A Polypyrrole-Bienzyme Electrode (Salicylate Hydroxylase-Polyphenol Oxidase) for the Interference-Free Determination of Salicylate

The electrochemical immobilization of salicylate hydroxylase (SH) within poly(amphiphilic pyrrole ammonium) films electrogenerated on carbon electrode is described. The amperometric determination of salicylate is carried out at 0.4 V (vs. Ag/AgCl) via the oxidation of the enzymically generated catechol. The detection limit and the sensitivity of the polypyrrole-SH electrode were 3×10−9 M and 1.7 A M−1 cm−2, respectively. Moreover, the co-entrapment of SH and polyphenol oxidase (PPO) in such polypyrrole films provides a bienzyme electrode also for the determination of salicylate. Contrary to the monoenzyme electrode, the functioning principle of the bienzyme electrode is based on the reduction of o-quinone enzymically generated from catechol. Consequently, the amperometric detection of salicylate was performed at −0.2 V without interferences from easily oxidizable compounds. The calibration range for salicylate measurement and the biosensor sensitivity were 5×10−8–3×10−6 M and 0.25 A M−1 cm−2, respectively.