  Optical nanoantennas are structures designed to manipulate light-matter
interactions at the nanoscale by interfacing propagating light with localized
optical fields. In recent years, a plethora of devices have been realized that
are able to efficiently tailor the absorption and/or emission rates of
fluorophores. By contrast, modifying the spatial characteristics of their
radiation fields remains a challenge. Up to date, the designs providing
directionality to fluorescence emission have required compound, complex
geometries with overall dimensions comparable to the operating wavelength.
Here, we present the fabrication and characterization of DNA-templated
ultracompact optical antennas, with sub-wavelength sizes and capable of
directing single-molecule fluorescence into predefined directions. Using the
DNA origami methodology, two gold nanorods are assembled side-to-side with a
separation gap of 5 nm. We show that a single fluorescent molecule placed at
the tip of one of the nanorods drives the dimer antenna in anti-phase, leading
to unidirectional emission.
