A multi-ratiometric fluorescence sensor integrated intrinsic signal amplification strategy for a sensitive and visual assay of the anthrax biomarker based on a bimetallic lanthanide metal–organic framework

The development of sensitive and prompt approaches for reliable determination of dipicolinic acid (DPA) is of great importance for human health and public security. Herein, we synthesized a bimetallic lanthanide metal–organic framework (Tb/Eu-MOF) using 2-hydroxyterephthalic acid as a ligand and lanthanide ions (Tb3+ and Eu3+) as central metal ions. The as-synthesized Tb/Eu-MOF possesses multiple recognition sites toward DPA. When present, DPA can displace the chelated water molecules and then coordinate with Tb3+ and Eu3+ to sensitize their luminescence. This causes the fluorescence of Tb3+ (546 nm) and Eu3+ (617 nm) to increase, while that of the ligand (432 nm) remains constant. Based on the multiple fluorescence signal responses of Tb/Eu-MOF toward DPA, a multi-ratiometric fluorescence sensor using (F546/F432) and (F617/F432) as output signals was developed to detect DPA. Moreover, an intrinsic signal amplification strategy is used to achieve more sensitive sensing of DPA by integrating the fluorescence signals of Tb3+, Eu3+, and ligand with (F546 + F617)/F432 as the output signal. Benefitting from the signal amplification and multiple fluorescence responses, this method shows high sensitivity and obvious fluorescence color variation toward DPA detection. This strategy offers a prompt, sensitive, and reliable method for the visual sensing of DPA.