Photocatalytic deposition of plasmonic Au nanostructures on a semiconductor substrate to enhance Raman sensitivity

Abstract The combination of noble metals and semiconductors opens new routes for surface enhancement of Raman signal. Gold nanostructures were here photocatalytically grown from solutions of gold (III) chloride trihydrate under UV illumination on sol-gel derived TiO2 coatings deposited on silicon wafers. Resulting nanoplatforms were designed to serve as superior SERS-active substrates. Architecture of Au deposits primarily depended on intensity of ultraviolet irradiation resulting in the formation of nanoflowers with a high enhancement factor of SERS when the titania film was shortly illuminated with a high number of UV photons. Using two molecular probes, 4-mercaptobenzoic acid and malachite green, we evaluated the TiO2-Au nanostructures performance under off- and resonance conditions of Raman scattering. SERS enhancement appeared in conjunction with charge transfer and electromagnetic mechanisms and with the type of adsorption occurring on metallic and semiconductor interface. For the monolayer of the thiol derivative, we achieved the micromolar limit of detection which is suitable for further functionalisation of the SERS sensor. In the case of SERRS effect achieved when malachite green is illuminated with a laser matched to electronic transition of the dye, we observed a linear response of the SERS signal with the limit of detection of 9 × 10−11 M.