TYROSINASE GRAPHITE-EPOXY BASED COMPOSITE ELECTRODES FOR DETECTION OF PHENOLS

The characterization and analytical performance of a tyrosinase graphite-epoxy electrode for the detection of phenolic compounds are described. The biocomposite configuration is based on the entrapment of commercially available tyrosinase in a graphite-epoxy matrix, and the mixing of the resulting conductive epoxy resin with a hardener. The enzyme electrode is mounted as a working electrode in an amperometric flow cell of the confined wall-jet type and studied in the flow injection mode. The bioprobe is electrochemically characterized by hydrodynamic and cyclic voltammetry for catechol and phenol. An applied potential of -100 mV vs. Ag/AgCl is found to be optimal for electrochemical reduction of the enzyme products (quinone forms) for the biocomposite electrode. The dependence of the response of the biocomposite on the flow rate, the amount of loaded enzyme, the buffer composition, pH, and oxygen is investigated. The response of the biosensor to different phenolic compounds is also evaluated. The limits of detection (S/N = 3) for phenol and catechol were 1/0 mu M and 0.04 mu M, respectively. No loss in response could be detected after 100 injections of catechol (R.S.D. <2%). Stability of the biocomposite depends on storage conditions. Theoretical advantages described in the literature for biocomposite electrodes, for example, repolishing and bulk modification, are empirically studied in this work.