Fluorescence probe based on boron-doped carbon quantum dots for high selectivity “on-off-on” mercury ion sensing and cell imaging

Mercury ions (Hg2+) are recognized as the typical inorganic contamination that can cause severe damage to the environment and humans. In this paper, boron-doped carbon quantum dots (B-CQDs) with a fluorescence quantum yield (QY) of 10.4% and good photoluminescent properties were synthesized via a one-step hydrothermal method using citric acid and histidine as the carbon source and borax as the provider of boron. The obtained B-CQDs exhibited a bright blue emission under excitation wavelength of 365 nm. As a fluorescent probe, it appears excellent selectivity and sensitivity to assay Hg2+. When Hg2+ were added to B-CQDs, its bright blue fluorescence was obviously quenched. Under optimum conditions, the sensor shows a wide linear range (0 ~ 150 μM) and a low detection limit (2.5 μM). Interestingly, the quenched fluorescence of B-CQDs containing Hg2+ could be turned on by adding reducing agent EDTA-2Na or I-. Furthermore, it was applied successfully to assay Hg2+ in real sample. More importantly, B-CQDs was found to be nontoxic and can be used as bioimaging agent for MCF-7 cell labeling. The possible fluorescence quenching mechanisms of the probe are also discussed in detail. This study provides a new approach for fabricating a multifunctional fluorescent probe and a prospective application in environmental monitoring.