Keeping nanoparticles fully functional: Long-term storage and alteration of magnetite

Magnetite is an iron oxide found in rocks. Its magnetic properties are used for paleoclimatic reconstructions. It can also be synthesized in the laboratory to exploit its magnetic properties for bio- and nanotechnological applications. However, although the magnetic properties depend on particle size in a well-understood manner, they also depend on the structure of the oxide, because magnetite oxidizes to maghemite under environmental conditions. The dynamics of this process have not been well described. Here, a study of the alteration of magnetite particles of different sizes as a function of their storage conditions is presented. Smaller nanoparticles are shown to oxidize more rapidly than larger ones, and that the lower the storage temperature, the lower the measured oxidation. In addition, the magnetic properties of the altered particles are not decreased dramatically, thus suggesting that this alteration will not impact the use of such nanoparticles as medical carriers.