Facile ratiometric fluorapatite nanoprobes for rapid and sensitive bacterial spore biomarker detection

Since bacterial spores, such as Bacillus anthracis spores, are extremely hazardous to human beings and animals, efforts have focused on the development of bacterial spore detector with rapid response and high selectivity and sensitivity. Therefore, we reported a facile one-step chelating-reagent-assisted hydrothermal synthesis of lanthanide-doped fluorapatite (FA) nanoprobes for detecting the biomarker of bacterial spores. In FA synthesis, ethylenediaminetetraacetic acid (EDTA) can serve not only as a shape controller and a stabilizer but also as a chelating reagent for lanthanide ions. After the fabrication, terbium (or europium) ions were not only embedded into lattice models of FA nanocrystals, but also chelated by EDTA on the surface of the FA nanocrystals, which can be available for detecting the biomarker (i.e., dipicolinic acid) of bacterial spores. The obtained FA: Ln-EDTA nanoprobes can provide reference fluorescence which play crucial roles in the calibration and correction of concentration. The fluorescence intensities of FA: Tb-EDTA or FA: Eu-EDTA from Tb3+ or Eu3+ emission were highly sensitive and increased gradually with increasing DPA concentrations. The limit of detection of FA: Tb-EDTA was 8.2 nM, which is lower than that of FA: Eu-EDTA (20.9 nM). It can be attributed to the fact that DPA can achieve a more effective energy transfer to Tb3+ than to Eu3+. Additionally, the nanoprobes were successfully applied for the determination of DPA in fetal calf serum samples. Given their rapid response and high sensitivity and selectivity, these ratiometric fluorescent nanoprobes are promising tools for the detection of bacterial spores.