Here, for the first time, we demonstrate
formation of virus-like
nanoparticles (VNPs) utilizing gold-coated iron oxide nanoparticles
as cores and capsid protein of brome mosaic virus (BMV) or hepatitis
B virus (HBV) as shells. Further, utilizing cryo-electron microscopy
and single particle methods, we are able to show that the BMV coat
on VNPs assembles into a structure very close to that of a native
virion. This is a consequence of an optimal iron oxide NP size (∼11
nm) fitting the virus cavity and an ultrathin gold layer on the maghemite
cores, which allows for utilization of SH-(CH<sub>2</sub>)<sub>11</sub>-(CH<sub>2</sub>-CH<sub>2</sub>-O)<sub>4</sub>-OCH<sub>2</sub>-COOH
as capping molecules to provide sufficient stability, charge density,
and small form factor. MRI studies show unique relaxivity ratios that
diminish only slightly with gold coating. A virus protein coating
of a magnetic core mimicking the wild-type virus makes these VNPs
a versatile platform for biomedical applications