Transparent, Flexible Plasmonic Ag NP/PMMA Substrates Using Chemically Patterned Ferroelectric Crystals for Detecting Pesticides on Curved Surfaces.

Transparent and flexible surface-enhanced Raman scattering (SERS) substrates have attracted much interest for the detection of probe molecules on the curved surfaces of real samples, but a facile route to fabricate such substrates is still lacking. Herein, we present a rationally designed, high-performance flexible SERS substrate fabricated using a simple drop and peel-off technique for the ultrasensitive detection of pesticides. The proposed SERS substrate consists of a polymethyl methacrylate (PMMA) film anchored with plasmonic silver nanoparticles (Ag NPs), which are photoreduced using chemically patterned ferroelectric templates. The photoreduced Ag NPs extracted onto the PMMA film offer strong electromagnetic enhancement and produce intensive hotspots for the effective enhancement of the Raman signal. They provide superior SERS performance for the detection of parathion (PT) and fenitrothion (FNT) at trace-level concentrations of 10-9 M and 10-10 M with excellent enhancement factors in the order of 108 and 109, respectively. Moreover, the Ag NP/PMMA SERS substrate has good spot-to-spot uniformity and batch-to-batch reproducibility with the reservation of high detection sensitivity even after the mechanical deformation of bending and torsion up to 50 cycles. The multiplex detection ability is also investigated for the simultaneous detection of PT and FNT. To ensure the practical feasibility, the in-situ, real-time detection of PT and FNT on the curved surfaces of tomato and lemon using a fiber-coupled Raman probe is performed with limits of detection of 4.24 × 10-8 M and 2.74 × 10-9 M. The proposed Ag NP/PMMA flexible SERS substrate possesses unique features, such as easy fabrication through a simple, economical, rapid process, and facilitates straightforward implementation of in-situ SERS detection on curved fruit/vegetable surfaces.