Dual-Ligand Lanthanide Metal–Organic Framework for Sensitive Ratiometric Fluorescence Detection of Hypochlorous Acid

Sensitivity, selectivity, visible detection, and rapid response are the main concerns for an analytical method. Herein, we reported a metal-organic framework (MOF)-based ratiometric fluorescence detection strategy for hypochlorous acid (HClO). The MOF was prepared with dual ligands, 2-aminoterephthalic acid (BDC-NH₂) and dipicolinic acid (DPA) and Eu³⁺ ions as a metal node, denoted as Eu-BDC-NH₂/DPA. The dual-ligand strategy realized the dual emission for ratiometric sensing and visual detection, adjusted the size and morphology of MOFs to obtain a good dispersion for a rapid response, and provided an amino group for the special recognition of HClO. Thus, the MOF exhibited a dual emission derived from BDC-NH₂ and Eu³⁺ ions at 433 and 621 nm, respectively, under a single excitation at 270 nm. A hydrogen bond forms between an -NH₂ group and HClO to weaken the blue fluorescence at 433 nm, while the antenna effect emission from Eu³⁺ ions kept stable, so ratiometric sensing was realized with an easy-to-differentiate color change for visible detection. The ratiometric sensing showed a self-calibration effect and reduced the background. Thus, the high sensitivity, visual detection, low detection limit (37 nM), and short response time (within 20 s) for the detection of HClO were realized with the MOF as a probe. The analysis of real samples demonstrated the practical application of the MOF for HClO. The introduction of mixed ligands is an effective strategy to regulate the emission behaviors of MOFs for the improved analytical performance.