▎ 摘　　要

Graphene quantum dots surface passivated by polyethylenimine (GQDs-PEI) were prepared with a simple solvothermal method. Compared with the unfunctionalized graphene quantum dots (GQDs), the GQDs-PEI were well dispersed with an ultrasmall average diameter of ca. 1.66 nm, and have achieved better optical properties including high quantum yield (53.0%) and narrow emission spectral features which is probably because of the positively charged amines on PEI which facilitated the dispersion of GQDs. By being applied to the bioimaging of MG-63 cells, the GQDs-PEI showed brighter luminescence and minor cytotoxicity. Moreover, the GQDs-PEI are clearly rendered in the nucleus region, which offered a further application in the diagnosis of diseased phenotypes and the targeted therapy of tumour cells.