Carbon dot nanoparticles as multifunctional fluorescent probes: from tunable synthesis to biomedical applications

Carbon dots (CDs) have emerged as highly promising fluorescent nanomaterials due to their exceptional optical properties, biocompatibility, and facile synthesis. These attributes position them as versatile platforms for bioimaging, biosensing, and diagnostic applications in modern biomedicine. Significant progress has been achieved in translating CDs from proof-of-concept studies toward practical biomedical tools, particularly in real-time bioimaging and sensing. This review summarizes recent advancements in the synthesis and fluorescence mechanisms of CDs, with a focus on their applications as targeted fluorescent probes for critical analytes (e.g., metal ions, reactive oxygen species, enzymes, biomolecules) and cellular organelles. We provide a comparative analysis of CDs classification and correlate synthesis parameters with optical performance. Additionally, we critically evaluate the role of CDs in key disease areas, including oncology, cardiovascular disorders, neurodegenerative conditions, pulmonary and inflammatory diseases, highlighting their capacity for early diagnosis, therapeutic monitoring, and intraoperative guidance. Furthermore, we discuss the transition toward sustainable, green synthesis and the emerging role of computational tools, such as machine learning and artificial intelligence, in optimizing CDs properties and enhancing image interpretation. Despite their transformative potential, challenges persist in achieving synthesis reproducibility, enhancing selectivity via "turn-on" mechanisms, and validating long-term biocompatibility in vivo. Addressing these limitations through interdisciplinary collaboration and advanced engineering strategies is essential for fully realizing the clinical potential of CD-based fluorescent probes in modern medicine.