A scanning force microscopy study of poly(phenol) films containing immobilized glucose oxidase

Scanning force microscopy has been used to characterize poly(phenol) films containing immobilized glucose oxidase (GOx). The films were grown by electrochemical polymerization of phenol from neutral aqueous solution at highly ordered pyrolytic graphite (HOPG) electrodes. Scanning force microscopy, in contact mode, shows the surface topography of the enzyme/polymer composite films. Films containing immobilized enzyme were found to be significantly rougher than either the bare substrate or enzyme free poly(phenol) films grown under the same conditions. The thickness of the electropolymerized films was determined by using the 'nanodozing' technique in which the scanning tip is used to scrape away an area of the polymer film to reveal the HOPG surface beneath. Using this method we find that the enzyme-containing films are 7.4 +/- 0.8 nm thick whereas the enzyme free poly(phenol) films are 3 +/- 1.2 nm thick. Amperometric measurements using the tetrathiafulvalene/tetrathiafulvalenium (TTF/TTF+) couple as a redox mediator for oxidation of the immobilized GOx confirm that the immobilized enzyme is catalytically active. Analysis of the amperometric response of the electrodes at different glucose concentrations allows us to determine the kinetic parameters for the immobilized enzyme. The amperometric responses are consistent with the presence of a thin active layer of GOx one or two molecules thick immobilized at the electrode surface and agree with the conclusions from the scanning force microscopy study. (C) 1998 Elsevier Science S.A. All rights reserved.