Glucose oxidase anode for biofuel cell based on direct electron transfer

This paper presents a new design concept of a glucose oxidase (GOx) electrode as an anode for the biofuel cell based on direct electron transfer (DET) between the active site of an enzyme and the multi-walled carbon nanotube (MWNT)-modified electrode surface. Toray® carbon paper (TP) with a porous three-dimensional network (78% porosity) was used as a matrix for selectively growing multi-walled carbon nanotubes. The incorporation of MWCNTs into TP was provided by the chemical vapor deposition technique after an electrochemical transition of cobalt metal seeds. This approach has the ability to efficiently promote DET reactions. The morphologies and electrochemical characteristics of the GOx modified electrodes were investigated by scanning electron microscopy, cyclic voltammetry, and potentiometric methods. The combination of poly-cation polyethylenimine (PEI) with negatively charged glucose oxidase provides formation of ∼100 nm thick films on the TP/MWCNT surface. The tetrabutylammonium bromide salt-treated Nafion® was used as GOx binder and proton-conducting medium. The TP/MWCNT/PEI/GOx/Nafion® modified electrode operates at 25 °C in 0.02 M phosphate buffer solution (pH 6.9) containing 0.1 M KCl in the presence of 20 mM glucose. The open circuit potential of GOx anode was between −0.38 V and −0.4 V vs. Ag/AgCl, which is closer to the redox potential of the FAD/FADH2 cofactor in the enzyme itself. The GOx electrode has a potential to work in vivo by using endogenous substances, such as glucose and oxygen. Such a glucose anode allows for the development of a new generation of miniaturized membrane-less biofuel cells.