An improved sensing process of ultra low concentration of nitrite anions using pre-etched silicon decorated with copper nanowires

This work presents a novel, cost-effective, and facile approach for fabricating an ultrasensitive Surface Enhanced Raman Scattering (SERS) sensor using copper nanowires (CuNWs) directly deposited on the surface of the pre-etched silicon substrate. Unlike conventional methods requiring complex surface modifications, our technique employs a simple 24h pre-etching process in a (1:1) hydrofluoric (HF) and ethanol solution, offering a practical alternative for large-scale or low-resource applications. The immersion plating of CuNWs was achieved by dipping the pre-etched Si surface in a (0.025) M of CuSO₄.5H₂O solution for (30) minutes, enabling spontaneous formation of a dense CuNWs network. Field Emission Scanning Electron Microscope (FE-SEM) confirmed the high density of distributed nanoscale pores (~ 3.2 × 10⁸ pores/cm²) on the bare etched surface and a homogeneous coverage of vertically aligned CuNWs (~ 6.5 × 10⁹ NWs/cm²) on the hybrid substrate. Compositional integrity of the CuNWs was validated by Energy Dispersive (EDS), while structural features were characterized via X-ray Diffraction (XRD), confirming their polycrystalline nature. Remarkably, the fabricated sensor exhibited a recorded enhancement factor (EF) of (2.11 × 10¹³) and an ultra-low detection limit (LOD) of (3.38 × 10^–11) for nitrite anions over a broad concentration range (5 × 10^–6 to 5 × 10^–12 M). The outstanding SERS performance is attributed to the high aspect ratio, sharp edges, and large density of CuNWs on the surface which collectively generate abundant electromagnetic hotspots. This work demonstrates a scalable, low-cost route for producing efficient Cu-based SERS substrates and offers a promising platform for ultrasensitive chemical sensing, especially in resource-limited or field-deployable settings.