Amperometric hydrogen peroxide sensor electrodes coated with electropolymerized tyrosine derivative and phenolic films

Amphiphilic decyl ester derivatives of the amino acids D- and L-tyrosine (DEDT and DELT) self-assemble into long rod-like or tubular aggregate structures in aqueous buffered solutions as visualized by SEM or light microscopy. We demonstrate that electrochemical polymerization of DEDT and DELT at concentrations lower than their critical micelle concentration values? via cyclic potential scanning between -0.20 and 1.00 V versus Ag \ AgCl in phosphate buffered solution pH 6.5, forms stable films on Pt electrodes. Enzymes such as horse-radish peroxidase (HRP) can be physically entrapped within the polymer films during electropolymerization. The ability of Pt electrodes, covered by these tyrosine based thin films as well as phenolic films, to measure varying H2O2 concentrations directly, or via enzymatic intermediates, was examined at two different potentials. The first is +0.85 V, the potential for direct electrode oxidation of H2O2. The second is -0.05 V, the potential for HRP reduction to its native state following the reduction of H2O2 by HRP. At both potentials, the thin film covered electrodes gave stable chronoamperometric responses to H2O2 in the concentration range from 1 x 10(-5) to 1 x 10(-2) hi, which were linear in two different concentration regions and which possessed linear log-log plots over the entire concentration range. The polymer thin films also significantly prevented electrochemical interference to H2O2 sensing from ascorbic acid. Tn these respects, the electropolymerized thin films derived from DEDT and DELT are similar to other electropolymerized phenolic thin films. These results demonstrate that stable H2O2 sensing electrodes may be formed electrochemically from amphiphilic derivatives of phenolic compounds. In certain sensing situations, these film electrodes may be advantageous due to potentially selective permeabilities associated with their hydrophobic derivatization. (C) 2001 Elsevier Science B.V. All rights reserved.