A design strategy of dual-ratiomentric optical probe based on europium-doped carbon dots for colorimetric and fluorescent visual detection of anthrax biomarker.

In this work, a novel dual-ratiometric optical probe based on europium-doped carbon dots (Eu-CDs) was developed for colorimetric and fluorescent visual sensing dipicolinic acid (DPA), a anthrax biomarker. Eu-CDs with recessive signals were prepared via thermal pyrolysis method. And the magenta appears when Eu-CDs coordinates with Eriochrome Black T (EBT). Based on the ligand displacement strategy, DPA reduces magenta and makes blue appear, which develop ratiometric colorimetric visual detection methods of DPA. Under 270 nm excitation, DPA make the red fluorescence signal of Eu in EBT-CDs@Eu appear, based on the absorbance-energy transfer-emission effect, the ratiometric fluorescent visual detection assay of DPA has been developed. Based above, dual-ratiometric optical probe was designed successfully. The limit of detection (LOD) is 10.6 nM for ratio colorimetric assay. More prominently, naked-eye determination of DPA without instrument is as low as 1.0 μM. Furthermore, its practicability was verified by quantifying the DPA in Bacillus subtilis spores and human urine (with RSD≤2.35%). The sensor shows great superiority in on-site analysis of DPA, especially in limited instruments conditions.