Anthrax biomarker: A fluorescent probe for dipicolinic acid using Eu(III)-doped nanosheets

A novel two-dimensional nanosheet fluorescent probe embedded with rare earth Eu(III) was developed to detect dipicolinic acid (DPA), a biomarker of Bacillus anthracis bacterial spores. DPA, a major component of Bacillus anthracis spores which were highly toxic to humans, was not found in other common bacteria. The ability to detect ultra-low concentrations of DPA would therefore be of great significance. Eu(III)-doped ytterbium hydroxide nanosheets were obtained by mechanical exfoliation from layered rare-earth hydroxide (LRH) materials. The crystallinities, layered structure and morphology of the as-synthesized nanosheets were studied by power X-ray diffraction, transmission electron microscopy and atomic force microscopy. Eu(III) emission increased linearly with DPA addition in the range of 0.1～30 μmol/L. Based on the antenna effect, the detection limit of DPA was 0.078 μmol/L and much lower than the infective dose of Bacillus anthracis in humans of 60 μmol/L. The nanosheet fluorescent probe exhibited good specificity toward DPA, and the interferences with selected aromatic ligands and amino acids were observed to be negligibly small in comparison with that of DPA. Our findings provide a basis for the application of Eu(III)-doped nanosheets for accurate, sensitive, and selective monitoring of DPA as a biomarker of anthrax.