16 research outputs found
Structural Color 3D Printing By Shrinking Photonic Crystals
The rings, spots and stripes found on some butterflies, Pachyrhynchus
weevils, and many chameleons are notable examples of natural organisms
employing photonic crystals to produce colorful patterns. Despite advances in
nanotechnology, we still lack the ability to print arbitrary colors and shapes
in all three dimensions at this microscopic length scale. Commercial nanoscale
3D printers based on two-photon polymerization are incapable of patterning
photonic crystal structures with the requisite ~300 nm lattice constant to
achieve photonic stopbands/ bandgaps in the visible spectrum and generate
colors. Here, we introduce a means to produce 3D-printed photonic crystals with
a 5x reduction in lattice constants (periodicity as small as 280 nm), achieving
sub-100-nm features with a full range of colors. The reliability of this
process enables us to engineer the bandstructures of woodpile photonic crystals
that match experiments, showing that observed colors can be attributed to
either slow light modes or stopbands. With these lattice structures as 3D color
volumetric elements (voxels), we printed 3D microscopic scale objects,
including the first multi-color microscopic model of the Eiffel Tower measuring
only 39-microns tall with a color pixel size of 1.45 microns. The technology to
print 3D structures in color at the microscopic scale promises the direct
patterning and integration of spectrally selective devices, such as photonic
crystal-based color filters, onto free-form optical elements and curved
surfaces
Silicon Nanoantenna Mix Arrays for a Trifecta of Quantum Emitter Enhancements
Dielectric nanostructures have demonstrated optical antenna effects due to
Mie resonances. Preliminary investigations on dielectric nanoantennas have been
carried out for a trifecta of enhancements, i.e., simultaneous enhancements in
absorption, emission directionality and radiative decay rates of quantum
emitters. However, these investigations are limited by fragile substrates or
low Purcell factor, which is extremely important for exciting quantum emitters
electrically. In this paper, we present a Si mix antenna array to achieve the
trifecta enhancement of ~1200 fold with a Purcell factor of ~47. The antenna
design incorporates ~10 nm gaps within which fluorescent molecules strongly
absorb the pump laser energy through a resonant mode. In the emission process,
the antenna array increases the radiative decay rates of the fluorescence
molecules via Purcell effect and provides directional emission through a
separate mode. This work could lead to novel CMOS compatible platforms for
enhancing fluorescence for biological and chemical applications.Comment: 20 pages, 4 figure
Nuclear Magnetic Resonance Observation of α‑Synuclein Membrane Interaction by Monitoring the Acetylation Reactivity of Its Lysine Side Chains
The
interaction between α-synuclein (αS) protein and
lipid membranes is key to its role in synaptic vesicle homeostasis
and plays a role in initiating fibril formation, which is implicated
in Parkinson’s disease. The natural state of αS inside
the cell is generally believed to be intrinsically disordered, but
chemical cross-linking experiments provided evidence of a tetrameric
arrangement, which was reported to be rich in α-helical secondary
structure based on circular dichroism (CD). Cross-linking relies on
chemical modification of the protein’s Lys C<sup>ε</sup> amino groups, commonly by glutaraldehyde, or by disuccinimidyl glutarate
(DSG), with the latter agent preferred for cellular assays. We used
ultra-high-resolution homonuclear decoupled nuclear magnetic resonance
experiments to probe the reactivity of the 15 αS Lys residues
toward <i>N</i>-succinimidyl acetate, effectively half the
DSG cross-linker, which results in acetylation of Lys. The intensities
of both side chain and backbone amide signals of acetylated Lys residues
provide direct information about the reactivity, showing a difference
of a factor of 2.5 between the most reactive (K6) and the least reactive
(K102) residue. The presence of phospholipid vesicles decreases reactivity
of most Lys residues by up to an order of magnitude at high lipid:protein
stoichiometries (500:1), but only weakly at low ratios. The decrease
in Lys reactivity is found to be impacted by lipid composition, even
for vesicles that yield similar αS CD signatures. Our data provide
new insight into the αS–bilayer interaction, including
the pivotal state in which the available lipid surface is limited.
Protection of Lys C<sup>ε</sup> amino groups by αS–bilayer
interaction will strongly impact quantitative interpretation of DSG
cross-linking experiments
Monomeric Aβ<sup>1–40</sup> and Aβ<sup>1–42</sup> Peptides in Solution Adopt Very Similar Ramachandran Map Distributions That Closely Resemble Random Coil
The
pathogenesis of Alzheimer’s disease is characterized
by the aggregation and fibrillation of amyloid peptides Aβ<sup>1–40</sup> and Aβ<sup>1–42</sup> into amyloid
plaques. Despite strong potential therapeutic interest, the structural
pathways associated with the conversion of monomeric Aβ peptides
into oligomeric species remain largely unknown. In particular, the
higher aggregation propensity and associated toxicity of Aβ<sup>1–42</sup> compared to that of Aβ<sup>1–40</sup> are poorly understood. To explore in detail the structural propensity
of the monomeric Aβ<sup>1–40</sup> and Aβ<sup>1–42</sup> peptides in solution, we recorded a large set of nuclear magnetic
resonance (NMR) parameters, including chemical shifts, nuclear Overhauser
effects (NOEs), and <i>J</i> couplings. Systematic comparisons
show that at neutral pH the Aβ<sup>1–40</sup> and Aβ<sup>1–42</sup> peptides populate almost indistinguishable coil-like
conformations. Nuclear Overhauser effect spectra collected at very
high resolution remove assignment ambiguities and show no long-range
NOE contacts. Six sets of backbone <i>J</i> couplings (<sup>3</sup><i>J</i><sub>HNHα</sub>, <sup>3</sup><i>J</i><sub>C′C′</sub>, <sup>3</sup><i>J</i><sub>C′Hα</sub>, <sup>1</sup><i>J</i><sub>HαCα</sub>, <sup>2</sup><i>J</i><sub>NCα</sub>, and <sup>1</sup><i>J</i><sub>NCα</sub>) recorded
for Aβ<sup>1–40</sup> were used as input for the recently
developed MERA Ramachandran map analysis, yielding residue-specific
backbone ϕ/ψ torsion angle distributions that closely
resemble random coil distributions, the absence of a significantly
elevated propensity for β-conformations in the C-terminal region
of the peptide, and a small but distinct propensity for α<sub>L</sub> at K28. Our results suggest that the self-association of
Aβ peptides into toxic oligomers is not driven by elevated propensities
of the monomeric species to adopt β-strand-like conformations.
Instead, the accelerated disappearance of Aβ NMR signals in
D<sub>2</sub>O over H<sub>2</sub>O, particularly pronounced for Aβ<sup>1–42</sup>, suggests that intermolecular interactions between
the hydrophobic regions of the peptide dominate the aggregation process
Low-Threshold near-Infrared GaAs–AlGaAs Core–Shell Nanowire Plasmon Laser
We demonstrate plasmonic lasing from
metal–organic chemical
vapor deposition (MOCVD)-grown GaAs–AlGaAs core–shell
nanowires (NWs) with subdiffraction limit diameters of ∼150
nm placed directly on a silver thin film. The absence of a low-index
dielectric spacer layer between the NW and the metal layer allows
for surface plasmon polariton (SPP) lasing using a nonhybridized plasmonic
mode. Unlike previously reported plasmonic NW lasers using the fundamental
SPP mode, we demonstrate for the first time plasmonic NW lasing under
pulsed optical excitation by using the higher order SPP mode. The
higher order mode allows us to alleviate the high losses associated
with the fundamental plasmonic mode. We observed lasing at temperatures
up to 125 K. Our demonstration of a plasmonic laser based on GaAs
emitting in the near-infrared region will be useful for the on-chip
integration of nanophotonic and electronic devices and the development
of GaAs-based plasmonic devices
Printing Beyond sRGB Color Gamut by Mimicking Silicon Nanostructures in Free-Space
Localized optical resonances in metallic
nanostructures have been
increasingly used in color printing, demonstrating unprecedented resolution
but limited in color gamut. Here, we introduce a new nanostructure
design, which broadens the gamut while retaining print resolution.
Instead of metals, silicon nanostructures that exhibit localized magnetic
and electric dipole resonances were fabricated on a silicon substrate
coated with a Si<sub>3</sub>N<sub>4</sub> index matching layer. Index
matching allows a suppression of substrate effects, thus enabling
Kerker’s conditions to be met, that is, sharpened transitions
in the reflectance spectra leading to saturated colors. This nanostructure
design achieves a color gamut superior to sRGB, and is compatible
with CMOS processes. The presented design could enable compact high-resolution
color displays and filters, and the use of a Si<sub>3</sub>N<sub>4</sub> antireflection coating can be readily extended to designs with nanostructures
fabricated using other high-index materials
Miniaturizing Color-Sensitive Photodetectors via Hybrid Nanoantennas towards Sub-micron Dimensions
Digital camera sensors utilize color filters on photodiodes to achieve color
selectivity. As color filters and photosensitive silicon layers are separate
elements, these sensors suffer from optical cross-talk, which sets limits to
the minimum pixel size. In this paper, we report hybrid silicon-aluminum
nanostructures in the extreme limit of zero distance between color filters and
sensors. This design could essentially achieve sub micron pixel dimensions and
minimize the optical cross-talk originated from tilt illuminations. The
designed hybrid silicon-aluminum nanostructure has dual functionalities.
Crucially, it supports a hybrid Mie-plasmon resonance of magnetic dipole to
achieve the color-selective light absorption, generating electron hole pairs.
Simultaneously, the silicon-aluminum interface forms a Schottky barrier for
charge separation and photodetection. This design could potentially replace the
traditional dye based filters for camera sensors at ultra-high pixel densities
with advanced functionalities in sensing polarization and directionality, as
well as UV selectivity via interband plasmons of silicon.Comment: 32 pages, 4 Figures (main text), 7 Figures (supplementary