Overoxidized Poly pyrrole

Most studies on enzyme immobilization in electropolymerized films are based on pyrrole and its derivatives. Conductivity of the polymer film is known to be destroyed by The GOx-based glucose sensors produce H2O2 even 

Preformed Nonconducting Polymer Poly(vinyl Chloride) Membrane 

Poly(vinyl chloride) (PVC) is an excellent selective membrane barrier widely used in ion-selective electrodes. The ion-selective properties of the membrane depend on incorporating a platicizer, ion exchanger, or neutral carrier molecule. Christie et applied PVC membranes (with no incorporated ion 

FIGURE 11.10. (A) Current time response obtained at different glucose concentrations without and (B) with Pt/GOx/poIy(pyrrole) microdialysis probe. Numbers indicate a millimolar concentration of glucose. An experimental setup is given in Ref. 118. 

Biosensor technology based on enzyme entrapment in polymeric films grown by gamma irradiation-induced polymerization has received only modest attention. Two techniques have generally been adopted in preparing such 

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Recent applications of nonconducting polymers, such as PPD and overoxidized poly(pyrrole), as permselective and biocompatible membranes hold great promise for the future of biosensors used for in vivo monitoring. Also the suitability of polymeric films (e.g., Eastman AQ 55) for organic-phase biosensors has led to a new opportunity for amperometric detection of analytes in real nonaqueous matrices. Since enzymes are stable in nonaqueous media, many analytes can be detected amperometrically with organic-phase biosensors. 

Figure 3.81 Typical cyclic voltammograms of a poly pyrrole film on Pt in Nrsatu rated 1 M NaClOj. The voltammograms were collected immediately after holding the film at -0.6 V vs, SCE for 5 min and after cycling for 5 min. The scan rate was 100 mV s "1 and the film thickness 84 nm. Reprinted from Electrochimica Acta, 36, P.A, Christensen and A. Hamnett, In situ Spectroscopic Investigations of the Growth, Electrochemical Cycling and Overoxidation of Polypyrrole in Aqueous Solution , pp. 1263-1286(1991), with kind permission from Pergamon Press Ltd., Headington Hill Hall, Oxford OX3 0BW, UK.

The ability of the material to withstand transient voltage excursions outside the reversible window is also a function of time and, mainly, electrolytic solution composition. In the literature on the subject there is no common opinion concerning the region of potentials where poly pyrrole is chemically stable. Christensen and Hamnet [116], for example, have found that overoxidation of polypyrrole in aqueous 1 M NaC104 starts with potentials higher than 700 mV versus SCE. Nov ... 

Because poly thiophene itself is prone to overoxidation during polymerization, most practical work has been carried out using alkylated thiophenes, which have higher overoxidation potentials. Synthesis of functionalized thiophenes (such as alkylated monomers) is much easier to achieve than that of its pyrrole counterpart. The decreased activity of the sulfur group compared to that of the -NH group means that the laborious steps involved in protecting the heteroatom during synthesis are not required for thiophene. 

In the latter example and others involving polypyrrole films electroformed from a complex between a transition metal (Ru(II)) and a bi- or terpyridine-substituted pyrrole [201, 202], the electron self-exchange was ensured by either the viologen or Ru(II) units and not by the polymer. As a matter of fact, the PPy matrix was undoped when poly(3) was used for electrocatalytic reduction experiments or overoxidized when the films containing ruthenium(II)-based complexes were involved in oxidation experiments [201, 202]. 

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