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 fluorescence 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 Fe 3+ ions in environmental water and   human oral keratinocytes (Hok) cells, with a detection limit of 0.51 μM and the linear range of 0–75 μM. Moreover, we have conducted an in-depth study on the mechanism of fluorescence quenching of CDs caused by Fe 3+ ions. Our study provides powerful evidences that the mechanism of fluorescence quenching to Fe 3+ ions   is a synergistic effect of static quenching (SQ) and aggregation-induced effect (AIE), which accompanied by forming   a non-fluorescent ground state complex between CDs and Fe 3+ 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.