The Chemical Record of Carbon Quantum Dots: Charting the Course From Mechanistic Insights to Sustainable Technologies

Nanotechnology has revolutionized scientific innovation through precise nanoscale manipulation of matter. Among carbon-based nanomaterials, carbon quantum dots (CQDs), carbon nanodots (CNDs), and graphene quantum dots (GQDs) have emerged as next-generation multifunctional nanostructures distinguished by exceptional optical tunability, superior biocompatibility, high aqueous solubility, and excellent chemical stability. These properties enable diverse biomedical applications, including bioimaging, targeted drug and gene delivery, biosensing, and photothermal therapy. Beyond biomedicine, CNDs demonstrate significant potential in optoelectronics and analytical applications as essential components in solar cells, light-emitting diodes (LEDs), and perovskite devices while enabling sensitive detection of heavy metals, hazardous chemicals, and biomolecules. Their intrinsic catalytic activity supports critical environmental and industrial processes such as CO₂ reduction, water splitting, and pollutant degradation. Unlike conventional semiconductor QDs containing toxic metals, carbon-based QDs offer a nontoxic, sustainable, and cost-effective alternative with comparable or superior optical and electronic functionalities. This review critically examines synthesis strategies including top-down, bottom-up, and green approaches structural characteristics, photophysical mechanisms, and multifunctional applications. Current challenges, emerging trends, and future directions are outlined, highlighting the promise of carbon-based QDs as sustainable nanoplatforms for advanced biomedical, environmental, and energy technologies.