Engineered Chiral Plasmonic Nanocrystal Using Ferritin‐Nanocage With Tunable Circular Dichroism

Adapting the optical properties of a chiral nanocrystal (NC) requires significant consideration of the morphology of the particular NC. However, there is still no consensus on approaches to readily synthesize such nanomaterials with great control and reproducibility. Here, we present a solution‐based method to controllably synthesize chiral NCs with significantly enhanced optical properties. Ferritin nanocages are employed as templates to direct the crystallization initiated from positionally accumulated gold ions, distributed on the surface and within the cavity of the protein. Our approach is highly responsive to modulation of reaction conditions, enabling one to actively fine‐tune the final morphology of the NCs. Dissymmetry analyses (g‐factor) reveal strong dependence on L‐ and H‐chain dominant structure, which also affords another avenue for shape‐directing the final structure. The synthesized NC exhibited a prominent chiral plasmonic property culminating in a g‐factor of about 0.04. Our key strategy to achieve highly pronounced chiral NCs involves using the optimum setup for each condition, ranging from the reaction pH, time, precursor concentration, and type of ferritin. We strongly anticipate that our method will pave the way for more rational design strategies for chiral nanoparticles inspired by naturally occurring biomolecules with intriguing optical properties.