Carbon Quantum Dots: A Multidimensional Review on Synthesis, Characterization and Biomedical Frontiers

Carbon quantum dots (CQDs), a class of carbon nanoparticles with diameter typically less than 10 nm are zero-dimensional, showcase exceptional attributes such as chemical stability, water solubility, biocompatibility and excellent photoluminescence. CQDs have been known to be an emerging substitute of the traditional semiconductor quantum dots due to its low toxicity. CQDs are highly fluorescent and promising candidate for progressive nanomaterials research for bioimaging and biomedicine due to their outstanding optical properties. We provide a detailed analysis of the synthetic approaches of CQDs which are divided into two broad categories, top-down and bottom-up methods, emphasizing on the shift towards green precursors for sustainable production. Moreover, we also analyze how heteroatom doping and surface functionalization regulates electronic density and enhance the photoluminescence quantum yield (PLQY). Finally, we probe into the carbon quantum dots, having a wide array of applications in gene therapy, drug delivery system, bioimaging, biosensing and a compelling claimant as an antimicrobial and antiviral agent, while addressing the challenges and the future prospects. In this comprehensive review, we also dive into the structure, characterization, chemical and optical properties of CQDs.