Viral protein-coating of magnetic nanoparticles using simian virus 40 VP1

•MNPs were coated by self-assemble activity of the virus capsid protein VP1.•Dispersity of MNPs was improved by the VP1-coating of simian virus 40.•Improved dispersion contributed prolonged retention in the body fluid.•The relaxivity of MNPs for MR imaging was not affected by VP1-coating.•EGF immobilization onto VP1-coated MNPs provided active targeting property. Artificial beads including magnetite and fluorescence particles are useful to visualize pathologic tissue, such as cancers, from harmless types by magnetic resonance imaging (MRI) or fluorescence imaging. Desirable properties of diagnostic materials include high dispersion in body fluids, and the ability to target specific tissues. Here we report on the development of novel magnetic nanoparticles (MNPs) intended for use as diagnosis and therapy that are coated with viral capsid protein VP1-pentamers of simian virus 40, which are monodispersive in body fluid by conjugating epidermal growth factor (EGF) to VP1. Critically, the coating of MNPs with VP1 facilitated stable dispersion of the MNPs in body fluids. In addition, EGF was conjugated to VP1 coating on MNPs (VP1-MNPs). EGF-conjugated VP1-MNPs were successfully used to target EGF receptor-expressing tumor cells in vitro. Thus, using viral capsid protein VP1 as a coating material would be useful for medical diagnosis and therapy.