Metal-modified carbon dots: Synthesis, properties, and applications in cancer diagnosis and treatment

Metal-modified carbon dots (M-CDs) are a novel class of nanomaterials, including doping metal ions into carbon dots (CDs) and compounding metal nanoparticles with CDs. Owing to their low-toxicity, excellent physicochemical properties, and good biocompatibility, M-CDs have received extensive attention. In this review, firstly, their synthesis methods are summarized with analysis of their advantages and disadvantages. Secondly, in addition to the biocompatibility of M-CDs, the regulation of the fluorescence properties and good magnetic properties of CDs by metal ions or nanoparticles are emphasized, suggesting that M-CDs need long-wavelength emission and high fluorescence quantum yield to improve fluorescence imaging (FLI) ability, high relaxation rate to improve magnetic resonance imaging (MRI) ability. Thirdly, the applications of M-CDs in cancer diagnosis and treatment are introduced. M-CDs can accurately detect cancer-related markers, break the limitation of single-modality imaging to realize dual/multi-modality imaging, construct cancer-targeted drug/gene delivery systems or as photothermal/photosensitive agents to kill cancer cells. Their dual/multi-modality imaging-guided cancer therapy can as an effective mean of integrating cancer diagnosis and treatment. Finally, their prospects and challenges are presented, for providing new ideas for cancer diagnosis and treatment.