Boron-nitrogen-carbon dots as effective probes for sensitive and selective detection of Hg2+

Mercury(II) is among the most hazardous heavy metal pollutants, necessitating the development of fluorescent sensors that are efficient, highly sensitive, and suitable for practical applications. Herein, we present a novel boron and nitrogen co-doped carbon dots (B,N-CDs) probe prepared via a hydrothermal method using borax, ethylenediamine, and citric acid as starting materials. Relative to previously reported B,N-CDs, our probe features a markedly higher fluorescence quantum yield (35.6%) and an ultralow detection limit of 10.5 nM for Hg 2+ , well below the WHO guideline for drinking water. The probe also exhibits excellent selectivity for Hg 2+ over competing metal ions, accompanied by a strong fluorescence quenching response. A combination of fluorescence lifetime measurements, density functional theory (DFT) calculations, and thermodynamic analysis reveals a static quenching mechanism mediated by photoinduced electron transfer (PET), which is entropy-driven and spontaneous. Beyond its outstanding analytical performance, the probe displays superior solubility in water and alcohols, low cytotoxicity (confirmed by L929 cell assays), and good biocompatibility in zebrafish fluorescence imaging. Furthermore, successful Hg 2+ detection in real water samples validates its practical utility. Taken together, the high quantum yield, ultralow detection limit, well-defined PET-based static quenching mechanism, and multi-level bioimaging validation set this B,N-CDs probe apart from existing carbon-dot sensors and highlight its potential for environmental and biological mercury monitoring.