Optimally distributed Ag over SiO2 nanoparticles as colloidal SERS substrate

Surface enhanced Raman spectroscopy (SERS) is a versatile and unique technique for the detection and identification of molecules. Over the past few decades this unique technique has grown as a tool for the qualitative and quantitative analysis. We report a novel and simple method for the synthesis of silica-silver nanospheres (Ag-SiO2) which can be used as colloidal SERS substrate. Geometrically confined hotspots with stable silver nanoparticles are obtained allowing a preferrential arrangement of hotspots. The prepared Ag-SiO2 nanospheres with varying size are used for the SERS detection of Rhodamine 6G. The SERS intensity is found to vary with the change in size of silica and distribution of silver nanoparticles. Both these quantities are optimized to get maximum enhancement of Raman signal and the detection limit is found to be 10(-18) M for Rhodamine 6G. Further, the work is extrapolated to an application which involves the SERS detection of Sudan I, a carcinogenic food adulterant, with a detection limit of 10(-8) M.