Glucose Oxidase Affects Laccase and Bilirubin Oxidase Direct Bioelectrocatalytic Cathodes

Glucose oxidase (GOx) is commonly incorporated into glucose-oxidising/oxygen-reducing enzymatic biological fuel cells (EBFCs), as the anodic biocatalyst. The flavin adenine dinucleotide (FAD) cofactor of GOx is tightly bound, and possesses an associated favourable low redox potential allowing the use of a wide range of electron mediators, which in turn increases the theoretical maximum open-circuit potential (OCP) of EBFCs. Furthermore, GOx is highly specific to glucose and offers high catalytic activity, making it a good choice for futuristic implantable EBFCs. GOx-based anodes do, however, exhibit a major significant drawback; electron transfer to the electrode following the enzymatic oxidation of glucose competes with the natural electron acceptor of GOx: oxygen. The reduction of oxygen by GOx can dramatically lower the dissolved oxygen concentration of a solution, whilst simultaneously producing hydrogen peroxide.

Laccase and bilirubin oxidase (BOd) can undergo the enzymatic 4-electron reduction of dissolved oxygen to water, and efficient direct electron transfer (DET) has been established for both enzymes. The inhibition of laccase and BOd by halides (primarily fluoride and chloride ions) is well documented; it is reported that BOd exhibits greater resistance to halide inhibition. Nevertheless, DET can also instil a degree of resistance to chloride inhibition. Lastly, BOd can efficiently reduce oxygen to water at near-neutral and physiological pH, making it a favourable choice of biocatalyst in implantable devices.

The research presented within this paper investigates the effect of the parasitic reduction of oxygen to hydrogen peroxide by GOx, on laccase and BOd direct bioelectrocatalytic cathodes. We report that GOx can produce significant quantities of hydrogen peroxide and thereby significantly affect laccase and BOd cathodes (albeit by different mechanisms), even when DET is established (a mode previously used to remediate chloride inhibition). Furthermore, we compare and contrast the performance of laccase and BOd when GOx is replaced with “oxygen-insensitive” FAD-dependent glucose dehydrogenase (FAD-GDH).

This research has implications for the future design of EBFCs.

This research is funded by the UK SuperGen Biological Fuel Cells Consortium (Contract: EP/H019480/1), National Science Foundation Grant #105797 and the Air Force Office of Scientific Research (AFOSR).