## 5 Conclusions and Future Perspectives  
CDs have emerged as potential candidates for cancer theranosis due to their easy synthesis and surface modification, low toxicity, good water solubility, tunable fluorescence, good photostability, and various therapeutic properties such as PTT and PDT. Owing to the aforementioned outstanding properties, CDs have received significant attention as alternatives to dyes and QDs in the field of biomedical imaging. In this review, we explored the recent advancements of CDs, emphasizing their potential use in cancer theranosis. We discussed various surface modification methods of CDs to decorate their surface with various functional molecules for cancer theranosis, in vitro and in vivo toxicity to demonstrate their suitability for biomedical applications, and then, a key focus was placed on discussing their in vitro and in vivo applications to cancer theranosis, including drug delivery, PDT, PTT, PTT+PDT, and siRNA therapy.  
As reviewed here, CDs have shown promising cancer theranostic properties in vivo and in vitro. However, several challenges must be addressed before the clinical application of CDs. Most current CDs exhibit absorption and emission in the visible region, which limits their use in deep tissue imaging and therapy. To overcome this limitation, there is an urgent need to develop CDs with strong absorption and emission in the NIR region. The NIR CDs can be used to improve tissue penetration and reduce background interference from autofluorescence. In addition, although CDs are known for their low toxicity, long-term in vivo toxicity studies (>1 year), including immunological assays, will be needed to confirm their safety for clinical translation. In addition, the scalable synthesis method of CDs with controlled particle size and a simple purification procedure is not currently available and thus needs to be developed to enhance commercial applications of CDs. In addition, CDs can be photodegradable, and thus, experimental conditions that provide no photodegradation under light irradiation need to be investigated for safe applications of CDs in PDT and PTT.  
The previous studies support the idea that the future use of CDs in cancer theranosis is highly promising. With continued research and interdisciplinary collaboration between material scientists, chemists, biologists, and medical professionals, CDs may pave the way for clinical translation in cancer theranosis in the future.  
Conceptualization, T.T.; methodology, T.T. and E.M.; validation, Y.L., D.Z., A.B. and X.C.; writing--original draft preparation, T.T.; writing--review and editing, Y.C. and G.H.L.; funding acquisition, J.K., Y.C. and G.H.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Basic Science Research Program of the National Research Foundation (NRF) funded by the Korea government (Ministry of Science, and Information and Communications Technology: MSIT) (Basic Research Laboratory, No. RS-2024-00406209) and NRF funded by the Ministry of Education (Post-Doc. Growth Type Cooperational Research, No. RS-2024-00459895).  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors declare no conflicts of interest.