Viruslike Nanoparticles with Maghemite Cores Allow for Enhanced MRI Contrast Agents

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-(CH2)11-(CH2-CH2-O)4-OCH2-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.