Portable smartphone-assisted fluorescence platform based on dual-excitation nitrogen-doped carbon dots for...

The pervasive issue of pharmaceutical overuse in agriculture and veterinary practice has led to the alarming accumulation of drug residues within the global food supply chain, posing a direct and escalating threat to consumer safety. Among these contaminants, compounds such as chlorogenic acid (CGA) and tinidazole (TNZ) are of particular concern due to their potential to provoke allergic responses and cause long-term adverse health effects. There is an urgent need for the development of rapid and reliable detection techniques capable of on-site monitoring to effectively mitigate these risks and ensure food safety. Herein, our work develops an innovative ratiometric sensing strategy that utilizes the dual-excitation properties of nitrogen-doped carbon dots (N-CDs) to simultaneously detect CGA and TNZ. Remarkably, as a fluorescent nanoprobe, N-CDs are capable of detecting CGA over a concentration range of 0.036-40 μM with a limit of detection (LOD) of 36 nM, which is attributed to static quenching (SQE) and the inner filter effect (IFE). Differently, the addition of TNZ results in fluorescence quenching of N-CDs via localization of inner filter effect (L-IFE), presenting the LOD of 68 nM within the 0.068-25 μM range. Furthermore, a portable smartphone-assisted platform which incorporates the N-CDs/PVA composite film successfully enables visual detection of CGA and TNZ with satisfactory recoveries in real samples. These results suggest that the developed portable smartphone-assisted fluorescence platform enables accurate dual-target detection of CGA and TNZ while offering outstanding stability and reproducibility suitable for on-site applications. Consequently, our methodology presents a versatile and practical strategy for real-time pharmaceutical residue screening, significantly advancing food safety monitoring capabilities.