One-step microwave-assisted preparation of oxygen-rich multifunctional carbon quantum dots and their application for Cu2+-curcumin detection

Carbon quantum dots (CQDs), owing to its unique optical properties , have achieved tremendous progress for the detection of different metal ions , organic small molecules, macromolecules , etc. Here we synthesized fluorescent CQDs by a simple one-step microwave-assisted method using 3,4-Dihydroxy- l -phenylalanine (levodopa) as the carbon resource. The CQDs proved to be a multifunctional probe which can be used for detection of various species including copper ion , biothiols and curcumin , via different mechanisms. The selective detection of copper ion was obtained by fluorescence quenching and the mechanism was proved to be static quenching by electrostatic interaction . The fluorescence of levoCQDs-Cu 2+ system can be recovered by biothiols (GSH, Cys and Hcy), implying levoCQDs-Cu 2+ system can also be applied for biothiols detection. The excitation spectrum of levoCQDs had a good overlap with the absorption peak of curcumin, making it as a suitable curcumin probe by fluorescence quenching via inner filter effect (IFE). Furthermore, the levoCQDs can also track the formation of Cu 2+ -Curcumin complexes by restoring the fluorescence of the CQDs in levoCQDs and Cu 2+ -Curcumin system, and this feature may be exploited in the mechanism study of Cu 2+ -Curcumin in the treatment of Alzheimer's disease. The fluorescent levoCQDs were finally used for Cu 2+ and curcumin detection in some real samples including different types of environmental water samples and human serum samples, providing a convenient strategy to monitor Cu 2+ and curcumin in environmental and biological samples.