Distinct off–on fluorescence signal from dual-response lanthanide metal–organic frameworks for ratiometric sensing of anthrax biomarker

Bacillus anthrax is a highly dangerous zoonotic pathogen that represents a significant threat to public health. 2,6-Dipicolinic acid (DPA) is typically designated as the primary biomarker of Bacillus anthrax, which is a distinctive major component of anthrax spores. The development of sensitive, efficient, and rapid detection of this marker has significant implications for the elimination of potential threats and the safeguarding of public health and food safety. In this study, we have designed a dual lanthanide ion (Ce³⁺, Eu³⁺) functionalized metal–organic framework fluorescent probe, Ce@Eu@MOF-808, for the detection of the anthrax biomarker DPA via a dual-response turn-off–on mode. The antenna effect, resulting from a change in energy transfer efficiency upon excitation at 260 nm, caused Ce@Eu@MOF-808 to exhibit a single Ce³⁺ characteristic emission peak. Upon the addition of DPA, the intensity of the characteristic emission peak of Ce³⁺ exhibited a gradual decrease (turn-off), while the fluorescence peak of Eu³⁺ demonstrated a gradual increase (turn-on). This outcome enabled the establishment of a ratiometric fluorescence detection method for DPA. The developed fluorescence switching probe exhibited a broad linear range (5–30 μM), high sensitivity (limit of detection 0.67 μM), and was successfully employed for the detection of DPA in real samples. This strategy provides a rapid, sensitive, and reliable method for the detection of DPA during the early diagnosis of anthrax and provides a new avenue for the development of ratiometric fluorescent probes with multi-response lanthanide ions.