Regulating Ratiometric Fluorescence of Nanoporous Dual-Centered Lanthanide Metal–Organic Frameworks for Quantitative and Visual Detection of Anthrax Biomarkers

Developing a sensitive, rapid, and accurate method for the quantitative and visual detection of the anthrax biomarker dipicolinic acid (DPA) is of great significance to human health and public safety. Due to the presence of the "antenna effect", the sensitization of Eu3+ ions and Tb3+ ions can be facilely achieved by the organic ligands with different degrees and exhibits excellent luminescence behavior of Eu3+ ions and Tb3+ ions, enabling a dual-centered lanthanide metal–organic framework (Ln-MOF) to be a promising ratiometric fluorescence sensor for the trace of DPA determination. Herein, we present a series of nanoporous dual-centered lanthanide metal–organic frameworks, denoted as {EuxTb1–x(BPDC)(μ3-OH)(H2O)·H2O·DMF}n (EuxTb1–x-BPDC) assembled with 2,2′-bipyridine-4,4′-dicarboxylic acid (H2BPDC), as ratiometric fluorescence sensors for DPA. Among these, Eu0.5Tb0.5-BPDC stands out as the optimal material, exhibiting superior fluorescence performance for quantitative, visual, and ratiometric DPA detection. Moreover, Eu0.5Tb0.5-BPDC demonstrates excellent fluorescence stability in aqueous solution and superior fluorescence capability for ratiometric DPA detection with remarkable sensitivity (limit of detection (LOD) = 0.608 μM), superior selectivity (Ksv = 6.46 × 106 M–1), excellent anti-interference, and impressive reusability. Due to the contribution of blocked energy transfer between the mixed-lanthanide ions and competitive absorption in the presence of DPA, Eu0.5Tb0.5-BPDC demonstrates a visual color change observation from red to greenish-yellow under the illumination of ultraviolet light. Most importantly, the colorimetric detection of DPA can be achieved by fluorescence test strips and portable hydrogels, facilitating the practical application of Eu0.5Tb0.5-BPDC as ratiometric fluorescence sensors for DPA detection.