Rapid and facile ratiometric detection of an anthrax biomarker by regulating energy transfer process in bio-metal-organic framework

A ratiometric fluorescent sensor based on luminescent bio-metal-organic framework was prepared by exchanging both Tb³⁺ and Eu³⁺ cations into anionic bio-MOF-1. Due to a highly efficient energy transfer from Tb³⁺ to Eu³⁺ (>89%), emission color of Tb/Eu@bio-MOF-1 was orange-red even though Tb³⁺ was the dominant content in this Tb/Eu co-doping material. More interestingly, this energy transfer process could be modulated by dipicolinic acid (DPA), an unique biomarker for bacillus spores. With DPA addition, corresponding DPA-to-Tb³⁺ energy transfer was gradually enhanced while the energy transfer from Tb³⁺ to Eu³⁺ was significantly weakened. By regulating the energy transfer process in Tb/Eu@bio-MOF-1, visual colorimetric sensing of DPA in porous MOF was realized for the first time. Detection limit of Tb/Eu@bio-MOF-1 for DPA was 34 nM, which was much lower than an infectious dosage of Bacillus anthracis spores (60 μM) for human being. Besides, Tb/Eu@bio-MOF-1 showed a remarkable selectivity over other aromatic ligands and amino acids. More importantly, this porous ratiometric sensor worked equally well in human serum. These particularly attractive features of Tb/Eu@bio-MOF-1 made the direct, rapid and naked-eye detection of DPA for practical application possible.