Ultrasensitive SERS Detection of Thiram and Chloramphenicol Using a Plasmonic Triple-Layered Nanocomposite for Food Safety Applications

Thiram (THR) and Chloramphenicol (CAP) are commonly used as pesticide and antibiotic agents to protect agricultural crops and livestock. However, even trace residues of these agrochemical agents can cause adverse effects on human health. To address this issue, we developed a nanoscale-engineered, plasmonic triple-layered composite, ZIF-67@AgNPs@PDA, by incorporating silver nanoparticles (3–5 nm) into the surface layer of Zeolitic Imidazole Frameworks-67 (ZIF-67) encapsulated with polydopamine (PDA) layer. The ZIF-67@AgNPs@PDA served as an excellent SERS-active substrate, enabling detection of THR and CAP at specific Raman shifts of 1378 and 1596 cm–1, with detection limits of 3.2 × 10–13 and 7.7 × 10–12 M, respectively. The higher sensitivity of ZIF-67@AgNPs@PDA toward THR could be attributed to the S–S cleavage and monolayer adsorption mechanism, which contrasts with the multilayer adsorption and weaker orientational interactions observed with CAP. Our plasmonic substrate achieved pico-molar detection levels, significantly outperforming previously reported nanomaterial-based systems. Furthermore, the SERS system demonstrated reliable performance with minimal pH sensitivity in real samples including tap water, apple juice, and pork fluids. These results underscore the potential of the ZIF-67@AgNPs@PDA nanoplatform for practical monitoring of chemical contaminants at ultratrace levels in food safety and biomedical diagnostics.