Direct electron transfer of glucose oxidase and carbon nanotubes entrapped with biocompatible organic materials

Efficient electron transfer between redox enzymes and electrodes is essential for enzyme-based biosensors, biofuel cells, and bioelectronic devices. Generally glucose oxidase (GOx) requires mediators for electrical communication with electrodes because the redox center of GOx is deeply buried in the insulating protein shell. In the present work, direct electron transfer (DET) between GOx and electrodes was attempted. GOx and carbon nanotubes (CNTs) were immobilized on a glassy carbon (GC) electrode by using biocompatible polymer, chitosan (CHI). Cyclic voltammograms revealed that the CHI/GOx/CNT-GC electrode showed a pair of well-defined redox peaks in 0.1M phosphate buffer solution (pH 7.0) saturated with argon. Under the same conditions, no redox peak was observed in the absence of CNTs. The formal redox potential was -450mV (vs. Ag/AgCl), which agreed well with that of FAD/FADH2, the redox center of GOx. This result clearly shows that the DET between the GOx and the electrode was achieved. The use of thin CNTs significantly improved the DET efficiency of the GOx. It was found that the GOx immobilized on the electrode retained catalytic activity for the oxidation of glucose.