Ratiometric fluorescent paper chip for monitoring the freshness of high protein foods

Accurately monitoring the freshness of high-protein foods has significant implications for both food safety and public welfare. Since a large amount of hydrogen sulfide (H₂S) is produced during spoilage-related processes, abnormal H₂S levels are often considered an important indicator of food spoilage. Therefore, we synthesized novel nanoparticles (NPs) containing Silicon (Si) dots and CdTe quantum dots to accurately assess the amount of sulfide ions (S^2-) and thus the quality of high-protein foods in the early stage of storage. As the concentration of S^2- increased, the fluorescence intensity of Si/CdTe NPs at λ_em = 488 nm increased, while the fluorescence intensity at λ_em = 620 nm was quenched. The fluorescence intensity ratio (F₆₂₀/F₄₈₈) was negatively linearly correlated to S^2- concentrations in the range of 1 to 20 μM, with a detection limit of 0.3 μM. Furthermore, to achieve portable detection, we mixed Si/CdTe NPs with sodium carboxymethyl cellulose to prepare effective visual fluorescent sensing paper chips, which exhibited ideal porous structure, good particle dispersion, and excellent fluorescence properties. Incubating the paper chips with high-protein foods allowed for accurate monitoring of food freshness during storage. Therefore, this approach provided a reliable and portable method to determine H₂S concentration using a novel concept to ensure the freshness and safety of high-protein foods.