passing, in a first phase of the continuous operation, a planar cellulosic substrate through an aqueous solution of nanoparticle precursors, wherein the planar cellulosic substrate has a basis weight of up to 300 grams per square meter, wherein the aqueous solution has a solids content of 7-60% solids, the nanoparticle precursors are applied to the planar cellulosic substrate between 30 grams per minute to 3,500 grams per minute for the basis weight between 30 and 300 grams per square meter, and the solids pickup is between 5% to about 30%, and wherein the nanoparticle precursors include a metal salt having a concentration of 10-150,000 ppm and a reducing agent and the aqueous solution does not include metal nanoparticles; and

after the first phase of the continuous operation, drying, in a second phase of the continuous operation, to expose the planar cellulosic substrate to temperatures of at least 90° C. in order to form metal nanoparticles directly on surfaces of cellulosic fibers of the planar cellulosic substrate, wherein the metal nanoparticles have a size that ranges from 1 to about 200 nanometers in at least one dimension.