Development of Biosensing Method Using Electrochemical AC Impedance Measurement

在含有电子介质和葡萄糖氧化酶的电解质溶液（pH 7）中，用玻碳电极进行循环伏安和电化学交流阻抗测量。本研究中使用的电子介质是二茂铁羧酸和锇联吡啶配合物。在仅使用含有电子介体的电解质溶液的情况下，阻抗图给出了斜率为45^○的线性关系，这意味着氧化还原物种的扩散控制了反应速率。当葡萄糖氧化酶和葡萄糖加入到溶液中时，得到了一个圆形的阻抗图，其直径随着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。由于阻抗曲线的直径减小意味着反应速率的增加，因此建立了从阻抗曲线测定葡萄糖浓度的方法，并发现交流阻抗测量是一种有效的传感方法，避免了溶液中干扰物质的影响。使用二茂铁羧酸的生物传感器可以避免抗坏血酸的影响。如果锇联吡啶配合物被用作电子介体，尿酸以及抗坏血酸的影响在所获得的数据被删除。这些结果有力地表明，电化学交流阻抗测量将发展新的生物传感方法。

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.