Electrochemical Impedance Study for

We have been investigated enzyme-functional electrodes utilized for biosensors and biofuel cells by electrochemical impedance spectroscopy. In the present paper, we discuss three topics as follows. (1) Faradaic impedance for analysis of a mediator-type enzyme immobilized electrode. (2) Branch structure transmission line model for analysis of an enzyme immobilized porous carbon electrode (3) Instantaneous impedance analysis for biofuel cell anode and cathode. (1) Faradaic impedance for analysis of a mediator-type enzyme immobilized electrode. We proposed a theoretical equation of Faradaic impedance (ZF) for amperometric biosensor analysis by introducing a new theoretical model in which the diffusion of mediator and substrate, enzymatic reaction and electrode reaction are considered 1,2. Figure 1 shows the typical Faradaic impedance spectrum. The Faradaic impedance spectrum describes the locus of the semicircle on the Nyquist plane, due to the electric double layer capacitance and charge transfer resistance of the mediator on the electrode surface. The finite diffusion impedance is also observed whose locus shows straight line of 45 degrees to real axis in and converges on real axis in the low frequency limit. In the present paper, we discuss the behaviors of the impedance spectra of a mediator-type amperometric biosensor using the Faradaic impedance simulation by changing in the simulation parameters