Development and optimization of electrospun polyamide-6 nonwoven substrate for surface-enhanced Raman scattering

Background and Objectives: Surface-enhanced Raman scattering (SERS) has emerged as a powerful analytical technique for ultrasensitive molecular detection, finding applications in biomedical diagnostics, environmental monitoring, and food safety. However, the widespread adoption of SERS is limited by the need for reproducible, cost-effective substrates with high enhancement factors. While various nanostructured platforms have been explored, polymer-based substrates decorated with noble metals offer unique advantages including flexibility, tunable morphology, and scalability. This study focuses on developing and optimizing SERS-active substrates using electrospun polyamide-6 (PA-6) nonwoven materials coated with gold via vacuum sputtering. The primary objectives were to: (i) systematically investigate the effect of gold deposition time (1–8 min) on substrate morphology and SERS performance; (ii) determine the optimal sputtering parameters for maximum signal enhancement; (iii) evaluate substrate reproducibility using statistical analysis of large-area SERS mapping data. Materials and Methods: PA-6 nonwoven substrates were produced by electrospinning from formic/acetic acid solution (1 : 1 ratio, 15 mass.%). Gold was deposited via magnetron sputtering at constant current (25 mA) with varying times (1–8 min). For reproducibility tests, patterned substrates were created using a mask with a 3×3 mm square holes. 4-mercaptobenzoic acid (4-MBA, 10−5 M in ethanol) was used as analyte. The reference Raman spectra were obtained from 4-MBA (10−3 M) on uncoated PA-6. 2500 SERS spectra/substrate (50×50 spectra, 8 substrates) were collected for substrates optimization. In reproducibility study, 22500 total SERS spectra were analyzed (3 substrates × 3 areas × 3 maps with 50× ×50 spectra/map). Results: SEM has revealed improved gold coverage uniformity at longer deposition times (6–8 min). Shorter times (2–4 min) have shown discontinuous coatings with defects. Principal component analysis (PCA, PC1 explained variance: 54.3%) has identified optimal performance at 8 min Au deposition. Maximum EF (8 min): (7.70±1.02) · 104 at 1073 cm−1. Characteristic 4-MBA peaks (1073, 1581 cm−1) have shown consistent enhancement profiles. Triplicate substrates have shown average EF = (7.71 ± 1.84) · 104 with relative standard deviation of 23.9% across all measurements. Conclusion: This study has demonstrated that vacuum-sputtered gold on electrospun PA-6 materials produces effective SERS substrates with enhancement factors >104. The 8-minute deposition time has yielded optimal performance, balancing coating uniformity with enhancement capability. While the substrates show promise for practical applications, the observed ∼24% signal variability suggests opportunities for further optimization. The developed substrates combine the advantages of polymer flexibility with metal-enhanced sensitivity, offering a viable platform for various SERS applications.