Innovative methodologies for reliably and inexpensively sequencing DNA can lead to a new era of personalized medicine. In this work, we performed a theoretical investigation of a nanogap-based all electronic DNA sequencing device. To do so, we used a nitrogen-terminated nanogap on a graphene sheet with the environment fully taken into account. Our investigation is performed using a hybrid methodology combining quantum and classical mechanics coupled to non-equilibrium Green's functions for solving the electron transport across the device. The obtained results show that the DNA nucleotides can be both detected and distinguished in such device, which indicates that it can be used as a DNA sequencing device providing very high sensitivity and selectivity. Furthermore, our results show that water plays a major role in electronic transport in nanoscopic tunneling devices, not only from an electrostatics point of view, but also by providing states that significantly increase the conductance in nanogap-based DNA sequencing devices.
We demonstrate that biological molecules such as Watson-Crick DNA base pairs can behave as biological Aviram-Ratner electrical rectifiers because of the spatial separation and weak hydrogen bonding between the nucleobases. We have performed a parallel computational implementation of the ab-initio non-equilibrium Green's function (NEGF) theory to determine the electrical response of graphene---base-pair---graphene junctions. The results show an asymmetric (rectifying) current-voltage response for the Cytosine-Guanine base pair adsorbed on a graphene nanogap. In sharp contrast we find a symmetri…
We study how double-stranded DNA translocates through graphene nanogaps. Nanogaps are fabricated with a novel capillary-force induced graphene nanogap formation technique. DNA translocation signatures for nanogaps are qualitatively different from those obtained with circular nanopores, owing to the distinct shape of the gaps discussed here. Translocation time and conductance values vary by $\sim 100$%, which we suggest are caused by local gap width variations. We also observe exponentially relaxing current traces. We suggest that slow relaxation of the graphene membrane following DNA transloca…
The fabrication of nanopores in atomically-thin graphene has recently been achieved and translocation of DNA has been demonstrated. Taken together with an earlier proposal to use graphene nanogaps for the purpose of DNA sequencing, this approach can resolve the technical problem of achieving single-base resolution in electronic nucleobase detection. We have theoretically evaluated the performance of a graphene nanogap setup for the purpose of whole-genome sequencing, by employing density functional theory and the non-equilibrium Green's function method to investigate the transverse conductance…
Graphene nanogaps and nanopores show potential for the purpose of electrical DNA sequencing, in particular because single-base resolution appears to be readily achievable. Here, we evaluated from first principles the advantages of a nanogap setup with functionalized graphene edges. To this end, we employed density functional theory and the non-equilibrium Green's function method to investigate the transverse conductance properties of the four nucleotides occurring in DNA when located between the opposing functionalized graphene electrodes. In particular, we determined the electrical tunneling …
In the last decade, solid state nanopores nanogaps have attracted significant interest in the rapid detection of DNA nucleotides. However, reducing the noise through the controlled translocating of the DNA nucleobases is a central issue for the developing nanogap nanopore based DNA sequencing to achieve single nucleobase resolution. Furthermore, the high reactivity of the graphene pores gaps exhibits clogging of the pore gap, leading to the blockage of the pores gaps, yielding sticking, and irreversible pore closure. To address the prospective of functionalization of carbon nanostructure and f…
Translocation of DNA through a nanopore with embedded electrodes is at the centre of new rapid inexpensive sequencing methods which allow distinguishing the four nucleobases by their different electronic structure. However, the subnanometer separation between nucleotides in DNA requires ultra-sharp probes. Here, we propose a device architecture consisting of a nanopore formed in bilayer graphene, with the two layers acting as separate electrical contacts. The 0.34 nm interlayer distance of graphene is ideally suited for electrical coupling to a single nucleobase, avoiding the difficulty of fab…
We propose using graphene electrodes with hydrogenated edges for solid-state nanopore-based DNA sequencing, and perform molecular dynamics simulations in conjunction with electronic transport calculations to explore the potential merits of this idea. The results of our investigation show that, compared to the unhydrogenated system, edge-hydrogenated graphene electrodes facilitate the temporary formation of H-bonds with suitable atomic sites in the translocating DNA molecule. As a consequence, the average conductivity is drastically raised by about 3 orders of magnitude while exhibiting signifi…
Single-molecule biosensing, with a promise of being applied in protein and DNA sequencing, could be achieved using tunneling current approach. Electrode-molecule-electrode tunneling current critically depends on whether molecular levels contribute to electronic transport or not. Here we found employing DFT and Non-Equilibrium Green's Function formalism that energies of benzene molecular levels placed between graphene electrodes are strongly influenced by electrode termination. Termination-dependent dipoles formed at the electrode ends induce in-gap field effect that is responsible for shifting…
Electronic DNA sequencing using two-dimensional (2D) materials such as graphene has recently emerged as the next-generation of DNA sequencing technology. Owing to its commercial availability and remarkable physical and conductive properties, graphene has been widely investigated for DNA sequencing by several theoretical and experimental groups. Despite this progress, sequencing using graphene remains a major challenge. This is due to the hydrophobic nature of graphene, which causes DNA bases to stick to its surface via strong π-π interactions, reducing translocation speed and increasing error …
We present a tight-binding model study of a two-terminal graphene nanopore device for sequential determination of DNA bases. Using Green's function technique we investigate the changes in electronic transport properties of the device due to insertion of different nucleotides into the nanopore created within a zigzag graphene nanoribbon. First we try to characterise the device in static condition and then go for sequencing application by setting the bias across it to a specific voltage and then recording the characteristic current signals corresponding to each nucleotides of a translocating DNA…
The interaction of DNA nucleobases with monolayer GaSe has been studied with in DFT framework using vdW functional. We found that nucleobases are physisorbed on the GaSe monolayer. The order of binding energy per atom is C > T > G > A. The room temperature recovery time estimated to be maximum of 113.88 micro sec. for T+GaSe indicting reusability of the GaSe based devices. The modulation in the electronic structures of GaSe has been clearly captured within the simulated STM measurements. We also demonstrate quantum capacitance as a key parameter for sensing applications. Furthermore, in optica…
Silicene, a hexagonal buckled 2-D allotrope of silicon, shows potential as a platform for numerous new applications, and may allow for easier integration with existing silicon-based microelectronics than graphene. Here, we show that silicene could function as an ultrafast electrical DNA sequencing device. We investigated the stability of this novel nano-bio system, its electronic properties and the pronounced effects on the transverse electronic transport, i.e., changes in the transmission and the conductance caused by adsorption of each nucleobase, explored by us through the non-equilibrium G…
Nanopore based sequencing has demonstrated significant potential for the development of fast, accurate, and cost-efficient fingerprinting techniques for next generation molecular detection and sequencing. We propose a specific multi-layered graphene-based nanopore device architecture for the recognition of single DNA bases. Molecular detection and analysis can be accomplished through the detection of transverse currents as the molecule or DNA base translocates through the nanopore. To increase the overall signal-to-noise ratio and the accuracy, we implement a new "multi-point cross-correlation…
We propose an aqueous functionalized molybdenum disulfide nanoribbon suspended over a solid electrode as the first capacitive displacement sensor aimed at determining the DNA sequence. The detectable sequencing events arise from the combination of Watson-Crick base-pairing, one of nature's most basic lock-and-key-binding mechanisms, with the ability of appropriately sized atomically thin membranes to flex substantially in response to sub-nanonewton forces. We employ carefully designed numerical simulations and theoretical estimates to demonstrate excellent (79 % to 86 %) raw target detection a…
We review recent advances in the DNA sequencing based on the measurement of transverse electrical currents. Device configurations proposed in the literature are classified according to whether the molecular fingerprints appear as the major (Mode I) or perturbing (Mode II) current signals. Scanning tunneling microscope and tunneling electrode gap configurations belong to the former category, while the nanochannels with or without an embedded nanopore belong to the latter. The molecular sensing mechanisms of Modes I and II roughly correspond to the electron tunneling and electrochemical gating, …
We propose a water-immersed nucleobase-functionalized suspended graphene nanoribbon as an intrinsically selective device for nucleotide detection. The proposed sensing method combines Watson-Crick selective base pairing with graphene's capacity for converting anisotropic lattice strain to changes in an electrical current at the nanoscale. Using detailed atomistic molecular dynamics simulations, we study sensor operation at ambient conditions. We combine simulated data with theoretical arguments to estimate the levels of measurable electrical signal variation in response to strains and determin…
The ability to detect and discriminate DNA bases by reading it directly using simple and cost-effective methods is an important problem whose solution can produce significant value for areas such as cancer and human genetic disorders. Two-dimensional (2D) materials have emerged as revolutionary materials for electronic DNA sequencing with strong potentials for fast, single-nucleotide direct-read DNA sequencing with a minimum amount of consumables. Among 2D materials, graphene is the most explored for DNA sequencing. This is due to its commercial availability. The major hindrance of graphene is…
Based on combined density functional theory and nonequilibrium Greens function quantum transport studies, we have demonstrated quantum interference effects on the transverse conductance of Hachimoji synthetic nucleic acids placed between the oxygen-terminated zigzag graphene nanoribbon nanoelectrodes. We theorize that the QI effect could be well preserved in pi-pi coupling between a nucleobase molecule and the carbon-based nanoelectrode. Our study indicates that QI effects such as anti-resonance or Fano-resonance that affect the variation of transverse conductance depending on the nucleobase c…
Topological line defects in graphene represent an ideal way to produce highly controlled structures with reduced dimensionality that can be used in electronic devices. In this work we propose using extended line defects in graphene to improve nucleobase selectivity in nanopore-based DNA sequencing devices. We use a combination of QM/MM and non-equilibrium Green's functions methods to investigate the conductance modulation, fully accounting for solvent effects. By sampling over a large number of different orientations generated from molecular dynamics simulations, we theoretically demonstrate t…
Rapid and cost-effective DNA sequencing at the single nucleotide level might be achieved by measuring a transverse electronic current as single-stranded DNA is pulled through a nano-sized pore. In order to enhance the electronic coupling between the nucleotides and the electrodes and hence the current signals, we employ a pair of single-walled close-ended (6,6) carbon nanotubes (CNTs) as electrodes. We then investigate the electron transport properties of nucleotides sandwiched between such electrodes by using first-principles quantum transport theory. In particular we consider the extreme cas…
Nanopores -- nanosized holes that can transport ions and molecules -- are very promising devices for genomic screening, in particular DNA sequencing. Both solid-state and biological pores suffer from the drawback, however, that the channel constituting the pore is long, viz. 10-100 times the distance between two bases in a DNA molecule (0.5 nm for single-stranded DNA). Here, we demonstrate that it is possible to realize and use ultrathin nanopores fabricated in graphene monolayers for single-molecule DNA translocation. The pores are obtained by placing a graphene flake over a microsize hole in…
Using first-principles quantum transport simulations, based on the nonequilibrium Green function formalism combined with density functional theory (NEGF+DFT), we examine changes in the total and local electronic currents within the plane of graphene nanoribbon with zigzag edges (ZGNR) hosting a nanopore which are induced by inserting a DNA nucleobase into the pore. We find a sizable change of the zero-bias conductance of two-terminal ZGNR + nanopore device after the nucleobase is placed into the most probable position (according to molecular dynamics trajectories) inside the nanopore of a smal…
The success of graphene for nanopore DNA sequencing has shown that it is possible to explore other potential single- and few-atom thick layers of 2D materials beyond graphene, and also that these materials can exhibit fascinating and technologically useful properties for DNA base detection that are superior to those of graphene. In this article, we review the state-of-the art of DNA base detection using 2D materials beyond graphene. Initially, we present an overview of nanopore-based DNA sequencing methods using biological and solid-state nanopores, and discuss several challenges that limit th…
Fast, reliable and inexpensive DNA sequencing is an important pursuit in healthcare, especially in personalized medicine with possible deep societal impacts. Despite significant progress of various nanopore-based sequencing configurations, challenges remain in resolution (due to thermal fluctuations or to sensitivity to molecular orientation) and speed, which are calling for new approaches. Here we propose a sequencing protocol for DNA translocation through a nanopore with side-embedded N-terminated carbon nanotube electrodes. Employing DFT and Non-Equilibrium Green's Function formalism, we sh…
In this study, we examine the mechanism of nanopore-based DNA sequencing using a voltage bias across a graphene nanoribbon. Using density functional theory and a non-equilibrium Green's function approach, we determine the transmission spectra and current profile for adenine, guanine, cytosine, thymine, and uracil as a function of bias voltage in an energy minimized configuration. Utilizing the transmission current, we provide a general methodology for the development of a three nanopore graphene-based device that can be used to distinguish between the various nucleobases for DNA/RNA sequencing…
In this study, structural stability, electronic, optical and vibrational properties of DNA nucleobase adsorbed Graphene Quantum Dot (GQD) has been investigated using density functional theory. Based on state-of-art electronic structure calculations, we predict order of GQD sensitivity for DNA nucleobase as Thymine > Cytosine > Guanine > Adenine. An interaction of GQD with DNA nucleobase leads to modulation in electronic energy gap. Our calculated UV/vis and IR vibrational spectra show unique spectral band that can be used fingerprints in next generation DNA sequencing diagnostics.
We propose two-terminal devices for DNA sequencing which consist of a metallic graphene nanoribbon with zigzag edges (ZGNR) and a nanopore in its interior through which the DNA molecule is translocated. Using the nonequilibrium Green functions combined with density functional theory, we demonstrate that each of the four DNA nucleotides inserted into the nanopore, whose edge carbon atoms are passivated by either hydrogen or nitrogen, will lead to a unique change in the device conductance. Unlike other recent biosensors based on transverse electronic transport through DNA nucleotides, which util…
The success of graphene for nanopore DNA sequencing has shown that it is possible to explore other potential single-atom and few-atom thick layers of elemental 2D materials beyond graphene (e.g., phosphorene and silicene). Using density functional theory, we studied the interaction of DNA bases with nanopores created in finite-size nanoribbons from graphene, phosphorene, and silicene. We observe that binding energies of DNA bases using nanopores from phosphorene and silicene are generally smaller compared to graphene. The band gaps of phosphorene and silicene are significantly altered due to i…
We present an unique way to detect basepair mismatches in DNA leading to different epigenetic disorder by the method of nanopore sequencing. Based on a tight-binding formulation of graphene nanopore based device, using Greens function approach we measure the changes in the electronic transport properties of the device as we translocate a double-stranded DNA through the nanopore embeded in a zigzag graphene nanoribbon. In the present work we not only successfully detect the usual AT and GC pairs, but also a set of possible mismatches in the complementary base-pairing without any ambiguity. Our …
We propose a DNA sequencing scheme based on silicene nanopores. Using first principles theory, we compute the electrical properties of such pores in the absence and presence of nucleobases. Within a two-terminal geometry, we analyze the current-voltage relation in the presence of nucleobases with various orientations. We demonstrate that when nucleobases pass through a pore, even after sampling over many orientations, changes in the electrical properties of the ribbon can be used to discriminate between bases.
