Polyethyleneimine modified fluorescent carbon dots and their application in cell labeling

Fluorescent carbon dots (CDs) were solvothermaly synthesized in water–glycol medium by using glucose as carbon source and then modified with polyethyleneimine (PEI) for the first time to improve fluorescence quality. The as-prepared CDs were monodispersed sphere particles with a diameter of about 7.5 nm, emitting strong fluorescence which is excitation wavelength-dependent, with a quantum yield of 3.5%. After PEI modification, there was a 300-fold enhancement in fluorescence intensity and also a red shift in emission wavelength. The as-prepared CDs were then conjugated with CEA8 antibody to label and image HeLa cells in vitro. We also tested the cytotoxicity of these CDs using HeLa cells. No apparent cytotoxicity was observed, demonstrating much better biosafety property compared with CdTe quantum dots.