Hydrogel-integrated europium metal-organic framework-based ratiometric fluorescent sensor for sensitive and instrument-free monitoring of anthrax biomarker.

Anthrax is a highly dangerous zoonotic disease that poses a significant threat to public safety. Accurate and convenient monitoring of anthrax biomarker, 2,6-dipicolinic acid (DPA), is particularly meaningful for preventing security incident outbreaks and treatment of anthrax. Herein, a dual-emissive ratiometric fluorescent and visual sensing platform has been elaborately constructed for facile, efficient and portable detection of DPA. The newly designed dual-ligand metal-organic framework was synthesized through one-pot solvothermal process that Eu3+ coordinated with 2,5-dihydroxyterephthalic acid (DHTA) and 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (TATB) to form rodlike europium metal-organic framework (EuDHTA). This obtained EuDHTA displayed excellent luminescent properties and satisfactory response behavior toward DPA. In the presence of target DPA, the fluorescence from DHTA at 536 nm was remarkably enhanced while the characteristic fluorescence for Eu3+ decreased dramatically that was attributed to DPA-induced structural alteration of EuDHTA. Furthermore, a hydrogel-integrated EuDHTA visual system for instrument-free analyzing DPA in real water samples and Bacillus subtilis spores was realized via a smartphone equipped with color recognition application, which revealed great possibilities of the developed sensor for on-site reliable monitoring anthrax.