Green synthesis of mustard seeds carbon dots and study on fluorescence quenching mechanism of Fe3+ions

A growing interest has emerged in carbon dot (CDs) fluorescent probes, as they are non-destructive, non-contact, sensitive, fast, and low-cost. However, the low fluorescence quantum yield (QY) and the uncertainty of fluo-rescence quenching mechanism are the main bottlenecks restricting its application. Here, we used mustard seeds as carbon source, CDs were synthesized by a simple hydrothermal method without further surface treatment with the QY reached a value as high as 17.92 % in 468 nm excitation energy. As a label-free fluorescent probe, CDs can be used to sense Fe3+ ions in environmental water and human oral keratinocytes (Hok) cells, with a detection limit of 0.51 mu M and the linear range of 0-75 mu M. Moreover, we have conducted an in-depth study on the mechanism of fluorescence quenching of CDs caused by Fe3+ ions. Our study provides powerful evidences that the mechanism of fluorescence quenching to Fe3+ ions is a synergistic effect of static quenching (SQ) and aggregation-induced effect (AIE), which accompanied by forming a non-fluorescent ground state complex be-tween CDs and Fe3+ ions. This work promises to provide new ideas for the most appropriate detection strategy and design the best performing sensor, allowing their effective application in the sensing field.