Facile and cost-effective fabrication of SERS substrate featuring high-density 3D nanopillars for sensitive pesticide detection

Surface-enhanced Raman scattering (SERS) technology is a simple, sensitive, and reliable method for detecting pesticide residues. Compared to 2D nanostructures, 3D nanostructured substrates boast a significantly larger surface area, enabling multi-dimensional exciton coupling and facilitating the creation of dense hotspots, and thus improving sensitivity. However, crafting large-scale, uniform 3D structures with small nanosizes and dense hotspots remains a costly, complex, and time-consuming challenge. Here, we introduce a controllable, facile, and cost-effective approach leveraging polymer blend phase separation combined with reactive ion etching (RIE) and electron beam evaporation (EBE). By spin coating a blend of low-viscosity, polarity-similar polystyrene (PS) and acrylate polysiloxane (APSI), followed by selective O2 etching and EBE, we obtain high-density, closely spaced 3D nanopillars adorned with protrusions, which serve as rich hotspots. The spontaneous irregular shapes during phase separation facilitate the formation of these protrusions, and the spontaneous aggregation of Au further amplifies the roughness and forms more protrusions. Precise control over nanostructure density is achieved by adjusting blend concentrations, component ratios, and etching durations, ensuring repeatability and tunability. These substrates exhibit excellent uniformity and detection sensitivity, with an enhanced factor of up to 2.12 x 1014 for 4-mercaptobenzoic acid (4-MBA) molecules. Even at ultra-low concentrations, as low as 10- 15 M, the Raman signal remains detectable. Based on the SERS substrate we prepared, thiram in ethanol at ultra-low concentrations (10-9 M) was successfully detected. Hence, this study provides an effective platform for monitoring food safety and the environment.