Glucose oxidase electron transfer between

It is noted that the anodic peak current prominently increases with an increase in the molar ratio of ferrocene to glucose oxidase whilst the amount of enzyme self-assembled on the electrode surface is fixed as presented in Figs. 14-16. This indicates that each modified ferrocene may contribute to electron transfer between the enzyme and the electrode in the case of gold-black electrode, the ferrocene-modified enzyme could form multi electron transfer paths on the porous gold-black electrode. 

Mizutani et al. [16] have demonstrated that ferrocene derivatives, attached by means of covalent bonds to the surface of bovine serum albumin, have been able to mediate the electron transfer between the glucose oxidase and the electrode through the osemium complex. 

In principle, glucose oxidase could be oxidized directly at the electrode, which would be the ultimate electron acceptor. However, direct electron transfer between redox enzymes and electrodes is not possible because the FADH2/FAD redox centers are buried inside insulating protein chains (Heller, 1990). If it were not the case, various membrane redox enzymes with different standard potentials would equalize their potentials on contact, thus effectively shorting out the biological redox chains. The electron transfer rate is strongly dependent on the distance x between the electron donor and the electron acceptor. 

J.Z. Xu, J.J. Zhu, Q. Wu, Z. Hu and H.Y. Chen, Direct electron transfer between glucose oxidase and multi-walled carbon nanotubes, Chin. J. Chem., 21 (2003) 1088-1091. 

A highly sensitive glucose biosensor based on immobilization of glucose oxidase ( GOx) onto tetragonal pyramid-shaped (TPSP) ZnO nanostructure is prepare [164], TPSP- ZnO nanostructure exhibits favorable biocompability for facilitating the electron transfer between... 

Besides being used as adsorbent for gas molecules, both SWCNTs and MWC-NTs can be cast as a random network or a porous thin film on metal electrodes [57-59] or used as a three-dimensional scaffold [41,42] for biosensors. CNTs serve both as large immobilization matrices and as mediators to improve the electron transfer between the active enzyme site and the electrochemical transducer. Various enzymes, such as glucose oxidase and flavin adenine dinucleotide (FAD) can adsorb onto the CNT surface spontaneously and maintain their substrate-specific enzyme activity over prolonged times [57]. Recently, cells have been grown on CNT scaffolds which provide a three-dimensional permeable environment, simulating the natural extracellular matrix in a tissue [60-62]. 

Polysiloxane random co-polymers (with molecular weights of 5,000-10,000) with pendant ferrocene groups have recently been synthesized 37 via hydrosilylation of vinylferrocene or 9-ferrocenyl-l-nonene with a poly(methylhy-drosiloxane)-r-poly(dimethylsiloxane) random co-polymer (Equation (12)). These materials were used as ampero-metric biosensors for the detection of glucose. In this case, the polymers effectively mediated electron transfer between reduced glucose oxidase and a conventional carbon paste electrode. The response of the sensor to glucose was dependent upon the nature of the polymeric backbone. The optimal response was achieved by finding a compromise between increased polymer flexibility and decreased spacing between individual relay (i.e., ferrocene) sites. 

GOx-poly(aniline) films have been grown from aqueous solutions, although acidic solutions (around pH 1) are necessary for electropolymerization, which can also adversely affect the enzyme. Although direct electron transfer between GOx and poly(aniline) has been postulated, " evidence to support this is not unequivocal. Based on experiments using poly(aniline) poly(aniline)/glucose oxidase bilayers, Hoa et al. have concluded that there is negligible direct electron transfer.This difference may reflect different deposition conditions used in the two sets of experiments. 

Schuhmann, W., Ohara, T., Heller, A., and Schmidt, H.-L., Electron transfer between glucose oxidase and electrodes via redox mediators bound with flexible chains to the enzyme surface, J. Am. Chem. Soc., 113, 1394-1397 (1991),... 

---