Room temperature phosphorescent carbon dot composites in aqueous solutions: synthesis, properties, and tumor diagnosis and therapy

Room temperature phosphorescence (RTP) materials have important applications in biosensing, bioimaging, drug delivery, and photodynamic therapy for tumor diagnosis and therapy owing to their long luminescence lifetimes, large Stokes shifts, and no need for real-time excitation. Carbon dots (CDs) are a new type of RTP materials, which have attracted wide attention because of their long RTP lifetime, tunable emission wavelength, low cytotoxicity, and other excellent properties compared with traditional RTP materials. However, most CDs only emit RTP in the solid state, which is quenched when dissolved in aqueous solutions. Therefore, recent studies on the synthesis and property modulation of RTP CD composites in aqueous solution have greatly expanded their applications in biomedicine. This review summarizes the latest research progress of aqueous RTP CD composites in tumor diagnosis and therapy, specifically including their synthesis methods, properties, and applications in tumor diagnosis and therapy. Beginning with the RTP emission mechanism of CDs in aqueous solutions, the interaction between CDs and matrix in RTP CD composites includes hydrogen bonding, covalent bonding, and inorganic salt confinement effects, and their structural influence laws on RTP emission are summarized. Secondly, the properties of RTP CD composites are summarized in terms of luminescence performance, photoinitiated generation of reactive oxygen species, and biotoxicity. Subsequently, the principles of RTP CD composites in biosensing, bioimaging, and tumor therapy are analyzed and the progress of their application in tumor diagnosis and therapy is reviews. Finally, the future challenges and opportunities of RTP CD composites in the biomedical field are presented to provide a reference for their controllable design and wide application.