AMPEROMETRIC BIOSENSORS FOR DETECTION OF L-AMINO AND D-AMINO ACIDS BASED ON COIMMOBILIZED PEROXIDASE AND L-AMINO AND D-AMINO-ACID OXIDASES IN CARBON-PASTE ELECTRODES

An apparent direct electron transfer between various electrode materia ls and peroxidases immobilized on the surface of the electrode has bee n reported in the last few years. An electrocatalytic reduction of hyd rogen peroxide promoted by the immobilized peroxidase starts at about +600 mV (vs. Ag/AgCl) at neutral pH. The efficiency of the electrocata lytic current increases as the applied potential is made more negative and starts to level off at about -100 mv (vs. Ag/AgCl). Amperometric biosensors for hydrogen peroxide can be constructed with these kinds o f peroxidase modified electrodes. By coimmobilizing a hydrogen peroxid e-producing oxidase with the peroxidase, amperometric biosensors can b e made responding to the substrate of the oxidase within a potential r ange essentially free of interfering electrochemical reactions. Sensor s for L- and D-amino acids are shown based on coimmobilizing HRP with L-amino acid oxidase (L-AAOD) or D-amino acid oxidase (D-AAOD). The ef fects of the immobilization procedure, buffer (flow carrier), pH, take n amounts of enzymes, flow rate, and injection volume on the response were investigated. The addition of polyethylenimine (PEI) into the pas te was found to increase the response considerably. All 20 of the most common L-amino acids could be detected.