Study of direct electron transfer and enzyme activity of glucose oxidase on graphene surface

In recent years, graphene has been widely used as a high performance two-dimensional material in the development of biosensors and biofuel cells for facilitating direct electron transfer (DET) of glucose oxidase (GOx). However, almost all of these reports perform experiments in the presence of oxygen (a natural mediator of oxidase) and whether the GOx with DET property retained their catalytic activity in the absence of mediators has not been studied in detail so far. In this paper, we investigated the DET property and enzyme activity of GOx on graphene surface without and with mediators. Experimental results showed that the biosensor had no response to glucose in mediator-free solutions, even though the DET of GOx was observed, indicating that the GOx with LET property lacked enzymatically catalytic activity. However, in the presence of mediators, the biosensor showed sensitive response to glucose, illustrating that the mediated enzymatic oxidation of glucose occurred, which can be attributed to the catalytically active GOx without DET capability. These results suggest that DET property and enzyme catalytic activity cannot occur on the same GOx simultaneously. Therefore, keeping enzyme activity and DET of GOx at the same time is still a major challenge for biosensor and biofuel cell researches. (C) 2014 Elsevier B.V. All rights reserved.