SERS-Based Detection of Thiram in Apple Peel Samples Using Thiomalic Acid-Ag/Au Nanoparticles

This study employs a seed-mediated growth method alongside galvanic replacement to synthesize thiomalic acid-silver/gold nanoparticles (TMA-Ag/AuNPs), with precise control over the morphology of the TMA-Ag/AuNPs achieved by adjusting the volume ratios of TMA-AgNPs to Au3+, which alters the rates of chemical reduction and galvanic replacement. In the exploration of surface-enhanced Raman scattering (SERS), Ag dendritic structures were electroplated onto FTO substrates to fabricate AgFTO substrates, which, when combined with TMA-Ag/AuNPs, exhibit enhanced Raman signals due to optimal particle size and increased surface roughness, facilitating significant adsorption of Raman probe molecules. This integration results in a SERS enhancement factor of 5.8 × 106. Specifically focusing on the thiram detection, the TMA-Ag/AuNPs demonstrate a strong affinity for sulfur components of thiram, promoting the cleavage of the S–S bond to form dimethylthiocarbamates, thereby amplifying the Raman signal. Under optimized conditions, the proposed method exhibits a linear detection range from 0.005 to 0.1 ppm, a coefficient of determination of 0.984, and a detection limit of 0.258 ppb. The method applied to fruit peel analysis showed a 93–109% recovery rate with a relative standard deviation of less than 5.95%. The developed TMA-Ag/AuNPs-AgFTO substrate showcases simplicity in preparation, excellent selectivity, and high sensitivity, successfully detecting thiram in real samples and offering a promising approach for enhancing food safety.