Optimizing SERS substrates for ultrasensitive menthol detection synergistic effects of polystyrene sphere size and silver film thickness

Trace detection of menthol in complex matrices remains challenging. Surface-enhanced Raman spectroscopy (SERS) offers a promising solution for rapid, label-free analysis; however, its practical application is often limited by significant performance variability inherent to substrate design. To address this limitation, this study establishes a co-optimization framework for polystyrene@silver (PS@Ag) core-shell SERS substrates, focusing on the synergistic tuning of polystyrene sphere diameter (D-PS 200-2000nm) and silver film thickness (T-Ag 60-140nm). Through controlled fabrication using Langmuir-Blodgett assembly and thermal evaporation, coupled with systematic characterization via FE-SEM and SERS mapping, we elucidate that menthol SERS enhancement is primarily governed by localized surface plasmon resonance (LSPR) coupling and electromagnetic (EM) hotspot density. Key findings reveal distinct optimal geometries: D-PS 200/400nm paired with T-Ag 100-120nm, and D-PS 600-1000nm requiring T-Ag 120nm. Notably, substrates with 2000nm PS spheres exhibited poor performance across all Ag thicknesses, attributed to plasmonic wavevector mismatch.