Facile fabrication of ultrahigh-sensitivity surface-enhanced Raman scattering sensor using porous silicon photonic crystals prepared on backside silicon wafer

Photonic crystals (PhCs) with rough surfaces can considerably enhance the formation of electromagnetic hotspots, which significantly promote surface-enhanced Raman scattering (SERS) activity. In this study, porous silicon PhCs with rough surfaces were synthesized. Deposition of gold nanoparticles on the substrate yielded a SERS substrate with good activity and reproducibility, consequently achieving the ultratrace detection of Rhodamine 6 G (R6G), with a minimum concentration of 10(-)(15) M. The SERS activity of this substrate was simulated via finite element modeling. The experimental and theoretical results confirmed that the optical characteristics of the "black silicon," created by inducing a rough surface, and the enhancement of the effective Raman susceptibility, or the time period of the light-matter interaction owing to photonic crystals, played an important role in the enhancement of the overall SERS activity. Furthermore, we demonstrated that the rough-surface porous silicon SERS substrate could be employed to selectively detect ultratrace military explosives containing picric acid (PA) with increased sensitivity. Accordingly, the detection limits of PA and the probe molecule R6G in the Raman spectra were 0.79 nM and 0.24 fM, respectively. This study suggests that the porous silicon PhCs with rough surfaces are promising candidates for ultratrace chemical sensing.