Three-Dimensional Reduced-Symmetry
of Colloidal Plasmonic
Nanoparticles
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Abstract
Owing to their novel optical properties, three-dimensional
plasmonic
nanostructures with reduced symmetry such as a nanocrescent and a
nanocup have attracted considerable current interest in biophotonic
imaging and sensing. However, their practical applications have been
still limited since the colloidal synthesis of such structures that
allows, in principle, for in vivo application and large-scale production
has not been explored yet. To date, these structures have been fabricated
only on two-dimensional substrates using micro/nanofabrication techniques.
Here we demonstrate an innovative way of breaking symmetry of colloidal
plasmonic nanoparticles. Our strategy exploits the direct overgrowth
of Au on a hybrid colloidal dimer consisting of Au and polystyrene
(PS) nanoparticles without the self-nucleation of Au in an aqueous
solution. Upon the overgrowth reaction, the steric crowding of PS
leads to morphological evolution of the Au part in the dimer ranging
from half-shell, nanocrescent to nanoshell associated with the appearance
of the second plasmon absorption band in near IR. Surface-enhanced
Raman scattering signal is obtained directly from the symmetry-broken
nanoparticles solution as an example showing the viability of the
present approach. We believe our concept represents an important step
toward a wide range of biophotonic applications for optical nanoplasmonics
such as targeting, sensing/imaging, gene delivery, and optical gene
regulations