Ultrathin membranes of M13 viruses are demonstrated. Genetically engineered viruses are first selectively bound on the edges of graphene-oxide nanosheets. Further applying a shear flow on the assembled viruses results in their unidirectional alignment with a constant interspacing. These unit viral layers are stacked such that each layer is perpendicular to the preceding layer, forming a nanomesh structure, which is utilized for the separation of nanoparticles.