Controllable synthesis of uniform chitosan hydrogel-based SERS substrates for rapid detection of thiram on various fruit surfaces.

Rapid, ultrasensitive, and nondestructive detection of pesticide residues on fruit surfaces remains a significant challenge. Herein, we developed a series of flexible silver nanoparticles@chitosan hydrogel (AgNPs@CSHG) SERS substrates by a controllable in-situ growth strategy, creating uniformly distributed SERS hot spots through electrostatic interactions between silver ions and the hydroxyl/amino groups in chitosan molecules. Hydrophilic CSHG exhibits excellent adsorption and permeability properties, enabling effective enrichment of probe molecules within hotspot regions to further improve detection sensitivity. The optimal AgNPs-45@CSHG SERS substrate achieves a remarkable detection sensitivity of 10-8 M and exceptional reproducibility (RSD = 8.14%) for 4-mercaptobenzoic acid (4-MBA). Importantly, the flexible and robust AgNPs@CSHG SERS substrates realize rapid, simple and nondestructive thiram detection at a concentration as low as 10-7 M on fruit peel by a simple stick-and-read method. The flexible, ultrasensitive and nondestructive AgNPs@CSHG SERS substrate presents significant potential for applications in food safety monitoring.