Electropolymerized Nonconducting Films

FIGURE 11.7. Response of an RVC/poly( 1,3-DAB/resorcinol)/GOx glucose biosensor after 5 weeks to (a) buffer, (b) 1-mM acetoaminophen, (c) 1-mM ascorbic acid, (d) 1- mM uric acid, (e) 2.5-mM glucose, (f) 5-mM glucose. (From Ref. 121). 

Electrochemical PPD films were applied by Wang et in the construction 

FIGURE 11.8. Electrochemical immobilization of GOx in poly(phenol) films on a 3-mm diameter platinum electrode. Experimental conditions 0.1-M phosphate buffer, 7 mg/ml GOx added electrolyte 0.15-M tetraethylammonium tetrafluoroborate potential sweep rate 50 mV s . Polymerization solution also contains (a) 50-mM phenol (b) 50 n 1/ml 1% w/w in methanol of [Os(byp)2(PVP)ioCl]Cl and 50-mM phenol. 

FIGURE 11.9. Catalytic efficiency (Ik/Id) of (a) GOx-[Os(bpy)2(PVP)ioCl]Cl electrostatic complex and (b) GOx alone, entrapped in poly(phenol) films on a 3-mm glassy carbon electrode. The Ik and Id are the oxidation currents at 0.4 V versus SCE from CVs in the presence and absence of glucose, respectively. The E/ = 0.0 V and E/ = 0.6 V potential sweep rate 5 mV/s. Other conditions are as in Fig. 11.8. Ferricyanide ion in solution was used as the electron transfer mediator in (b). 

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This means that we can follow the empirical kinetics of the electropolymerization process, at a constant overpotential (Fig. 6), by tracking the weight of the rinsed and dried polymer film,37 41 as we do in homogeneous polymerization processes of conducting or nonconducting poly-... 

Electropolymerization is also an attractive method for the preparation of modified electrodes. In this case it is necessary that the forming film is conductive or permeable for supporting electrolyte and substrates. Film formation of nonelectroactive polymers can proceed until diffusion of electroactive species to the electrode surface becomes negligible. Thus, a variety of nonconducting thin films have been obtained by electrochemical oxidation of aromatic phenols and amines Some of these polymers have ligand properties and can be made electroactive by subsequent inincorporation of transition metal ions... 

Although most metal-containing polythiophenes have been synthesized by electropolymerization on an electrode surface, there are many reasons to chemically synthesize these polymers. Chemical synthesis may allow isolation of soluble polymers, enabling complete solution characterization (GPC, light scattering, NMR, etc.) and facilitating conductivity studies. Moreover, it can enable improved thin-film preparation and film deposition onto nonconducting substrates. Finally, monomers that are unsuitable for electropolymerization may be polymerized by chemical methods. 

In contrast to the area of redox protein electrochemistry, redox enzyme electrochemistry has received much greater attention, driven in many cases by the desire to construct practical, self-contained enzyme electrodes for commercial applications. Redox enzyme electrochemistry is also easier to study in many ways because the substrate or product is often detected electrochemically rather than the enzyme itself. Various types of electroactive polymers have been used with redox enzymes, including redox polymers, redox-active hydrogels, and electropolymer-ized films of conducting and nonconducting, polymers. We discuss each type of polymer in turn, starting with electropolymerized films. 

Role of Water. With increasing water content in acetonitrile the current efficiency for the galvanostatic electropolymerization of thiophene decreases rapidly, but much more slowly for the polymerization of 3-methylthiophene and bithiophene. The competition for radical cations generated from the monomer in the initial electrochemical step between the main reaction (the electropolymerization) and the side reaction (nucleophilic attack of the radical cation by water) explains this decrease in current efficiency [673]. A decrease in the monomer concentration increases the water/monomer ratio and impairs the electrical properties of PT. The presence of water in the electropolymerization process leads to more nonconducting and passivated films [264]. 

Enzymes, especially oxidases, notably GOx, have been entrapped in single- and multicomponent conducting and nonconducting electropolymerized films, as well as carbon paste, clay, and metal powder composites, for applications in biosensing, molecular electronics, and molecular recognition [162-167]. 

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