Polyaniline, immobilization matrix

When constructing biosensors, which are to be used continuously in vivo or in situ, maintaining sensor efficiency while increasing sensor lifetime are major issues to be addressed. Researchers have attempted various methods to prevent enzyme inactivation and maintain a high density of redox mediators at the sensor surface. Use of hydrogels, sol-gel systems, PEI and carbon paste matrices to stabilize enzymes and redox polymers was mentioned in previous sections. Another alternative is to use conductive polymers such as polypyrrole [123-127], polythiophene [78,79] or polyaniline [128] to immobilize enzymes and mediators through either covalent bonding or entrapment in the polymer matrix. Application to various enzyme biosensors has been tested. 

Chen JP, Wang HY (1998) Improved properties of bilirubin oxidase by entrapment in alginate-silicate sol-gel matrix. Biotechnol Tech 12(ll) 851-853 Chen Y, Kang ET, Neoh KG et al. (2000) Covalent immobilization of invertase onto the surface-modified polyaniline from graft copolymeiization with acrylic acid. Eur Polym J 36(10) 2095-2103... 

Xue, H.G., and Z.Q. Shen. 2002. A highly stable biosensor for phenols prepared by immobilizing polyphenol oxidase into polyaniline-polyacrylonitrile composite matrix. Talanta 57 (2) 289. 

Electroactive polyaniline films were synthesized by the catalysis of biUru-bin oxidase (BOD, a copper-containing oxidoreductase). The polymerization of aniline was carried out on the surface of a sohd matrix such as glass sUde, plastic plate, or platinum electrode to form homogeneous films [33]. The BOD was immobilized on the surface by physical absorption. The optimum pH was around 5.5. Some aniline derivatives such as p-aminophenol and p-phenylenediamine were good substrates for BOD. Structural analysis suggested the BOD synthesized polyanihne possessed partially 1,2-substititued structures. Cyclic voltammetric studies demonstrated that the PANl films were electrochemically reversible in redox properties, but differed from that of chemically or electrochemically synthesized PANl. The difference was attributed to the partial 1,2-substitution. Laccases are known to oxidize phenolic compounds in nature in the presence of oxygen and are capable in polyaniline synthesis in vitro [34-36]. 

BOD was entrapped in the enzymatically synthesized polyanQine film and the enzyme in the film was still active. Therefore, it is expected that this enzymatic synthesis of polyaniline film can be applied in the preparation of electroactive and enzyme-immobilized membranes on various solid matrixes. 

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