Fabrication of Zinc Oxide Semiconductor Nanoparticles in the Apoferritin Cavity

We developed a liquid phase ZnO nanoparticles (NPs) fabrication method which employed the cage-shaped protein apoferritin as a biotemplate. The suppression of the chemical reaction outside apoferritin by stabilizing Zn2+ with ammonia allowed the selective NP synthesis inside the cavity at room temperature. The composition of synthesized NPs was confirmed to be that of ZnO, and their size was determined to be 5.1 +/- 0.8 nm in diameter through energy-dispersive X-ray spectroscopy and high-resolution transmission electron microscopy. In-depth studies about the effect of anion species on the NP formation proved that the anion introduction through the channels was competitive and also that the decrease in hydroxide ion (OH-) concentration ratio in the reaction solution led to less ZnO NPs formation.