  The strong interaction of light with metallic nanoparticles enables field
confinement well below the diffraction limit. Plasmonic waveguides consisting
of metal nanoparticle chains could be used for the propagation of energy or
information on the nanoscale, but high losses have thus far impeded practical
applications. Here we demonstrate that efficient waveguiding is possible
through gold nanoparticle chains despite the high dissipative losses of gold. A
DNA origami directed self-assembly of monocrystalline, spherical nanoparticles
allows the interparticle spacing to be decreased to 2 nm or below, which gives
rise to lower-energy plasmon resonance modes. Our simulations imply that these
lower energy modes allow efficient waveguiding but collapse if interparticle
gap sizes are increased. Individual waveguides are characterized with
nanometer-resolution by electron energy loss spectroscopy, and directed
propagation of energy towards a fluorescent nanodiamond and nanoscale energy
conversion is shown by cathodoluminescence imaging spectroscopy on a
single-device level. With this approach, micrometer-long propagation lengths
might be achieved, enabling applications in information technology, sensing and
quantum optics.
