Green Synthesis of Carbon Dots: Advancements, Characterization, and Emerging Biological Applications

Carbon dots (CDs), a novel class of zero-dimensional nanomaterials, have garnered significant attention due to their exceptional optical properties, superior biocompatibility, and robust chemical stability. Among the diverse synthesis approaches, green synthesis has emerged as a sustainable and environmentally friendly strategy, leveraging natural precursors such as plant extracts, biomass, and other renewable resources. This review presents a comprehensive analysis of the principles, methodologies, and recent advancements in the green synthesis of CDs, emphasizing the use of non-toxic, cost-effective precursors and energy-efficient fabrication techniques. The key physicochemical attributes of CDs-including particle size, surface functionality, fluorescence characteristics, and quantum yield-are critically examined, supported by advanced characterization techniques such as transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and UV-visible spectroscopy. The review further explores a wide spectrum of biological applications, including bioimaging, targeted drug delivery, biosensing, and antimicrobial activity, underscoring their growing potential in nanomedicine and biotechnology. By synthesizing recent progress and emerging trends, this work highlights the current challenges and outlines future research directions to enhance green synthesis strategies and expand the biomedical and sustainable applications of carbon dots.