A ratiometric fluorescent sensor enabled by hydrogen bond-reinforced carbon quantum dots and SiO2-encapsulated CdSe-ZnS for high-performance Hg2+ detection in aquatic food.

Hg2+ contamination in aquatic food requires sensitive and reliable detection methods. Herein, thymidine-derived blue-emissive carbon quantum dots (CQDs) with intrinsic Hg2+ affinity are synthesized and reinforced by a hydrogen bond acceptor (DMSO). Mixing the CQDs/DMSO complex with yellow-emissive silica-coated CdSe-ZnS quantum dots (QD@SiO2) yields a ratiometric fluorescent sensor with a biphasic response to Hg2+. At trace levels, Hg2+ disrupts the hydrogen-bonding network, reducing the blue emission and the blue-to-yellow emission intensity ratio accordingly. At higher concentrations, Hg2+ coordinates with the uncarbonized thymine residues on the surface of CQDs, further decreasing the blue-to-yellow emission intensity ratio. The distinct mechanism achieves an exceptionally wide dynamic range over six orders of magnitude and a low detection limit of 0.76 nM. The sensor exhibits high selectivity, anti-interference from the internal calibration of yellow emission, and excellent biocompatibility, enabling Hg2+ detection in fish samples and semi-quantitative imaging in live aquatic animals.