Boron and nitrogen codoped carbon dots as fluorescence sensor for Fe³⁺ with improved selectivity

Carbon dots (CDs) are popular as fluorescence sensors, and metal ions are typical analytes. However, CDs used as fluorescent sensors for Fe³⁺ have some interferences coming from co-existed ions. In this study, we suspect that sp³ boron atom in phenylboronic acid group will be more compatible with Fe³⁺ to form coordination bonds, thereby increasing the selectivity to Fe³⁺. Hence, we designed and synthesized boron and nitrogen codoped carbon dots (BN-CDs) for detection of Fe³⁺ via a hydrothermal method using o-phenylenediamine (OPA) and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzylchloroformate as precursors. From the results, we found that BN-CDs had superior selectivity to Fe³⁺ in the presence of the other common interfering metal ions like Cu²⁺, Fe²⁺ and Pb²⁺. Besides, the obtained BN-CDs exhibited good water solubility, favorable photostability, excellent pH stability between pH 2-11, and strong fluorescence intensity with quantum yield up to 31.5 %. These excellent properties of carbon dots validate that our idea is feasible, and can be used for design CDs for Fe³⁺ detection. Quenching mechanism study showed the fluorescence intensity of BN-CDs could be dramatically quenched by Fe³⁺ through dynamic and static synergy process. Finally, the as prepared BN-CDs were successfully applied to the determination of Fe³⁺ in fetal bovine serum and lake water.