Long-Range Plasmon-Assisted Chiral Interactions in Nanocrystal Assemblies

Molecular recognition, which is key to the correct functioning of most biological processes, is based on chiral entities fitting into and onto each other. Consequently, the concept of chirality appears virtually everywhere in biology and biochemistry. One striking optical manifestation of the chirality of biomolecules is circular dichroism (CD), which is very typical for biorelated systems. It has been demonstrated over the past decade that bioassembled plasmonic nanostructures offer amazing possibilities regarding chirality and optical responses, and the active research field of chiral bioplasmonics has recently generated a variety of new sensing platforms. In both molecular and nanoscale systems, optical manifestations of chirality arise from complex interactions between nonchiral elements. Such interactions decay rapidly with the distance between the elements, and therefore, a system with strong optical chiral responses typically is tightly packed. Here we show how to transfer chiral interactions efficiently in specially designed plasmonic geometries over unprecedented distances. In our model, a long-range chiral interaction occurs between two nanorods (NRs) separated by a long distance, via transmitter nanoparticles (NPs). We establish specific conditions for the geometry of the NR-NP-NR complexes where such long-range chiral interactions should appear. The proposed chiral effect is expected to be observable under realistic experimental conditions in nanocrystal bioassemblies, for example, by employing the so-called DNA origami technology. These and similar chiral bioassembled plasmonic nanostructures can be used for applications in the field of optical bioassembled nanomaterials.