Characterization of carbon dots from fructus gardeniae (Zhi-zi) and gardenia charcoal (black Zhi-zi) via microwave-assisted extraction.

We employed a straightforward microwave-assisted extraction technique to investigate the presence of carbon dots (CDs) in Chinese herbal extracts derived from fructus gardeniae and gardenia charcoal, designated as CDs-1 and CDs-2, respectively. The found CDs exhibited unique photoluminescence with quantum yields of 0.95% for CDs-1 and 1.81% for CDs-2, indicating significant potential for bioimaging applications. Both CD types maintain approximately 80% of their fluorescence intensity after 120 min of continuous 365 nm UV exposure, underscoring their stability and suitability for prolonged biological studies. Moreover, antioxidant activity tests showed that CDs-2 have a higher scavenging capacity, with an SC-50 value of 21.7 μg/mL, compared to 35.9 μg/mL for CDs-1, attributed to their higher content of surface functional groups during the extraction procedure. Notably, the results indicated that the carbonization process of fructus gardeniae leads to the formation of CDs, suggesting a potential link between traditional herbal treatments and modern nanotechnology. This research demonstrates that active compounds in Chinese herbal medicine could possess therapeutic properties when adsorbed on the surface of CDs.