Sensitive SERS detection of antibiotics using Ag-coated nanostructures fabricated by femtosecond laser cross-scanning.

The excessive use of antibiotics in medicine, agriculture, and aquaculture has led to widespread environmental contamination and public health concerns, underscoring the urgent need for rapid, sensitive, and cost-effective detection methods. Here, we report a scalable surface-enhanced Raman scattering (SERS) platform based on silver-coated cross-scanned laser-induced periodic surface structures (CS-LIPSS) fabricated via femtosecond laser processing. By employing cylindrical lens-assisted beam shaping followed by orthogonal double-pass scanning, we generated periodic nanostructures enriched with dense nanoparticles. Subsequent Ag deposition produce a dense distribution of plasmonic hotspots, enabling strong electromagnetic enhancement. Compared with conventional mesh and single-scanned LIPSS substrates, the CS-LIPSS demonstrate superior SERS activity, with an enhancement factor of 6.4×107 and a detection limit down to 10-11 M for crystal violet. More importantly, the platform enable reliable identification of representative antibiotics including amoxicillin, tetracycline, and neomycin sulfate at concentrations as low as 1 ppm, highlighting its sensitivity and molecular specificity. The fabrication process is chemical-free, template-free, and compatible with wafer-scale production, offering a cost-effective route to reproducible, high-performance SERS substrates.