Gold nanoflower-functionalized flexible hydrogel patches for on-site SERS monitoring of pesticides in fresh agricultural products via dynamic evaporation-driven enrichment

Fabricated hydrogel SERS patches with controllable dehydration-triggered analyte enrichment. • Dynamic modulation of plasmon coupling and analyte accumulation synergistically boosts SERS sensitivity. • The flexible sensing platform achieves on-site detection of multiple pesticide residues on fresh agricultural products. On-site surface-enhanced Raman scattering (SERS) detection of trace pesticide residues on fresh agricultural products is essential for food safety assurance, which limited by poor conformal contact, severe biomolecular interference, and insufficient in-situ analyte enrichment of conventional substrates. Herein, a flexible sodium alginate hydrogel patch embedded with branched gold nanoflowers (AuNFs-SA) was designed for on-site quantitative detection of agricultural pesticide residues. The dendritic gold nanoflowers generate dense plasmonic hotspots, while Ca 2+ crosslinking improves conformal adhesion and molecular sieving within the hydrogel, thereby minimizing matrix interference from fruit and vegetable surfaces. A controllable dehydration-induced enrichment strategy was then introduced to dynamically regulate plasmonic coupling and analyte accumulation. Under optimal detection conditions, the AuNFs-SA patch enables reliable quantitative detection of four representative pesticides, with a linear range of 10–2500 ng·cm −2 (R 2  ≥ 0.98) and surface-based limits of detection as low as 1.10–6.85 ng·cm −2 . It exhibits excellent intra- and inter-batch signal reproducibility, with relative standard deviation values below 6.81%, and outstanding long-term stability, retaining over 88.87% of initial SERS intensity after 49 days of ambient storage. Combined with principal component analysis, accurate discrimination among four representative pesticide residues on the surfaces of fresh agricultural products was realized. This work proposes a feasible and portable hydrogel SERS platform for efficient on-site pesticide monitoring, providing a promising tool for practical food safety supervision. Download: Download high-res image (169KB) Download: Download full-size image