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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. [Display omitted] • B-CQDs were successfully synthesized by one-step hydrothermal method. • B-CQDs as fluorescent probe were specific for Hg2+ with low detection limit and wide linear range. • B-CQDs were used for Hg2+ determination with selectivity, immunity and recovery. • B-CQDs were successfully applied to assay Hg2+ in tap water. • B-CQDs as the fluorescent marker could label MCF-7 cancer cells. [ABSTRACT FROM AUTHOR]

The carbon quantum dot (CQD), a fluorescent carbon nanoparticle, has attracted considerable interest due to its photoluminescent property and promising applications in cell imaging and bioimaging. In this work, biocompatible, photostable, and sustainably sourced CQDs were synthesized from byproducts derived from a biorefinery process using one-pot hydrothermal treatment. The main components of byproducts were the degradation products (autohydrolyzate) of biomass pretreated by autohydrolysis. The as-synthesized CQDs had a size distribution from 2.0–6.0 nm and had high percentage of sp2 and sp3 carbon groups. The CQDs showed blue-green fluorescence with a quantum yield of ~13%, and the fluorescence behaviors were found to be stable with strong resistance to photobleaching and temperature change. In addition, it is found that the as-synthesized CQDs could be used for imaging of cells and tumors, which show potential applications in bioimaging and related fields such as phototherapy and imaging. [ABSTRACT FROM AUTHOR]