Carbon Quantum Dots as Versatile Nanosystems for Biomedical Innovation: Mechanisms, Applications, and Translational Prospects.

Carbon quantum dots (CQDs) represent a rapidly developing class of fluorescent nanomaterials with increasing relevance in biomedical research and application. Their tuneable photoluminescence (PL), favourable biocompatibility, and versatile surface chemistry has supported applications in bioimaging, biosensing, and therapeutic strategies. Advances in top-down, bottom-up, and green synthesis routes have improved control over emission profiles, heteroatom doping, and surface functionalisation. Recent work has begun to elucidate how synthesis conditions and surface states govern biological interactions, intracellular transport, and subcellular localisation. This review provides an updated, mechanistic evaluation of these developments, with particular emphasis on how defined structural attributes influence antimicrobial activity, organelle-specific targeting, and integrated imaging-therapy platforms. Despite these advances, significant challenges continue to hinder clinical translation. These include variability in synthesis protocols, inconsistent batch-to-batch reproducibility, and insufficient data on long-term toxicity and biodistribution. The absence of standardised characterisation frameworks and clear regulatory pathways further complicate translational progress. Through critically linking synthesis strategies to surface chemistry and biological behaviour, this review depicts key design considerations necessary for advancing CQDs toward clinical application in next-generation nanomedicine.