Competitive Coordination-Driven Ratiometric Fluorescent Ln-MOFs: Logic Gate-Integrated Platform with Smartphone RGB Analysis for Visual Detection of Anthrax Biomarker DPA

Modulating host–guest interactions between target analytes and lanthanide(III)-containing metal–organic frameworks (Ln-MOFs) via competitive coordination yields an effective strategy for realizing dynamic ratiometric fluorescence behavior. In this work, a series of competitive coordination-driven ratiometric fluorescent [Tb 1– x Eu x (TCA)(DEF)(H 2 O)]·DEF ( x = 0, 0.0025, 0.0050, 0.0075, 0.0100, 0.0150, 1, H 3 TCA = 4,4′,4″-nitrilotribenzoic acid, DEF = N, N ′-diethylformamide) for visual determination of anthrax biomarker 2,6-dipicolinic acid (DPA) were constructed by systematically modulating the Tb 3+ /Eu 3+ ratio. Benefiting from the cooperative effect of competitive coordination between DPA and TCA ligands (confirmed by experimental studies and theoretical calculations), Ln-MOFs exhibit bichromatic emission signals from both TCA ligands and Ln 3+ centers (Tb 3+ /Eu 3+ ), endowing them with superior ratiometric fluorescence sensing performance toward DPA, including excellent selectivity, fast response, and high sensitivity with low limits of detection (LODs) (3.76 μM for Tb-TCA, 3.85 μM for Tb 0.9975 Eu 0.0025 -TCA, and 4.5 μM for Eu-TCA ). Moreover, the distinct color changes under UV light from yellow via white to blue enable quantitative detection of DPA by the naked eye. Moreover, a smartphone-integrated intelligent platform, depending on RGB chromaticity analysis, was established for online quantitative measurement of DPA, and a shrewd detection platform for logic gate operation was constructed. This work elaborates the mechanism of competitive coordination-driven ratiometric fluorescence sensing of DPA and provides a valuable strategy for promoting the development of monitoring technologies for anthrax biomarkers.