A ratiometric lanthanide-free fluorescent probe based on two-dimensional metal-organic frameworks and carbon dots for the determination of anthrax biomarker

A lanthanide-free fluorescent probe has been constructed for the first time based on two-dimensional metal-organic frameworks (2D MOFs) and carbon dots (CDs) for ratiometric determination of dipicolinic acid (DPA), the biomarker of Bacillus anthracis . The fluorescence intensity at 659 nm increased due to the release of organic ligands TCPP resulting from the selective interaction between DPA and Zn 2+ of 2D MOFs. CDs provided a reference signal at 445 nm which was almost unaffected, realizing self-calibration DPA sensing. F 659 /F 445 versus the concentration of DPA shows good linear relationships in the range 0.01–0.2 μM and 0.2–10 μM under 390-nm excitation, with a detection limit of 7 nM. The ratiometric probe was prepared from 2D lanthanide-free MOFs so that the drawbacks of lanthanide-based probes were overcome. The proposed sensing system was successfully applied to the determination of DPA in spiked biological samples. These results suggest that a novel, simple, and selective strategy of determining DPA with 2D lanthanide-free MOFs is implemented. Graphical abstract Zn-TCPP nanosheets and a blue carbon dots (b-CDs) are synthesized to construct the ratiometric probe, which can exhibit fluorescence at 445and 659 nm with 390-nm excitation. Dipicolinic acid (DPA) can deprive the junction ions of Zn-TCPP nanosheets, triggering the collapse ofZn-TCPP nanosheets. The fluorescence at 659 nm is enhanced due to the release of TCPP, while the peak of b-CDs at 445 nm is almost not affected. Thus, the fluorescence intensity ratio (F 659 /F 445 ) can serve as the response signal for sensitive DPA sensing.