Recent Advances in the Synthesis of Tailored Carbon Quantum Dots and Their Biomedical Applications

Carbon quantum dots (CQDs) are zero-dimensional nanoparticles with sizes smaller than 10 nm and are distinguished by their excellent luminescence, high photostability, and good biocompatibility. The wide range of their applications includes bioimaging and biosensing, drug delivery, energy storage, environmental remediation, and catalysis. The CQDs can be synthesized through two main approaches: the top-down method, which includes techniques such as arc discharge, laser ablation, electrochemical processes, and acid-reflux, and the bottom-up method, which encompasses microwave, hydrothermal, and pyrolysis techniques. This review provides a brief discussion of the optical properties, electrochemiluminescence, biocompatibility, and toxicity profile of CQDs, their source-based synthesis approaches, and various structural and functional ways of modifying CQDs to alter their optical properties, stability, water solubility, and biocompatibility. Bioimaging, biosensing, and drug delivery applications of CQDs have also been elaborated with relevant research studies. The current challenges and opportunities in tailoring CQD synthesis and providing insights into potential areas of improvement and innovation are also discussed.