Apoferitin-Mediated Synthesis of Uniform Cobalt Nanoparticles

Nanoparticle (NP) is getting more and more important as the indispensable material for medical and industrial applications [1,2]. Methods of the production of nanoparticles which have been conventially carried out involve physical grinding methods, chemical synthesis methods and the such like. In these processes, nanoparticles are grown in a free space, such as a vaccum or liquid, and thus generally a size distribution cannot be avoided. To get homogeneous NPs, a template for regulating particle growth is required. The bio-templates used for NPs synthesis so far include mammalian protein cages, small protein cages from bacteria, and viral protein cages. The most intensively studied bio-template for NPs synthesis is apo-ferritin. Apoferritin is a glubolar protein in which 24 monomer subunits each being composed of a polypeptide chain assemble and form non-covalant bonds, which has a molecular weight of about 460,000 D. The globular protein exhibits higher thermal stability and higher pH stability. The outer diameter of the shell is about 12nm, and the core size is about 7nm. There are narrow channels connecting the inner cavity and outside, through which metal ions enter the inner the cavity. Up until today, there have been reports of synthesis of metals or metal compounds into apoferritin, [3,4] . In this study, we utilized the ability of apoferritin to sequester inorganic material and oxidize it to create size-cotrolled cobalt nanoparticls (Figure1).