Green and One-step Synthesis of Fluorescent Carbon Dots with the Significant Antibacterial Effects

Fluorescent carbon dots (CDs) have attracted great attention for the biomedical applications as a new group of nanoparticles with high biocompatibility and interesting optical properties. In this study, the fluorescent CDs were synthesized by a biogenic hydrothermal method using Taxus baccata extract and ethylene diamine (EDA). The CDs, predominantly semi-spherical and smaller than 20 nm, exhibit high colloidal stability. They have a hydrodynamic size of 43.6 nm, a polydispersity index (PI) of 0.526, and a zeta potential of -56.7 mV. Their surface is rich in hydroxyl and carbonyl groups. They also exhibit fluorescence emission, with a quantum yield (QY) of 11.6% at 490 nm, when excited at 400 nm. The in vitro cytotoxicity assay on the human fibroblast (HFB) and umbilical vein endothelial (HUVEC) cells confirmed the biocompatibility of CDs. These CDs represent significant antibacterial effects on Staphylococcus aureus and Escherichia coli with the minimum inhibitory concentrations (MIC) of 40 and 160 mu g mL- 1, respectively. The rapid and efficient uptake of CDs with E. coli and HFB cells was confirmed by the fluorescence imaging. Based on the results, the biogenic CDs can be a suitable alternative to the antibiotics against pathogenic bacteria and also for the staining and labeling of the microbial cells.