Development of Biosensing Method Using Electrochemical AC Impedance Measurement

用玻璃碳电极在含电子介质和葡萄糖氧化酶的电解质溶液（pH 7）中进行了循环伏安法和电化学交流阻抗测量。本研究使用的电子介质为二茂铁羧酸和联吡啶锇配合物。当只使用含电子介质的电解质溶液时，阻抗曲线呈线性关系，斜率为45^ n，表明氧化还原物质的扩散控制了反应速率。当葡萄糖氧化酶和葡萄糖同时加入溶液时，阻抗图呈半圆形，其直径随葡萄糖浓度的增加而减小。这一行为表明电子转移步骤决定了反应速率。由于图中半圆直径的减小意味着反应速率的增加，因此该原理允许建立一种从阻抗图中测定葡萄糖浓度的方法。结果表明，交流阻抗测量是一种有效的传感方法，可以避免溶液中干扰物质的影响。二茂铁羧酸生物传感器可以避免抗坏血酸的影响。如果使用联吡啶配合物锇作为电子介质，则在所获得的数据中消除了尿酸和抗坏血酸的影响。这些结果有力地表明，利用电化学交流阻抗测量可以开发新的生物传感方法。

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.