Ratiometric fluorescence sensor based on bimetallic organic frameworks for anthrax biomarker detection

It is of great significance to construct ratiometric fluorescence sensors with simple operation and desirable anti-interference ability. In this study, a bimetallic organic framework was prepared for the first time by a one-pot solvothermal method, using 4,4'-biphenyl dicarboxylic acid as ligand, lanthanide metal terbium ions (Tb³⁺) and transition metal zirconium ions (Zr⁴⁺) as central metal ions. This preparation method was easy to carry out. On this basis, a novel ratiometric fluorescence sensor Tb-Zr-MOF was constructed successfully for the detection of anthrax biomarker (2,6-pyridinedicarboxylic acid (DPA)). When DPA was added into the detection system, the fluorescence of Tb³⁺ was enhanced due to the energy transfer from DPA to Tb³⁺. Therefore, under the single excitation at 285 nm, the fluorescence emission intensity of Tb-Zr-MOF at 402 nm remained unchanged and the fluorescence emission intensity at 546 nm increased. As a ratiometric fluorescence sensor, Tb-Zr-MOF showed good linear response to DPA in the range of 5∼100 μM and the limit of detection was 1.72 μM. This sensor reduces the interference of environmental factors and achieves high sensitivity detection, which is superior to the traditional single emission peak fluorescence sensor. In addition, the developed Tb-Zr-MOF sensor was used to detect DPA in Bauhinia bark samples successfully. The recovery rate was 98.80%∼104.8%, which proved the practical application of Tb-Zr-MOF in complex environment. It is expected to provide a reliable method for the detection of biomarkers of Bacillus anthracis.