Highly monodispersed Ag embedded SiO2 nanostructured thin film for sensitive SERS substrate: growth, characterization and detection of dye molecules

Highly monodispersed Ag embedded SiO2 nanostructured thin films are synthesized and their sensitivity towards SERS investigated. The possible mechanism for the formation of a highly monodispersed SiO2 nanostructured thin film and its self-assembled nanogap with Ag are discussed. It is found that the architecture of Ag embedded SiO2 (Ag@SiO2) are drastically influenced by precursor concentration and the reaction time. The morphology and monodispersity of the silica thin film were confirmed using FESEM and AFM. The crystallinity and existence of Ag on SiO2 were confirmed using XRD and XPS. The substrate shows enhanced SERS efficiency due to the reduced size (around 15 nm) of the Ag nanoparticles and the nano gap of (below 3 nm) between SiO2 and Ag. Based on the FDTD (finite-difference time-domain) simulation, the creation of hotspots was confirmed for the obtained nanogap. The prepared thin film possesses strong Surface Plasmon Resonance (SPR) with widely tunable peaks between 407–430 nm in the UV visible spectrum. The Ag@SiO2 nanosphere-based SERS platform provides highly enhanced effects and reveals a reproducible enhancement (EF = 7.79 × 108) of R6G (Rhodamine 6G), allowing a detection limit from a 10–18 mol L−1 solution. The prepared substrate was also used to detect trace levels of melamine from a 10–8 mol L−1 solution.