There is no evidence to support literature claims of direct electron transfer (DET) for native glucose oxidase (GOx) at carbon nanotubes or graphene

It is widely claimed that native GOx undergoes direct electron transfer (DET) at nanostructured electrodes. In this paper we argue that the vast majority, if not all, of these claims are incorrect. We present results for GOx adsorbed on MWCNTs, a typical nanostructured electrode. We show that the surface redox peaks usually attributed to DET to GOx actually arise from flavin, and possibly catalase, impurities present in the as supplied commercial enzyme that are adsorbed at the electrode surface. We show that the observed response to glucose is due to enzymatic activity, but not electroactivity, of adsorbed GOx that catalyses the reaction of d-glucose with dissolved oxygen leading to a decrease in the oxygen reduction current that correlates with the glucose concentration.