Redox Polymers for Electrically Wiring Enzymes

Enzyme electrodes have been constructed by covalent immobilization of enzyme on functionalized conducting polymers, such as poly(3-aminopyrrole).  

In some cases the polymer incorporates the mediator, producing a redox macromolecule, e.g., poly[(ferrocenyl)amidopropyl]pyrrole, ferrocene-modified poly(ethylene oxide), and highly flexible ferrocene-modified silox-ane. These redox polymers have short chains and low molecular weights ( 20 kDa) they function as a special kind of diffusional mediators and do not alleviate the loss of a mediator to the bulk solution during amperometric detection. 

Constructing amperometric glucose sensors that incorporate nondiffusional mediators was accomplished with GOx by chemical modifications of the enzyme that perturbs the carbohydrate Covalent binding of the enzyme to 

Direct unmediated electrical communication between enzyme redox centers and the electrode by molecular wiring has been attracting attention recently/ In this technique the natural ability of polyanionic oxidoreductases to form electrostatic complexes with redox proteins for effective electron transfer can be applied in biosensor technology. However, in place of the redox protein, a polycationic redox macromolecule is used. The result is a three-dimensional network of an electrostatic complex of the enzyme and the redox polymer. In this system membranes are not needed, nor is unique orientation of the enzymes necessary. This is 

FIGURE 11.4. Computer graphics display of the C backbone of the GOx monomer, showing the location of the 15 lysine residues at the surface of glucose oxidase. (From Ref. 101). 

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