Development of highly sophisticated Labs-on-a-Chip with integrated active microfluidic systems

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Electrochemical microfluidic systems were fabricated and were used in micro analysis systems. Also, basic researches to realize these systems were conducted. In this study, microfluidic systems based on electrowetting and gas-bubble formation were mainly studied. In the system based on electrowetting, a solution to be transported is confined in a gap between a working electrode and a protruding structure of PDMS. By changing the potential of the working electrode, wettability of the electrode surface changes and the solution is mobilized in the flow channel. By placing several working electrodes in a row, solutions could be transported even in a network of branched flow channels. Mixing of solutions could also be conducted in the system. Micro analysis systems for ammonia, urea, creatinine, and amino acids were constructed using the microfluidic system. By mixing necessary solutions on the chip, enzymatic reactions could be proceeded at optimum pHs. As a result, highly sensitive detection could be achieved. Electrowetting can also be used to form valves. A microfluidic system which can conduct sequential introduction and flushing of solutions was fabricated, and on-chip immunoassay was conducted.In the system based on the gas-bubble formation, hydrogen gas bubbles were produced or extinguished on a platinum black working electrode and the volume change was converted into the displacement of a diaphragm. A system with two pumps and four valves was fabricated and on-chip microfluidic transport and mixing was conducted. By detecting fluorescence originating from amplex red, the concentration of hydrogen peroxide and L-glutamate could be measured. Also, by using two such pumps at the inlets of a Y-shaped flow channel, a micro analysis system for the determination of the activities of GOT and GPT was fabricated, and the performance was evaluated.