We employed Ar–CH4 to synthesize carbon nanosheets (CNSs), which are two-dimensional carbon nanostructures, by microwave plasma-enhanced chemical vapor deposition at relatively low temperatures and working pressures. The CNSs consist of few-layer graphene nanosheets with 1–3 nm thick sharp edges and possess a large amount of defects, as characterized by scanning and transmission electron microscopies, energy-dispersive X-ray and Raman spectroscopy. Owing to their extraordinary characteristics, the synthesized CNSs can be used to modify the electrodes and exhibit fast electron transfer kinetics in the inner sphere redox system of Fe(CN)63-/4- and remarkably active electrocatalytic and biosensing properties.