Ferrocene-modified pyrrole

Perhaps the original hope for these polymers was that they would act simultaneously as immobilisation matrix and mediator, facilitating electron transfer between the enzyme and electrode and eliminating the need for either O2 or an additional redox mediator. This did not appear to be the case for polypyrrole, and in fact while a copolymer of pyrrole and a ferrocene modified pyrrole did achieve the mediation (43), the response suggested that far from enhancing the charge transport, the polypyrrole acted as an inert diffusion barrier. Since these early reports, other mediator doped polypyrroles have been reported (44t45) and curiosity about the actual role of polypyrrole or any other electrochemically deposited polymer, has lead to many studies more concerned with the kinetics of the enzyme linked reactions and the film transport properties, than with the achievement of a real biosensor. 

Foulds, N.C. and Lowe, C.R. (1988) Immobilization of glucose oxidase in ferrocene-modified pyrrole polymers. Analytical Chemistry, 60, 2473-2478. 

Foulds, N. C., Lowe, C. R., Immobilization of Glucose Oxidase in Ferrocene-Modified Pyrrole Polymers , Anal. Chem. 60 (1988) 2473-2478. 

The best method of enzyme and mediator immobilization seems to be an electrochemical polymerization and deposition. For example, a 50 mmol/1 solution of monomer, either pyrrole or N-methylpyrrole, in an aqueous buffer containing the enzyme(s) can be pulse-electrolyzed under potentiostatic or galvanostatic control. A conducting polymer film then grows on the metal anode. When ferrocene-modified pyrrole polymer (e.g., based on [(ferrocenyl)amidopropyl]pyrrole) is used [135], then the polymer also works as the electron-acceptor and mediates electron transfer from the reduced form of an enzyme to the metal electrode. 

In an effort to immobilize glucose oxidase in ferrocene-modified pyrrole copolymers, Foulds and Lowe [155] synthesized [(ferrocenyl)amidopropyl]pyr-role (FAPP) and ([(ferrocenyl)amidopentyl]amidopro-... 

Functionalized conducting monomers can be deposited on electrode surfaces aiming for covalent attachment or entrapment of sensor components. Electrically conductive polymers (qv), eg, polypyrrole, polyaniline [25233-30-17, and polythiophene/23 2JJ-J4-j5y, can be formed at the anode by electrochemical polymerization. For integration of bioselective compounds or redox polymers into conductive polymers, functionalization of conductive polymer films, whether before or after polymerization, is essential. In Figure 7, a schematic representation of an amperomethc biosensor where the enzyme is covalendy bound to a functionalized conductive polymer, eg, P-amino (polypyrrole) or poly[A/-(4-aminophenyl)-2,2 -dithienyl]pyrrole, is shown. Entrapment of ferrocene-modified GOD within polypyrrole is shown in Figure 7. 

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. 

A ferrocene derivative was synthesised with a pyrrole group attached to ferrocene through an alkyl chain (Figure 14.38). This molecule was mixed with 3-hexadecylpyrrole and spread onto FeCla containing water to form a copolymer monolayer. The monolayer was deposited on an electrode surface the resulting modified electrode can be used for reoxidising reduced glucose oxidase [264,265]. 

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