The present invention provides an inherently non-fouling nano-filter characterized by a shape chosen from the group comprising (a) substantially two-dimensional and (b) three-dimensional, said nano-filter comprising a shaped wall, said wall comprising at least one slot-like aperture having a minimal width d and a maximal length L, where d ranges from about 1 nm to 100 nm, L is at least N times larger than d, and N is equal to or greater than 2.