Reversible “Off–On” Fluorescence of Zn²⁺-Passivated Carbon Dots: Mechanism and Potential for the Detection of EDTA and Zn²⁺

Zn 2+ -passivated carbon dots (named Z-CDs) were synthesized from zinc gluconate for the first time through a one-step pyrolysis treatment. The mechanism of Zn 2+ -enhanced fluorescence was carefully investigated, and a new strategy to passivate the surfaces of CDs by Zn 2+ was proposed. Inspired by the complexation reaction between Zn 2+ and ethylenediaminetetraacetic acid (EDTA), a reversible “off–on” fluorescent nanosensor for the detection of EDTA and Zn 2+ was constructed based on the depassivation and repassivation of Z-CDs, with a limit of detection as low as 3.2 × 10 –7 M and 5.1 × 10 –7 M, respectively. The proposed Z-CD-based nanosensor had been further utilized for EDTA and Zn 2+ monitoring in tap water with excellent recovery. To the best of our knowledge, this was the first report of a fluorescence-based sensor of EDTA and a turn-on sensor of Zn 2+ based on CDs with reversible detection capability. Also, benefiting from the low toxicity of zinc, Z-CDs were applied for multicolor bioimaging and in vitro detection in cells.