Recent developments of Red/NIR carbon dots in biosensing, bioimaging, and tumor theranostics

Carbon dots (CDs) that exhibit near-infrared (NIR) emission are emerging nanomaterials with potential for advanced biomedical applications due to their low toxicity, superior photostability and targeting ability compared to currently used photoluminescence (PL) agents. While yellow and green CDs offer advantages such as excellent photostability, water solubility, and biocompatibility, R/NIR-CDs provide additional benefits including minimal autofluorescence, reduced photodamage, and deep tissue penetration. As a result, R/NIR-CDs are particularly intriguing for their biomedical applications in early tumor diagnostics and treatments both in vitro and in vivo. This review article highlights recent progress in the development of vital strategies, PL mechanisms, potential biomedical applications, and future directions for overcoming key limitations of R/NIR-CDs. The influence of physicochemical parameters on the formation mechanism toward longer wavelengths is comprehensively discussed. Moreover, multicolor CDs with various fluorescence properties are categorized based on their size or other factors. We hope that the perspectives presented in this review will facilitate the advancements in developing new and improved R/NIR-CDs better suited for the respective applications.