Eu-doped ZIF-8 as a ratiometric fluorescence-scattering probe for the anthrax biomarker in food samples based on competitive coordination

Bacillus anthracis spores can cause contagious anthrax, so it is significant for the public safety to detect its biomarker dipicolinic acid (DPA). Ratiometric fluorescent probes for DPA have attracted great interest because of the self-calibration effect, but they suffer from the complicated construction of dual-emitting materials. With combining fluorescence and second-order scattering (SOS), Eu-doped Zn-based metal-organic framework (ZIF-8) was here designed as a ratiometric probe for DPA, avoiding the completed construction of dual-emitting materials. Eu-doped ZIF-8 exhibited no fluorescence but possessed strong SOS ascribed to the nanostructure. However, the competitive coordination of DPA not only triggered the antenna effect of Eu3+ but also caused the decomposition of Eu-doped ZIF-8. As a consequence, the fluorescence enhancement and the SOS weakness were observed upon the addition of DPA to Eu-doped ZIF-8. And thus, a ratiometric probe for DPA was constructed based on Eu-doped ZIF-8 by integrating fluorescence with SOS. The probe as-constructed could quantify DPA in a wide range of 0.1-150 μM with a rapid response (1 min) and a low detection limit (31 nM). It also displayed excellent manifestation for the analysis of food samples with reasonable accuracy (recoveries, 90.0%-101.5%) and satisfactory precision (RSDs, 0.6%-5.7%), offering a reliable tool for the supervision of the public safety.