A metal-free substrate for enhancing Raman scattering in thiram detection using a chitosan/carbon quantum dots nanocomposite film.

A dithiocarbamate fungicide in agriculture is known as thiram (TH), which is extensively used, while its toxicity raises concerns about residues that irritate the respiratory, skin, and digestive systems and cause long-term damage to the kidneys and liver. TH often remains in food and packaging during processing and transportation, influenced by temperature and improper storage conditions. Implementing accurate, trace-level detection of TH in food and agricultural settings is essential for safeguarding public health and protecting environmental safety. The surface-enhanced Raman scattering (SERS) technique is used to quantify residual TH, using a non-destructive, highly sensitive analytical method. Nevertheless, this SERS requires a specific substrate with a uniform, stable structure, nano-patterned with metal nanoparticles, resulting in complex and costly processes. This study used a chitosan (CS) film, a biocompatible polysaccharide, as the SERS substrate because of its biodegradability and widespread use in biomedical, food packaging, and sensor applications. CS was modified with carbon quantum dots (CQDs) as a nanocomposite structure, offering tunable photoluminescence, good biocompatibility, and facile surface functionalization. CS matrix film was fabricated by dispersing CQDs (10-40 vol%) in the CS/CQDs nanocomposite film to serve as the SERS substrate. These films were examined in chemical Raman enhancement mode (CERS) without the addition of metal nanoparticles, achieving TH detection across various concentrations (20-1000 μM) and yielding a detection limit of 0.884 μM. These CS/CQDs films were characterized and analyzed, enabling tracking of TH via the CERS mechanism for sustainable packaging, smart coatings, and biomedical devices.