Ag/ZnO/Au 3D hybrid structured reusable SERS substrate as highly sensitive platform for DNA detection

Ultra-sensitive hybrid Silver/Zinc oxide/Gold (Ag/ZnO/Au) structure based three dimensional (3D) surface enhanced Raman scattering (SERS) substrates have been prepared by three step fabrication process using thermal evaporation, hydrothermal growth, and sputtering techniques. The size and inter-particle (IP) gap of decorated Au nanoparticles (NPs) on ZnO nanorods (NRs) in the sub-nanometer range have been achieved through varying the sputtering time of Au. The superhydrophobic nature, the formation of the Schottky barrier at ZnO/Au interface and the broad optical absorption spectrum facilitated towards higher SERS activity of Ag/ZnO/Au hybrid structures. The higher SERS activity of 3D SERS substrate as compared with two dimensional (2D) SERS substrate has been studied. The good SERS signal reproducibility of 3D hybrid structures have been explored through Raman mapping. Higher SERS enhancement factor (EF) of 1 × 10¹⁰ has been achieved with a limit of detection (LOD) up to 10⁻¹⁶ M and 10 ng/μL for Rhodamine-6 G (Rh6G) and lambda DNA (λ-DNA), respectively. The degradation of Rh6G and λ-DNA molecules have been studied through photocatalytic degradation process to explore the reusability of the SERS substrates up to 10 and 4 times, respectively, with maintaining good SERS signal reproducibility. This metal/semiconductor/metal hybrid structure based SERS substrate with reusable capability indicates potential application towards biosensor for the detection of biologically important molecules at very low concentration level.