Bioinspired Synthesis of Homogenous Cerium Oxide Nanoparticles and Two- or Three-Dimensional Nanoparticle Arrays Using Protein Supramolecules

We developed an environmentally friendly method for the synthesis of cerium (Ce) oxide nanoparticles (NPs) and their two- and three-dimensional array formation using the cage shaped protein apoferritin. Apoferritin was used as a biotemplate for Ce oxide NP synthesis, and the cavity served as a restricted chemical reaction space where the trivalent Ce ions were oxidized and formed a Ce oxide NP through a process similar to iron oxide formation. The obtained Ce oxide NPs were characterized as CeO2, and their size was 5.0 +/- 0.7 nm. Salt bridge formation between ferritins (apoferritins each containing a NP) by multivalent Ce ions was investigated. The best conditions of salt bridge formation produced a two-dimensional array of Ce oxide NP containing ferritin with a domain size of over 500 nm which has the potential to be used as an effective catalytic NP array. Three-dimensional arrays of Ce oxide NP containing ferritin with either an octahedral or prismlike morphology were also studied.