Meta-grating-based SERS sensor capable of efficiently trapping target molecules in hotspots

Although extensive past efforts were devoted to designing substrates exhibiting abundant hotspots for improving the detection sensitivity of surface-enhanced Raman spectroscopy (SERS), how to transport analyte molecules under detection to those hotspots remains challenging. Here, we propose a meta-grating-based SERS sensor with periodically arranged nanogaps exhibiting gradient shapes that can efficiently transport molecules to the hotspots with significantly intensified electromagnetic fields, thus pronouncedly enhancing the sensitivity and signal uniformity of the SERS detection. We fabricate the proposed SERS substrate and demonstrate the desired SERS-detection improvement with experimental measurements on rhodamine 6 G (R6G, 10−6–10−11 M), crystal violet (CV, 10−8–10−13 M), and glycine molecules (40–0.1 mM) with different concentrations. Our measured two-dimensional mappings of SERS intensity exhibit good signal uniformity, with calculated relative intensity deviation less than 10%, obtained by analyzing 100 randomly selected points, either for R6G, CV, or for glycine. Our results lay a solid foundation for quantitative molecule detection based on SERS technology.