A large-scale and flexible SERS substrate based on sliver decorated nano-cone arrays and its applications for pesticide residue detection

Abstract

This paper demonstrates a large-scale, flexible SERS substrate (Ag@R-SERS substrate) based on silver-decorated nano-cone arrays. The substrate was fabricated via a two-step process: pre-designed nano-cone arrays were replicated over a large area with high structural uniformity using roll-to-roll ultraviolet nanoimprint lithography (R2R UV-NIL); subsequently, silver nanoparticles (Ag NPs) were self-assembled onto the nano-cone arrays. The performances of the Ag@R-SERS substrate were evaluated using rhodamine 6G (R6G) as a probe molecule with a portable Raman spectrometer. The enhancement factor (EF) and limit of detection (LOD) of R6G detected on Ag@R-SERS substrate were determined to be 5.9 × 10⁷ and 2.65 × 10⁻⁸ M. The relative standard deviations (RSDs) of R6G Raman intensities at 1513 cm⁻¹ were 5.6% within a single substrate and 6.7% among different substrates. No obvious changes were observed in the line curve of R6G detected by the SERS substrate stored for 20 days. These results demonstrated satisfactory sensitivity, uniformity, reproducibility and stability. Numerical simulations were established to illustrate the electromagnetic enhancement effects of the Ag@R-SERS substrates, which were jointly attributed to the strong coupling effects of densely distributed AgNPs and Ag clusters at the tips of nano-cones. Furthermore, the potential application of the Ag@R-SERS substrate in pesticide detection was explored. Linear relationships between the SERS intensity at 1386 cm⁻¹ and thiram concentration were established with R² of 0.9986, 0.9940, 0.9974 and the LOD of thiram was determined to be 0.46, 0.49 and 0.55 ppm in ethanol, apple juice and tomato juice, respectively. These results confirm the feasibility of the two-step fabrication method for large-scale, flexible Ag@R-SERS substrates and their applicability for rapid and sensitive pesticide residue detection.