Coordination-Regulated Ratiometric Fluorescent Europium(III) Metal–Organic Framework for Smartphone-Integrated Visual Detection of Anthrax Biomarker in Real Samples

Regulating host-guest interactions between targeted analytes and lanthanide(III)-based metal-organic frameworks (Ln-MOFs) provides an effective strategy for achieving dynamic fluorescence behavior, enabling Ln-MOFs with attractive ratiometric sensing behavior. In this work, we demonstrate a 3D chain-based <b>Eu-MOF</b> {[Eu₄(NBC)₆·(μ₂-H₂O)₂·(H₂O)₄]·2H₂O}_<i>n</i>, constructed from 2,6-naphthalenedicarboxylic acid (H₂NBC), which exhibits fluorescent dynamics behavior for the online and visual detection of anthrax biomarker 2,6-dipicolinic acid (DPA) via a coordination-induced strategy. Owing to photoinduced electron transfer (PET), competitive absorption, and coordination interactions, the <b>Eu-MOF</b> displays dual-emission signals from H₂NBC ligands and Eu³⁺ centers, endowing it with superior ratiometric fluorescence sensing performance, including exceptional selectivity and high sensitivity (<i>Ksv</i> = 1.90 × 10⁴ M^-1), low LOD of 0.080 μM, and rapid response (60 s). Furthermore, a distinct colorimetric transition from red to blue under UV light enables naked eye detection of DPA, facilitating the development of portable <b>Eu-MOF</b> hydrogels for real-time monitoring. Additionally, a smartphone-integrated platform utilizing RGB analysis is developed for online DPA detection, while a <b>Eu-MOF@PU</b> film is designed for practical visual trace detection. Notably, the <b>Eu-MOF</b> demonstrates excellent recovery rates of 97.7-105.9% in tap water and 99.7-111.3% in Poyang Lake water for DPA detection, confirming its reliability for real-world applications.