Feedback-driven self-assembly of symmetry-breaking optical metamaterials in solution.

Thermodynamically driven self-assembly offers a direct route to organize individual nanoscopic components into three-dimensional structures over a large scale. The most thermodynamically favourable configurations, however, may not be ideal for some applications. In plasmonics, for instance, nanophotonic constructs with non-trivial broken symmetries can display optical properties of interest, such as Fano resonance, but are usually not thermodynamically favoured. Here, we present a self-assembly route with a feedback mechanism for the bottom-up synthesis of a new class of symmetry-breaking optical metamaterials. We self-assemble plasmonic nanorod dimers with a longitudinal offset that determines the degree of symmetry breaking and its electromagnetic response. The clear difference in plasmonic resonance profiles of nanorod dimers in different configurations enables high spectra selectivity. On the basis of this plasmonic signature, our self-assembly route with feedback mechanism promotes the assembly of desired metamaterial structures through selective excitation and photothermal disassembly of unwanted assemblies in solution. In this fashion, our method can selectively reconfigure and homogenize the properties of the dimer, leading to highly monodispersed aqueous metamaterials with tailored symmetries and electromagnetic responses.