Green Synthesis of Nitrogen-Doped Carbon Dots from Fresh Tea Leaves for Selective Fe3+ Ions Detection and Cellular Imaging

In this research, we successfully developed a green, economical and effective one-step hydrothermal method for the synthesis of fluorescent nitrogen-doped carbon dots (N-CDs) by utilizing fresh tea leaves and urea as the carbon and nitrogen sources, respectively. The obtained N-CDs were characterized by TEM, XPS and FT-IR. We found that the N-CDs were near-spherical with an average size of about 2.32 nm, and contained abundant oxygen and nitrogen functional groups. The N-CDs exhibited bright blue fluorescence under ultraviolet illumination, with the maximum emission at 455 nm. Meanwhile, the as-prepared N-CDs could be selectively quenched by Fe3+ ions. The quenching of N-CDs is linearly correlated with the concentration of Fe3+ in the range of 0.1-400 mu M with a low detection limit of 0.079 mu M. Significantly, the N-CDs present excellent biocompatibility and high photostability. The results also depict that multicolor fluorescence is displayed under a fluorescence microscope and successfully applied for the detection of intracellular Fe3+. To sum up, the fluorescent N-CDs are expected to be a sensitive detection probe for Fe3+ in biological systems.