Glucose oxidase entrapped in polypyrrole on high-surface-area Pt electrodes: a model platform for sensitive electroenzymatic biosensors

Enzyme entrapped in an electrosynthesized polymer film on a high-surface-area electrode is shown to be an attractive platform for the important class of amperometric biosensors based on oxidases and electrooxidation of the H2O2 generated by enzyme-catalyzed oxidation of analyte. Two Pt electrode surface morphologies, Pt black (Pt-BLK) and Pt nanowire brush (Pt-NW) were electrodeposited from chloroplatinic acid. Glucose oxidase (GOx) served as the model enzyme. which was entrapped in an elect ropolymerized polypyrrole (PPY) film on the high-surface-area Pt electrodes. The glucose sensitivity of the GOx electrodes can be controlled simply through Pt deposition conditions and varies roughly linearly with electrode microscopic roughness, factor-A sensitivity of 103 muA mM(-1) cm(-2) was achieved with the Pt-BLK/PPY-immobilized GOx system at an underlying electrode surface roughness of 318, which is 150-fold higher than the sensitivity of a bare evaporated PUPPY-immobilized GOx electrode with a surface roughness of similar to2-3. The apparent Michaelis constant for PPY-immobilized GOx (similar to30 mM) is similar to that for free enzyme (25 mM) suggesting that the overall electrode kinetics are not limited by glucose mass transfer. Scanning electron micrographs, of enzyme electrode surfaces and a fluorescence assay to determine immobilized GOx concentration revealed that the PPY-GOx layer is deposited as a thin film that follows the contours of the electrode surface and that up to 3-fold greater enzyme is entrapped on the roughest electrodes examined. The orders of magnitude greater sensitivity of enzyme electrodes based on high-surface-area Pt appears likely to be due to increased H2O2 electrooxidation efficiency. (C) 2004 Elsevier B.V. All rights reserved.