Silver coated porous silicon used as a surface enhanced Raman scattering (SERS)-active substrate for methylene blue detection
Porous silicon (PSi) coated with silver (Ag) was used as surface-enhanced Raman scattering (SERS)-active substrate for detection of methylene blue (MB). The PSi was formed via electrochemical etching of silicon (Si) wafer in a solution of hydrofluoric acid and ethanol. Porosities of 55% and 63% of PSi were fabricated using anodic current of 5 mA and 10 mA for 1000 s and 625 s respectively. These were immersed into Ag nitrate solution with 0.01 molar concentration for Ag coating. An-order-of-magnitude enhancement of Raman signal of MB was observed using SERS-active substrate with 63% PSi’s porosity. This suggests that more Ag were deposited on the high-porosity SERS-active substrate which resulted to Raman signal amplification due to surface plasmon resonance. Another factor that might cause such enhancement is the charge-transfer between the MB molecules and the substrate. Different molar concentrations of MB were synthesized. The MB molar concentration dependent studies showed that the substrate based on Ag coated PSi is sensitive up to 10-7 M.