Tuning the electro-catalytic activity of the Zn-Cu MOF/rGO nanocomposite as a novel enzyme-free electrochemical sensor for the detection of Oxytocin hormone

Oxytocin (OXY), a peptide hormone and neurotransmitter essential to biological processes with nine distinct amino acid residues, has significantly received attention due to illegal use in food adulteration and stimulating milk ejection in cattle. Herein, for the first time, the electrochemical detection of Oxytocin (OXY) is reported using a novel nanocomposite consisting of a Zn-Cu metal-organic framework (Zn-Cu MOF) decorated on the reduced graphene oxide (rGO). An octahedral surface morphology with a crystalline structure of the size 45 nm, formation of a metal-oxygen bond, an enhanced pore diameter of 6.8 nm, a specific surface area of 70.8 m2/g, and pore volume of 0.08 cm3/g, revealed from the different characterization technique. The electro-catalytic behavior of Zn-Cu MOF/rGO nanocomposite has been increased substantially attributed to the synergistic effect, evident from the cyclic voltammetry (CV) when compared to Zn MOF, Cu MOF, Zn MOF/rGO, Cu MOF/rGO, Zn-Cu MOF keeping other parameters same. Moreover, the electrochemical impedance spectroscopy (EIS) spectra reveal the excellent conductivity of nanocomposite. The experimental parameters, viz. electrolyte pH (5), supporting electrolyte (0.1 M ABS), and volume of coating (12 µL), were optimized. The differential pulse voltammetry (DPV) technique was adopted to determine the OXY with the lowest limit of detection (LOD) to be 1.1 nM (S/N=3) with a linear range of 40 - 400 nM. The analytical application of the modified electrode was examined by spiking the OXY in pasteurized toned milk, skimmed powder milk, animal milk, and RO water, with a good recovery range of 95-106%.