A ratiometric fluorescence sensor based on integrated bimetallic Zr/Eu-MOF for rapid and visual detection of...

The widespread use of glyphosate in agriculture has raised concerns about environmental contamination and associated health risks, creating an urgent need for rapid, sensitive, and field-deployable analytical tools. In this work, Zr/Eu-metal-organic framework (Zr/Eu-MOFs) as an integrated bimetallic ratiometric fluorescent hydrogel sensor for fast and highly sensitive visual detection of glyphosate has been developed. By doping Eu³⁺ into a robust Zr-based MOF framework, Zr/Eu-MOFs exhibit dual-emission bands at 445 and 618 nm, enabling an intrinsic self-referenced signal without multicomponent assembly. Upon glyphosate addition, the sensor responds within 10 s. Zr/Eu-MOFs display a reliable ratiometric response over 0.05 - 10.0 mg/L with a low detection limit of 0.03 mg/L (0.2 μmol/L), which is far below the permissible maximum residue limit (MRL) for drinking water by the US EPA and China (4.1 μmol/L). Mechanistic evidence indicates that glyphosate forms P-O-Zr coordination linkages and interfacial interactions which modulate the ligand-to-metal charge transfer (LMCT) process, resulting in an enhanced ratiometric fluorescence response at 445 nm, while the Eu³⁺ emission at 618 nm remains essentially unchanged. Moreover, an agarose hydrogel format coupled with smartphone image analysis enables rapid visual detection. A spraying-enabled fluorescence imaging strategy further allows rapid screening of glyphosate contamination on leaves, apple surfaces, and soil-water matrices under UV illumination. Overall, this work provides a facile, integrated, and visually readable ratiometric platform for on-site glyphosate monitoring.