Smart Carbon Dot Nanomaterials: Emerging Structure, Properties, and Biomedical Insights—A Comprehensive Review

Nanotechnology has revolutionized science and technology by enabling the design and application of materials at the nanoscale, where unique size‐dependent physicochemical properties emerge. Among the diverse nanostructures, carbon dots (CDs) have gained remarkable attention since their serendipitous discovery in 2004, owing to their facile synthesis, exceptional photoluminescence, excellent aqueous dispersibility, high photostability, biocompatibility, and low toxicity. Typically, less than 10 nm in size, CDs possess abundant surface functional groups that facilitate tunable fluorescence, surface passivation, and heteroatom doping, thereby broadening their applicability. These distinctive attributes have positioned CDs as promising candidates for a wide spectrum of applications, including bioimaging, biosensing, drug delivery, catalysis, photocatalytic degradation, tissue engineering, photodynamic therapy, energy conversion, and environmental monitoring. This review provides a comprehensive overview of luminous carbon dot nanomaterials, with emphasis on their synthesis strategies, doping effects, structural features, and fluorescence mechanisms, including quantum yield enhancement and fluorescence quenching. Furthermore, the review highlights their multifaceted biomedical applications, particularly their emerging role as smart scaffolds in therapeutic platforms, while also addressing the key challenges that limit large‐scale production and clinical translation. Finally, perspectives on future research directions are presented, underscoring the immense potential of carbon dots to advance next‐generation biomedical technologies and sustainable nanomaterial applications.