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

•The synthesis method and properties regulation of M-CDs are introduced in detail.•The application of M-CDs in cancer diagnosis and treatment is described.•The challenges and future perspective of M-CDs are proposed. 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. The synthetic methods and properties of metal-modified carbon dots and their applications and mechanisms in the integration of cancer diagnosis and treatment are reviewed. [Display omitted]