Gap-enhanced V-shaped SERS substrate for multiplex trace dye pollutants detection in river water

Surface-enhanced Raman scattering (SERS) is a powerful analytical tool for detecting trace pollutants due to its molecular fingerprint specificity and single-molecule sensitivity. However, conventional two-dimensional gap-enhanced substrates suffer from limited analyte diffusion into nanogap caused by plasmonic material hydrophobicity. Herein, we present a V-shaped SERS substrate designed to overcome these challenges through three synergistic mechanisms: (i) three-dimensional (3D) plasmonic nanogaps, (ii) gravity-driven analyte enrichment enabling efficient aqueous-phase molecule transport, and (iii) light-trapping nanopores amplifying electromagnetic fields. By utilizing atomic layer deposition (ALD)-defined ultrathin alumina sacrificial layers, we achieved precisely tunable nanogaps (2–10 nm) between gold nanoparticles (AuNPs) and the underlying gold film (Au) within V-shaped architectures. The optimized 6 nm AuNPs-gap-Au nanostructure balances near-field intensity and aqueous analyte accessibility, achieving sub-nanomolar sensitivity for rhodamine 6G with outstanding reproducibility (RSD < 9 % across 10⁻⁹–10⁻⁵ M). Significantly, the substrate enables multiplex detection of dye pollutants (basic blue 3, malachite green, methylene blue) at sub-nanomolar level in river water, showing great potential for real-time, on-site monitoring of emerging pollutants in natural water systems.