AN BIENZYME ELECTRODE (ALKALINE-PHOSPHATASE POLYPHENOL OXIDASE) FOR THE AMPEROMETRIC DETERMINATION OF PHOSPHATE

The electropolymerization of an alkaline phosphatase (AP)-amphiphilic pyrrole ammonium mixture previously adsorbed on the electrode surface provides efficient entrapment of AP in a polypyrrole film. The resulti ng biosensor was applied to the detection of phenyl phosphate via ampe rometric oxidation at 0.6 V vs SCE of the enzymic generated phenol. Th e sensitivity and detection limit of the biosensor were 862 mu A M-1 c m(-2) and 20 mu M, respectively. The co-immobilization of polyphenol o xidase and AP leads to a bienzyme electrode for the determination of p henyl phosphate on the basis of amperometric detection of the enzymica lly generated o-quinone at -0.2 V. An amplification factor of 9.7 was calculated as the ratio of the bienzyme to monoenzyme electrode sensit ivities. In the presence of 5 mM MgCl2, the sensitivity and detection limit of the biosensor for phenyl phosphate were 36.82 mA M-1 cm(-2) a nd 0.2 mu M, respectively. Phosphate competitively inhibited the hydro lysis of phenyl phosphate. Consequently, its determination is based on the decrease of the biosensor response to phenyl phosphate, The sensi tivity and detection limit of the biosensor for phosphate were 1.27 mA M-1 cm-2 and 2 mu M, respectively.