Comparative SERS study carried out on unsilanized and silanized oxidized porous silicon surface coated by small gold nanoparticles

Porous silicon (PSi) was formed by electrochemical anodization and was oxidized before silanization and immersion in colloidal gold nanoparticles (GNP) (5 nm size) solution. The oxidized PSi (OPSi) coated with nanoparticles was used as surface enhanced Raman scattering (SERS) substrate, where bovine serum albumin (BSA) was used as a target molecule. Also, rhodamine 6G (R6G) dyes were used to confirm the SERS efficiency. Firstly, the bio-conjugation between protein and GNP was investigated by localized surface plasmon resonance spectroscopy. Then a comparative SERS study from silanized and unsilanized OPSi was performed and showed a good vibrational BSA bands resolution with the unsilanized one. The silanized surface did not show any improvement on the SERS enhancement of the BSA due to the interferences between the vibrational modes of 3-aminopropyltriethoxysilane and BSA. Furthermore, we have investigated the BSA solution pH effect on the SERS results in the case of unsilanized OPSi surface. The results prove the efficiency of the SERS substrate at pH 4.9, corresponding to BSA iso-electric point. A detection limit of about 10−8 M was obtained for both BSA and R6G molecules.