Graphite-Teflon-Peroxidase Composite Electrochemical Biosensors. A Tool for the Wide Detection of Phenolic Compounds

Graphite-Teflon-peroxidase composite electrodes, constructed by simple physical inclusion of the enzyme into the bulk of the electrode matrix, have been used for the amperometric detection of 18 phenolic compounds. Monitoring of the enzyme reaction was carried out by the electrode reduction of the generated phenoxy radicals, in the presence of a constant concentration of 5.0×10−4 mol L−1 H2O2, at an applied potential of 0.00 V. Different aspects regarding the stability of the composite bioelectrode showed the robustness of the biosensor design. The kinetic constants of the enzyme reactions for the phenolic compounds tested were calculated. The limits of detection obtained were better than those found in the literature for peroxidase biosensors using other composite matrices, and the differences in sensitivity observed for the different phenolic substrates are discussed in terms of their pKa values and substituents. The analytical signals obtained with the graphite-Teflon-HRP electrodes have been compared with those yielded by a graphite-Teflon-tyrosinase composite electrode constructed in a similar way. With the aim of monitoring the largest possible number of phenolic compounds with the highest possible sensitivity, coimmobilization of peroxidase and tyrosinase into the composite electrode matrix was carried out.