10 research outputs found
High-Yield Synthesis of Gold Nanorods with Longitudinal SPR Peak Greater than 1200 nm Using Hydroquinone as a Reducing Agent
While gold nanorods have been extensively studied and
used in many
biological, plasmonics, and sensing applications, their conventional
seed-mediated synthesis still presents a number of limitations. Its
high sensitivity to the concentration of the reducing agent (ascorbic
acid) leads to problems with reliability as well as extremely poor
yield of ionic-to-metallic gold conversion, which is only ∼15%.
In addition, the synthesis of high purity nanorods with longitudinal
surface plasmon resonance (LSPR) peak higher than 1000 nm is particularly
difficult utilizing this technique. This report demonstrates the use
of hydroquinone for the synthesis of gold nanorods which addresses
these two major limitations. By replacing ascorbic acid with a large
excess of hydroquinone, rods with LSPR up to 1230 nm can be synthesized
with a high degree of purity, reliability, and near quantitative conversion
of gold ions to metallic gold. The growth of the rods is tracked by
TEM utilizing a thiolation reaction to halt their growth. Finally,
the effect of changing various parameters including hydroquinone,
seed, gold, and silver concentration is examined, demonstrating the
tunability of the procedure over the broad range of attainable LSRPs
from 770 to 1230 nm
Starfruit-Shaped Gold Nanorods and Nanowires: Synthesis and SERS Characterization
Recently, branched and star-shaped gold nanoparticles
have received
significant attention for their unique optical and electronic properties,
but most examples of such nanoparticles have a zero-dimensional shape
with varying numbers of branches coming from a quasi-spherical core.
This report details the first examples of higher-order penta-branched
gold particles including rod-, wire-, and platelike particles which
contain a uniquely periodic starfruitlike morphology. These nanoparticles
are synthesized in the presence of silver ions by a seed-mediated
approach based on utilizing highly purified pentahedrally twinned
gold nanorods and nanowires as seed particles. The extent of the growth
can be varied, leading to shifts in the plasmon resonances of the
particles. In addition, the application of the starfruit rods for
surface-enhanced Raman spectroscopy (SERS) is demonstrated
Accelerating Gold Nanorod Synthesis with Nanomolar Concentrations of Poly(vinylpyrrolidone)
A novel
modification for the seedless synthesis of gold nanorods
(AuNRs) has been developed. Nanomolar concentrations of 10 kDa poly(vinylpyrrolidone)
(PVP) can be introduced to a growth solution containing 25, 50, or
100 mM cetyltrimethylammonium bromide (CTAB) to significantly reduce
the dimensions of AuNRs. We found that PVP accelerates the growth
rate of AuNRs by more than two times that of nanorods grown in 50
and 100 mM CTAB solutions. Additionally, there is a time-dependent
effect of adding PVP to the nanorod growth solution that can be utilized
to tune their aspect ratio. Because the concentration of PVP is far
below the concentration of HAuCl<sub>4</sub> in the reaction mixture,
PVP primarily functions not as a reducing agent, but as a capping
or templating ligand to stabilize the growing nanorods. Our reproducible
protocol enables the synthesis of AuNRs in high yield with tunable
sizes: 45 × 6.7, 28 × 5.5, and 12 × 4.5 nm for 100,
50, and 25 mM CTAB, respectively. We estimated the number of PVP chains
per nanorod in growth solutions to be around 30, which suggests that
the effect on the aspect ratio is caused by a direct interaction between
the AuNR surface and the PVP
Why Single-Beam Optical Tweezers Trap Gold Nanowires in Three Dimensions
Understanding whether noble-metal nanostructures can be trapped optically and under what conditions will enable a range of applications that exploit their plasmonic properties. However, there are several nontrivial issues that first need to be resolved. A major one is that metal particles experience strong radiation pressure in optical beams, while stable optical trapping requires an attractive force greater than this radiation pressure. Therefore, it has generally been considered impossible to obtain sufficiently strong gradient forces using single-beam optical tweezers to trap relatively large metal nanostructures in three dimensions. Here we demonstrate that a single, tightly focused laser beam with a wavelength of 800 nm can achieve three-dimensional optical trapping of individual gold (Au) nanowires with lengths over 2 μm. Nanowires can be trapped by the beam at one of their ends, in which case they undergo significant angular fluctuations due to Brownian motion of the untrapped end. They can also be trapped close to their midpoints, in which case they are oriented approximately perpendicular to the light polarization direction. The behavior is markedly different from that of Ag nanowires with similar length and diameter, which cannot be trapped in three dimensions by a single focused Gaussian beam. Our results, including electrodynamics simulations that help to explain our experimental findings, suggest that the conventional wisdom, which holds that larger metal particles cannot be trapped, needs to be replaced with an understanding based on the details of plasmon resonances in the particles
Collection des papiers et des livres imprimés annotés de Silvestre de Sacy, comprenant 62 volumes de toute dimension, reliés ou cartonnés, qui formaient autrefois la « Collection de Sacy ». Grammaire arabe de Silvestre de Sacy. Arabe 5222
Numérisation effectuée à partir d'un document de substitution
Why Single-Beam Optical Tweezers Trap Gold Nanowires in Three Dimensions
Understanding whether noble-metal nanostructures can be trapped optically and under what conditions will enable a range of applications that exploit their plasmonic properties. However, there are several nontrivial issues that first need to be resolved. A major one is that metal particles experience strong radiation pressure in optical beams, while stable optical trapping requires an attractive force greater than this radiation pressure. Therefore, it has generally been considered impossible to obtain sufficiently strong gradient forces using single-beam optical tweezers to trap relatively large metal nanostructures in three dimensions. Here we demonstrate that a single, tightly focused laser beam with a wavelength of 800 nm can achieve three-dimensional optical trapping of individual gold (Au) nanowires with lengths over 2 μm. Nanowires can be trapped by the beam at one of their ends, in which case they undergo significant angular fluctuations due to Brownian motion of the untrapped end. They can also be trapped close to their midpoints, in which case they are oriented approximately perpendicular to the light polarization direction. The behavior is markedly different from that of Ag nanowires with similar length and diameter, which cannot be trapped in three dimensions by a single focused Gaussian beam. Our results, including electrodynamics simulations that help to explain our experimental findings, suggest that the conventional wisdom, which holds that larger metal particles cannot be trapped, needs to be replaced with an understanding based on the details of plasmon resonances in the particles
Influence of Cross Sectional Geometry on Surface Plasmon Polariton Propagation in Gold Nanowires
We investigated the effects of cross sectional geometry on surface plasmon polariton propagation in gold nanowires (NWs) using bleach-imaged plasmon propagation and electromagnetic simulations. Chemically synthesized NWs have pentagonally twinned crystal structures, but recent advances in synthesis have made it possible to amplify this pentagonal shape to yield NWs with a five-pointed-star cross section and sharp end tips. We found experimentally that NWs with a five-pointed-star cross section, referred to as SNWs, had a shorter propagation length for surface plasmon polaritons at 785 nm, but a higher effective incoupling efficiency compared to smooth NWs with a pentagonal cross section, labeled as PNWs. Electromagnetic simulations revealed that the electric fields were localized at the sharp ridges of the SNWs, leading to higher absorptive losses and hence shorter propagation lengths compared to PNWs. On the other hand, scattering losses were found to be relatively uncorrelated with cross sectional geometry, but were strongly dependent on the plasmon mode excited. Our results provide insight into the shape-dependent waveguiding properties of chemically synthesized metal NWs and the mode-dependent loss mechanisms that govern surface plasmon polariton propagation
Shape-Dependent Oriented Trapping and Scaffolding of Plasmonic Nanoparticles by Topological Defects for Self-Assembly of Colloidal Dimers in Liquid Crystals
We demonstrate scaffolding of plasmonic nanoparticles
by topological
defects induced by colloidal microspheres to match their surface boundary
conditions with a uniform far-field alignment in a liquid crystal
host. Displacing energetically costly liquid crystal regions of reduced
order, anisotropic nanoparticles with concave or convex shapes not
only stably localize in defects but also self-orient with respect
to the microsphere surface. Using laser tweezers, we manipulate the
ensuing nanoparticle-microsphere colloidal dimers, probing the strength
of elastic binding and demonstrating self-assembly of hierarchical
colloidal superstructures such as chains and arrays
Shape-Dependent Oriented Trapping and Scaffolding of Plasmonic Nanoparticles by Topological Defects for Self-Assembly of Colloidal Dimers in Liquid Crystals
We demonstrate scaffolding of plasmonic nanoparticles
by topological
defects induced by colloidal microspheres to match their surface boundary
conditions with a uniform far-field alignment in a liquid crystal
host. Displacing energetically costly liquid crystal regions of reduced
order, anisotropic nanoparticles with concave or convex shapes not
only stably localize in defects but also self-orient with respect
to the microsphere surface. Using laser tweezers, we manipulate the
ensuing nanoparticle-microsphere colloidal dimers, probing the strength
of elastic binding and demonstrating self-assembly of hierarchical
colloidal superstructures such as chains and arrays
Optimization of Spectral and Spatial Conditions to Improve Super-Resolution Imaging of Plasmonic Nanoparticles
Interactions
between fluorophores and plasmonic nanoparticles modify
the fluorescence intensity, shape, and position of the observed emission
pattern, thus inhibiting efforts to optically super-resolve plasmonic
nanoparticles. Herein, we investigate the accuracy of localizing dye
fluorescence as a function of the spectral and spatial separations
between fluorophores (Alexa 647) and gold nanorods (NRs). The distance
at which Alexa 647 interacts with NRs is varied by layer-by-layer
polyelectrolyte deposition while the spectral separation is tuned
by using NRs with varying localized surface plasmon resonance (LSPR)
maxima. For resonantly coupled Alexa 647 and NRs, emission to the
far field through the NR plasmon is highly prominent, resulting in
underestimation of NR sizes. However, we demonstrate that it is possible
to improve the accuracy of the emission localization when both the
spectral and spatial separations between Alexa 647 and the LSPR are
optimized