Flexible and recyclable PI/Ag Nanofiber SERS substrates for ultrasensitive detection of pesticide residues

Although surface enhanced Raman spectroscopy (SERS) has become a powerful analytical technique for ultrasensitive molecular detection, it still faces challenges including instability, unrepeatability, and non-recyclable. The rational design and fabrication of SERS substrates that are simultaneously stable, reproducible, and recyclable remains a critical yet unmet need. Here, we present a flexible polyimide-silver (PI/Ag) nanofiber-based SERS platform, synthesized via electrospinning and in-situ reduction techniques. The spatial distribution and density of Ag nanoparticles (NPs) were precisely regulated by tuning the type and concentration of reducing agents, which effectively modulated the localized surface plasmon resonance (LSPR) effect to optimize SERS performance. Among the tested formulations, the PI/Ag-NB substrate—prepared using NaBH 4 as the reducing agent—exhibited the most favorable nanoparticle dispersion and the strongest SERS activity. Using 4-aminothiophenol (4-ATP) as a probe molecule, the PI/Ag-NB substrate achieved a maximum enhancement factor (EF) of 1.17 × 10 7 . Beyond its high sensitivity, the substrate demonstrated broad spectral responsiveness, enabling the reliable detection of diverse analytes such as methylene blue (MB), methyl violet (CV), Congo red (CR) and malachite green (MG). To further validate its practical utility, long-term stability, and recyclability, the substrate was employed for the detection of 2,4-dichlorophenoxyacetic acid (2,4-D) pesticide residues both in aqueous solutions and soil extracts. Notably, the substrate stored for 30 days maintained performance over 10 consecutive detection cycles, their robustness and reproducibility. The platform achieved a measured detection limit of 10 −10  M, with a theoretical limit reaching as low as 3.12 × 10 −11  M, highlighting the ultrasensitive detection capability of the substrate. Collectively, these findings establish PI/Ag-NB nanofibers as a versatile and high-performance SERS platform, paving the way for their practical applications in environmental monitoring, food safety, and chemical sensing.