Advantages of Electroactive Polymers

Since the first reports of electrode modification in the 1970s, electroactive polymers deposited at electrode surfaces have been a consistent and continuing area of research in electrochemistry. A wide variety of different types of electroactive polymer coating have been studied in greater or lesser detail, and much effort has been directed toward using modified electrode surfaces as electrocatalysts for many different types of application. 

Electroactive polymers have a number of attractive features that account for this continuing interest. First they present a distributed array of catalytic sites. Thus in contrast to monolayer chemically modified electrodes, there are potentially a much greater number of reactive sites that can contribute to the catalytic current. Since these sites are distributed throughout the film, it is essential to consider the mass transport of reagents into the film and the mass transport of products out of these films when studying the overall kinetics of these processes. The coupled mass transport and kinetics in redox polymer films have been investigated in some detail, and good models exist for these processes.  

A final advantage of the electroactive polymer film particularly relevant to its use with redox enzymes is that the film can be used to entrap species at the electrode surface. This can confer several advantages. First it localizes the biological catalyst close to the electrochemical interface and in the right place for its efficient use. Second the electroactive film can be used to provide a favorable microenvironment in which an enzyme reaction can proceed. Third the polymer can be used to protect the electrode from fouling by nonspecific protein adsorption, and in certain circumstances, it can help exclude interferent species that might lead to undesirable side reactions or background currents. 

When an enzyme is entrapped, it is necessary to consider the combined effects of mass transport, partition, and reaction within the film and enzyme kinetics to understand processes that determine the overall response. These interactions can be quite complex, although some progress has been made toward developing models for these systems.  

Electroactive polymers can be divided into three broad classes electronically conducting polymers, such as poly(pyrrole), in which conduction is associated with motion of charge carriers along the chains redox polymers, such as poly(vinylfer-rocene), in which conduction is associated with cross-exchange reactions between discrete redox sites and polymer electrolytes, such as Nafion, in which conduction is associated with ion motions within the film. Examples of polymers from all three classes have been used in bioelectrochemical applications. 

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In this chapter we first describe components and the organization of some important biological redox systems. We then discuss advantages of electroactive polymers for this type of application and review the work so far in different areas of redox protein electrochemistry, redox enzyme electrochemistry, and redox... 

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