Development of Biosensing Method Using Electrochemical AC Impedance Measurement

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Cyclic voltammetry and electrochemical AC impedance measurements were made by using a glassy carbon electrode in electrolyte solution (pH 7) containing electron mediator and glucose oxidase. The electron mediators used in this study were ferrocenecarboxylic acid and osmium bipyridine complex. In case of using the electrolyte solution containing the electron mediator alone, impedance plots gave linear relation with a slope angle of 45^○, implying that diffusion of the redox species controlled the reaction rate. When glucose oxidase and glucose were added to the solution, impedance plots with a semicircle shape were obtained and its diameter decreased with an increase in concentration of glucose. This behavior indicated that the electron transfer step determined the reaction rate. Since the decrease in diameter of the semicircle of plots means an increase in the reaction rate, then this principle allowed it to establish a method to determine glucose concentration from the impedance plots.It was, furthermore, found that the AC impedance measurement was useful sensing method with avoiding infuence of interference material in the solution. The biosensor with use of ferrocenecarboxylic acid could avoid influence of ascorbic acid. If osmium bipyridine complex was used as an electron mediator, influence of uric acid as well as ascorbic acid was erased in the obtained data. Those results strongly suggested that new biosensing way would be developed with use of electrochemical AC impedance measurements.