A cortisol nanocomposite-based electrochemical sensor for enantioselective recognition of mandelic acid

Abstract

An electrochemical chiral sensor was designed based on graphene (GR) as a catalyst for signal enhancement. Hydrocortisone has been immobilized as a chiral selector on GR to discriminate electrochemical signals of mandelic acid (MA) enantiomers. A two-step electrodeposition strategy was used to fabricate hydrocortisone-loaded overoxidized polypyrrole film (HC-OPPy) on graphene-modified glassy carbon electrode, which was successfully utilized as a working electrode for direct monitoring of MA enantiomers based on an inhibitory sensing mechanism. The stepwise modification of the surface was confirmed by cyclic voltammetry, impedance spectroscopy, and scanning electron microscopy. Because of the different interactions of enantiomers with the chiral electroactive platform, voltammetric signals with different intensities were observed for S-MA and R-MA at 1.36 and 1.40 V (vs. Ag/AgCl), respectively. The introduced design for the chiral sensor, with exploiting the chemometrics tools such as partial least squares, principle component regression, and genetic algorithm, was able to discriminate highly overlapping signals of MA enantiomers in their mixtures. The hydrocortisone-based sensor showed a linear response towards MA enantiomers within a concentration range of 1.0–25 mM with a detection limit of 0.25 mM (S/N = 3). The sensor not only extends the enantioselective sensing of MA enantiomers but also stimulates new opportunities for investigating stereo-selective behavior of hydrocortisone. The recognition mechanism was also investigated using docking analysis and DFT calculations.