6 research outputs found
Nanoparticle-Mediated, Light-Induced Phase Separations
Nanoparticles
that both absorb and scatter light, when dispersed in a liquid, absorb
optical energy and heat a reduced fluid volume due to the combination
of multiple scattering and optical absorption. This can induce a localized
liquid–vapor phase change within the reduced volume without
the requirement of heating the entire fluid. For binary liquid mixtures,
this process results in vaporization of the more volatile component
of the mixture. When subsequently condensed, these two steps of vaporization
and condensation constitute a distillation process mediated by nanoparticles
and driven by optical illumination. Because it does not require the
heating of a large volume of fluid, this process requires substantially
less energy than traditional distillation using thermal sources. We
investigated nanoparticle-mediated, light-induced distillation of
ethanol-H<sub>2</sub>O and 1-propanol-H<sub>2</sub>O mixtures, using
Au–SiO<sub>2</sub> nanoshells as the absorber-scatterer nanoparticle
and nanoparticle-resonant laser irradiation to drive the process.
For ethanol-H<sub>2</sub>O mixtures, the mole fraction of ethanol
obtained in the light-induced process is substantially higher than
that obtained by conventional thermal distillation, essentially removing
the ethanol-H<sub>2</sub>O azeotrope that limits conventional distillation.
In contrast, for 1-propanol-H<sub>2</sub>O mixtures the distillate
properties resulting from light-induced distillation were very similar
to those obtained by thermal distillation. In the 1-propanol-H<sub>2</sub>O system, a nanoparticle-mediated, light-induced liquid–liquid
phase separation was also observed
Fluorescence Enhancement of Molecules Inside a Gold Nanomatryoshka
Metallic
nanoparticles exhibiting plasmonic Fano resonances can
provide large enhancements of their internal electric near field.
Here we show that nanomatryoshkas, nanoparticles consisting of an
Au core, an interstitial nanoscale SiO<sub>2</sub> layer, and an Au
shell layer, can selectively provide either a strong enhancement or
a quenching of the spontaneous emission of fluorophores dispersed
within their internal dielectric layer. This behavior can be understood
by taking into account the near-field enhancement induced by the Fano
resonance of the nanomatryoshka, which is responsible for enhanced
absorption of the fluorophores incorporated into the nanocomplex.
The combination of compact size and enhanced light emission with internal
encapsulation of the fluorophores for increased biocompatibility suggests
outstanding potential for this type of nanoparticle complex in biomedical
applications
Hot-Electron-Induced Dissociation of H<sub>2</sub> on Gold Nanoparticles Supported on SiO<sub>2</sub>
Hot-electron-induced photodissociation
of H<sub>2</sub> was demonstrated
on small Au nanoparticles (AuNPs) supported on SiO<sub>2</sub>. The
rate of dissociation of H<sub>2</sub> was found to be almost 2 orders
of magnitude higher than that observed on equivalently prepared AuNPs
on TiO<sub>2</sub>. The rate of H<sub>2</sub> dissociation was found
to be linearly dependent on illumination intensity with a wavelength
dependence resembling the absorption spectrum of the plasmon of the
AuNPs. This result provides strong additional support for the hot-electron-induced
mechanism for H<sub>2</sub> dissociation in this photocatalytic system
The Surprising <i>in Vivo</i> Instability of Near-IR-Absorbing Hollow Au–Ag Nanoshells
Photothermal ablation based on resonant illumination of near-infrared-absorbing noble metal nanoparticles that have accumulated in tumors is a highly promising cancer therapy, currently in multiple clinical trials. A crucial aspect of this therapy is the nanoparticle size for optimal tumor uptake. A class of nanoparticles known as hollow Au (or Au–Ag) nanoshells (HGNS) is appealing because near-IR resonances are achievable in this system with diameters less than 100 nm. However, in this study, we report a surprising finding that <i>in vivo</i> HGNS are unstable, fragmenting with the Au and the remnants of the sacrificial Ag core accumulating differently in various organs. We synthesized 43, 62, and 82 nm diameter HGNS through a galvanic replacement reaction, with nanoparticles of all sizes showing virtually identical NIR resonances at ∼800 nm. A theoretical model indicated that alloying, residual Ag in the nanoparticle core, nanoparticle porosity, and surface defects all contribute to the presence of the plasmon resonance at the observed wavelength, with the major contributing factor being the residual Ag. While PEG functionalization resulted in stable nanoparticles under laser irradiation in solution, an anomalous, strongly element-specific biodistribution observed in tumor-bearing mice suggests that an avid fragmentation of all three sizes of nanoparticles occurred <i>in vivo</i>. Stability studies across a wide range of pH environments and in serum confirmed HGNS fragmentation. These results show that NIR resonant HGNS contain residual Ag, which does not stay contained within the HGNS <i>in vivo</i>. This demonstrates the importance of tracking both materials of a galvanic replacement nanoparticle in biodistribution studies and of performing thorough nanoparticle stability studies prior to any intended <i>in vivo</i> trial application
Toward Surface Plasmon-Enhanced Optical Parametric Amplification (SPOPA) with Engineered Nanoparticles: A Nanoscale Tunable Infrared Source
Active
optical processes such as amplification and stimulated emission promise
to play just as important a role in nanoscale optics as they have
in mainstream modern optics. The ability of metallic nanostructures
to enhance optical nonlinearities at the nanoscale has been shown
for a number of nonlinear and active processes; however, one important
process yet to be seen is optical parametric amplification. Here,
we report the demonstration of surface plasmon-enhanced difference
frequency generation by integration of a nonlinear optical medium,
BaTiO<sub>3</sub>, in nanocrystalline form within a plasmonic nanocavity.
These nanoengineered composite structures support resonances at pump,
signal, and idler frequencies, providing large enhancements of the
confined fields and efficient coupling of the wavelength-converted
idler radiation to the far-field. This nanocomplex works as a nanoscale
tunable infrared light source and paves the way for the design and
fabrication of a surface plasmon-enhanced optical parametric amplifier
Impurity-Induced Plasmon Damping in Individual Cobalt-Doped Hollow Au Nanoshells
The
optical properties of plasmonic nanoparticles in the size range
corresponding to the electrostatic, or dipole, limit have the potential
to reveal effects otherwise masked by phase retardation. Here we examine
the optical properties of individual, sub-50 nm hollow Au nanoshells
(Co-HGNS), where Co is the initial sacrificial core nanoparticle,
using single particle total internal reflection scattering (TIRS)
spectroscopy. The residual Co present in the metallic shell induces
a substantial broadening of the homogeneous plasmon resonance line
width of the Co-HGNS, where the full width at half-maximum (fwhm)
broadens proportionately with increasing Co content. This doping-induced
line broadening provides a strategy for controlling plasmon line width
independent of nanoparticle size, and has the potential to substantially
modify the relative decay channels for localized nanoparticle surface
plasmons