The Synthesis of the Folate Acid Quantum Dots and Its Endocytosis in the Hepatoma Cells Mediated by the Folate Receptor

Objectives: To synthesize folate acid conjugated quantum dots (QDs) by a simple and green method and explore endocytosis of the QD-folic acid conjugates (FA-QDs) into hepG2 cells. Methods: CdS QDs were prepared using stearic acid as synthetic medium, and were conjugated with mercaptoacetic acid (MAA) to be water-soluble. Then folic acid moiety was coupled to the surface of the QDs using EDC (1-ethyl-3-(3-dimethylamino propyl)carbodiimide) as a coupling agent. The CdS QDs and FA-QDs were characterized by X-ray spectroscopy (XRD), transmission electron microscopy (TEM), spectro fluorimetry and infrared spectroscopy. Endocytosis of the FA-QDs into hepG2 cells was observed by confocal microscopy and TEM. Results: TEM shows that the CdS QDs and FA-QDs were spherical in shape and had a diameter of 10 nm. Fluorescence spectrum of the QDs also shows their narrow size distribution. Confocal microscopic and TEM results show that FA-QDs were successfully internalized into the hepG2 cells. In addition, confocal results show that when the cells were first be saturated with excess free FA, the endocytosis of the FA-QDs became less, and CdS QDs that were not conjugated with FA were not able to be internalized into the hepG2 cells. Conclusions: The FA-QDs can be synthesized by a simple and green method and be used to successfully target tumor cells: hepG2 cell lines, which was probably mediated by the FA receptor.