Differential sensitization toward lanthanide metal–organic framework for detection of an anthrax biomarker

A novel Tb-doped Eu-based metal–organic framework (Eu-MOF@Tb) has been developed by incorporating hexanuclear europium cluster and 2,2′-bipyridine-5,5′-dicarboxylic acid as well as coordination with Tb(III). Owing to the diverse coordination status of Tb(III) and Eu(III) in MOF, antenna effect emission from Tb(III) can be invoked by dipicolinic acid (DPA), but the luminescence originating from Eu(III) remains unchanged. Taking advantage of this phenomenon, a ratiometric luminescent method for detection of DPA, a biomarker for Bacillus subtilis spores, was developed through differential sensitization toward lanthanide ions. This analysis method allowed for the detection of DPA in the 0.2–10 μM concentration range, with a detection limit of 60 nM. It was further validated by spiked recoveries (89.3–110%) of real-world samples with RSD values in the range 3.9–11%. Alongside this, a paper indicator test was prepared for naked-eye detection of DPA via a dose-sensitive color evolution from red to green under UV light. The effectiveness of the proposed approach was explored in the detection of bacterial spores in real biological and environmental samples and indicated great potential for applications as a real-time monitoring system against the anthrax threat. Graphical Abstract