This review presents a comprehensive synopsis of the recent developments and achievements in the research of nanosensors composed of plasmonic nanoparticles (NPs) and silicon nanostructures (NSs) for effective trace-level molecular detection. This review focuses intensively on the methodologies for the preparation and enforcement of a variety of SiNSs including (a) metal nanoparticles decorated silicon nanowires (NWs), (b) metal nanodendrites (NDs) on Si substrate, (c) plasmonic NPs decorated nanocrystalline porous silicon (pSi), and (d) silicon composed hybrid nanostructures with favorable parameters of importance in sensing. Furthermore, their potency in wide molecular sensing applications, especially chemical, biological, and explosive molecules based on surface enhanced Raman scattering (SERS) phenomenon is discussed in detail. Various demonstrations and categorizations are provided on the topic of Si-based NSs for a clear understanding to diverse readers. A roadmap is also provided at the end for achieving superior sensing materials or devices in the future.

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We report on the influence of resistivity in picosecond (ps) laser ablation of Silicon (Si) leading to the formation of diverse surface micro- and nanostructures. Subsequently, we investigated their potential in sensing applications based on the surface enhanced Raman scattering (SERS) technique. The varying resistivity (ρ1: 1-10 Ωcm, ρ2: 0.01-0.02 Ωcm, ρ3: 0.001-0.005 Ωcm) Si wafers were subjected to cross patterned ps laser ablation in ambient air. Ladder-like microstructures embedded with numerous nano growths were formed on low resistivity Si (ρ3) while similar micro- and nanostructures were observed on higher resistivity Si (ρ2 <ρ1). The structures were non-plasmonic and anti-reflecting in nature with an optical reflectance of <6 % over a broad range of wavelengths (350-1200 nm). Non-plasmonic Si microstructures were subsequently transformed to plasmonic by means of deposition of a thin layer of gold (Au). Additionally, the effect of annealing on the evolution of nanostructures was also investigated. We employed these hybrid substrates for the trace detection of an explosive molecule, ammonium nitrate (AN), and dye, malachite green (MG). Our detailed SERS studies have demonstrated a superior enhancement in the trace detection of analytes for low resistivity Si substrate. However, the annealed hybrid substrates have demonstrated further improvement in the SERS signal (by at least one order of magnitude). These detailed SERS investigations provide us a proof of the sensitivity of different resistivity Si nano/microstructures.

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