A ratiometric dual-emission Eu³⁺@Cd-MOF fluorescent platform for multi-pollutant detection and visual sensing

The development of reliable and portable dual-emission fluorescent platforms is highly desirable for real-time environmental pollutant monitoring. In this work, a Eu³⁺-functionalized Cd-based metal-organic framework (Eu³⁺@Cd-MOF) probe was prepared via a post-synthetic modification strategy. The resulting material exhibits both ligand-centered emission and characteristic Eu³⁺ emission. This dual-emission probe displays distinct fluorescence responses toward multiple contaminants, including ciprofloxacin (CIP), tetracycline (TET), ornidazole (ODZ), and p-nitrophenol (4-NP). Notably, CIP induces an enhancement of the emission at 470 nm and a concurrent decrease at 617 nm, resulting in a ratiometric signal decline (I₆₁₇/I₄₇₀) with excellent linearity. In contrast, TET, ODZ, and 4-NP mainly caused significant quenching over wide linear detection ranges. To extend practical applicability, we established a smartphone-assisted quantitative readout for CIP detection and fabricated a flexible Eu³⁺@Cd-MOF/PVDF hybrid film for portable visual analysis. The probe also provides reliable detection of CIP, TET, and 4-NP in lake water samples, with recoveries ranging from 98.30% to 106.17% and RSD values of 0.63-5.70%. This work not only provides an efficient dual-emission platform for multiple pollutant detection but also promotes the development of intelligent and portable sensing systems for environmental monitoring.