Liquid-assisted femtosecond laser fabrication of nanostructured Al-alloy SERS substrates

Surface-enhanced Raman scattering (SERS) is a powerful, label-free technique for trace-level molecular detection; however, its broad application is limited by the lack of low-cost, scalable, and reproducible substrates. Here, we introduce a facile route to large-area SERS nanoplatform using liquid-assisted femtosecond (fs) laser direct writing (FLDW) in sucrose solution, followed by thermal evaporation of a thin Au nanofilm composed of nanoparticle clusters on aluminum-alloy substrates. By optimizing sucrose concentration and fs laser power, densely packed arrays of nanocones, nanoplates, and nipple-like protrusions are produced, serving as robust scaffolds for plasmonic hotspots. After thermal evaporation, the substrate exhibits super hydrophobicity with water contact angle (WCA) ∼157°, which concentrates analyte droplets and further amplifies Raman signals. Using Rhodamine 6 G (R6G) and malachite green (MG) as probe molecules, the limits of detection (LODs) were determined to be 3.5 × 10 −14 M for R6G and 6.6 × 10 −11 M for MG, with corresponding enhancement factors (EFs) of 1.19 × 10 11 and 6.13 × 10 7 , respectively. Uniformity tests yielded relative standard deviations (RSDs) below 4 %, and cycle reusability assays showed < 15 % signal loss. After 150 days, more than 80 % of the initial SERS signals were retained, confirming long-term stability under ambient conditions. Simulation results reveal intense electromagnetic hotspots localized at nanostructure tips and junctions, accounting for the substrate’s exceptional SERS performance. This straightforward, contamination-free approach enables scalable production of durable, high-performance SERS substrates for environmental monitoring, food safety, and biomedical diagnostics.