Fabrication of Bi-Enzymatic Electrodes Base on Graphene Oxide-Modified ITO for Enzymatic Fuel Cell Utilizing Trehalose

Abstract

Graphene has been widely utilized in electronic devices and biosensors because it has large surface area, high electron conductivity, and stability. This paper describes a graphene as the platform substrate for enzyme immobilization as well as enhancing electron transfer in the fabrication of enzymatic biofuel cells utilizing trehalose. The graphene oxide (GO) film was formed over ITO surfaces by electrodeposition and it was reduced by applying electric potential ranging from -1.5 to -0.5 V (vs. Ag/AgCl). The electrodes were examined by using XPS, FESEM, and AFM and then their electrochemical performances were evaluated. The deposition time in deposition stage and pH of buffer solution in reduction stage, greatly influenced on GO loading and the extent of GO reduction. Glucose oxidase (GOD) or trehalase (Tre) was immobilized on the reduced graphene-modified ITO electrodes (r-GO-ITO) by physical adsorption. Electrodes with difference sequences of two enzymes were evaluated. The effects of GOD layers and units of Tre were investigated. Electrochemical impedance spectra and cyclic voltammograms showed that electrodes generated maximum peak currents with the lowest electron transfer resistance when electrode was covered with four-GOD layer and 2.6 U of Tre. Enzyme assay was performed to investigate whether increase in the unit of Tre influences on the mass transfer of substrate to GOD. Enzyme fuel cell was assembled in which anode was optimized GOD-Tre electrode while cathode was bilirubin oxidase immobilized r-GO-ITO. The fuel cell generated the power density of 0.42 μW/cm2 in 100 mM PBS buffer (pH, 7.0) containing 30 mM trehalose solution.