Immersion-plated Palladium Nanoparticles onto Meso-porous Silicon Layer as Novel SERS Substrate for Sensitive Detection of Imidacloprid Pesticide

Herein, we report a rapid and highly effective methodology for the fabrication of active and stable surface-enhanced Raman scattering (SERS) substrate by an electrochemical anodization and immersion plating routes. Porous silicon (PSi) layers were fabricated by the electrochemical anodization of a silicon wafer in ethanoic fluoride solution, followed by uniformly deposition of palladium nanoparticles (Pd NPs) via a simple immersion plating technique. The structural features and morphology of fabricated frameworks of PSi-Pd NPs have been investigated by field emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectra. The PSi substrate demonstrates a meso-porous morphology with good distribution, good pore density and average pore sizes around 20 nm. The SERS performance of Si–Pd NPs and PSi–Pd NPs substrates has been examined taking imidacloprid (an insecticide) as a target analyte. The SERS signal of imidacloprid using PSi–Pd NPs substrate exhibited immense enhancement compared to the Si-Pd NPs substrate. The active substrate revealed excellent detectable performance with a concentration as low as 10-9 M imidacloprid and an enhancement factor (EF) of 1.2×105. This large EF is fundamentally ascribed to the combined effect of electromagnetic improvement and charge transfer mechanism. Additionally, no aging effect was observed for the present substrates kept in air for two weeks. Striking enhancement in Raman spectral signals obtained with the current PSi–Pd NPs substrates provides a simple and smooth platform towards the sensitive detection of various target analytes.