Functionalized PVP nanofibers achieved using electrospinning as flexible SERS substrates for multiple explosives sensing

In this study, metal (Ag/Au) nanoparticles-embedded polymer-based [polyvinylpyrrolidone (PVP)] nanofibers were fabricated via the <i>in situ</i> reduction of metallic precursors (<i>A</i><i>g</i><i>N</i><i>O</i>₃/<i>H</i><i>A</i><i>u</i><i>C</i><i>l</i>₄) in PVP before electrospinning. The presence of metal nanoparticles was confirmed through surface plasmon resonance peaks observed in the ultraviolet-visible absorption spectra. Several analytical techniques were utilized to characterize the electrospun nanofibers. X-ray diffraction confirmed the crystalline structure and the presence of metallic nanoparticles. Field emission scanning electron microscopy revealed the surface morphology and depicted a variation in nanofiber diameter, ranging from 100 to 300 nm, depending on the concentration of metal precursors (5, 10, and 50 mM). Transmission electron microscopy images confirmed the spherical shape of the nanoparticles, with sizes ranging from 10 to 50 nm across all samples. Among the three solvents (distilled water, DMF, and ethanol) used, the nanofibers obtained with distilled water were devoid of any microbeads on the nanofibers. The smooth nanofibers achieved with different-sized Ag/Au NPs were then utilized as flexible SERS (surface-enhanced Raman scattering)-based sensors for detecting methylene blue molecules. Interestingly, the PVP-Ag nanofiber obtained at a 10 µM concentration of the silver/gold salt demonstrated the highest enhancement. The PVP-Ag nanofiber was further used for the fingerprint detection of explosive molecules such as picric acid, ammonium nitrate, TNT, and HMX at low concentrations (weight equivalent of 500 µg) via a simple swabbing method.