13 research outputs found
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Mechanotunable Surface Lattice Resonances in the Visible Optical Range by Soft Lithography Templates and Directed Self-Assembly
We demonstrate a novel colloidal self-assembly approach toward obtaining mechanically tunable, cost-efficient, and low-loss plasmonic nanostructures that show pronounced optical anisotropy upon mechanical deformation. Soft lithography and template-assisted colloidal self-assembly are used to fabricate a stretchable periodic square lattice of gold nanoparticles on macroscopic areas. We stress the impact of particle size distribution on the resulting optical properties. To this end, lattices of narrowly distributed particles (ā¼2% standard deviation in diameter) are compared with those composed of polydisperse ones (ā¼14% standard deviation). The enhanced particle quality sharpens the collective surface lattice resonances by 40% to achieve a full width at half-maximum as low as 16 nm. This high optical quality approaches the theoretical limit for this system, as revealed by electromagnetic simulations. One hundred stretching cycles demonstrate a reversible transformation from a square to a rectangular lattice, accompanied by polarization-dependent optical properties. On the basis of these findings we envisage the potential applications as strain sensors and mechanically tunable filters. Ā© 2019 American Chemical Society
Septal Course of the Left Main Coronary Artery Originating From the Right Sinus of Valsalva
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Direct Observation of Plasmon Band Formation and Delocalization in Quasi-Infinite Nanoparticle Chains
Chains of metallic nanoparticles sustain strongly confined surface plasmons with relatively low dielectric losses. To exploit these properties in applications, such as waveguides, the fabrication of long chains of low disorder and a thorough understanding of the plasmon-mode properties, such as dispersion relations, are indispensable. Here, we use a wrinkled template for directed self-assembly to assemble chains of gold nanoparticles. With this up-scalable method, chain lengths from two particles (140 nm) to 20 particles (1500 nm) and beyond can be fabricated. Electron energy-loss spectroscopy supported by boundary element simulations, finite-difference time-domain, and a simplified dipole coupling model reveal the evolution of a band of plasmonic waveguide modes from degenerated single-particle modes in detail. In striking difference from plasmonic rod-like structures, the plasmon band is confined in excitation energy, which allows light manipulations below the diffraction limit. The non-degenerated surface plasmon modes show suppressed radiative losses for efficient energy propagation over a distance of 1500 nm. Ā© 2019 American Chemical Society
Magnetic and Electric Resonances in Particle-to-Film-Coupled Functional Nanostructures
We
investigate the plasmonic coupling of metallic nanoparticles with
continuous metal films by studying the effect of the particle-to-film
distance, cavity geometry, and particle size. To efficiently screen
these parameters, we fabricated a particle-to-film-coupled functional
nanostructure for which the particle size and distance vary. We use
gold-core/polyĀ(<i>N</i>-isopropylacrylamide)-shell nanoparticles
to self-assemble a monolayer of well-separated plasmonic particles,
introduce a gradient in the nanoparticle size by an overgrowth process,
and finally add a coupling metal film by evaporation. These assemblies
are characterized using surface probing and optical methods to show
localized magnetic and electric field enhancement. The results are
in agreement with finite-difference time-domain modeling methods
and calculations of the effective permeability and permittivity. Finally,
we provide a proof of concept for dynamic tuning of the cavity size
by swelling of the hydrogel layer. Thus, the tunability of the coupled
resonance and the macroscopic self-assembly technique provides access
to a cost-efficient library for magnetic and electric resonances
Silver-Overgrowth-Induced Changes in Intrinsic Optical Properties of Gold Nanorods: From Noninvasive Monitoring of Growth Kinetics to Tailoring Internal Mirror Charges
We investigate the effect of surfactant-mediated,
asymmetric silver overgrowth of gold nanorods on their intrinsic optical
properties. From concentration-dependent experiments, we established
a close correlation of the extinction in the UV/vis/NIR frequency
range and the morphological transition from gold nanorods to Au@Ag
cuboids. Based on this correlation, a generic methodology for <i>in situ</i> monitoring of the evolution of the cuboid morphology
was developed and applied in time-dependent experiments. We find that
growth rates are sensitive to the substitution of the surfactant headgroup
by comparison of benzylhexadecyldimethylammonium chloride (BDAC) with
hexadecyltrimethylĀammonium chloride (CTAC). The time-dependent
overgrowth in BDAC proceeds about 1 order of magnitude slower than
in CTAC, which allows for higher control during silver overgrowth.
Furthermore, silver overgrowth results in a qualitatively novel optical
feature: Upon excitation inside the overlap region of the interband
transition of gold and intraband of silver, the gold core acts as
a retarding element. The much higher damping of the gold core compared
to the silver shell in Au@Ag cuboids induces mirror charges at the
core/shell interface as shown by electromagnetic simulations. Full
control over the kinetic growth process consequently allows for precise
tailoring of the resonance wavelengths of both modes. Tailored and
asymmetric silver-overgrown gold nanorods are of particular interest
for large-scale fabrication of nanoparticles with intrinsic metamaterial
properties. These building blocks could furthermore find application
in optical sensor technology, light harvesting, and information technology
Xyloglucan from Tropaeolum majus Seeds Induces Cellular Differentiation of Human Keratinocytes by Inhibition of EGFR Phosphorylation and Decreased Activity of Transcription Factor CREB
Xyloglucan
XG (molecular weight 462 kDa, 1,4-/1,4,6-(<i>p</i>Glc) linked
backbone, side chains of 1-<i>p</i>Xyl, 1,2-<i>p</i>Xyl, 1-<i>p</i>-Gal) was isolated from the seeds
of Tropaeolum majus. XG (100 Ī¼g/mL)
induced terminal cellular differentiation of human keratinocytes,
as demonstrated by immunofluorescence staining and Western blot using
cytokeratin 10 and involucrin as marker proteins. Differentiation
was also induced by XG-derived oligosaccharides (degree of polymerization
7ā9). Quantitative real-time polymerase chain reaction (qPCR)
revealed the induction of gene expression of typical differentiation
markers (cytokeratin, filaggrin, involucrin, loricrin, transglutaminase)
in a time-dependent manner. Whole human genome microarray indicated
that most of upregulated genes were related to differentiation processes.
Microarray findings on selected genes were subsequently confirmed
by qPCR. For identification of the molecular target of xyloglucan
PAGE of keratinocyte membrane preparations was performed, followed
by blotting with fluorescein isothiocyanate-labeled XG. XG interacting
proteins were characterized by MS. Peptide fragments of epidermal
growth factor receptor (EGFR) and integrin Ī²4 were identified.
Subsequent phospho-kinase array indicated that phosphorylation of
EGFR and transcription factor cAMP response element-binding protein
(CREB) was decreased in the XG-treated cells. Thus, the XG-induced
differentiation of keratinocytes is proposed to be mediated by the
inhibition of the phosphorylation of EGFR, leading to a dimished CREB
activation, which is essential for the activation of cellular differentiation
Macroscopic Strain-Induced Transition from Quasi-infinite Gold Nanoparticle Chains to Defined Plasmonic Oligomers
We
investigate the formation of chains of few plasmonic nanoparticlesīøso-called
plasmonic oligomersīøby strain-induced fragmentation of linear
particle assemblies. Detailed investigations of the fragmentation
process are conducted by <i>in situ</i> atomic force microscopy
and UVāvisāNIR spectroscopy. Based on these experimental
results and mechanical simulations computed by the lattice spring
model, we propose a formation mechanism that explains the observed
decrease of chain polydispersity upon increasing strain and provides
experimental guidelines for tailoring chain length distribution. By
evaluation of the strain-dependent optical properties, we find a reversible,
nonlinear shift of the dominant plasmonic resonance. We could quantitatively
explain this feature based on simulations using generalized multiparticle
Mie theory (GMMT). Both optical and morphological characterization
show that the unstrained sample is dominated by chains with a length
above the so-called infinite chain limitīøabove which optical
properties show no dependency on chain lengthīøwhile during
deformation, the average chain length decrease below this limit and
chain length distribution becomes more narrow. Since the formation
mechanism results in a well-defined, parallel orientation of the oligomers
on macroscopic areas, the effect of finite chain length can be studied
even using conventional UVāvisāNIR spectroscopy. The
scalable fabrication of oriented, linear plasmonic oligomers opens
up additional opportunities for strain-dependent optical devices and
mechanoplasmonic sensing
Visualizing Single-Cell Secretion Dynamics with Single-Protein Sensitivity
Cellular secretion
of proteins into the extracellular environment
is an essential mediator of critical biological mechanisms, including
cell-to-cell communication, immunological response, targeted delivery,
and differentiation. Here, we report a novel methodology that allows
for the real-time detection and imaging of single unlabeled proteins
that are secreted from individual living cells. This is accomplished
via interferometric detection of scattered light (iSCAT) and is demonstrated
with Laz388 cells, an EpsteināBarr virus (EBV)-transformed
B cell line. We find that single Laz388 cells actively secrete IgG
antibodies at a rate of the order of 100 molecules per second. Intriguingly,
we also find that other proteins and particles spanning ca. 100 kDaā1
MDa are secreted from the Laz388 cells in tandem with IgG antibody
release, likely arising from EBV-related viral proteins. The technique
is general and, as we show, can also be applied to studying the lysate
of a single cell. Our results establish label-free iSCAT imaging as
a powerful tool for studying the real-time exchange between cells
and their immediate environment with single-protein sensitivity