Dual-ligand lanthanide metal–organic framework for ratiometric fluorescence detection of the anthrax biomarker dipicolinic acid

The dual-ligand functionalized UiO-66-(COOH)2-NH2 were synthesized and used to construct stable lanthanide-doped MOFs by completing with Eu3+ ions (UiO-66-(COOH)2-NH2/Eu) to construct a sensing platform for detection of DPA. Under the excitation of 270 nm, the UiO-66-(COOH)2-NH2/Eu showed excellent fluorescence at 453 nm, which is ascribed to the characteristic peak of NH2-BDC. After the UiO-66-(COOH)2-NH2/Eu reacts with DPA, the fluorescence emission of Eu3+ can be dramatically enhanced due to the replacement of coordinated H2O by DPA and the antenna effect (AE). Meanwhile, the fluorescence emission of NH2-BDC was gradually reduced via the inner filter effect (IFE). UiO-66-(COOH)2-NH2/Eu displays a noticeable fluorescence color change from blue to red, which is easy to be recognized by the naked eye. So, a smartphone-assisted colorimetric platform was constructed for semi-quantitative detection of DPA. [Display omitted] •Dual-ligand lanthanide metal–organic framework was constructed and characterized.•UiO-66-(COOH)2-NH2/Eu exhibit excellent fluorescence properties for detection of DPA.•The smartphone-assisted sensing platform was developed for the visual assay of DPA. Dipicolinic acid (DPA) is a unique biomarker of Bacillus anthracis. Development of a simple, fast, sensitive and timely DPA detection method is of great importance and interest for preventing mass disease outbreaks and treatment of anthrax. In this work, a novel lanthanide-doped fluorescence probe was constructed by coordination of Eu3+ with bifunctional UiO-66-(COOH)2-NH2 MOFs materials for efficient monitoring DPA. UiO-66-(COOH)2-NH2 MOFs were prepared using Zr4+ as a metal node, 1,2,4,5-benzenetetracarboxylic acid (H4BTC) and 2-aminoterephthalic acid (NH2-BDC) as bridging ligand through a simple one-pot synthesis method. By virtue their abundant carboxyl groups, UiO-66-(COOH)2-NH2 can readily grasp Eu3+ to form UiO-66-(COOH)2-NH2/Eu with coordinated water molecules at Eu sites. Upon interaction with DPA molecules, the coordinated H2O molecules were replaced by DPA molecules which transfer energy to Eu3+ in UiO-66-(COOH)2-NH2/Eu and sensitize Eu3+ luminescence. Meanwhile, DPA has a characteristic absorption band at 270 nm, which overlapped with the excitation spectrum of NH2-BDC, allowing the fluorescence of UiO-66-(COOH)2-NH2/Eu at 453 nm to be greatly quenched by DPA through inner filter effect (IFE). Therefore, the rationally designed UiO-66-(COOH)2-NH2/Eu complex not only exhibits stro