Enzyme polyanilines

Regardless of the mechanism operating in these enzymatic electrode processes, the success of synthetic metal electrodes is due to rate enhancement resulting from favourable interactions of the electrode constituents with the active redox site of the enzyme. Polyaniline has been shown to be a good glucose oxidase electrode by Bartlett et al. [286], Shinohara et al. [287]... 

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. 

C.L. Wang and A. Mulchandani, Ferrocene-conjugated polyaniline-modified enzyme electrodes for determination of peroxides in organic media. Anal. Chem. 67, 1109-1114 (1995). 

Figure 1.10 Production scheme for polyaniline nanotubules, loading of enzymes into the tubes and finally exposure to an analyte. (Reprinted with permission from Ref [47]. 1999 American Chemical Society.)...

Xu P, Singh A, Kaplan DL (2006) Enzymatic catalysis in the synthesis of polyanilines and derivatives of polyanilines. Enzyme Catal Synth Polym 194 69-94... 

Jim Z, Su Y, Duan Y (2001) A novel method for polyaniline synthesis with the immobilized horseradish peroxidase enzyme. Synth Met 122(2) 237-242... 

Oliveira GB, Eilho JLL, Chaves MEC, Azevedo WM, Carvalho LB (2008) Enzyme immobilization on anodic aluminium oxide/polyethyleneimine or polyaniline composites. React Fund Polym 68(l) 27-32... 

Rumbau V, Marcilla R, Ochoteco E, Pomposo JA, Mecerreyes D (2006) Ionic liquid immobilized enzyme for biocatalytic synthesis of conducting polyaniline. Macromolecules 39(25) 8547-8549... 

Fig. 15.2. Scanning electron micrographs of enzyme containing polyaniline protrusions at (a) 250 x, (b) 1000 x, (c) side view at an angle of 50° 1000 x, (d) side view 5000 x. ...

During the last decade, immobilization of oxidase type enzymes by physical entrapment in conducting or ionic polymers has gained in interest, particularly in the biosensor field. This was related to the possibility for direct electron tranfer between the redox enzyme and the electroconducting polymers such as polypyrrole (1,2), poly-N-methyl pyrrole (3), polyindole (4) and polyaniline (5) or by the possibility to incorporate by ion-exchange in polymer such as Nafion (6) soluble redox mediators that can act as electron shuttle between the enzyme and the electrode. 

Aizawa presented an overview on the principles and applications of the electrochemical and optical biosensors [61]. The current development in the biocatalytic and bioaffinity bensensor and the applications of these sensors were given. The optical enzyme sensor for acetylcholine was based on use of an optical pH fiber with thin polyaniline film. 

Raitman OA, Katz E, Biickmann AF et al (2002) Integration of polyaniline/poly(acrylic acid) films and redox enzymes on electrode supports an in situ electrochemical/surface plasmon resonance study of the bioelectrocatalyzed oxidation of glucose or lactate in the integrated bioelectrocatalytic systems. J Am Chem Soc 124 6487-6496... 

Sakharov IY, Vorobiev AC, Leon JJC (2003) Synthesis of polyelectrolyte complexes of polyaniline and sulfonated polystyrene by palm tree peroxidase. Enzyme Microb Technol 33 661-667... 

Immobilized HRP on polyaniline activated with glutaraldehyde (PANIC) The immobilized HRP in PANIG showed better tolerance to organic solvents, thermostability, and higher activity in the alkaline range (from pH 9.0 to 11.0) than the free enzyme [47,48]... 

The formation of conductive conjugated polymers [e.g., polyacetylene, polypyrrole, polythiophene, polyaniline and poly(p-phenylene)] [92, 94] on electrodes by electropolymerization has been studied thoroughly [95]. If the electropolymerization is performed in a solution containing both the monomer and enzyme, then enzymes present in the immediate vicinity of the electrode surface become trapped in the... 

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. 

Amperometric Biosensors with Enzymes Electrohemically Communicated Via Sulfonate-Functionalized Polyanilines... 

Figure 8 is a possible redox cycle occurring in an amperometric sensor for hydrogen peroxide involving enzyme-wiring of a typical enzyme (Horseradish peroxidase, HRP) with polyaniline. HRP immobilized on the electrode surface can be oxidized by H2O2 to compound I that contains an oxyferryl centre with the iron in the ferryl state (Fclv = O), and a porphyrin 7r cation radical, followed by further direct (mediatorless) electroreduction of compound I at the electrode surface to the initial HRP state [106], The electrode is considered as an electron donor. 

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