Surface Modification, Toxicity, and Applications of Carbon Dots to Cancer Theranosis: A Review

Cancer remains one of the leading causes of death worldwide, prompting extensive research into novel theranostic (combined word of diagnostic and therapeutic) strategies. Nanomedicine has emerged as a potential breakthrough in cancer theranosis, overcoming limitations of conventional approaches. Among such approaches, carbon dots (CDs) with a size smaller than 10 nm have garnered significant attention for their potential use in cancer theranosis, owing to their low toxicity, good water solubility, easy synthesis, facile surface modification, and unique optical and photothermal and photodynamic properties. Researchers have demonstrated that surface functionalization of CDs with diverse hydrophilic groups can be easily achieved by choosing proper carbon precursors in synthesis, and further surface modification of CDs with cancer-targeting ligands, photosensitizers, anticancer drugs, and genes can also be easily achieved using various methods, thereby establishing a versatile approach for cancer theranosis. This review described the various surface modification methods of CDs, in vitro and in vivo toxicity of CDs, and various cancer theranostic methods such as drug delivery, photodynamic therapy, photothermal therapy, gene therapy, sonodynamic therapy, and gas therapy. Therefore, CDs can serve as various mono and combined theranostic modalities, offering us new methods for cancer theranosis.