CQDs are quasispherical carbon structures with sizes less than 10 nm, in which core carbon atoms are sp2-hybridized. As quantum dots, their excellent photoluminescence, good water solubility, and low cytotoxicity enable their predominant applications in biomedical fields. The quantum yield of CQDs can be well tuned not only by doping them with heteroatoms such as nitrogen, phosphorus, and sulfur but also by surface functionalizations, which offer them plenty of structural com ponents in order to exhibit excellent optical or photocatalytic properties.Both top-down and bottom-up approaches can be utilized in CQDs preparations and surface passivation tech niques have been developed over the years.In addition, the degree of CQDs oxidation offers them with a wide color range in photoluminescence .All these outstanding properties of CQDs make them a promising material in the fields of drug delivery and bio-imaging for cancer therapy