Red to near-infrared carbon dots: synthesis, cellular interactions, drug loading, and therapeutic applications

The emergence of nanoparticles (NPs) has profoundly revolutionized targeted drug delivery systems, overcoming numerous limitations associated with conventional therapies. Red to near-infrared (NIR) emissive carbon dots (RNCDs) have emerged as promising theranostic candidates owing to their unique combination of superior photophysical properties, including high quantum yield (QY) and photostability, and excellent biocompatibility. This review provides a comprehensive examination of the synthesis methods of RNCDs, with a particular focus on the bottom-up approach. We explore how variations in precursor selection, solvent type, heteroatom doping, and thermal conditions influence the photophysical characteristics of RNCDs. Furthermore, we have analysed strategies for drug loading, targeting mechanisms (both passive and active), and cellular uptake pathways, highlighting methodologies employed to enhance therapeutic efficacy. The review also assesses the specific applications of RNCDs in cancer therapy and microbial infection treatments, focusing on their biocompatibility, reduced systemic phototoxicity, and minimal autofluorescence interference. Lastly, we discuss controlled drug release mechanisms, including pH-responsive, redox-sensitive, and photothermal systems, that enable controlled release profiles.