Self-assembly of 3D Ternary Crystals Consisting of Biological and Synthetic Nanoparticles

Inorganic nanoparticles can be assembled into ordered superlattices, where their collective properties lead to new optical, magnetic, or catalytic behavior. Protein cages, known for their highly symmetric and uniform structures as well as propensity for crystallization, can bind or encapsulate nanoparticles and serve as self-assembly templates, facilitating the formation of ordered superlattices. While binary systems based on protein cages have been successfully demonstrated, examples of ternary crystals incorporating protein cages remain largely unexplored. Here, we study the electrostatic self-assembly of three-component nanoparticle arrays composed of two protein cages: cowpea chlorotic mottle virus and ferritin as well as synthetic positively charged gold nanoparticles. We demonstrate that they can self-sort into binary crystals or form ternary complexes by tuning the particle interactions through the solution ionic strength. The cationic gold particles play a crucial role in modulating the crystallization process through electrostatic interactions, significantly impacting the formation of the nanoparticle array.