A method of treating a condition related to iron deficiency. The method includes steps of identifying a patient having a condition related to iron deficiency and administering an effective amount of biocompatible iron oxide nanoparticles to the patient. The biocompatible iron oxide nanoparticles each contains an iron oxide core that is covered by one or more biocompatible polymers, each of which has a polyethylene glycol group, a silane group, and a linker linking, via a covalent bond, the polyethylene glycol group and the silane group.
