Engineering gold nanoparticles aggregation in acrylate hydrogel-photopolymers for SERS-based on-site highly sensitive dimethoate detection on olives

Hydrogel-based flexible plasmonic devices represent a cutting-edge technology for real-time monitoring of food safety, particularly for pesticide detection. This study presents a cost-effective, portable, and sensitive method to detect dimethoate (DMT), a hazardous organophosphorus pesticide, at concentrations below the maximum residue limit (MRL) of 0.01 ppm on olives. By integrating surface-enhanced Raman scattering (SERS) with gold nanoparticles (AuNPs) embedded in polyethylene glycol diacrylate (PEGDA) hydrogels, detection at parts-per-billion (ppb) levels is achieved. The hydrogel matrix enhances sensitivity and reproducibility by forming AuNP dimers, whose concentration increases with DMT levels, boosting signal output. The system uses UV polymerization of a pre-polymer solution, enabling direct application onto olive surfaces and achieving a detection limit of 3 ppb with a signal enhancement of ∼10⁶. Tests with fungicides (RidoMil, Glyphosate) confirmed excellent selectivity for DMT. Validated on-site with a portable Raman spectrometer, this method is adaptable for detecting sulfur-containing pesticides, offering a practical solution for food safety.