Construction of a MEMS-style Miniaturized Chemical Analysis System for Blood Analysis

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A miniaturized analysis system (μTAS) aiming for blood analysis system was realized by stacking modules for blood gases, blood electrolytes, and a reference electrode module. Although realization of such a system on a single chip is difficult, a highly sophisticated system with various functions can be realized easily using the modular structure.A peculiar point is that the structure and operational mode of the miniature Ag/AgCl reference electrode were studied to improve the long-term stability. By protecting the silver layer with a polyimide layer and growing AgCl during the use of the element, a lifetime of approximately 300 h was achieved, which was approximately 2000 times compared with that of a conventional structure. A liquid-junction reference electrode could be constructed using the element. As a result, determination of K^+, Na^+, and Cl^- as well as pH could be made independently only in this device. The potentials of the ion-selective electrodes measured with the miniature reference electrode were compared with those measured with a macroscopic reference electrode. The deviation of the measured values was at most several mV. In addition to this, distinct responses were observed with the oxygen electrode and the carbon dioxide electrode. An on-line style analysis for six analysts could be performed with a system constructed with the stacked modules.In addition to the development of the sensing modules, a micropump for liquid transport was developed. A hydrogen bubble was generated or extinguished electrochemically and liquid could be transported with the help of the exserted pressure. A sample solution could actually be introduced into a microflow channel and the pumping rate could be changed.