A correlation of results measured by cyclic voltammogram and impedance spectroscopy in glucose oxidase based biocatalysts

A new biocatalyst consisting of glucose oxidase (GOx) and polyethylenimine (PEI) immobilized on carbon nanotube (CNT) (CNT/PEI/GOx) was developed, while cyclic voltammogram (CV) behaviors of several related catalysts including the CNT/PEI/GOx were analyzed in terms of charge transfer resistances (R_cts) obtained by measuring Nyquist plots using electrochemical impedance spectroscopy (EIS). A qualitative correlation between the flavin adenine dinucleotide (FAD) redox reactivity measured by the CV and R_ct was established. As factors affecting both the FAD reactivity and R_ct, concentrations of GOx, glucose, and phosphate buffer solution, electrolyte pH and ambient condition were considered and evaluations of the catalysts using the CV curves and Nyquist plots confirmed that a pattern in the FAD reactivity was closely linked to that in the R_ct, implying that FAD reactivities of the catalysts are predicted by the measurements of their R_cts. Even regarding performance of the enzymatic biofeul cells (EBCs) using the reacted catalysts, a pattern of the R_cts is compatible with that in the maximum power densities (MPDs) of the EBCs.