Construction of S, O-Doped g-C3N4 QDs Encapsulated in Eu-MOF with Dual-Emission for Ratiometric Fluorescence Detection of Hg²⁺.

Mercury ions (Hg2+) are categorized as environmental pollutants, which distributed in water, soil, and food systems due to environmental contamination. Hence, designing a sensitive assay for the convenient determination of Hg2+ is of great importance. Herein, S and O-doped graphite phase nitrogenized carbon quantum dots (S, O-C3N4QDs) was encapsulated within a europium -based metal-organic framework (Eu-MOF) to construct a novel ratiometric fluorescent nanoprobe for the quantitative detection of Hg2+. The native emission of S, O-C3N4QDs at 445 nm is used as a response signal, while Eu-MOF with fluorescence offers a reference signal at 619 nm. Hg2+ exhibits high affinity for the surface functional groups of S/O-C3N4 QDs, forming non-fluorescent chelation complexes that induce static quenching. This results in significant attenuation of the fluorescence intensity at 445 nm, while the emission at 619 nm remains invariant. A ratiometric fluorescence sensing platform was established based on the intensity ratio (F445/F619) for the selective detection of Hg2+. The linear range of S, O-C3N4QDs/Eu-MOF of Hg2+ was 0.25-35 µM and with a detection limit of 4.3 nM. The satisfying results demonstrate the effectiveness of the developed S, O-C3N4QDs/Eu-MOF-based fluorescence probe for Hg2+ detection, highlighting its promising potential for environmental monitoring applications.