Elevating the density and intensity of hot spots by repeated annealing for high-efficiency SERS.

The simultaneous output of highly sensitive and reproducible signals for surface-enhanced Raman spectroscopy (SERS) technology remains difficult. Here, we propose a two-dimensional (2D) composite structure using the repeated annealing method with MoS film as the molecular adsorbent. This method provides enlarged Au nanoparticle (NP) density with much smaller gap spacing, and thus dramatically increases the density and intensity of hot spots. The MoS films distribute among the hot spots, which is beneficial for uniform molecular adsorption, and further increases the sensitivity of the SERS substrate. Three kinds of molecules were used to evaluate the SERS substrate. Ultra-sensitive, highly repetitive, and stable SERS signals were obtained, which would promote the application process of SERS technology in quantitative analysis and detection.