A grafted nonwoven substrate is disclosed having average fiber sizes of 0.7 to 15 microns, and a void volume of 50 to 95%, and a polymer comprising cationic aminoalkyl(meth)acryloyl monomer units grafted to the surface of the nonwoven substrate. The article may be used as a filter element to purify or separate target materials, such as oligonucleotides or monoclonal antibodies (MAb), from a fluid mixture.