Immersion-plated palladium nanoparticles onto meso-porous silicon layer as novel SERS substrate for sensitive detection of imidacloprid pesticide

Herein, we demonstrate the effectiveness of surface-enhanced Raman scattering (SERS) to detect trace concentration of potentially harmful imidacloprid pesticide. To achieve this ultimate objective, a rapid and highly effective methodology for the fabrication of active and stable porous silicon (PSi) plated palladium nanoparticles (PdNPs) SERS substrates by an electrochemical anodization and immersion plating routes was applied. The PSi layers were fabricated by the electrochemical anodization of a silicon wafer in ethanoic fluoride solution, followed by uniformly deposition of PdNPs 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 × 10(5). This large EF is fundamentally ascribed to the combined effect of the electromagnetic improvement and charge transfer mechanisms. 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 can provide a simple and smooth platform towards the sensitive detection of various target analytes.