Electrochemical detection of thiols with a coenzyme pyrroloquinoline quinone modified electrode

A modified electrode sensor for the detection of thiols is described. The s ensor was constructed by incorporation of the coenzyme pyrroloquinoline qui none (PQQ) into a polypyrrole (PPy) film on a glassy carbon electrode subst rate by the electropolymerization of pyrrole in the presence of PQQ The ele ctrochemical properties of entrapped PQQ in the Pgr film were influenced by the applied potential during electropolymerization and by film thick;less, both of which were optimized to yield a stable and reproducible response f or entrapped PQQ The PQQ/PPy sensor was utilized for the amperometric detec tion of cysteine, homocysteine, penicillamine, N-acetylcysteine, and glutat hione. The response for each thiol in pH 8.42 berate buffer was found to be linear with detection limits (S/N = 3) ranging from 13.2 muM for glutathio ne to 63.7 nM for cysteine with sensitivities of 0.023 nA/muM and 4.71 nA/m uM, respectively. The response and detection limits were found to be sensit ive to the nature of the thiol and the solution pH. Furthermore, in the pre sence of dopamine, ascorbic acid, or uric acid, the pH-dependent redox pote ntial of the PQQ catalyst allows tuning of the detection potential to enhan ce the selectivity for thiols over these potential electroactive interferen ces.