Faculty Profiles - KIWA Toshihiko

Papers - KIWA Toshihiko

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Thickness Measurement at High Lift-Off for Underwater Corroded Iron-Steel Structures Using a Magnetic Sensor Probe

Shoya Adachi, Minoru Hayashi, Taisei Kawakami, Yuto Ando, Jin Wang, Kenji Sakai, Toshihiko Kiwa, Toshiyuki Ishikawa, Keiji Tsukada

Sensors 2022.12

Dispersion of Fe₃O₄ Nanoparticle Beads Driven by Femtosecond Laser Pulses for Quantitative Magnetic Immunoassay Measurements

Kouhei Kishimoto, Hiroto Kuroda, Misaki Tsubota, Kei Yamashita, Jin Wang, Kenji Sakai, Mohd Mawardi Saari, Toshihiko Kiwa

ACS Applied Nano Materials 5 ( 11 ) 17258 - 17263 2022.11

Electric Potential Mapping of All-Solid-State Lithium Ion Batteries using A Terahertz Chemical Microscope

Ryota Tomie, Taketo Yamaguchi, Masashi Shimizu, Kashu Hamada, Takashi Teranishi, Hidetoshi Nose, Masaki Kobayashi, Jin Wang, Kenji Sakai, Toshihiko Kiwa

2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz) 2022.8

Terahertz Chemical Microscope for Calcium Ions and Stress Biomarker Sensing

Jin Wang, Sota Yoshida, Masaki Ando, Kenji Sakai, Toshihiko Kiwa

2022 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz) 2022.8

Optimization of Microchannels and Application of Basic Activation Functions of Deep Neural Network for Accuracy Analysis of Microfluidic Parameter Data

Feroz Ahmed, Masashi Shimizu, Jin Wang, Kenji Sakai, Toshihiko Kiwa

Micromachines 2022.8

Optimization of Microchannels and Application of Basic Activation Functions of Deep Neural Network for Accuracy Analysis of Microfluidic Parameter Data

Feroz Ahmed, Masashi Shimizu, Jin Wang, Kenji Sakai, Toshihiko Kiwa

Micromachines 2022.8

Rational Design of Peptides Derived from Odorant-Binding Proteins for SARS-CoV-2-Related Volatile Organic Compounds Recognition

Jin Wang, Kenji Sakai, Toshihiko Kiwa

Molecules 27 ( 12 ) 3917 - 3917 2022.6

Rational Design of Peptides Derived from Odorant-Binding Proteins for SARS-CoV-2-Related Volatile Organic Compounds Recognition

Jin Wang, Kenji Sakai, Toshihiko Kiwa

Molecules 2022.6

A Versatile Terahertz Chemical Microscope and Its Application for the Detection of Histamine

Jin Wang, Kosuke Sato, Yuichi Yoshida, Kenji Sakai, Toshihiko Kiwa

Photonics 2022.1

A Versatile Terahertz Chemical Microscope and Its Application for the Detection of Histamine

Jin Wang, Kosuke Sato, Yuichi Yoshida, Kenji Sakai, Toshihiko Kiwa

Photonics 2022.1

Crack Detection for Welded Joint with Surface Coating Using Unsaturated AC Magnetic Flux Leakage

Minoru Hayashi, Taisei Kawakami, Shoya Adachi, Jin Wang, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada, Yohei Miyamoto, Mikihito Hirohata, Toshiyuki Ishikawa

IEEE Transactions on Magnetics 1 - 1 2022

Development of impedance measurement of lithium ion batteries electrode using terahertz chemical microscope

Masashi Shimizu, Ryoji Yamanaka, Takashi Teranishi, Jin Wang, Kenji Sakai, Keiji Tsukada, Toshihiko Kiwa

Electrical Engineering in Japan 214 ( 4 ) 2021.12

Visualization of Charge-Transfer Complex for the Detection of 2,4,6-Trinitrotoluene Using Terahertz Chemical Microscope

Jin Wang, Hiroki Nagata, Masaki Ando, Yuichi Yoshida, Kenji Sakai, Toshihiko Kiwa

JOURNAL OF THE ELECTROCHEMICAL SOCIETY 168 ( 11 ) 2021.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELECTROCHEMICAL SOC INC

This study focuses on the visualization of a charge-transfer complex, namely a Meisenheimer complex, for the detection of uncharged 2,4,6-trinitrotoluene (TNT) explosives by developing a terahertz chemical microscope (TCM) imaging system. The organic amine 3-aminopropyltriethoxysilane (APTES) was immobilized on an SiO2-film-coated TCM sensing plate, where it interacted with TNT molecules. The surface electrical potential distribution of TNT, APTES, and the charge-transfer complex was mapped. An electrical potential shift occurred due to the formation of a charge-transfer complex between the electron-rich amino-silane APTES and electron-deficient TNT molecules on the surface of the sensing plate. The electrical imaging and detection of TNT explosives by using the TCM imaging system were demonstrated by measuring the amplitude of the terahertz pulse caused by this electrical potential shift. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane and N1-(3-trimethoxysilylpropyl)diethylenetriamine were used for further evaluation and comparison of color changes arising from the amine-TNT interactions. The results have shown that TCM imaging is a promising method for the detection of uncharged TNT explosives at a low (sub-parts-per-million) concentration.

DOI： 10.1149/1945-7111/ac3a2c

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Design and validation of microfluidic parameters of a microfluidic chip using fluid dynamics

Feroz Ahmed, Yuichi Yoshida, Jin Wang, Kenji Sakai, Toshihiko Kiwa

AIP ADVANCES 11 ( 7 ) 2021.7

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

The internal fluidic parameters of microfluidic channels must be analyzed to solve fundamental microfluidic problems, including microscale transport problems involving thermal analysis, chemical reactivity, velocity, pressure drop, etc., for developing good-quality chemical and biological products. Therefore, the characterization and optimization of the interaction of chemical and biological solutions through microfluidic channels are vital for fluid flow design and engineering for quality assurance in microfluidic platforms. As the internal structures and kinetics of microfluidic channels are becoming increasingly complex, experiments involving optimal fluidic and transport designs are challenging to perform with high accuracy. However, highly integrated simulation tools can guide researchers without specialized computational fluid backgrounds to design numerical prototypes of highly integrated devices. In this study, a microfluidic chip with two inlet wells and one outlet well was fabricated from polydimethylsiloxane following which simulations were performed using an ANSYS Fluent tool influenced by computational fluid dynamics at a nearly identical scale. The pressure drop and velocity profiles of the interaction of two pH buffer solutions (pH 4 and 10) through the designed microfluidic chip were qualitatively estimated from experimental data analysis and validated with the simulation results obtained from the CFD-influenced ANSYS Fluent tool. (c) 2021 Author(s).

DOI： 10.1063/5.0056597

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Noninvasive, label-free, and quantitative monitoring of lipase kinetics using terahertz emission technology

Sharifun Nahar, Ahmed Mohamed, Xavier Ropagnol, Amir Hassanpour, Toshihiko Kiwa, Tsuneyuki Ozaki, Marc A. Gauthier

BIOTECHNOLOGY AND BIOENGINEERING 118 ( 11 ) 4246 - 4254 2021.7

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

Enzymes catalyze chemical transformations of great importance in many fields, and analysis of the rate of these transformations is equally important. The latter are typically monitored using surrogate substrates that produce quantifiable optical signals, owing to limitations associated with "label-free" techniques that could be used to monitor the transformation of original substrate molecules. In this study, terahertz (THz) emission technology is used as a noninvasive and label-free technique to monitor the kinetics of lipase-induced hydrolysis of several substrate molecules (including the complex substrate whole cow's milk) and horseradish peroxidase-catalyzed oxidation of o-phenylenediamine in the presence of H2O2. This technique was found to be quantitative, and kinetic parameters are compared to those obtained by proton NMR spectroscopy or UV/Vis spectroscopy. This study sets the stage for investigating THz emission technology as a tool for research and development involving enzymes, and for monitoring industrial processes in the food, cosmetic, detergent, pharmaceutical, and biodiesel sectors.

DOI： 10.1002/bit.27893

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Properties of single- and multi-core magnetic nanoparticles assessed by magnetic susceptibility measurements

Mohd Mawardi Saari, Mohd Herwan Sulaiman, Nurul Akmal Che Lah, Zulkifly Aziz, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 528 2021.6

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

Characterization of structural and magnetic properties of MNP ensembles is crucial in tailoring their performance for biomedical applications. In this work, we evaluate the size distribution of magnetic cores in single- and multi-core nanoparticles in water suspension using transmission electron microscopy (TEM) and static magnetization curve, with the geometrical core size ranges from 8.3 to 40.2 nm. A reasonable core size derived from the magnetization curve is obtained in comparison to the geometrical size from TEM image. The magnetic moment distribution possibly reveals that the reduction of effective magnetic core size is due to the magnetization degradation in cores. The hydrodynamic size and average anisotropy energy ratio obtained from the AC susceptibility response of MNPs from 5 Hz to 100 kHz are also evaluated. The complex distribution of relaxation time is constructed by applying a non-negative least square method to an AC susceptibility model that incorporates the inter- and intra-potential-well contributions. It is found that a log-normal distribution might not be adequate to represent the hydrodynamic size distribution reconstructed from the AC susceptibility responses of the suspended samples. It is demonstrated that the AC susceptibility model used in this study can be used to fairly estimate the average anisotropy energy ratio for MNP ensembles dominated by thermally blocked particles. Moreover, it can be suggested that besides the geometrical core size, the degree of core aggregation also plays an important role in determining the anisotropy energy ratio and effective magnetic moment.

DOI： 10.1016/j.jmmm.2021.167812

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Evaluation of penetration speed of liquids into skin using a terahertz time-of-flight method

Sota Sueda, Tomoya Niki, Kenji Sakai, Toshihiko Kiwa

JAPANESE JOURNAL OF APPLIED PHYSICS 60 ( 3 ) 2021.3

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

Analyzing the penetration of cosmetic/medical lotions and creams into the skin is important for evaluating their effectiveness. Hence, the penetration speed of liquids into chicken and pig skins was evaluated using a terahertz (THz) time-of-flight method. An arsenide-free disposable THz emitter comprising a silicon film on a sapphire substrate was developed for practical measurements using skin samples. The skin sample was mounted on the THz emitter surface directly so that the generated THz pulses in the silicon film were easily focused on the skin sample. To evaluate the time evolution of the penetration depth, the arrival times of the reflected THz pulses at the edge of the liquid-penetrated region on the skin were observed. As a preliminary experiment, measurements using a stack of conventional glass slides were conducted. In addition, the penetration speed into the chicken and pig skin was compared to prove the practical applicability of our method.

DOI： 10.35848/1347-4065/abdd03

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Terahertz imaging technique for monitoring the flow of buffer solutions at different pH values through a microfluidic chip

Feroz Ahmed, Atsuya Mahana, Katsuya Taniizumi, Jin Wang, Kenji Sakai, Toshihiko Kiwa

Japanese Journal of Applied Physics 60 ( 2 ) 2021.2

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

© 2021 The Japan Society of Applied Physics Polydimethylsiloxane (PDMS)-based mold prepared using a 3D-printed structure is a cost-effective material and tool to fabricate robust microfluidic chips (MCs) without requiring expensive clean room facilities. A capillary-based MC made of PDMS can be attached onto a glass substrate to visualize the chemical reactions in different types of pH buffer solutions (BSs) flowing through microflow channels (MFCs) using terahertz (THz) image sensing technology. In this study, we designed a microfluidic structure with two inlet wells and an outlet well, equipped with a Si:sapphire substrate to visualize the chemical interaction between BSs injected at different pH values (4 and 10) through an MFC. THz imaging maps were captured during the flow of the BSs using a THz chemical microscope, and the fluid dynamics was studied. We determined and plotted the variation in the THz amplitude data with respect to the BS concentration and analyzed the characteristics of the data.

DOI： 10.35848/1347-4065/abd86e

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Imaging of Defect Signal of Reinforcing Steel Bar at High Lift-Off Using a Magnetic Sensor Array by Unsaturated AC Magnetic Flux Leakage Testing

Minoru Hayashi, Taisei Kawakami, Taisuke Saito, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

IEEE Transactions on Magnetics 57 ( 2 ) 2021.2

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

© 1965-2012 IEEE. Reinforcing steel bars (rebars) in the concrete need to be inspected to prevent the structure from collapsing. Magnetic nondestructive testing methods can inspect the rebar without the influence of concrete. However, since the inspection is performed at a high lift-off on concrete, a strong applied magnetic field is required in order to measure a sufficient magnetic signal generated from the rebar. In addition, if a single sensor is used to measure the rebar, this requires the scanning of extensive area along the invisible rebar covered with the concrete. To overcome these problems, we have developed a method to detect and image the defect signal using unsaturated ac magnetic flux leakage (USAC-MFL) testing combining a magnetic sensor array probe. The USAC-MFL is a method that uses an alternating magnetic field in the initial magnetization characteristics of steel, which does not require a strong applied magnetic field compared to the conventional MFL method. By measuring the magnetic flux from the rebar in a wide area using the magnetic sensor array probe, the defect signal was able to be detected and imaged. The defect signal was able to be confirmed up to the lift-off of 100 mm even when the defect was half length of the rebar or located on the back side.

DOI： 10.1109/TMAG.2020.3017722

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A sensitive magnetometer utilizing high-T <inf>c</inf> SQUID for magnetic property characterization

Mohd Mawardi Saari, Kenji Sakai, Toshihiko Kiwa, Keiji Tsukada

Microsystem Technologies 27 ( 9 ) 3413 - 3420 2021

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

© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature. Magnetometer is one of the indispensable instruments utilized for the magnetic property characterization of materials, where it evaluates the magnetic response originated from the materials. The non-invasive magnetic technique has promoted magnetometer to be utilized in new applications such as in biomedical applications. In this work, we report the development of a magnetometer utilizing a high critical temperature superconducting quantum interference device (high-Tc SQUID) and a flux transformer composed of an induction coil. The high-Tc SQUID is used in order to realize high sensitivity, compact, and low-running cost magnetometer for biomedical applications such as characterization of magnetic nanoparticles. A first-order planar gradiometer with a compensation coil was used as the detection coil to achieve high sensitivity and cancellation factor. We fabricate an electromagnet with primary and small secondary excitation coils to enable a wide range of the excitation magnetic field with a high resolution. To reduce the magnetic field’s drift, we apply a digital feedback program to control the electrical current of the electromagnet. The performance of the developed system is demonstrated by measuring the magnetization curve and AC responses of an iron oxide composite sample. The sensitivity showed by the developed magnetometer reveals its potential for a highly sensitive magnetic property characterization.

DOI： 10.1007/s00542-020-05198-6

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