Carbon dots (CDs) are relatively new and one of the most propitious nanomaterials ever known to humanity, primarily consisting of a carbonized carbon core with heteroatoms in organic functional groups attached. CDs show various fascinating properties, such as tunable excitation/emission, chemical inertness, photostability, low toxicity, good biocompatibility, ease of handling, and eco-friendliness. Due to the anomalous optical and chemical properties of the CDs, they have a wide range of applications in the fields of bioimaging, biosensing, photocatalysis, optoelectronics, etc. In this Review, we intend to cover the many strides in CDs chemistry, which is an emerging paradigm, in conjunction with the most recent discoveries of CDs with near-infrared fluorescence, phosphorescence, electroluminescence, chirality, and antibacterial activity. Our main emphasis will be on the contemporary evolution in synthetic strategies, optical properties, and biomedical applications of CDs in nanomedicine and nanotheranostics.

Compared with graphene quantum dots (GQDs), fluorine-containing GQDs (F-GQDs) present higher 1O2 generation under light irradiation and thus cause obvious toxicity to HepG2 cells. F-GQDs can be used as a photosensitizer for photodynamic therapy.

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A single-atom metal doped on carbonaceous nanomaterials has attracted increasing attention due to its potential applications as high-performance catalysts. However, few studies focus on the applications of such nanomaterials as nanotheranostics for simultaneous bioimaging and cancer therapy. Herein, it is pioneeringly demonstrated that the single-atom Gd anchored onto graphene quantum dots (SAGd-GQDs), with dendrite-like morphology, was successfully prepared. More importantly, the as-fabricated SAGd-GQDs exhibits a robustly enhanced longitudinal relaxivity (r 1 = 86.08 mM −1 s −1 ) at a low Gd 3+ concentration of 2 μmol kg −1 , which is 25 times higher than the commercial Gd-DTPA (r 1 = 3.44 mM −1 s −1 ). In vitro and in vivo studies suggest that the obtained SAGd-GQDs is a highly potent and contrast agent to obtain high-definition MRI, thereby opening up more opportunities for future precise clinical theranostics.