Iron [26Fe], a metal in the first transition series, is one of the most ubiquitous and abundant elements existing in the inner and outer core of the Earth. Iron has sixteen oxides and hydroxides; two stable oxidation states in an aqueous solution of ferrous, Fe(II), and the ferric, Fe(III)[1]. Iron oxides are widespread in nature; they are also conveniently synthesized in the laboratory. More likely it indicates that iron has a great tendency to be reactive in large-scale applications, so it leads to the importance in nano-scale applications. That's why it has considerably become important for the recent developments in the field of nanotechnology since it potentially has the magnetic and catalytic properties.
The most common iron oxides existed in nature are arguably the magnetite, Fe3O4, maghemite, γ-Fe2O3, and hematite, α-Fe2O3, which have been perfected in the field of magnetic nanoparticles. While the hematite (α-Fe2O3) is weakly ferromagnetic or antiferromagnetic, the magnetite (Fe3O4) and the maghemite (γ-Fe2O3) are ferrimagnetic. Besides, the magnetite (Fe3O4) is superparamagnetic when the size is less than 15nm. Already, it is possible technologically to control the physical and chemical properties of nanoparticles in applying solvents. Knowing that magnetic iron oxide nanoparticles holding a large amount of surface to volume ratio acquiring high surface energies, that's why they desire to be gathered to decrease the surface energy. What is more, the individual iron oxide nanoparticles mostly the magnetites exceedingly tend to be oxidized in the air, which is disadvantage of it magnetism and dispersibility[2][3].
Ferritins, uniformly nano sized protein cages, existed naturally, have an iron-storage function in a non-toxic and bioavailable form, and are where the reaction between iron and oxygen occurred. Ferritin cages can be genetically engineered to be utilized for a broad application in the field of nanotechnology[4][5][6].