The electrochemical detection of glucose using glucose oxidase (GOx) has been conducted by means of AC impedance measurements. In the absence of glucose, the Nyquist plots were straight line due to a reversible redox reaction involving the electron mediator. On the other hand, the Nyquist plots became a circular arc in the presence of glucose, and its radius decreased with an increase in the glucose concentration. The shape of the Nyquist plots were explained with assistance of numerical calculations. Since the reaction impedance due to direct oxidation of interfering species was significantly higher than that of glucose oxidation catalyzed by glucose oxidase, unfavorable influence from interfering species could be eliminated without needing a complicated sensor device. When ferrocenecarboxylic acid was used as an electron mediator, the calibration curve obtained from the Nyquist plots was not affected by the presence of ascorbic acid. Based on those findings, a sensing system, which has no interference from both ascorbic acid and uric acid, was fabricated by using [Os(bpy) 3 ]Cl 2 , which has a highly positive redox potential (0.65 V), as an electron mediator. A method to prepare calibration curves from AC impedance measurements with a fixed frequency was established so that this technique can be put to practical use.
Application of the ac impedance technique to the electrochemical glucose sensing allowed determination of glucose concentration without influence of a serious interference material, ascorbic acid.
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