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Dive into the research topics where Katsuya Morimoto is active.

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Featured researches published by Katsuya Morimoto.


Electrophoresis | 2008

Electrochemical techniques for microfluidic applications

Fumihiro Sassa; Katsuya Morimoto; Wataru Satoh; Hiroaki Suzuki

Electrochemical principles provide key techniques to promote the construction of bio/chemical microsystems of the next generation. There is a wealth of technology for the microfabrication of bio/chemical sensors. In addition, microfluidic transport in a network of flow channels, pH regulation, and automatic switching can be realized by electrochemical principles. Since the basic components of the devices are electrode patterns, the integration of different components is easily achieved. With these techniques, bio/chemical assays that require the exchange of solutions can be conducted on a chip. Furthermore, autonomous microanalysis systems that can carry out necessary procedures are beginning to be realized. In this article, techniques developed in our group will be comprehensively introduced.


Analytical Chemistry | 2008

Automatic Electrochemical Micro-pH-Stat for Biomicrosystems

Katsuya Morimoto; Mariko Toya; Junji Fukuda; Hiroaki Suzuki

A microelectrochemical pH-stat with an automatic feedback function was fabricated. The operation of the device is based on the nonstandard use of an electrochemical three-electrode system with a pH-sensitive reference electrode, a Ag/AgCl working electrode, and an iridium auxiliary electrode that functions as an actuator to adjust the solution pH. The combination of the electrodes caused a negative feedback in response to a pH change. The shift of the potential of the pH-sensitive reference electrode caused an overpotential on the Ag/AgCl working electrode, which then caused a significant current increase. This led to the electrolysis of water on the auxiliary electrode and the rapid recovery of the pH. The negative feedback function to stabilize the initial state could be confirmed for changes to both the acidic and basic directions. The performance of the pH-stat was characterized in the titration of acetic acid or ammonia. The charge generated in the feedback process changed linearly with respect to the concentration. The pH-stat was also used in the determination of urea by urease and that of the activities of trypsin and pepsin while maintaining the optimum pH for the enzymes. The pH to be fixed could be changed by changing the working electrode potential. Moreover, the two pH-stats could be used to form a pH gradient in a microflow channel by fixing the pH values at two positions.


Biosensors and Bioelectronics | 2009

Electrowetting-based pH- and biomolecule-responsive valves and pH filters.

Shigeki Yamaguchi; Katsuya Morimoto; Junji Fukuda; Hiroaki Suzuki

An electrowetting-based pH-responsive valve that uses a nonstandard electrochemical three-electrode system is proposed. The system comprises a gold valve electrode and an iridium electrode that act as the working and auxiliary electrodes, depending on the purpose, while an iridium oxide pH-sensitive electrode acts as the reference electrode. To make the valve open at pH higher than a threshold, the gold valve electrode is used as the working electrode and a voltage is applied to it with respect to the pH-sensitive reference electrode. To make the valve open at pH lower than the threshold, the gold valve electrode is used as the auxiliary electrode, while the iridium electrode is used as the working electrode. The wettability of the valve electrode is altered when a voltage is applied to it. When the pH of a solution crosses the threshold, the potential of the gold valve electrode exceeds a threshold potential because of the change in the potential of the pH-sensitive reference electrode. Consequently, the gold valve electrode becomes more hydrophilic, thereby allowing the solution to pass through the valve. Furthermore, by combining two valve electrodes, we realized a pH filter that allows solutions with pH within a limited range to pass through it. Urea- and glucose-responsive valves that opened at concentrations higher than the threshold could also be formed by immobilizing an enzyme on the pH-sensitive reference electrode.


Japanese Journal of Applied Physics | 2006

Superhydrophobic phenomena on three-dimensional surface structures coated with plasma polymer

Shuichi Tsuruta; Katsuya Morimoto; Toshihiro Hirotsu; Hiroaki Suzuki

Three-dimensional surface structures composed of micropillars with different diameters (8–110 µm) and interpillar distances were fabricated using a thick-film photoresist, and the surface was modified with a hydrophobic plasma-polymerized film using hexamethyldisiloxane (HMDS) as a monomer. Surface hydrophobicity was examined by measuring contact angle using a pure water droplet. The effect of adding ethanol was also examined. Water static contact angle increased significantly on the surface coated with the HMDS plasma polymer. Structural parameters, including the diameter and height of the micropillars, were changed, as was the interpillar distance. The dependence of apparent contact angle on these parameters was explained using Cassies and Wenzels models.


ieee sensors | 2005

Micro analysis system with an integrated microfluidic system based on electrowetting

Wataru Satoh; Hiroki Hosono; Katsuya Morimoto; Hiroaki Suzuki

Electrowetting was used to fabricate an integrated highly efficient microfluidic transport system. As an option, a row of elongated gold working electrodes were used to generate a driving force to mobilize a solution in a flow channel. Flow velocity could be changed by changing the potential of the working electrode. The solutions could be transported to any desired direction without using any valves. In another option, a working electrode was formed in a hydrophilic flow channel and used as a valve. When the valve was switched on, a solution in the flow channel passed the area and went forward by capillary action. Furthermore, two solutions transported through two flow channels could be mixed based on the same principle. Integrated biosensing systems could easily be constructed using these microfluidic components. In this study, the concentration of L-amino acids was determined by generating electrochemical luminescence (ECL) on an integrated platinum working electrode. Also, the activity of protease could be determined using an integrated potentiometric pH-sensing system


Journal of Applied Physics | 2009

Towards microsystems for automatic acquisition of in vivo gastrointestinal information

Katsuya Morimoto; Shigeki Yamaguchi; Junji Fukuda; Hiroaki Suzuki

The possibility to develop a microanalysis system for the acquisition of gastrointestinal information is presented here. The system consists of four assay sites for trypsin, pepsin, and other biochemical compounds. The major components in each assay site were a pH-responsive valve, a pH-stat used to maintain the pH of the solution to be analyzed and used for electrochemical pH-titration, and a freeze-dried enzyme substrate stored in the pH-stat. The operation of the valve is based on electrowetting, and the valve is made pH-responsive by means of a nonstandard three-electrode system. The sample solution was automatically injected into the compartment and rapidly dissolved into the substrate layer. The automatic pH-stat, based on another nonstandard use of the electrochemical three-electrode system, maintained the solution pH and, at the same time, conducted pH-titration. The determination of the activity of the proteases was conducted at their optimum pHs. The output current showed a clear dependence on t...


ieee sensors | 2007

Micro Analysis System for Digestive Enzymes Based on Integrated Automatic pH-Stats

Katsuya Morimoto; Junji Fukuda; Hiroaki Suzuki

Aiming for the application to an ingestible micro system, a microanalysis system for the determination of the activity of digestive enzymes was realized. The analysis was conducted by using an on-chip micro-pH-stat which worked on the basis of an irregular use of the electrochemical three-electrode system. The operation using a potentiostat caused a negative feedback, maintaining the solution pH at a constant value. The system used a freeze-dried enzyme substrate. The very porous matrix facilitated rapid dissolution and mixing with the enzyme solution. The determination of the activity of pepsin and trypsin was conducted at the optimum pHs for the respective enzymes by measuring the generated charge accompanying the hydrolysis of hemoglobin. In both cases, a distinct increase in the generated charge was observed as the enzymatic reaction proceeded. Linear relationships were observed between the initial rate of charge increase and the activity of the enzymes.


TRANSDUCERS 2009 - 2009 International Solid-State Sensors, Actuators and Microsystems Conference | 2009

Automatic on-chip sequential processing for bio-microsystems

Noriyuki Ohnishi; Wataru Satoh; Katsuya Morimoto; Junji Fukuda; Hiroaki Suzuki

As a trial to realize an automatic microfluidic system, functions such as automatic valve operation, adjustment of mixing time, pH-regulation, and sensing were integrated on a chip. Microfluidic transport was achieved by capillary action. The transport and merge of solutions was controlled by gold working electrodes that functioned as valves. The mixing valve was also used as a delay line to take enough time for mixing. The pH of the mixed solution could be adjusted using an electrochemical pH-regulator, and gaseous ammonia produced from the solution could be measured using an air-gap ammonia sensor. The function of the entire system was checked in the enzymatic reaction of urea.


TRANSDUCERS 2007 - 2007 International Solid-State Sensors, Actuators and Microsystems Conference | 2007

Microanalysis System Based on Electrochemiluminescence with Automatic Mixing and pH-Regulation Functions

Wataru Satoh; Hiroki Hosono; Mariko Toya; Katsuya Morimoto; Junji Fukuda; Hiroaki Suzuki

In conducting a bio/chemical analysis on a chip, several different procedures are usually required. In this study, we demonstrate the possibility to conduct necessary procedures on a single chip. Our fabricated device has functions such as automatic mixing of solutions, pH-regulation, and detection based on electrochemiluminescence (ECL). A reagent solution containing Ru(bpy)3 2+ and a sample solution containing an amino acid were mixed and the solution pH was adjusted using the above- mentioned mechanisms. When a potential was applied to the electrode for ECL, red luminescence was observed. The ECL intensity increased with the increase in the concentration of amino acids.


ieee sensors | 2006

On-Chip pH-Regulator and its Application to Bio/Chemical Sensing

Katsuya Morimoto; Mariko Toya; Junji Fukuda; Hiroaki Suzuki

An on-chip pH-regulator based on an irregular use of an electrochemical thin-film three-electrode system will be presented. The device is operated using only an ordinary potentiostat. A pH-sensitive electrode was used for the reference electrode, whereas a non-polarizable Ag/AgCl electrode was used for the working electrode. Auxiliary electrode was placed around the working electrode, which worked as an actuator electrode. A pH change of the solution in the reaction chamber increased the overpotential and then a large current was generated. Accompanying the electrolysis of water on the auxiliary electrode, the pH of the reaction chamber recovered to the initial value rapidly. Recovery of pH was rapid and the pH in the reaction chamber could be controlled. The device could be used for the titration of an acid or a base. Linear relationships were observed between the generated charge and the concentration of analytes including acetic acid, ammonia, and urea. The output values were not affected by the buffering capacity.

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Junji Fukuda

Yokohama National University

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