An electrochemical microfluidic sensor based on a Cu₂O-GNP nanocomposite integrated hydrogel for nitrite detection in food samples

The integration of a nanocomposite composed of cuprous oxide-graphene nanoplatelet hydrogel (Cu₂O-GNP hydrogel) has been investigated as an electrochemical interface for nitrite (NO₂^-) detection. The nanocomposite hydrogel was prepared through the sonochemical technique and characterized by Field Emission Scanning Electron Microscopy (FE-SEM), EDX (energy dispersive X-ray analysis), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Electrochemical performance was further evaluated using Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), and Differential Pulse Voltammetry (DPV). Cu₂O provides a catalytic active site that lower the activation energy for NO₂^- oxidation, while GNPs enhance the electrode conductivity and increase the surface area for superior electron transfer. Additionally, a PDMS-based microfluidic device was developed and integrated with an electrochemical detection system, enabling continuous and real-time monitoring of NO₂^-. A syringe pump was used to maintain a stable NO₂^- solution flow through the microfluidic channels at a 10 μL per min flow rate, ensuring sufficient diffusion of NO₂^- ions to the electrode surface, and preventing excess analyte accumulation that could lead to signal distortion. The integrated microfluidic sensor exhibited excellent electrochemical performance, achieving a high sensitivity of 13.97 μA μM^-1 cm^-2 and a low detection limit (LOD) of 0.56 μM, with a linear range of 5-130 μM. Cu₂O-GNP hydrogel/SPCE exhibited excellent selectivity and reproducibility for NO₂^- sensing. The developed sensor demonstrated good recovery percentages in sausages, pickled vegetables, and water samples, confirming its suitability for the food industry.