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

Abstract

Oxytocin (OXY), a peptide hormone and neurotransmitter essential for biological processes with nine distinct amino acid residues, has received significant attention due to its illegal use in food adulteration and stimulating milk ejection in cattle. Herein, for the first time, electrochemical detection of oxytocin (OXY) is reported using a novel nanocomposite consisting of a Zn–Cu metal–organic framework (Zn–Cu MOF) decorated on reduced graphene oxide (rGO). An octahedral surface morphology with a crystalline structure of 45 nm in size, formation of a metal–oxygen bond, an enhanced pore diameter of 6.8 nm, a specific surface area of 70.8 m² g⁻¹, and a pore volume of 0.08 cm³ g⁻¹ were revealed by different characterization techniques. The electro-catalytic activity of the Zn–Cu MOF/rGO nanocomposite increased substantially owing to the synergistic effect, which is evident from cyclic voltammetry (CV) when compared to those of the Zn-MOF, the Cu-MOF, Zn MOF/rGO, Cu MOF/rGO, and Zn–Cu MOF, keeping other parameters the same. Moreover, the electrochemical impedance spectroscopy (EIS) spectra reveal the excellent conductivity of the 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) of 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 OXY in pasteurized toned milk, skimmed powder milk, animal milk, and RO water, with a good recovery range of 95–106%.