A novel L-Cysteine voltammetric sensor based on a dual-nucleation copper (II) complex

A novel platform of simple and cost-effective carbon paste electrode (CPE)-modified with a binuclear copper (II)8-hydroxyquinoline complex was used for catalytic electroxidation of L-Cysteine. The modified electrode described was observed to significantly reduce the electrooxidation potential of L-Cysteine. Electrochemical impedance spectroscopy confirmed a significant decrease in the charge transfer resistance at the electrode surface by introducing the binuclear copper complex in the CPE. It was proposed that the two molecules of cysteine, adsorbed to the modified electrode surface, are oxidized to a cystine molecule via copper (II) centers of the complex which are consequently reduced to copper (I) species, responsible for the voltammetric peak observed when the potential was scanned toward the positive direction. To improve the electrode signal for cysteine, the electrode composition was also optimized. Two electrochemical techniques of cyclic voltammetry and amperometry were applied for the establishment of the calibration curve for cysteine determination by this electrode. The linear ranges of the calibration curves are obtained utilizing two electrochemical techniques of cyclic voltammetry and amperometry were 286-5000 mu M and 11.6-500 mu M, respectively. Also, the detection limits of cysteine assay by the above-cited techniques were calculated and equal to 86.7 mu M and 3.5 mu M, respectively. The electrode described was applied for cysteine determination in some vegetable samples which showed satisfactory results. Also, the selectivity of the sensor was checked against some biomolecules and amino acids such as Glycine, Alanine, Arginine, Methionine, Glucose, Urea, BrO3 - and Citric acid. The introduced sensor exhibited excellent selectivity for cysteine determination in food samples.