Electrocatalytic Oxidation and Sensitive Detection of Cysteine on a Lead Ruthenate Pyrochlore Modified Electrode

Electrocatalytic oxidation of cysteine (CySH) at Nafion/lead ruthenate pyrochlore (Py) chemically modified electrodes was thoroughly studied. Electrochemical ac impedance spectroscopy analysis indicated the formation of Py microparticles in the interfacial galleries of Nafion. Experiments with benchmark systems of Fe(CN)63-/4- and Ru(bpy)2+/3+ reveal the suppression of Nafion's anionic character after the in situ precipitation of Py. Michaleis−Menten-type kinetics with the rate determination step of CyS−Py−RuVI → Py−RuIV + CyS−SCy was proposed for this catalytic oxidation. The electrocatalytic behavior is further developed as a sensitive detection scheme for CySH by square-wave voltammetry (SWV) and flow injection analysis (FIA). Under the optimized conditions, the calibration curve is linear up to 560 μM with a detection limit (signal/noise 3) of 1.91 μM in SWV. The detection limit can be improved to 1.70 nM (i.e., 24.22 ng in a 20-μL sample loop) in FIA. This is the lowest value ever reported for direct...