Iranian researchers applied apoferritin protein cage to synthesize cobalt nanoparticles for designing an appropriate biosensor to detect various compounds, including hydrogen peroxide, phenol, etc. The synthesized nanoparticles have applications in different fields, including medical purposes and industries. The aim of the research was to synthesize cobalt nanoparticles by using ferritin protein cage. The nanoparticles are very important in various applications such as medical and other industries. The purpose of the second part of the research was to produce a biosensor to detect various compounds such as hydrogen peroxide, phenol, and other materials by using ferritin–cobalt complex. One of the characteristic of the research is that the protein does not change during the synthesis process, and the size of the synthesized nanoparticles is in corporation with the size of protein voids. In addition, nanoparticles produced in protein cage can be used as a biosensor, which definitely has high stability because ferritin is able to stand a temperature of up to 80°C and a pH value of 2-10 and a 6 M concentration of urea and guanidine hydrochloride. Nanoparticles with similar shape and morphology can be produced by using this synthesis method. Therefore, this method is appropriate when nanoparticles should be produced at the same size. Scientists also hope to reach low detection limits at nanomolar scale by designing this type of biosensors, which is very important in many cases. Results of the research have been published in details in Molecular Biology Reports, vol. 39, issue 9, 2012, pp. 8793-8802.