Nitrogen-doped carbon dots synthesized from acrylic acid and ethylenediamine for simple and selective determination of cobalt ions in aqueous media

Fluorescent nitrogen-doped carbon dots (NCDs) with a quantum yield of 22.7% and an average size of about 4.28 nm were hydrothermally synthesized using acrylic acid and ethylenediamine in one pot. When excited at 350 nm, the NCDs showed a strong emission peak centered at 425 nm, corresponding to blue fluorescence. Interestingly, for NCDs, significant decrease in fluorescence was observed upon addition of cobalt ions (Co2+). On the basis of this particular phenomenon, the synthesized NCDs are demonstrated as an effective fluorescence probe for the selective and quantitative analysis of low concentration Co2+ in a linear range of 1.0-60 mu M. Limit of detection (LOD) is 0.25 mu M. Further detailed investigations on the interactions of NCDs with Co2+ as quencher by using various techniques (UV-vis absorption and time-resolved fluorescence techniques) confirmed that the fluorescence quenching is mainly induced by the interaction of between Co2+ and some functional groups of NCDs.