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-Cu2+ system can be recovered by biothiols (GSH, Cys and Hcy), implying levoCQDs-Cu2+ 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 Cu2+ Curcumin complexes by restoring the fluorescence of the CQDs in levoCQDs and Cu2+ -Curcumin system, and this feature may be exploited in the mechanism study of Cu2+-Curcumin in the treatment of Alzheimer's disease. The fluorescent levoCQDs were finally used for Cu2+ and curcumin detection in some real samples including different types of environmental water samples and human serum samples, providing a convenient strategy to monitor Cu2+ and curcumin in environmental and biological samples.