis, which is based on a multiple sample injection technique, was combined with laser-induced fluorometry and utilized in the determination of analytes at subpicomolar levels. The sensitivity was substantially improved by increasing the order, i.e., the number of elements, of the Hadamard matrix. In facts the signal-to-noise ratio was enhanced 18-fold by the use of a matrix of order 2047. A feasibility study was carried out by computer simulation to study the detection of an average of less than a single molecule in a single injection volume. The signal peak was clearly observable even under conditions at which only 0.3 molecule is present in the volume. Thus, this approach is potentially useful for ultratrace analysis, in which conventional single-injection capillary electrophoresis cannot be applied.

DOI： 10.1021/ac011149b

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We describe the use of micellar electrokinetic chromatography with diode laser-induced fluorometry (MEKC-DLIF) as a tool to characterize a labeling reaction between sulfoindocyanine succinimidyl ester (Cy5), a cyanine fluorescent dye, and a model protein, bovine serum albumin (BSA). To decrease the influence of imprecise injection, methylene blue was added as an internal standard. Labeled BSA was completely separated from the unconjugated Cy5, and methylene blue under optimized conditions. A kinetic study of the reaction was performed by changing some parameters, such as reaction buffer pH, reaction buffer concentration and the initial concentration of BSA. A comparison between the current method and traditional methods was made.

DOI： 10.1002/1522-2683(200202)23:4<550::AID-ELPS550>3.0.CO;2-F

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The development of an optical channel, a new analytical technique for evaluating the elasticity of biological cells, is described in this study. Two types of erythrocyte cells, i.e., young and old cells, were examined via their introduction into a flowing medium, to which a laser beam was focused in the opposite direction. An erythrocyte cell is trapped in a laser beam by a gradient force, moves in the downstream direction, and is then elongated at the beam waist. The change in shape was measured directly using a microscope equipped with a charge-coupled-device camera. It is probable the main driving force for the cell deformation is a shear stress generated by a medium flow, since an estimate of the gradient force suggests that it is too small to change the shape of an erythrocyte. The average values of the elongation of young and old cells were 2.4 +/- 0.6 and 2.1 +/- 0.5, respectively. These values are in reasonably good agreement with values obtained using a rheoscope method. The deformation was measured without any physical contact to the solid surface, and therefore, damage to cells such as these are minimal.

DOI： 10.1021/ac010441g

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Capillary electrophoresis combined with semiconductor laser-induced fluorometry was applied to an immunoassay of human serum albumin. Human serum albumin was labeled with a fluorescent molecule (Cy5), which has an absorption maximum at 649 nm. The labeled albumin was purified by ultrafiltration in order to reduce signals, which are unreacted labeling reagent, product, and fragment products derived therefrom. After the purification, no signal for unreacted labeling reagent and fragment products was detectable in the electropherogram of the labeled albumin. The labeled albumin was then reacted with anti-albumin to form an immunocomplex, which was separated from the excess free albumin. The competitive immunoassay was used in the determination of human serum albumin in a controlled serum sample, using die labeled albumin. The obtained value was found to be 0.21 +/-0.02 mg/ml, which is in good agreement with other known values. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0378-4347(01)00228-6

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An application of capillary electrophoresis (CE) using sulfated beta -cyclodextrin (SCD) has been investigated for separating alkylphenols with different chain lengths, as well as bisphenol A and bisphenol S. In the absence of SCD in running buffer, all the phenols migrated at the same velocity as the electroosmotic now (EOF), whereas the addition of SCD effectively led to the baseline separation of alkylphenols on the basis of the difference in the abilities to bind into the hydrophobic cavity of CD. The host-guest binding constants between analyte phenols and SCD were evaluated from Benesi-Hildebrand plots of the data obtained by two independent methods, CE and UV-visible measurements, demonstrating that the greater the hydrophobicity of the phenols, the larger the binding constants. The effects of organic solvents on the resolution for alkylphenols and bisphenols were also examined. This system using SCD was effective for the separation of 4-octylphenol and 4-nonylphenol isomers having longer alkyl chains.

DOI： 10.2116/analsci.17.763

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG  

Capillary electrophoresis (CE) using sulfobetaine-type zwitterionic micelles as the background electrolyte (BGE) has been used to determine inorganic anions in human saliva. The zwitterionic micelles resulted in unique migration behavior for the separation of inorganic anions. They also prevented adsorption of proteins on the inner wall of the capillary. These properties of the zwitterionic micelles enabled the direct determination of inorganic anions in human saliva. Three species of inorganic anions, NO2-, NO3-, and SCN-, were found in real samples and the analysis was achieved within 3 min. Direct UV-absorption was used as the detection method and the detection limits for these anions were 2.0, 1.0, and 5.0 mu mol L-1, respectively (0.09, 0.06, and 0.30 mug mL(-1)).

DOI： 10.1007/s002160100804

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An optical funnel, a new technique for the evaluation of the force of a microorganism, was applied to the determination of the motility force of bovine sperm cells. In this approach, sperm cells, suspended in an aqueous solution, are introduced into a now cell, to which radiation pressure is applied from the direction opposite to a medium flow. The sperm cell, which is moving in a stream, is captured by radiation pressure and forced to move to the position at which the force induced by the laser radiation is equal to the force induced by a medium now. The sperm cell then escapes by its own power on the way to this equilibrium (entrapping) position. The radiation force increases with decreasing distance from the focal point, and as a result, the force of the sperm cell can be determined by measuring the position where the sperm cell escaped against the laser irradiation field. The motility farce of the sperm cell was measured in aqueous solution at different pH values and potassium ion concentrations, It was possible to measure more than 250 sperm cells in 3 h, Thus, the optical funnel has potential for use as a rapid and repetitive means for the determination of the motility force of the sperm cell.

DOI： 10.1021/ac991458q

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Optical chromatography, which is a technique for the separation of microscopic particles using a radiation force, is applied to kinetic studies of an immunoreaction. Polystyrene beads coated with antibodies react with antigens to produce conjugated beads, which comprise two beads and some antigens. The resulting conjugated beads are separated from the single beads. The detection limit of the antigen is &lt;1 ng ml(-1), which is smaller than that reported in a previous paper [T. Hatano, T Kaneta, T. Imasaka, Anal. Chem. 69 (1997) 2711], and can be achieved using 2 mu m-diameter beads. The sensitivity in the present method can be further enhanced by increasing the particle size. In addition, the dissociation reaction of the conjugated beads is evaluated by using an on-column reaction technique, which allows the direct monitoring of the formation and dissociation of the conjugated beads. The rate constant for the dissociation of the conjugated beads is determined to be 4.0 x 10(-3) s(-1) for the case of conjugated beads combined by a single bond. (C)2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0003-2670(99)00669-8

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This paper reports the first demonstration of a multiplex sample injection technique in capillary electrophoresis, The sample was injected into a capillary (effective length, 4 cm) as a pseudorandam Hadamard sequence by a photodegradation technique using a high-power gating laser, and the fluorescence signal, which was measured using a probe excitation beam, was decoded by an inverse Hadamard transformation. The signal-to-noise ratio was improved by a factor of 8, which was in good agreement with the theoretically predicted value of 8.02. This approach is potentially useful for the enhancement of the sensitivity by 3 orders of magnitude in high-resolution capillary electrophoresis, combined with fluorescence detection.

DOI： 10.1021/ac990625j

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A new type of chemical sensor based on light absorption is proposed. An array of zones alternatively containing the pH indicator thymolphthalein is formed in a gelatin film. By changing the sample solution from acidic to alkaline, a blue stripe appears in the gelatin film. This acts as a transmission grating and diffracts the introduced laser beam. Theory predicts that this method, which is based on light absorption/beam diffraction, is as sensitive as or more sensitive than fluorometry.

DOI： 10.1021/ac990216n

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A new method for the determination of particle size was developed using optical chromatography. After separating polystyrene particles, the laser power was gradually reduced, permitting the elution of small to large particles. Particle size was calculated from the laser power when the particle was eluted with a medium flow. This approach is more accurate than the technique previously reported because there is no need to determine the position of the beam waist. Advantages of the new approach are discussed theoretically and experimentally. The precision in size determination was improved by a factor of 3.3, i.e. the standard deviation in the measurement was reduced from 10 to 3% for 1 mu m beads by replacing optical chromatography with the present method. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0039-9140(98)00272-0

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Indirect fluorescence detection in cyclodextrin (CD)-modified micellar electrokinetic chromatography (MEKC) was demonstrated by using a diode laser as an excitation source. Amino-substituted polycyclic aromatic hydrocarbons (PAHs), which have no absorption band in the deep-red region, were used as model compounds since it was difficult to separate them by conventional MEKC. In the preliminary study, the separation of amino-substituted PAHs was achieved using gamma-CD as a modifier. The fluorescence intensity of the visualizing reagent, oxazine 750, increased in the presence of gamma-CD due to the complex formation of oxazine 750 with gamma-CD. Consequently, the peak areas of amino-substituted PAHs were observed to decrease with increasing concentration of gamma-CD. Detection limits were improved due to the enhancement in efficiency and dynamic reserve by adding small amounts of gamma-CD. The results obtained in this study were in good agreement with the proposed model. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0021-9673(98)00925-X

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DOI： 10.2116/analsci.14.1017

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A novel and potentially useful optical technique called an "optical funnel" has been developed, The technique utilizes a system in which a microorganism is suspended by equilibrium between the medium now and the radiation pressure applied in the opposite direction. At equilibrium, i.e., when the force of the laser pressure Is equal to the force of the moving stream, the microorganism is captured. At this point, it has the ability to escape on its own power, Since the force applied to the microorganism is calculated on the basis of a ray-optics model, it is possible to measure the magnitude of the microorganism's power. A Trachelomonas volvocina cell was determined to have a power of similar to 1 pN, This technique is superior to the laser trapping technique, which is currently used in these determinations, since it is possible to capture numerous organisms in a single experiment, thus allowing the calculation of the average power for an organism with minimal effort, in terms of repetitive samplings and measurements.

DOI： 10.1021/ac980199m

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Silver-coated capillaries were used for direct sample injection in multiplexed capillary electrophoresis. The absence of an additional electrode simplifies mechanical alignment, reduces contamination, and decreases the amount of sample needed. Capillaries were coated by a silver paint which is a suspension of silver particles in an organic solvent. To provide electrical contact, the upper part of the capillary and a platinum wire were wound together by a copper wire. Electrical resistance from the platinum wire to the tip of the capillary was small enough (7 Omega to 50 Omega) to inject large amounts of DNA samples. Electrokinetic injection from eight separate sample vials to eight capillaries was demonstrated for DNA sequencing by multiplexed capillary electrophoresis. Signal-to-noise ratio and resolution were good enough to call up to 350 base pairs.

DOI： 10.1002/(SICI)1521-4168(19980501)21:5<287::AID-JHRC287>3.0.CO;2-#

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Enantiomeric amino acids were labeled with a cyanine derivative (Cy5) for selective determination by capillary electrophoresis combined with diode laser-induced fluorometry. Cyanine-labeled glutamic acid has a high negative charge so that it was difficult to detect by conventional capillary zone electrophoresis due to its electrophoretic mobility being greater than the electroosmotic mobility. Thus, cyclodextrin-modified capillary gel electrophoresis using replaceable poly(vinylpyrrolidone) (PVP), which effectively suppresses the electroosmotic flow, was employed to separate Cy5-labeled amino acid enantiomers. The separation of six amino acid enantiomers could be achieved by using 1% PVP solution containing 70 mM gamma-cyclodextrin. It was also shown that PVP does not affect the selectivity of optical isomers. (C) 1998 Elsevier Science B.V.

DOI： 10.1016/S0021-9673(98)00023-5

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Optical chromatography, a new separation technique involving the use of a radiation force and a medium flow, is used for trace analysis of protein. Two polystyrene beads, coated with antibody (anti-mouse IgG), are combined in the presence of an antigen (mouse IgG). The bound (B) and free (F) beads are readily separated by optical chromatography, and the B/F ratio can be correlated with the concentration of antigen (protein). Nanomolar concentrations of protein can be measured by this technique. The rates of the forward and reverse immunological reactions were independently determined by measuring the time of formation and dissociation, respectively, of the immunobeads.

DOI： 10.1021/ac970081q

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To evaluate the performance of optical chromatography, a number of equations are theoretically derived using a ray-optics model. These mathematical formalisms are experimentally verified by determining the relationship between the velocity of motion of a polystyrene bead with respect to the intensity of an applied radiation force under the condition where there exists no applied fluid now. The force is confirmed to be at a maximum at the focal point and to decrease with increasing distance from this position. The radiation force is verified to be proportional to the square of the particle size when the particle diameter is much smaller than the beam diameter. In addition, the radiation force is ascertained to be proportional to the laser power. These results are in excellent agreement with the proposed theoretical model, which is based on ray optics. Furthermore, by analogy with conventional chromatography, fundamental parameters such as retention distance, selectivity, theoretical plate number, and resolution are calculated, and optimum conditions for chromatographic separation are discussed. Based on the results obtained, the dynamic range can be extended by increasing laser power and decreasing now rate. Peak broadening is primarily caused by variations in laser power and now rate of the medium for large particles (&gt; 1 mu m). It is possible, in theory, to distinguish particles whose diameters differ by less than 1% for particles with a diameter larger than 1 mu m. Three sizes of polystyrene beads are well separated at a now rate of 20 mu m s(-1) and a laser power of 700 mW. This technique is also applied to the separation of human erythrocytes. Two fractions, one consisting of cells ranging from 1.5 to 2.4 mu m in diameter and another consisting of cells ranging from 3.5 to 5.7 mu m in diameter, are observed. Optical chromatography is useful for separation and size measurement of particles and biological cells.

DOI： 10.1021/ac970079z

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Semiconductor laser-induced fluorescence detection of native (target) DNA has been accomplished by free-solution capillary electrophoresis (CE) using an oligonucleotide labeled with a cyanine dye as a DNA probe. A mixture of probe DNA and target DNA, which is complementary to probe DNA, is incubated to form hybrid DNA; the mixture is then injected into a capillary. Single-stranded probe DNA and double-stranded hybrid DNA were separated by free-solution CE. A 19mer oligonucleotide labeled with fluorescein isothiocyanate (FITC) was used as probe DNA in a preliminary study. The stability of double-stranded DNA during migration was evaluated by changing the temperature of the solution in the capillary, i.e. the applied voltage in CE. The dissociation of double-stranded DNA was appreciable at high applied voltages. Thus, suppressing the temperature in the capillary, i.e. optimization of the voltage, was required in order to prevent the dissociation of double-stranded DNA. Furthermore, a new labeling reagent, a cyanine derivative, was synthesized in order to be applied to semiconductor laser-induced fluorometry. The detection limit was 8 x 10(-9) M for probe DNA.

DOI： 10.2116/analsci.12.875

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The migration behaviour of niacin derivatives was investigated by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). When the pH of the buffer solution is lower than the pK(a) of the pyridine ring in the niacin derivatives, they are positively charged by protonation on the pyridine ring and migrate electrophoretically. The mobilities of niacin derivatives in CZE were controlled by the pH of the migrating buffer. Good separation of thirteen niacin derivatives was achieved at pH 2.8. Further, to shorten the analytical time and to achieve a more complete separation, an investigation by MEKC using sodium dodecyl sulfate micelles was performed. All thirteen niacin derivatives were eluted within 30 min and a satisfactory separation was achieved.

DOI： 10.1016/0021-9673(95)00634-6

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A new and potentially useful method for separation of particles by optical radiation pressure is described and demonstrated in this study, A laser beam is focused into the solution, which contains particles counterflowing coaxially in a capillary, The particle is focused into the center line of the laser beam by radiation pressure, The particle is turned around, accelerated, passed through a beam waist, decelerated by a liquid now, and drifts, at which point the radiation pressure is identical to the force induced by the liquid now, resulting in separation of particles as a function of size.

DOI： 10.1021/ac00107a003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A semiconductor laser is used as an exciting light source in indirect fluorescence detection of neutral samples separated by micellar electrokinetic chromatography. A surfactant, tetradecyltrimethylammonium chloride, is used to form micelles, which act as a pseudostationary phase in the chromatographic separation. This surfactant has a positive charge, thus preventing adsorption of a visualizing agent, oxazine 750 (which contains a positive charge), to the capillary wall (which is negatively charged). The detection mechanism is based on the exclusion of the fluorophore, which is located in the hydrophilic part of the micelle, by a hydrophilic sample. The fluorescence intensity is reduced when the fluorophore is released into the aqueous solution. Separations of several aromatic compounds are demonstrated, and the parameters affecting the selectivity are discussed.

DOI： 10.1021/ac00101a007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Polycyclic aromatic hydrocarbons (PAHs) were separated by micellar electrokinetic chromatography and were detected by laser fluorometry. The PAHs with large molecular weights were separated by using dimethylformamide as an organic modifier. A He-Cd laser (325 nm, 5 mW) or a blue semiconductor laser (415 nm, 50 mu W) was used as an exciting light source. The detection limit (S/N = 3) for perylene was 1.4 X 10(-7) M under He-Cd laser excitation or 3.4 x 10(-7) M under semiconductor laser excitation.

DOI： 10.1016/0003-2670(94)00317-F

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE - INT SOC OPTICAL ENGINEERING  

DOI： 10.1117/12.208464

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：VCH PUBLISHERS INC  

Three organic modifiers, methanol, acetonitrile, and dimethylformamide, were used as organic modifiers to improve the resolution of hydrophobic compounds in micellar electrokinetic chromatography. The capacity factor decreased with increasing concentration of organic modifier. Acetonitrile and dimethylformamide were more effective modifiers to decrease the capacity factor than methanol. Maximum resolution was obtained when the capacity factor was reduced to about 2. Methanol enhanced the resolution for less hydrophobic compounds, while acetonitrile and dimethylformamide were better modifiers to improve the resolution for strongly hydrophobic compounds.

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The effect of a cationic surfactant, cetyltrimethylammonium chloride (CTAC), on the electroosmotic mobility and the electrophoretic mobility of organic anions in capillary zone electrophoresis was investigated. The electroosmotic mobility showed four stepwise changes, including a reversal, with increasing CTAC concentration. The behaviour, especially the reversal of the electroosmotic mobility, was explained by assuming the formation of hemimicelles on the capillary wall. That is, CTAC first adsorbs individually by electrostatic interactions and then begins to associate into hemimicelles by Van der Waals attraction. The formation of hemimicelles changes the surface charge of the capillary wall from negative to positive and causes the reversal of the electroosmotic mobility. The effective electrophoretic mobilities of organic anions such as benzoic acid analogues were also influenced by the CTAC concentration. It was concluded that the behaviour was due to the interaction with hemimicelles on the capillary wall and also ion association with the monomer of CTAC and the interaction of micelles in bulk solution.

DOI： 10.1016/0021-9673(93)83189-Y

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Glucose was investigated as a possible additive for the improvement of resolution in micellar electrokinetic capillary chromatography. Addition of glucose to the micellar solution facilitated the complete separation of a mixture of nine nucleosides by both extending the elution range and changing the selectivity. Extension of the elution range can be attributed to an increase in the electrophoretic mobility of the micelle. It is also apparent that glucose selectively reduces the distribution coefficients for solutes containing a hydrophilic functional group. This effect was valuable in the separation of some solutes with hydrophilic functional groups and large capacity factors.

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The interactions between inorganic anions and a cationic surfactant were investigated using micellar electrokinetic capillary chromatography (MECC). Using cetyltrimethylammonium chloride (CTAC) as a cationic surfactant, the effective electrophoretic mobilities of inorganic anions decreased due to two processes. The first was the ion association equilibria with a monomeric surfactant below the critical micellar concentration (cmc) and the other was partitioning into the micelle above the cmc. Fundamental equations for migration of ionic species in MECC were derived using the effective electrophoretic mobility as an electrochemical parameter. Ion association constants of inorganic anions with cationic surfactant and distribution coefficients into the micelle were estimated on the basis of these equations.

DOI： 10.1021/ac00031a017

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Language：English   Publisher：ELSEVIER SCIENCE BV  

The isotachophoretic separation of catecholamines based on inclusion complex formation with beta-cyclodextrin (beta-CD) was investigated. Separability was improved with increasing concentration of beta-CD in the leading electrolyte. It was found that a neutral surfactant, added to suppress the electroosmotic flow and to form sharp zone boundaries, affects the resolution. Six catecholamines were separated by using complex formation with beta-CD.

DOI： 10.1016/0021-9673(91)85186-J

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Language：English   Publisher：JAPAN SOC ANALYTICAL CHEM  

Developments in the migrating systems to improve the resolution and sensitivity of capillary tube isotachophoresis (ITP) are described. They are related to the use of complex-forming equilibria in the migrating column and nonaqueous solvents as the migrating medium. The considered sources of ligand for the complex-forming equilibria are (a) the counter ion in the leading electrolyte, (b) the neutral ligands added into the leading electrolyte and (c) the terminating ions. Actual separations performed by these systems are shown and their features and advantages are discussed. Migrating systems consisting of nonaqueous solvents such as dimethylformamide and acetonitrile enable the migration of analyte species which can not be realized in an aqueous medium to improve the selectively and sensitivity. Combining ITP with solvent extraction provides useful analytical techniques.

DOI： 10.2116/analsci.7.673

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Language：English   Publisher：ELSEVIER SCIENCE BV  

EDTA and TTHA solutions were used as terminating electrolytes and 10 mM HCl containing 45% (v/v) acetone as the leading electrolyte. Gd, Eu, Sm, Pr, Ce and La ions were separated as their anionic chelates when EDTA was used as the terminating ion. The migration order of the chelates was in accord with the order of their stability constants.

DOI： 10.1016/S0021-9673(01)88841-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

In order to improve the resolution of catecholamines, the control of both the electroosmotic and the electrophoretic mobilities were carried out. The former was controlled by the addition of borate ion and a change in pH. The control of the latter was carried out by addition of a cationic surfactant. Ten catecholamines were sufficiently separated.

DOI： 10.1016/S0021-9673(01)88859-2

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Language：English   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/0021-9673(90)85076-8

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Language：English   Publisher：JAPAN SOC ANALYTICAL CHEM  

DOI： 10.2116/analsci.6.467

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/S0021-9673(01)84248-5

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Language：English   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/S0021-9673(00)94120-7

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Language：English   Publisher：JAPAN SOC ANALYTICAL CHEM  

DOI： 10.2116/analsci.5.217

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Language：English   Publisher：ELSEVIER SCIENCE BV  

DOI： 10.1016/0021-9673(88)90048-9

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Total pages：527   Language：English

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ASIN

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Total pages：512   Responsible for pages：61－68   Language：English Book type：Scholarly book

Total pages：234   Responsible for pages：11－23   Language：English Book type：Scholarly book

Language：Japanese Book type：Textbook, survey, introduction

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Language：Japanese  

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Language：Japanese   Publisher：The Spectroscopical Society of Japan  

DOI： 10.5111/bunkou.44.21

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J-GLOBAL

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Event date： 2020.5.25 - 2020.5.27

Language：English   Presentation type：Oral presentation (invited, special)  

Country：Japan  

Event date： 2020.5.23 - 2020.5.24

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：札幌 (Web)   Country：Japan  

Event date： 2020.5.23 - 2020.5.24

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌 (Web)   Country：Japan  

Event date： 2020.5.23 - 2020.5.24

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2020.5.23 - 2020.5.24

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌 (Web)   Country：Japan  

Event date： 2020.5.23 - 2020.5.24

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌 (Web)   Country：Japan  

Event date： 2020.2.7

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Changwon, Korea   Country：Korea, Republic of  

Event date： 2019.12.1 - 2019.12.5

Language：English   Presentation type：Poster presentation  

Venue：Kyoto, Japan   Country：Japan  

Event date： 2019.11.6 - 2019.11.8

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：埼玉大学   Country：Japan  

Event date： 2019.9.25 - 2019.9.27

Language：English   Presentation type：Oral presentation (keynote)  

Venue：Malang, Indonesia   Country：Indonesia  

Event date： 2019.9.11 - 2019.9.13

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学   Country：Japan  

Event date： 2019.9.11 - 2019.9.13

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：千葉大学   Country：Japan  

Event date： 2019.9.1 - 2019.9.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Toulouse, France   Country：France  

Event date： 2019.9.1 - 2019.9.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Toulouse, France   Country：France  

Event date： 2019.6.6 - 2019.6.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山   Country：Japan  

Event date： 2019.5.18 - 2019.5.19

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州   Country：Japan  

Event date： 2019.5.18 - 2019.5.19

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州   Country：Japan  

Event date： 2019.5.18 - 2019.5.19

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.5.18 - 2019.5.19

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州   Country：Japan  

Event date： 2019.5.18 - 2019.5.19

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州   Country：Japan  

Event date： 2019.2.21 - 2019.2.22

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Changwon, Korea   Country：Korea, Republic of  

Event date： 2019.2.7 - 2019.2.8

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Bangkok, Thailand   Country：Thailand