A facile method in removal of PVP ligands from silver nanowires for high performance and reusable SERS substrate

Silver nanowires (i.e., AgNWs) can act as effective surface-enhanced Raman spectroscopy (i.e., SERS) substrates to detect small molecules. However, a lot of prepared AgNWs were often wrapped by polyvinylpyrrolidone (i.e., PVP) thin film to form an insulating layer to produce ill-defined AgNWs-PVP-AgNWs interface, limiting the plasmonic coupling among the stacked AgNWs. Herein, we reported a facile method in removal of PVP ligands from AgNWs for high performance and reusable SERS substrate. Sodium borohydride (NaBH₄) was used to completely remove the PVP ligands from the surface of AgNWs and produce a clean AgNWs-AgNWs interface that effectively enhances the localized surface plasmon resonance (i.e., LSPR) was produced, greatly improving the SERS activity of the AgNWs thin film. The SERS detection of rhodamine 6G (i.e., R6G) used with PVP AgNWs and without PVP AgNWs is 1.0 × 10^-9 and 1.0 × 10^-15 M, and the average enhancement factor (EF) is about 0.86 × 10⁴ and 9.35 × 10⁴, respectively. Moreover, the recyclable behavior of the AgNWs with several analyte molecules is much more interesting than that of the PVP@AgNWs. The SERS detection of AgNWs for R6G, the 3-mercaptopropionic acid (i.e., 3-MPA) and melamine with good recyclability in nanomolar and millimolar concentration can be easily detected.