Polymeric redox mediators applications

Quinone modified polymeric electron transfer systems The redox mechanism of quinone (two electron-proton acceptor/donor) is pH dependent and somewhat more complicated than for ferrocene or osmium (one electron accepter/donor). However, quinones are naturally occurring redox mediators and therefore, many researchers have studied their application to biosensors [107-109]. 

Recent development in multilayer sensor architecture using sequential electrochemical polymerization of pyrrole and pyrrole derivatives to entrap enzymes was tested on a tyrosinase-based phenol sensor [127]. A phenothia-zine dye, thionine served as redox mediator and was covalently attached to the thin, functionalized first polypyrrole layer on Platinum disk electrodes. Then, a second layer of polypyrrole with entrapped tyrosinase was electrochemically deposited. The phenol sensor constructed in this manner effectively transferred electron from enz3Tne to the electrode surface. As all steps in preparation, including deposition of the enzyme-containing layer are carried out electrochemically, this technique may prove to be applicable for mass production of miniature sensors. 

Mediators can be polymerized on the electrode surface prior to enzyme immobilization, co-immobilized with enzyme, or simply added to the fuel solution. Common mediators used in BFC applications include low molecular weight, polymerizable, organic dyes such as methylene green, phenazines, and azure dyes, along with other redox-active compounds such as ferrocene, ferrocene derivalives, and conductive salts [14]. These mediators are often required for nicotinamide adenine dinucleotide (NAD )- and flavin adenine dinucleotide (FAD)-dependent enzymes, such as ADH, ALDH, and GOx. MET has been achieved at both cathodic and anodic interfaces through solution-phase mediators and mediators immobilized in various ways with or near the enzymes themselves [16,17]. However, these mediated systems do have drawbacks in that the species used to assist electron transfer are often not biocompatible, have short lifetimes themselves, or cause large potential losses. Table 5.1 lists common enzyme cofactors that can mediate or undergo DET with an enzyme on the electrode. 

---