Glucose oxidase electron transfers with small

Another possibility to keep the distance between an immobilized redox protein and an electrode surface small is seen in using SAMs for modification of mostly Au electrodes. SAM provides an interface with specific functions such as functional head-groups for binding of proteins, suitable charges for anisotropic orientation of proteins, and often they prevent denaturation of the proteins. Astonishingly, even direct electron transfer from SAM-immobilized glucose oxidase has been proved, although the mechanism remains unclear [181]. 

The bioelectrocatalytic oxidation or reduction of substrates at biocatalyst electrodes can be accelerated by the presence of a small molecule which functions as an electron transfer mediator between the electrode and the prosthetic group of the immobilized enzyme " . Two types of the enzyme-modified electrode with entrapped mediator have been designed" , a carbon paste electrode and a porous electrode, both modified with enzyme and a reservoir of mediator. In the former type of electrode , where glucose oxidase (GOD) was immobilized on the surface of a carbon paste electrode along with p-benzoquinone (BQ) by coating the enzyme-loaded surface with a semipermeable membrane, BQ was dissolved into the immobilized enzyme layer and retained there effectively to serve as an electron transfer mediator between the carbon paste electrode and the immobilized enzyme. It has been shown " that the kinetics of the bioelectrocatalytic oxidation of D-glucose (Glc) at the membrane-coated GOD-modified carbon paste electrode with mixed-in BQ can be explained by theoretical equations in which the diffusion enzyme reaction of the substrate and mediator in the immobilized-enzyme layer and the diffusion of the substrate (and mediators) in the coating membrane are taken into account - . In this study, a number of quinone derivatives and a few ferrocene derivatives were examined as electron transfer mediators in the GOD electrode, and the mediator activity of the compounds was evaluated on the basis of theoretical equations. 

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