Fluorescent smartphone sensing platform based on Eu³⁺-functionalized metal-organic framework for ultra-sensitive...

Ciprofloxacin (CIP) residues in environmental and food matrices lead to potential public health and safety issues, necessitating the development of a sensing platform for ultra-sensitive detection of CIP residues to achieve rapid on-site detection. Here, a high-performance fluorescence sensing platform based on Eu³⁺-functionalized metal-organic framework (Eu³⁺@UiO-(COOH)₂) was developed for the sensitive detection and visual analysis of CIP in environmental and food samples. First, ligand screening was achieved through theoretical calculations (ligand excited-state energy levels, frontier molecular orbitals, and electrostatic potential distribution) to probe the ligand modulation of fluorescence properties. Subsequently, based on the ligand engineering strategy for synthesizing Eu³⁺@UiO-(COOH)₂ with excellent fluorescence performance and CIP self-fluorescence, a smartphone-integrated ratiometric fluorescence sensing platform was constructed to achieve rapid quantification of CIP via the blue/red light intensity ratio (B/R), with a limit of detection (LOD) as low as 36 nM, along with a mobile phone-based rapid visualization and quantification function. The systematic study demonstrated that the quenching effect of CIP on Eu³⁺@UiO-(COOH)₂ fluorescence originated from a synergistic multipath mechanism: photoinduced electron transfer (PET) between the ligand and CIP was dominant, supplemented by dynamic quenching and inner filter effects (IFE). In addition, the sensing platform demonstrated reliability in complex matrices. This study provides a novel solution for antibiotic contamination monitoring with both laboratory accuracy and field applicability.