High Temperature Decomposition of Cerium Precursors To Form Ceria Nanocrystal Libraries for Biological Applications

Nanocrystalline ceria is an interesting inorganic material for biological application that can exhibit antioxidant properties due to facile electron transfer between cerium(III) and cerium(IV). In this work, ceria nanocrystals with uniform and tunable size, surface chemistry, and variable cerium(III) content were formed via the high temperature thermal decomposition of ceria precursors including cerium acetylacetonate hydrate, cerium oleylamine, and cerium nitrate hexahydrate. When combined with organic acid and amine surfactants at temperatures between 260 and 320 °C, these cerium precursors decomposed to yield near-spherical cerium oxide nanocrystals with diameters ranging from 3 to 10 nm. For all shapes of nanocrystals, the smallest primary particle sizes had the most cerium(III) content. Both poly(acrylic acid)–octyl amine as well as oleic acid could be used to transfer the hydrophobic nanocrystals into water; acute in vitro toxicology studies revealed that even at high concentrations (e.g., 10 ppm) 3 nm nanocrystalline ceria suspensions had had no measurable effect on human dermal fibroblasts (HDF). Additionally, hydrogen peroxide effectively converted cerium(III) to cerium(IV) without any change in the colloidal stability of the nanocrystals. These data illustrate that highly uniform nanocrystalline cerium oxide formed in organic solutions can be a potential antioxidant in the aqueous environments relevant for biological applications.