An article that can be used for biomaterial capture comprises (a) a porous substrate; and (b) borne on the porous substrate, a polymer comprising interpolymerized units of at least one monomer consisting of (1) at least one monovalent ethylenically unsaturated group, (2) at least one monovalent ligand functional group selected from acidic groups, basic groups other than guanidino, and salts thereof, and (3) a multivalent spacer group that is directly bonded to the monovalent groups so as to link at least one ethylenically unsaturated group and at least one ligand functional group by a chain of at least six catenated atoms.