Curvature-optimised multilevel SERS substrates formed by femtosecond laser shaping based on electrons dynamics control

Surface-enhanced Raman scattering (SERS) is widely used for trace detection and compositional analysis of biochemical samples. Constructing multidimensionally ordered hotspots with high densities and intensities is crucial for achieving superior SERS substrate performance. Here, we propose a multilevel SERS substrate based on curvature and structural optimisation strategies. We fabricated microlenses with various curvatures via modification and etching using a temporally-shaped femtosecond laser. These lenses were decorated with wrinkles and Ag nanoparticles (AgNPs) via sequential pre-strain application and chemical deposition. Experimental and simulation results demonstrated that the coupling of the wide-field electric field induced by the microlens with the localised plasmonic hot spots on the AgNPs and wrinkles enhanced the localised surface electric field. Curvature-optimised microlenses can increase the wide-field electric fields. The fabricated SERS substrates achieved a low minimum detection limit of 10⁻¹¹ M and an enhancement factor of approximately 1.22 × 10⁷. These substrates can be employed to detect thiram fungicide on crops using two different methods (in situ detection and solution-assisted detection), demonstrating potential for operating efficiently under different usage conditions.