Filter and method of making same

A method for the removal of submicron contaminants from biological liquid comprising passing the contaminated liquid through a filter media sheet consisting essentially of fine particulate and self-bonding matrix of cellulose fiber, the surfaces of at least one of which are modified with a sufficient amount of an inorganic cationic colloidal silica to provide a positive zeta potential to the surface of the filter media sheet, wherein the cationic colloidal silica is derived from a dispersion of positively charged colloidal particles having a dense silica core modified with a polyvalent metal-oxygen compound wherein the polyvalent metal is aluminum, and a sufficient amount of the compound is provided to coat the silica to a level of at least 13% by weight of colloidal solids.