21 research outputs found
Existence of Multiple Phases of Water at Nanotube Interfaces
Water,
because of its anomalous properties, can exhibit complex
behavior under strong confinement. At room temperature and pressure,
water is assumed to exist in a single phase as a liquid under confinement
(e.g., in a carbon nanotube). In this study, using extensive molecular
dynamics simulations, we show the existence of multiple phases of
water when water meets a nanotube surface under atmospheric conditions
(<i>T</i> = 300 K, <i>P</i> = 1 atm). Vapor, high-density
ice, and liquid water phases coexist in the region within âź1
nm from the surface. Structure factor, entropy, pressure, viscosity,
and rotational diffusion of water layers near the surface reveal substantial
phase anomalies induced by confinement. We show the presence of a
new high-density solid-state ice layer (Ď = 3.9 g/cm<sup>3</sup>) with rhombic structure coexisting adjacent to vapor and liquid
water. The existence of multiple phases of water near an interface
can explain, for example, the slip phenomena, self-filling behavior
of a carbon nanotube, and fast transport of water
Mechanistic Insights into Hydration of Solid Oxides
Some of the solid
oxide materials, used in solid oxide fuel and
electrolysis cells, are known to conduct protons once they are hydrated.
However, the mechanisms by which solid oxide materials get hydrated
is not clear. By performing detailed density functional theory calculations,
we investigate hydration of two typical solid oxides with a single-crystal
structureî¸a proton-conducting yttrium-doped strontium zirconate
(SZY) and an oxide ion-conducting yttria-stabilized zirconia (YSZ).
We suggest a four-step process to understand the hydration of solid
oxidesî¸water adsorption on the surface, proton migration from
the surface to bulk, proton migration in the bulk, and oxide ion vacancy
migration in the bulk. The hydroxide ion migration with a lower energy
barrier, compared to the proton hopping mechanism, is proposed for
the conduction of proton between the surface and subsurface of the
perovskite oxide. Our analysis provides mechanistic insights into
the hydration of single-crystal SZY and nonhydration of single-crystal
YSZ. The study presented here not only explains the hydration of materials
but also provides the importance of structural rearrangement when
a proton is incorporated into the bulk of the solid oxide material
DNA Base Detection Using a Single-Layer MoS<sub>2</sub>
Nanopore-based DNA sequencing has led to fast and high-resolution recognition and detection of DNA bases. Solid-state and biological nanopores have low signal-to-noise ratio (SNR) (< 10) and are generally too thick (> 5 nm) to be able to read at single-base resolution. A nanopore in graphene, a 2-D material with sub-nanometer thickness, has a SNR of âź3 under DNA ionic current. In this report, using atomistic and quantum simulations, we find that a single-layer MoS<sub>2</sub> is an extraordinary material (with a SNR > 15) for DNA sequencing by two competing technologies (<i>i.e.</i>, nanopore and nanochannel). A MoS<sub>2</sub> nanopore shows four distinct ionic current signals for single-nucleobase detection with low noise. In addition, a single-layer MoS<sub>2</sub> shows a characteristic change/response in the total density of states for each base. The band gap of MoS<sub>2</sub> is significantly changed compared to other nanomaterials (<i>e.g.</i>, graphene, h-BN, and silicon nanowire) when bases are placed on top of the pristine MoS<sub>2</sub> and armchair MoS<sub>2</sub> nanoribbon, thus making MoS<sub>2</sub> a promising material for base detection <i>via</i> transverse current tunneling measurement. MoS<sub>2</sub> nanopore benefits from a craftable pore architecture (combination of Mo and S atoms at the edge) which can be engineered to obtain the optimum sequencing signals
Antibody Subclass Detection Using Graphene Nanopores
Solid-state nanopores
are promising for label-free protein detection.
The large thickness, ranging from several tens of nanometers to micrometers
and larger, of solid-state nanopores prohibits atomic-scale scanning
or interrogation of proteins. Here, a single-atom thick graphene nanopore
is shown to be highly capable of sensing and discriminating between
different subclasses of IgG antibodies despite their minor and subtle
variation in atomic structure. Extensive molecular dynamics (MD) simulations,
rigorous statistical analysis with a total aggregate simulation time
of 2.7 Îźs, supervised machine learning (ML), and classification
techniques are employed to distinguish IgG2 from IgG3. The water flux
and ionic current during IgG translocation reveal distinct clusters
for IgG subclasses facilitating an additional recognition mechanism.
In addition, the histogram of ionic current for each segment of IgG
can provide high-resolution spatial detection. Our results show that
nanoporous graphene can be used to detect and distinguish antibody
subclasses with good accuracy
Legislative Documents
Also, variously referred to as: House bills; House documents; House legislative documents; legislative documents; General Court documents
Quantitative Chemical Imaging of Nonplanar Microfluidics
Confocal
and multiphoton optical imaging techniques have been powerful
tools for evaluating the performance of and monitoring experiments
within microfluidic devices, but this application suffers from two
pitfalls. The first is that obtaining the necessary imaging contrast
often requires the introduction of an optical label which can potentially
change the behavior of the system. The emerging analytical technique
stimulated Raman scattering (SRS) microscopy promises a solution,
as it can rapidly measure 3D concentration maps based on vibrational
spectra, label-free; however, when using any optical imaging technique,
including SRS, there is an additional problem of optical aberration
due to refractive index mismatch between the fluid and the device
walls. New approaches such as 3D printing are extending the range
of materials from which microfluidic devices can be fabricated; thus,
the problem of aberration can be obviated simply by selecting a chip
material that matches the refractive index of the desired fluid. To
demonstrate complete chemical imaging of a geometrically complex device,
we first use sacrificial molding of a freeform 3D printed template
to create a round-channel, 3D helical micromixer in a low-refractive-index
polymer. We then use SRS to image the mixing of aqueous glucose and
salt solutions throughout the entire helix volume. This fabrication
approach enables truly nonperturbative 3D chemical imaging with low
aberration, and the concentration profiles measured within the device
agree closely with numerical simulations
Solution-Synthesized Chevron Graphene Nanoribbons Exfoliated onto H:Si(100)
There
has been tremendous progress in designing and synthesizing graphene
nanoribbons (GNRs). The ability to control the width, edge structure,
and dopant level with atomic precision has created a large class of
accessible electronic landscapes for use in logic applications. One
of the major limitations preventing the realization of GNR devices
is the difficulty of transferring GNRs onto nonmetallic substrates.
In this work, we developed a new approach for clean deposition of
solution-synthesized atomically precise chevron GNRs onto H:Si(100)
under ultrahigh vacuum. A clean transfer allowed ultrahigh-vacuum
scanning tunneling microscopy (STM) to provide high-resolution imaging
and spectroscopy and reveal details of the electronic structure of
chevron nanoribbons that have not been previously reported. We also
demonstrate STM nanomanipulation of GNRs, characterization of multilayer
GNR cross-junctions, and STM nanolithography for local depassivation
of H:Si(100), which allowed us to probe GNRâSi interactions
and revealed a semiconducting-to-metallic transition. The results
of STM measurements were shown to be in good agreement with first-principles
computational modeling
X-ray scattering analysis of lipid films.
Reconfiguration of SLM films as a function of compression. A) 2D GIWAXS diffraction patterns of DPPC films before and after compression by 10%. The brackets denote a family of planes hkl. The inset are schematics of the changes in layer alignment corresponding with changes in correlation length Ξ induced in the DPPC SLM by compression. B) Linear integration of the GIWAXS data. C) Schematic of GIWAXS peak shift and widening related to the effect of compression at the hydrocarbon chain length scale. D) Schematic of DPPC hexagonal phase from GIWAXS data which displays changes in lattice spacing a and increased disorder of lipid tails.</p
Effect of compression on lipid tilt.
A) Color coded representation of the simulated DPPC systems at three compressive strains. The color represents lipid orientation (tilt) angle with respect to z-axis. The box represents the simulation unit cell. B) The tilt angle distributions of the Lβ phase DPPC lipids. The inset shows the average order parameter values.</p