Evaluation of Enzymatic Kinetics of GOx-based Electrodes by Scanning Electrochemical Microscopy at Redox Competition Mode

Glucose oxidase (GOx) is an enzyme, which is used for the development of enzymatic biofuel cells. Therefore in this research redox competition mode of scanning electrochemical microscopy (RC-SECM) was applied for the investigation of glucose oxidase (GOx) catalyzed reaction kinetics. The GOx was immobilized by glutaraldehyde on substrates of different electrical conductivity: (i) gold covered glass was used as conducting substrate and (ii) plastic poly(methyl methacrylate) was used as non-conducting substrate. Current vs distance dependencies were registered by SECM at different concentrations of glucose in the absence of redox mediator. The potential of -750 mV vs Ag/AgCl(3 M KCl) was applied to the microelectrode (ME), which was used as a probe in SECM, in order to register oxygen reduction current. Consumption of oxygen by the GOx based layer was evaluated according to principles determined by Michaelis-Menten kinetics. Apparent Michaelis constants K-M(app.) were calculated from the dependencies of current vs glucose concentration. In both these cases the KM(app.) value increased when the distance between ME and enzyme modified surface was increasing from 10 to 30 mm, while the KM(app.) value decreased by increasing the distance from 30 to 60 mu m.