Immobilization of glucose oxidase in thin polypyrrole films: Influence of polymerization conditions and film thickness on the activity and stability of the immobilized enzyme

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Abstract
Using monomers that polymerize to form electrically conducting polymers, one can control the thickness of the polymer film and the amount of enzyme that can be immobilized in the films. First, an investigation of the major variables that influence the immobilization of glucose oxidase by entrapment in polypyrrole films, prepared by electropolymerization from aqueous solutions containing the enzyme and monomer, was carried out. Then the optimized conditions were used to assess the effects of film thickness on the activity and stability of immobilized enzyme. For the films ranged in thickness from 0.1 μm to 1.6 μm, the resulting apparent activity and stability of the immobilized enzyme were found to be a strong function of the polymer film thickness. Above a thickness of 1.0 μm, the apparent activity of the immobilized enzyme increases linearly with increasing film thickness. The nonlinearity observed for films of thickness less than 1.0 μm can be attributed to the changes observed in the morphology of the resulting polypyrrole films. Furthermore, it was noted that when the glucose oxidase/polypyrrole films are stored in phosphate buffer, at 4°C, the observed rate of loss in apparent activity of the immobilized enzyme is highest for the first few days, also being higher for the thinner films. However, after the loosely entrapped enzyme is leached from the polymer film, the rate of loss in activity is very low indicating that the well-entrapped enzyme, as well as the polypyrrole films, exhibit good stability. Finally, the reproducibility of the immobilization technique is excellent. © 1993 John Wiley & Sons, Inc.

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