SERS substrate for detecting toxic malachite green molecules based on a multilayer Ag/Cu/Ag nanosphere shell array

The design of surface-enhanced Raman spectroscopy (SERS) substrates critically requires large-area, spatially uniform distributions of electromagnetic hot spots to ensure high SERS enhancement and broad applicability across analytical, environmental, and biomedical domains. However, conventional fabrication approaches, largely reliant on top-down micro- and nanofabrication techniques, are inherently expensive and involve multistep, labor-intensive processes, which impedes scalability and commercial viability. In this work, we report the scalable synthesis of Ag/Cu/Ag spherical shell ordered arrays via nanosphere lithography with a cost-effective, reproducible, and operationally simple bottom-up strategy. Using rhodamine 6G as a model Raman-active probe, we systematically investigate the influence of Cu layer thickness on SERS performance. Experimental results demonstrate that the substrate incorporating a 10 nm Cu interlayer delivers optimal enhancement, achieving a detection limit of 10^-9 M and an analytical enhancement factor of 5.36 × 10⁸. Furthermore, the platform enables sensitive detection of malachite green, a hazardous aquaculture contaminant, at concentrations as low as 10^-8 M. Mechanistic analysis reveals that the pronounced SERS signal amplification originates from strong plasmonic coupling between the inner and outer Ag layers, which collectively generate highly localized and intense electromagnetic hot spots across the curved shell surface. These findings provide a rational, structure-property-guided framework for engineering high-density hot spot architectures, thereby advancing the practical deployment of SERS in surface catalysis, biosensing, and environmental monitoring.