Recent advances in red-emissive carbon dots and their biomedical applications

Recently, there has been a lot of interest in the use of red-emissive carbon dots (R-CDs) due to their low toxicity, solubility in water, and excellent optical properties. These properties make them perfect for use in various biomedical applications. One of the main advantages of R-CDs is that they can penetrate deep into biological tissue without any interference from the tissue's fluorescence. More and more studies have been conducted to explore the potential applications of R-CDs in medicine, making them an exciting area of research. However, one of the challenges is preparing R-CDs with a high fluorescence quantum yield in the deep-red or near-infrared region, and this is still a significant hurdle. Therefore, it is crucial to investigate the preparation approaches of R-CDs with high quantum yield, narrow emission, and multi-functionality to overcome this challenge. This review aims to discuss the synthetic strategies, optical properties, and potential biomedical applications of R-CDs. The focus will mainly be on the research progress of their applications in biological imaging, tumor photodynamic/photothermal therapy, and in the field of synergistic therapy. Additionally, we will also discuss the challenge of achieving R-CDs with specific properties favorable for prospects in biomedical applications.