This disclosure relates to nanoparticle drug delivery systems composed of casein (CN) coated nanoparticles, e.g., iron oxide nanoparticles coated with an inner layer and an out layer comprising the milk protein casein. In certain embodiments, drug molecules are incorporated into an inner polymeric layer coating the nanoparticles, which are subsequently coated with a casein containing outer layer, i.e., a layer-by-layer (LBL) construction. Oral administration of these casein coated nanoparticles are contemplated as experiments indicated sufficiently stability in conditions that simulate the conditions of the gut. Drugs that were loaded into the nanoparticle systems were released when the casein outer layer was gradually degraded in the presence of an intestinal protease meant to simulate conditions of the intestine.