Carbon dots-based modularization fluorescent probe for simultaneous detection of Hg2+and Cu2+in water, cells and zebrafish

Modular assembly of carbon dots with organic luminescent small molecules can be devoted to picking up a predetermined fluorescent probe detection system for specific targets. In this work, the blue fluorescent carbon dots B-CDs were prepared by using sodium citrate and nitrogen-rich branched polyethyleneimine as precursors through a functional preservation strategy. A modularized, difunctional and ratiometric fluorescent probe B-CDs@RBH with dual-emission was dexterously prepared by simply blending B-CDs and rhodamine b-hydrazide for the detection of Hg2+ and Cu2+. B-CDs can be quenched by Hg2+ through static quenching, while Cu2+ can specifically open the lactam of rhodamine b-hydrazide to form rhodamine B through hydrolysis accompanied by a turn-on orange fluorescence. More interestingly, rhodamine B can absorb the fluorescence of B-CDs through fluorescence resonance energy transfer, resulting in a blue to orange fluorescence color change in the presence of Cu2+. B-CDs@RBH has a low detection limit of 17.79 nM and 4.19 nM for Hg2+ and Cu2+ respectively with a detection range of 0.1-5 mu M, which was applied for the ratiometric fluorescence detection of Hg2+ and Cu2+ in cells and zebrafish, and achieved smartphone-assisted on-site water samples detection. The facile modular design of B-CDs@RBH fluorescent probe and convenient on-site detection application are of great benefit in further ascertaining the migration and transformation of heavy metals in biological and environmental samples.