Electron transfer from FAD-dependent glucose dehydrogenase to single-sheet graphene electrodes

Continuous glucose monitoring (CGM) is an emerging technology that can provide a more complete picture of the diabetes patient's glucose levels. Amperometric blood glucose tests typically require redox mediators to facilitate charge transfer from the enzyme to the electrode, that are not ideal in CGM settings because of their potential toxicity or long-term stability issues. Direct electron transfer (DET) would eliminate this need and has therefore attracted substantial interest. However, most DET-based glucose biosensor studies so far have used glucose oxidase (GOx) leading to controversial results because the oxygen dependency may be misinterpreted as DET. Here, we overcome this challenge by using an oxygen-insensitive glucose dehydrogenase (GDH). To enable direct electron transfer, the enzyme was immobilized on the surface of high-quality single-layer graphene electrodes via short pyrene linkers (<1 nm). The biosensor strongly responded to glucose even without a redox mediator, implying direct electron transfer. Control measurements on different surfaces further confirm that the response is enzyme-specific. The activity of immobilized enzymes was confirmed by glucose measurements with a conventional ferrocenemethanol mediator as well as relatively unexplored redox mediator - nitrosoaniline. The influence of a most potent interferent in blood, ascorbic acid, was assessed. This is the first demonstration of application of single-layer graphene electrode to obtain DET from an oxygen insensitive enzyme (GDH), highlighting the potential of such devices for applications in CGM. (C) 2019 Published by Elsevier Ltd.