Rational design of a functionalized metal–organic framework for ratiometric fluorimetric sensing of Hg2+ in environmental water

A target-responsive ratiometric fluorimetric sensing strategy for Hg²⁺ has been rationally designed. The sensing probe was established based on a functionalized metal-organic framework, which was prepared with 3,5-dicarboxyphenylboronic acid (DCPB) as the functional ligand and Eu³⁺ as the metal junction. The porous nano-spheres of Eu-MOF with an arylboronic acid as the functional recognition group for Hg²⁺ exhibited tunable optical properties with dual emission fluorescence signals at 338 nm and 615 nm. In the presence of Hg²⁺, arylmercury was formed by a specific transmetalation reaction between Hg²⁺ and arylboronic acid groups, which blocks the energy transfer between the ligand and Eu³⁺. Thereby, the fluorescence signal of Eu-MOF/BA at 615 nm decreased, while the fluorescence signal at 338 nm remained almost constant. The ratiometric fluorimetric sensing for Hg²⁺ was achieved by calculating the peak intensity ratio of F₆₁₅/F₃₃₈ based on the reference signal at 338 nm and the response signal at 615 nm. The detection limit of Hg²⁺ was as low as 0.0890 nM, and the recovery rate of the actual environmental water sample ranged from 90.92% to 118.50%. Therefore, the excellent performance of the ratiometric fluorimetric sensing method for Hg²⁺ makes it attractive for the detection of heavy metal ions in environmental monitoring.