Highly sensitive and reproducible SERS substrates of bilayer Au and Ag nano-island arrays by thermal evaporation deposition

Abstract

Attainment of excellent Raman enhanced effect in a surface-enhanced Raman scattering (SERS) substrate requires uniform and precise control over inter-particle distances of the metal nanoparticles on large surface area. Here, we report a facile fabrication of SERS substrate comprising uniformly distributed bilayer structure of silver (Ag) and gold (Au) nano-island arrays (NIA), deposited by thermal evaporation method and demonstrate its use for SERS detection of rhodamine 6G (R6G). In our SERS substrate, the mandatory Ag NIA layer acts as the main Raman signal enhancement layer while the layer of Au NIA helps to attenuate the background fluorescence and suppress the air exposure of highly reactive surfaces of Ag NIA, thus also acting as a protective layer and ensuring reproducibility of SERS sensing. The results show that bilayer structure of Ag-4 nm and Au-2 nm NIA SERS substrate exhibits the optimal signal-to-background (S/B) ratio (up to 7, compared with 1.35 of bare Ag-4 nm) and excellent reproducibility (~8% fluctuations in 7 sample tests, compared with ~34% fluctuations in bare Ag-4 nm). Due to the high sensitivity (the limit of detection: <10−8 of R6G) and reproducibility, our sandwich structured SERS substrate seems to be promising for detection of various biomolecules and pollutants in water.