Encapsulation of Gold Nanoparticles into Redesigned Ferritin Nanocages for the Assembly of Binary Superlattices Composed of Fluorophores and Gold Nanoparticles

Nanomaterials with a defined composition and structure can be synthesized by exploiting natural templates or biomolecular matrices. In the present work, we use protein nanocages derived from human ferritin as a nanoscale building block for the assembly of gold nanoparticles and fluorescent molecules in the solid state. As a generalizable strategy, we show that prior to material synthesis, the cargo can be encapsulated into the protein nanocages using a dis- and reassembly approach. Toward this end, a new ligand system for gold nanoparticles enables efficient encapsulation of these particles into the nanocages. The gold nanoparticle-loaded protein nanocages are co-assembled with fluorophore-loaded protein nanocages. Binary superlattices are formed because two oppositely charged ferritin nanocages are used as templates for the assembly. The binary crystals show strong exciton-plasmon coupling between the encapsulated fluorophores and gold nanoparticles, which was spatially resolved with fluorescence lifetime imaging. The strategy outlined here offers a modular approach toward binary nanomaterials with highly ordered building blocks.