Interfacially Assembled Hollow AuAg Nanostars on Flexible PDMS for Sensitive SERS Detection

Optimizing the morphology and structure of noble metal nanomaterials is critical for the design of high-performance surface-enhanced Raman scattering (SERS) substrates for trace analyte detection. A plasmon-tunable SERS platform consisting of AuAg alloy nanostars anchored on a hydrophobic polydimethylsiloxane (PDMS) matrix was developed, which combined the chemical stability of Au and the strong localized surface plasmon resonance of Ag. AuAg alloy nanostars with sharp tips were synthesized via a galvanic replacement reaction, in which the precise modulation of Ag seed concentration enabled a morphological evolution from solid to hollow nanostructures. The optimized AuAg-3 nanostars exhibited the highest SERS response due to a dual synergistic mechanism: strong electromagnetic enhancement at the sharp branched tips and additional plasmonic enhancement from the hollow cavity through light scattering and trapping, which increased the optical path length and excitation efficiency. Furthermore, these nanostars were transferred onto a flexible PDMS film through interfacial self-assembly. The resulting hydrophobic PDMS-AuAg-3 substrate synergistically combined the strong electromagnetic enhancement from the nanostars with efficient analyte enrichment driven by the hydrophobic surface, achieving an ultra-low detection limit of 2.4 × 10−10 M for methylene blue (MB). This strategy effectively balances high sensitivity and excellent reproducibility, offering a robust pathway for the development of next-generation flexible SERS sensors.