Electrochemical detection of thiols with a coenzyme pyrroloquinoline quinone modified electrode

A modified electrode sensor for the detection of thiols is described. The sensor was constructed by incorporation of the coenzyme pyrroloquinoline quinone (PQQ) into a polypyrrole (PPy) film on a glassy carbon electrode substrate by the electropolymerization of pyrrole in the presence of PQQ The electrochemical 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 for entrapped PQQ The PQQ/PPy sensor was utilized for the amperometric detection of cysteine, homocysteine, penicillamine, N-acetylcysteine, and glutathione. 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 glutathione to 63.7 nM for cysteine with sensitivities of 0.023 nA/muM and 4.71 nA/muM, respectively. The response and detection limits were found to be sensitive to the nature of the thiol and the solution pH. Furthermore, in the presence of dopamine, ascorbic acid, or uric acid, the pH-dependent redox potential of the PQQ catalyst allows tuning of the detection potential to enhance the selectivity for thiols over these potential electroactive interferences.