Electropolymerization, advantages

Electropolymerization of polymers directly onto the surface of an electrode has been used for a number of enzyme-based biosensors. By polymerizing from a solution containing the monomer, as well as the other components of the sensor, enzymes for example, a multifunctional polymer film can be fabricated. As the polymer film grows on the electrode, the enzyme and other components are entrapped in the film [9]. GOD and other enzymes have been incorporated into sensors using electropolymerization. Advantages of electropolymerization are that the film thickness can be easily controlled by the amount of polymerization charge passed, and that the polymer film is deposited only on the sensing electrode. 

The enzyme can be immobilized on the electrode by several techniques (53). The simplest method, first used in 1962, is to trap an enzyme solution between the electrode surface and a semipermeable membrane. Another technique is to immobilize the enzyme in a polymer gel such as polyacrylamide which is coated on the electrode surface. Very thin-membrane films can be obtained by electropolymerization techniques (49,54,55) using polypyrrole, polyindole, or polyphenylenediamine films, among others. These thin films (qv) offer the advantage of improved diffusion of substrate and product that... 

Most suitable for electrically conducting materials such as carbon fibers, the electrochemical processes involve deposition of polymer coatings on the fiber surface through electrodeposition or electropolymerization techniques. The major advantage of these processes is that a uniform layer of controlled thickness and variable polymer structure and properties can be obtained by controlling the current and the solution concentration. 

The preparation of molecular composites by electropolymerization of heterocycles in solution with polyelectrolytes is an extremely versatile technique, and many polyelectrolyte systems have been studied. The advantages of this method include the use of aqueous systems for the polymerization. Also, the physical and mechanical properties of the overall composite depend on the properties of the polyelectrolyte, so material tailorability is feasible by selection of a polyelectrolyte with desirable properties. 

Through the combination of SPR with a - poten-tiostat, SPR can be measured in-situ during an electrochemical experiment (electrochemical surface plasmon resonace, ESPR). Respective setups are nowadays commercially available. Voltammetric methods, coupled to SPR, are advantageously utilized for investigations of - conducting polymers, thin film formation under influence of electric fields or potential variation, as well as - electropolymerization, or for development of -> biosensors and - modified electrodes. Further in-situ techniques, successfully used with SPR, include electrochemical - impedance measurements and -+ electrochemical quartz crystal microbalance. 

It was observed that the direct electrodeposition of H2(ETRPyP) from a DMF solution leads to poor quality films, due to the looseness of the presumably low molecular weight polymeric chains. Considering that the supramolecular porphyrin is able to form quite homogeneous films by dip coating (122, 167, 170, 184, 250, 286, 296) and that such films are poorly soluble in acetonitrile, an altenative procedure was devised. This procedure was carried out by an electropolymerization reaction on pre-formed films (53, 172), whose advantages are the high concentration of the monomer on the electrode surface and the presence of suitably preoriented molecules, which keep the n-stacking structure of the dip-coated films. Such characteristics increase the efficiency of the electropolymerization, since only one or two scans in the... 

Their biosensor consisted in a Pt wire on which GOD was immobilized by the electropolymerization of m-phenylenediamine. The advantage of this type of immobilization consists in creating an effective barrier against electrochemical interference due to the polymer formed onto the electrode. Moreover, an extended linearity for the glucose sensor was also obtained, and this was a requisite for the direct measurement of the subcutaneous glucose at diabetic levels, since in practice an extremely low dilution of the subcutaneous fluid was realized. 

Redox polymers for enzyme entrapment have been developed in order to combine the advantages of electropolymerization technology with those of MCME. The group led by Lowe in Cambridge (UK) (Hall et al., 1986) employed ferrocene derivatives of pyrrole for immobilization by electropolymerization. In these systems ferrocene takes the electrons up from the reduced prosthetic group of the enzyme and conducts them to the electrode. Shaojun et al. (1985) studied the direct polymerization of ferrocene derivatives the redox polymer formed might be suitable for coupling with enzymes. 

In a vast majority of cases electrochemistry just offers some moderate advantages but not revolutionary advances. Therefore a slow expansion of industrial electro-organic processes and, consequently, a problematic introduction of electropolymerization into industrial practice should be expected. 

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