Nonenzymatic Electrochemical Sensor Device for On-Site Nitrate Determination Using Copper Anchored Magnetite Nanocomposites

Elevated nitrate (NO₃^-) levels in potable water due to anthropogenic and geogenic activities pose a significant environmental threat. Herein, we report a highly efficient electrochemical sensor device for NO₃^- detection using a copper-anchored magnetite (Cu@Fe₃O₄) nanocomposite. The electrochemical performance of the NO₃^- sensor was highly durable and reliable on a glassy carbon electrode (GCE) and as a proof of concept, it has been translated to thermal vapor deposited gold electrodes (Au electrodes) chip integrated with a hand-held portable potentiostat connected to a smartphone with read out capabilities for onsite real field application. The Cu@Fe₃O₄ nanocomposite was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM) mapping, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) to confirm phase purity and successful synthesis. The sensor exhibited high selectivity for NO₃^- (<i>P</i> ≤ 0.05), stability up to 21 days with a minimal 1.2% signal decrease, and a linear detection range of 10-1000 μM, with a detection limit of 1.35 μM and sensitivity of 0.0342 μA/μM. It also showed reproducibility of a relative standard deviation (RSD 1.33%) and successfully detected NO₃^- in real water samples. This robust sensor provides an effective tool for real-time environmental assessment of NO₃^-, aiding public health protection.