DNA-Assembled Nanoparticle Rings Exhibit Electric
and Magnetic Resonances at Visible Frequencies
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Abstract
Metallic nanostructures can be used
to manipulate light on the subwavelength scale to create tailored
optical material properties. Next to electric responses, artificial
optical magnetism is of particular interest but difficult to achieve
at visible wavelengths. DNA-self-assembly has proved to serve as a
viable method to template plasmonic materials with nanometer precision
and to produce large quantities of metallic objects with high yields.
We present here the fabrication of self-assembled ring-shaped plasmonic
metamolecules that are composed of four to eight single metal nanoparticles
with full stoichiometric and geometric control. Scattering spectra
of single rings as well as absorption spectra of solutions containing
the metamolecules are used to examine the unique plasmonic features,
which are compared to computational simulations. We demonstrate that
the electric and magnetic plasmon resonance modes strongly correlate
with the exact shape of the structures. In particular, our computations
reveal the magnetic plasmons only for particle rings of broken symmetries,
which is consistent with our experimental data. We stress the feasibility
of DNA self-assembly as a method to create bulk plasmonic materials
and metamolecules that may be applied as building blocks in plasmonic
devices