Flexible Sponge Surface Enhances Raman Scattering (SERS) Substrate with Patterned Superwettability for Ultrasensitive Pesticide Detection

Surface-enhanced Raman scattering (SERS) has been widely applied in the field of food safety due to its exceptional molecular recognition capabilities. In this study, a simple method for preparing a flexible SERS substrate was designed for the ultrasensitive real-time detection of the banned drugs malachite green (MG) and crystal violet (CV). The substrate was prepared by patterned spraying of a superhydrophobic coating prepared from candle soot onto the surface of a poly(vinyl alcohol) (PVA) sponge, followed by simple Ag nanoparticle (Ag NP) deposition in the superhydrophilic region. The PVA sponge with special hydrophilicity can completely absorb the droplets to be measured within 1–5 s without additional drying treatment. And the Ag NPs aggregated by potassium iodide (KI) resulted in a significant enhancement of the Raman signal, enabling the substrate to realize the detection of MG and CV as low as 100 fg/mL (2.74 × 10–13 M) and 1 pg/mL (2.45 × 10–12 M), respectively, with a long lifetime (90 days). Thanks to the excellent mechanical properties of the flexible substrate, the substrate can realize the simultaneous detection of very small amounts of MG and CV on the surface of crayfish by simple wiping, which has great application prospects in the field of food safety and field inspection.