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, NO₂, NH₃, 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 NO₂, while it appears incapable of sensing CO and NH₃. 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]^2– Polyanion Containing Peierls-like Ga–H Chains

The hydride NdGaH_1+<i>x</i> (<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_1+<i>x</i> 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 “NdGaH₂” (0.93 wt % H) and a two-step desorption process, respectively. The crystal structure of NdGaH_1+<i>x</i> was characterized by neutron diffraction (<i>P</i>2₁/<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_1+<i>x</i> were analyzed by first-principles DFT calculations. NdGaH1H2 (NdGaH₂) may be expressed as Nd³⁺(H1^–)­[GaH2]^2–. The two-dimensional polyanion [GaH]^2– 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_1.66 were obtained. The former indicates antiferromagnetic interactions, and the latter attains a value of ∼3.6 μ_B, which is typical for compounds containing Nd³⁺ ions

Hydrogenation-Induced Structure and Property Changes in the Rare-Earth Metal Gallide NdGa: Evolution of a [GaH]^2– Polyanion Containing Peierls-like Ga–H Chains

The hydride NdGaH_1+<i>x</i> (<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_1+<i>x</i> 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 “NdGaH₂” (0.93 wt % H) and a two-step desorption process, respectively. The crystal structure of NdGaH_1+<i>x</i> was characterized by neutron diffraction (<i>P</i>2₁/<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_1+<i>x</i> were analyzed by first-principles DFT calculations. NdGaH1H2 (NdGaH₂) may be expressed as Nd³⁺(H1^–)­[GaH2]^2–. The two-dimensional polyanion [GaH]^2– 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_1.66 were obtained. The former indicates antiferromagnetic interactions, and the latter attains a value of ∼3.6 μ_B, which is typical for compounds containing Nd³⁺ 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 NaAlH₄, 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 NaAlH₄ 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