Electrospun Gold Nanoprism/Poly(vinyl alcohol) Nanofibers for Flexible and Free-Standing Surface-Enhanced Raman Scattering Substrates

Plasmonic resonance from 2D anisotropic metallic nanoparticles for surface-enhanced Raman scattering (SERS) has attracted substantial attention for applications in chemical and environmental monitoring because of its intrinsic electromagnetic "hotspot" and orientation-dependent optical properties. Nevertheless, their sensing applications have been limited by their poor stability toward oxidation and moisture and complicated fabrication processes for large-scale assembly, especially on flexible substrates. In this work, we demonstrate water-stable nanofibers as active SERS substrates electrospun from anisotropic gold nanoprisms (AuNPs) mixed with poly(vinyl alcohol) (PVA) at a concentration of 2.5-20 nM, followed by cross-linking by glutaraldehyde (GA) vapor at room temperature. Using 4-mercaptobenzoic acid (4-MBA) as the target molecule, we show that the nanofiber mat with 20 nM AuNPs exhibits high sensitivity at a concentration as low as 10^-10M 4-MBA with an enhancement factor of 10⁷and good uniformity over a very large area (20 cm²) with an average relative standard deviation of <0.074. The cross-linked PVA/AuNP nanofibers are stable against water without an obvious decrease in the SERS signal. In the detection of Rhodamine 6G (R6G) molecules in the water solution, the Raman intensity of R6G shows almost no decay over 3 months compared to that of the as-prepared mat. Further, we show the detection of trace pesticide (10^-6M) on the orange exocarp, suggesting that our fiber mat could be applied for potential applications including food safety, biomedicine, and environmental monitoring.