Enantioselective electrochemical sensor for R-mandelic acid based on a glassy carbon electrode modified with multi-layers of biotin-loaded overoxidized polypyrrole and nanosheets of reduced graphene oxide

The authors describe an electrochemical method for quantitation of R-mandelic acid (R-MA). A glassy carbon electrode (GCE) was modified by electrochemical deposition of several layers of D-(+)-biotin-loaded overoxidized polypyrrole (OPPy-biot) on nanosheets of reduced graphene oxide. The deposited film was characterized by scanning electron microscopy, differential pulse voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy. The modified GCE is shown to enable stereoselective recognition of R-MA even in the presence of high concentrations of S-mandelic acid (S-MA), best at a voltage of around 1.5 V (vs. Ag/AgCl). The analytical performance of the electrode was studied by differential pulse voltammetry which revealed a linear range that extends over the 5 to 80 mM R-MA concentration range, a 1.5 mM detection limit, and an enanotiospecific characteristic toward R-MA. Under optimum conditions, the method displays high reproducibility and stability. It was applied to the determination of R-MA in a synthetic mixture and no interference was observed by S-MA.