Marjan Borazjani - Department of Chemistry, Faculty of Science, K. N. Toosi University of Technology, Tehran, Iran
Ali Mehdinia - Department of Marine Living Science, Ocean Sciences Research Center, Iranian National Institute for Oceanography and Atmospheric Science, Tehran, Iran
Ehsan Ziaei - Department of Chemistry, Faculty of Science, K. N. Toosi University of Technology, Tehran, Iran
Ali Jabbari - Department of Chemistry, Faculty of Science, K. N. Toosi University of Technology, Tehran, Iran

Analysis of chiral mandelic acid (MA) is essential, owing to its important role in natural product synthesis and drug development [1]. Stereoselective electrochemical sensing based on chiralmodified-electrodes has recently been reported to provide a promising entry to direct screening ofchiral molecules, especially MA [2-8]. Enantioselective sensing based on electrochemical sensors offers a variety of advantages over chiral chromatographic and spectrophotometric techniques, such as simplicity, low cost, rapid detection and possibility of real time analysis [9]. A novelchiral biosensor for enantioselective detection of mandelic acid enantiomers was fabricated based on multilayered electrochemically deposition of D-(+)-biotin-loaded overoxidized polypyrrole(OPPy-biot) film on the nanosheets of reduced graphene oxide (rGO)-modified glassy carbon electrode (OPPy-biot/rGO/GCE). The nanocomposite film was characterized by scanning electron microscopy (SEM), differential pulse voltammetry (DPV), cyclic voltammetry (CV) andelectrochemical impedance spectroscopy (EIS). The composite of D-(+)-biotin-loaded OPPy and reduced graphene oxide (rGO) was highly stereoselective toward the R-mandelic acid (R-MA) in the presence of high concentrations of S-mandelic acid (S-MA). The sensing performance of the chiral-modified electrode was investigated by differential pulse voltammetry (DPV), revealing a linear range of 5–80 mM with a detection limit of 1.5 mM.Under the optimum conditions, the sensor exhibited good reproducibility and stability for R-MA determination. The designed sensor has been successfully applied for determination of R-MA and S-MA in a synthetic mixture and the satisfactory results were obtained

Chiral electrochemical biosensor, D-(+)-Biotin, Mandelic acid, Enantioselective recognition