A double-layered nanoporous membrane suitable for virus filtration has been fabricated. The top layer has cylindrical pores with diameters of 15 nm and a narrow pore size distribution (see figure). The bottom support layer is a conventional microfiltration membrane. This asymmetric membrane completely blocks human rhinovirus type 14 (colored green) from penetrating into pores, while proteins such as bovine serum albumin (colored yellow) freely pass through the pores.