7 research outputs found
Boosting DNA Recognition Sensitivity of Graphene Nanogaps through Nitrogen Edge Functionalization
One
of the challenges for next generation DNA sequencing is to
have a robust, stable, and reproducible nanodevice. In this work,
we propose how to improve the sensing of DNA nucleobase using functionalized
graphene nanogap as a solid state device. Two types of edge functionalization,
namely, either hydrogen or nitrogen, were considered. We showed that,
independent of species involved in the edge passivation, the highest-to-lowest
order of the nucleobase transmissions is not altered, but the intensity
is affected by several orders of magnitude. Our results show that
nitrogen edge tends to p-dope graphene, and most importantly, it contributes
with resonance states close to the Fermi level, which can be associated
with the increased conductance. Finally, the translocation process
of nucleobases passing through the nanogap was also investigated by
varying their position from a certain height (from +3 to −3
Å) with respect to the graphene sheet to show that nitrogen-terminated
sheets have enhanced sensitivity, as moving the nucleobase by approximately
1 Å reduces the conductance by up to 3 orders of magnitude
Salt-Gradient Approach for Regulating Capture-to-Translocation Dynamics of DNA with Nanochannel Sensors
Understanding
the physical mechanisms that govern the ion and fluidic
transport in salt-concentration-based nanochannel/nanopore systems
is essential for the potential applications in bioanalysis. One central
challenge is to interpret the observed four-stage change from osmosis
to the reverse one with increasing salt gradient. Here we provide
a unified model that outlines the intriguing role of two competing
factors, the exclusion- and diffusion-induced electrical potentials.
We demonstrate theoretically a direction control of a hydrodynamic
flow via the salt gradient. Based on this, we also propose a salt-gradient
approach for regulating DNA motion in nanochannels that enables voltage-free
single-molecule capture with a significantly low translocation speed.
The present method would be used as a useful protocol to overcome
the key hurdle of tailoring the capture-to-translocation dynamics
of polynucleotides for nanopore sequencing
Highly Sensitive and Selective Gas Detection Based on Silicene
Recent advances in the fabrication
of silicene devices have raised
exciting prospects for practical applications such as gas sensing.
We investigated the gas detection performance of silicene nanosensors
for four different gases (NO, NO<sub>2</sub>, NH<sub>3</sub>, and
CO) in terms of sensitivity and selectivity, employing density functional
theory and nonequilibrium Green’s function method. The structural
configurations, adsorption sites, binding energies and charge transfer
of all studied gas molecules on silicene nanosensors are systematically
discussed in this work. Our results indicate that pristine silicene
exhibits strong sensitivity for NO and NO<sub>2</sub>, while it appears
incapable of sensing CO and NH<sub>3</sub>. In an attempt to overcome
sensitivity limitations due to weak van der Waals interaction of those
latter gas molecules on the device, we doped pristine silicene with
either B or N atoms, leading to enhanced binding energy as well as
charge transfer, and subsequently a significant improvement of sensitivity.
A distinction between the four studied gases based on the silicene
devices appears possible, and thus these promise to be next-generation
nanosensors for highly sensitive and selective gas detection
Thermophoretic Manipulation of DNA Translocation through Nanopores
Manipulating DNA translocation through nanopore is one crucial requirement for new ultrafast sequencing methods in the sense that the polymers have to be denatured, unraveled, and then propelled through the pore with very low speed. Here we propose and theoretically explore a novel design to fulfill the demands by utilizing cross-pore thermal gradient. The high temperature in the <i>cis</i> reservoir is expected to transform double-stranded DNA into single strands and that temperature would also prevent those single strands from intrastrand base-pairing, thus, achieving favorable polymer conformation for the subsequent translocation and sequencing. Then, the substantial temperature drop across the pore caused by the thermal-insulating membrane separating <i>cis</i> and <i>trans</i> chambers would stimulate thermophoresis of the molecules through nanopores. Our theoretical evaluation shows that the DNA translocation speeds will be orders smaller than the electrophoretic counterpart, while high capture rate of DNA into nanopore is maintained, both of which would greatly benefit the sequencing
Hydrogenation-Induced Structure and Property Changes in the Rare-Earth Metal Gallide NdGa: Evolution of a [GaH]<sup>2–</sup> Polyanion Containing Peierls-like Ga–H Chains
The
hydride NdGaH<sub>1+<i>x</i></sub> (<i>x</i> ≈
0.66) and its deuterized analogue were obtained by sintering the Zintl
phase NdGa with the CrB structure in a hydrogen atmosphere at pressures
of 10−20 bar and temperatures near 300 °C. The system
NdGa/NdGaH<sub>1+<i>x</i></sub> exhibits reversible H storage
capability. H uptake and release were investigated by kinetic absorption
measurements and thermal desorption mass spectroscopy, which showed
a maximum H concentration corresponding to “NdGaH<sub>2</sub>” (0.93 wt % H) and a two-step desorption process, respectively.
The crystal structure of NdGaH<sub>1+<i>x</i></sub> was
characterized by neutron diffraction (<i>P</i>2<sub>1</sub>/<i>m</i>, <i>a</i> = 4.1103(7), <i>b</i> = 4.1662(7), <i>c</i> = 6.464(1) Å, β = 108.61(1)° <i>Z</i> = 2). H incorporates in NdGa by occupying two distinct
positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by
Nd atoms. The H2 position displays flexible occupancy, and H2 atoms
attain a trigonal bipyramidal coordination by centering a triangle
of Nd atoms and bridging two Ga atoms. The phase stability and electronic
structure of NdGaH<sub>1+<i>x</i></sub> were analyzed by
first-principles DFT calculations. NdGaH1H2 (NdGaH<sub>2</sub>) may
be expressed as Nd<sup>3+</sup>(H1<sup>–</sup>)[GaH2]<sup>2–</sup>. The two-dimensional polyanion [GaH]<sup>2–</sup> features
linear −H–Ga–H–Ga– chains with
alternating short (1.8 Å) and long (2.4 Å) Ga–H distances,
which resembles a Peierls distortion. H2 deficiency (<i>x</i> < 1) results in the fragmentation of chains. For <i>x</i> = 0.66 arrangements with five-atom moieties, Ga–H–Ga–H–Ga
are energetically most favorable. From magnetic measurements, the
Curie–Weiss constant and effective magnetic moment of NdGaH<sub>1.66</sub> were obtained. The former indicates antiferromagnetic
interactions, and the latter attains a value of ∼3.6 μ<sub>B</sub>, which is typical for compounds containing Nd<sup>3+</sup> ions
Hydrogenation-Induced Structure and Property Changes in the Rare-Earth Metal Gallide NdGa: Evolution of a [GaH]<sup>2–</sup> Polyanion Containing Peierls-like Ga–H Chains
The
hydride NdGaH<sub>1+<i>x</i></sub> (<i>x</i> ≈
0.66) and its deuterized analogue were obtained by sintering the Zintl
phase NdGa with the CrB structure in a hydrogen atmosphere at pressures
of 10−20 bar and temperatures near 300 °C. The system
NdGa/NdGaH<sub>1+<i>x</i></sub> exhibits reversible H storage
capability. H uptake and release were investigated by kinetic absorption
measurements and thermal desorption mass spectroscopy, which showed
a maximum H concentration corresponding to “NdGaH<sub>2</sub>” (0.93 wt % H) and a two-step desorption process, respectively.
The crystal structure of NdGaH<sub>1+<i>x</i></sub> was
characterized by neutron diffraction (<i>P</i>2<sub>1</sub>/<i>m</i>, <i>a</i> = 4.1103(7), <i>b</i> = 4.1662(7), <i>c</i> = 6.464(1) Å, β = 108.61(1)° <i>Z</i> = 2). H incorporates in NdGa by occupying two distinct
positions, H1 and H2. H1 is coordinated in a tetrahedral fashion by
Nd atoms. The H2 position displays flexible occupancy, and H2 atoms
attain a trigonal bipyramidal coordination by centering a triangle
of Nd atoms and bridging two Ga atoms. The phase stability and electronic
structure of NdGaH<sub>1+<i>x</i></sub> were analyzed by
first-principles DFT calculations. NdGaH1H2 (NdGaH<sub>2</sub>) may
be expressed as Nd<sup>3+</sup>(H1<sup>–</sup>)[GaH2]<sup>2–</sup>. The two-dimensional polyanion [GaH]<sup>2–</sup> features
linear −H–Ga–H–Ga– chains with
alternating short (1.8 Å) and long (2.4 Å) Ga–H distances,
which resembles a Peierls distortion. H2 deficiency (<i>x</i> < 1) results in the fragmentation of chains. For <i>x</i> = 0.66 arrangements with five-atom moieties, Ga–H–Ga–H–Ga
are energetically most favorable. From magnetic measurements, the
Curie–Weiss constant and effective magnetic moment of NdGaH<sub>1.66</sub> were obtained. The former indicates antiferromagnetic
interactions, and the latter attains a value of ∼3.6 μ<sub>B</sub>, which is typical for compounds containing Nd<sup>3+</sup> ions
Excellent Catalytic Effects of Graphene Nanofibers on Hydrogen Release of Sodium alanate
One of the most technically challenging barriers to the
widespread commercialization of hydrogen-fueled
devices and vehicles remains hydrogen storage. More environmentally
friendly and effective nonmetal catalysts are required to improve
hydrogen sorption. In this paper, through a combination of experiment
and theory, we evaluate and explore the catalytic effects of layered
graphene nanofibers toward hydrogen release of light metal hydrides
such as sodium alanate. Graphene nanofibers, especially the helical
kind, are found to considerably improve hydrogen release from NaAlH<sub>4</sub>, which is of significance for the further enhancement of
this practical material for environmentally friendly and effective
hydrogen storage applications. Using density functional theory, we
find that carbon sheet edges, regardless of whether they are of zigzag
or armchair type, can weaken Al–H bonds in sodium alanate,
which is believed to be due to a combination of NaAlH<sub>4</sub> destabilization
and dissociation product stabilization. The helical form of graphene
nanofibers, with larger surface area and curved configuration, appears
to benefit the functionalization of carbon sheet edges. We believe
that our combined experimental and theoretical study will stimulate
more explorations of other microporous or mesoporous nanomaterials
with an abundance of exposed carbon edges in the application of practical
complex light metal hydride systems