Reaction inside a viral protein nanocage: Mineralization on a nanoparticle seed after encapsulation via self-assembly

Protein nanocages are ideal templates for the bio-inspired fabrication of nanomaterials due to several advantageous properties. During the mineralization of nanoparticles (NPs) inside protein nanocages, most studies have employed a common strategy: seed formation inside protein nanocages followed by seeded NP growth. However, the seed formation step is restricted to gentle reaction conditions to avoid damage to the protein nanocages, which may greatly limit the spectrum of seed materials used for NP growth. We put forward a simple route to circumvent such a limitation: encapsulation of a preformed NP as the seed via self-assembly, followed by the growth of an outer metal layer. Using such a method, we succeeded in mineralizing size-tunable Au NPs and Au@Ag core-shell NPs (< 10 nm in diameter) with narrow size distributions inside the virus-based NPs of simian virus 40. The present route enables the utilization of NPs synthesized under any conditions as the starting seeds for nanomaterial growth inside protein nanocages. Therefore, it potentially leads to novel bioinorganic chimeric nanomaterials with tailorable components and structures.