▎ 摘　　要

We report a novel procedure involving polyethylenimine-assisted hydrothermal cutting and subsequent ultrafiltration for fabricating nearly monodisperse graphene quantum dots with a uniform lateral size and confined layer number. The isolated monolayer quantum dots exhibit a sharp band-edge absorption feature and strong photoluminescence (quantum yield of 21%) independent of excitation wavelength and pH. Their preliminary application in bioimaging has been demonstrated.