A facile methodology has been developed for covalently derivatizing the surfaces of common materials with a designed antibacterial polycation, poly(vinyl-pyridinium bromide), wherein the first, key step involves surface coating with a nanolayer of silica. Various commercial synthetic polymers derivatized in this manner become bactericidal-they kill up to 99% of deposited, from either an aerosol or an aqueous suspension, Gram-positive and Gram-negative bacteria on contact.