A counterion (A-) is incorporated during synthesis to balance the charge on the polymer backbone. The anion of the chemical oxidants used provides the dopant A-. Electrochemical oxidation provides greater flexibility in terms of the anion that can be incorporated from the electrolyte used as the polymerization medium. Polypyrroles can be formed from neutral aqueous solutions while acidic conditions are required for aniline solubilization and polymerization. Thiophene polymerization is commonly undertaken in organic solvents due to poor monomer solubility in aqueous solutions.

1.1.1. Polypyrroles

The mild oxidation potentials needed to initiate formation of polypyrrole in aqueous solution have enabled the formation of a wide range of polypyrrole structures by simply varying the dopant.

Simple metal recognition capabilities are introduced by incorporation of metal complexing groups as dopants [20, 21], or electrocatalytic effects are induced by use of appropriate dopants [22], covalently attached redox sites [23, 24], and/or inclusion of micron-sized metallic particles [25, 26]. Conducting polymers are also known to promote electron transfer into/out of biological entities [27]. Biomolecular/recognition can be introduced by incorporation of antibodies or enzymes or even nerve growth factors into the polymer at the time of synthesis, as reviewed recently [28].

The incorporation of complex biomolecules as dopants can be accomplished while retaining the unique electronic properties of the polymer backbone. For example, the

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