Cu(II)-assisted orange/green dual-emissive carbon dots for the detection and imaging of anthrax biomarker

The spores of Bacillus anthracis are highly deadly to human beings and animals, and are concurrently potential biological warfare agents. Hence, the rapid and sensitive monitoring Bacillus anthracis biomarker, dipicolinic acid (DPA), is very desirable. Herein, orange/green dual-emissive carbon dots (OG-CDs) were synthesized via the hydrothermal approach. The OG-CDs not only emitted dual fluorescence at 527 and 590 nm under the single 503 nm excitation, but also exhibited excellent water solubility, good photostability and great salt tolerance. The fluorescence of the OG-CDs at 527 nm can be completely quenched when chelated with Cu(II). However, because of the stronger chelation between DPA and Cu(II), the fluorescence restored rapidly on subsequent addition of DPA. As such, the CD-Cu(II) system can be used for determination of DPA based on the fluorescence “off-on” response. Under optimum conditions, the detection limit for DPA was 56 nM, with a linear range of 0.5–12.5 μM. The established CD-Cu(II) based spectrofluorometric method has been applied to the analysis of DPA in real water samples with recoveries of 93.6%–104.3%. More remarkably, the CD-Cu(II) probe also has been successfully applied for the imaging of DPA in Escherichia coli with excellent bio-compatibility.