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

The integration of a nanocomposite composed of cuprous oxide-graphene nanoplatelet hydrogel (CuO-GNP hydrogel) has been investigated as an electrochemical interface for nitrite (NO) 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). CuO provides a catalytic active site that lower the activation energy for NO 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 NO. A syringe pump was used to maintain a stable NO solution flow through the microfluidic channels at a 10 μL per min flow rate, ensuring sufficient diffusion of NO 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 cm and a low detection limit (LOD) of 0.56 μM, with a linear range of 5-130 μM. CuO-GNP hydrogel/SPCE exhibited excellent selectivity and reproducibility for NO sensing. The developed sensor demonstrated good recovery percentages in sausages, pickled vegetables, and water samples, confirming its suitability for the food industry.