Analysis of porous carbon biocathodes via three-dimensional impedance spectroscopy using a double channel transmission line model

Porous carbon electrodes have considerably improved the performance of biofuel cells and biosensors in recent years. In this paper, we propose a novel in-situ analysis method for porous enzyme electrodes. By combining three-dimensional (3D) impedance measurement and a double-channel transmission line model, the stability of porous enzyme electrodes during operation can be evaluated. The proposed method can distinguish between the functional stability of the enzyme and mediator reaction and the general structural stability of the electrode. We demonstrated this method by evaluating bilirubin oxidase-modified carbon cloth (CC) electrodes with and without a magnesium oxide (MgO)-templated carbon coating. In case of the CC electrode, a remarkable increase in the charge transfer resistance within the first 500 s indicated the elution of the enzyme and mediator. When the CC was coated with MgO-templated carbon before enzyme modification, the charge transfer resistance remained constant, indicating an effective suppression of the elution of the enzyme and mediator. The electric double-layer capacitance values of both electrodes indicated that their general electrode structures were stable during the analysis. Thus, the proposed analytical method, based on 3D impedance, can be a powerful tool for simultaneously detecting possible changes in the general electrode structure of enzyme electrodes and in the amount of active enzymes and mediators on the electrode surface.