A high density nanopore 3-triangulene kagome lattice.

Nanopore-containing two-dimensional materials have been explored for a wide range of applications including filtration, sensing, catalysis, energy storage and conversion. Triangulenes have recently been experimentally synthesized in a variety of sizes. In this regard, using these systems as building blocks, we theoretically examined 3-triangulene kagome crystals with inherent holes of ∼12 Å diameter and a greater density array of nanopores (≥1013 cm-2) compared to conventional 2D systems. The energetic, electronic, and transport properties of pristine and B/N-doped 3-triangulene kagome crystals were evaluated through a combination of density functional theory and non-equilibrium Green's function method. The simulated scanning tunneling microscopy images clearly capture electronic perturbation around the doped sites, which can be used to distinguish the pristine system from the doped systems. The viability of precisely controlling the band structure and transport properties by changing the type and concentration of doping atoms is demonstrated. The findings presented herein can potentially widen the applicability of these systems that combine unique electronic properties and intrinsically high-density pores, which can pave the way for the next generation of nanopore-based devices.

Boron-doped graphene topological defects: unveiling high sensitivity to NO molecule for gas sensing applications.

Global air quality has deteriorated significantly in recent years due to large emissions from the transformation industry and combustion vehicles. This issue requires the development of portable, highly sensitive, and selective gas sensors. Nanostructured materials, including defective graphene, have emerged as promising candidates for such applications. In this work, we investigated the B-doped topological line defect in graphene as a sensing material for various gas molecules (CO, CO2, NO, and NH3) based on a combination of density functional theory and the non-equilibrium Green's function method. The electronic transport calculations reveal that the electric current can be confined to the line defect region by gate voltage control, revealing highly reactive sites. The B-doped topological line defect is metallic, favoring the adsorption of NO and NH3 over CO and CO2 molecules. We notice changes in the conductance after gas molecule adsorption, producing a sensitivity of 50% (16%) for NO (NH3). In addition, the recovery time for nitride gases was calculated for different temperatures and radiation frequencies. At 300 K the ultraviolet (UV) has a fast recovery time compared to the visible (VIS) one by about two orders of magnitude. This study gives an understanding of how engineering transport properties at the microscopic level (by topological line defect and chemical B-doping) leads to promising nanosensors for detecting nitride gas.

Topological line defects in hexagonal SiC monolayer.

Defect engineering of two-dimensional (2D) materials offers an unprecedented route to increase their functionality and broaden their applicability. In light of the recent synthesis of the 2D Silicon Carbide (SiC), a deep understanding of the effect of defects on the physical and chemical properties of this new SiC allotrope becomes highly desirable. This study investigates 585 extended line defects (ELDs) in hexagonal SiC considering three types of interstitial atom pairs (SiSi-, SiC-, and CC-ELD) and using computational methods like Density Functional Theory, Born-Oppenheimer Molecular Dynamics, and Kinetic Monte-Carlo (KMC). Results show that the formation of all ELD systems is endothermic, with the CC-ELD structure showing the highest stability at 300 K. To further characterize the ELDs, simulated scanning tunneling microscopy (STM) is employed, and successfully allow identify and distinguish the three types of ELDs. Although pristine SiC has a direct band gap of 2.48 eV, the presence of ELDs introduces mid-gap states derived from the pz orbitals at the defect sites. Furthermore, our findings reveal that the ELD region displays enhanced reactivity towards hydrogen adsorption, which was confirmed by KMC simulations. Overall, this research provides valuable insights into the structural, electronic, and reactivity properties of ELDs in hexagonal SiC monolayers and paves the way for potential applications in areas such as catalysis, optoelectronics, and surface science.

Gas-sensing detection in the carbon phosphide monolayer: improving COx sensitivity through B doping.

A challenge in 2D materials engineering is to find a nanodevice that is capable of detecting and distinguishing gas molecules through an electrical signal. Herein, the B-doped carbon phosphide monolayer (B-doped γ-CP) was explored as a gas sensor through a combination of density functional theory (DFT) and the non-equilibrium Green's function (NEGF). Formation of the B-doped system is governed by an exothermic process, and the doping increases bands crossing at the Fermi level, contributing to an increment in the number of transmission channels compared with the undoped system. The interaction between the nanodevice and each gas molecule (CO, CO2, NO, and NH3) was explored. The electronic transmission is characteristically modulated by each target molecule, enabling each to be distinguished through the conductance change in the material. Our finds propose B-doped γ-CP as a promising candidate for use in highly sensitive and selective gas nanosensors.

C-doping anisotropy effects on borophene electronic transport.

The electronic transport anisotropy for different C-doped borophene polymorphs (ß12andχ3) was investigated theoretically combining density functional theory and non-equilibrium Green's function. The energetic stability analysis reveals that B atoms replaced by C is more energetically favorable forχ3phase. We also verify a directional character of the electronic band structure on C-doped borophene for both phases. Simulated scanning tunneling microscopy and also total density of charge confirm the directional character of the bonds. The zero bias transmission forß12phase atE-EF= 0 shows that C-doping induces a local current confinement along the lines of doped sites. TheI-Vcurves show that C-doping leads to an anisotropy amplification in theß12than in theχ3. The possibility of confining the electronic current at an specific region of the C-doped systems, along with the different adsorption features of the doped sites, poses them as promising candidates to highly sensitive and selective gas sensors.

Nanogap-based all-electronic DNA sequencing devices using MoS2 monolayers.

The realization of nanopores in atom-thick materials may pave the way towards electrical detection of single biomolecules in a stable and scalable manner. In this work, we theoretically study the potential of different phases of MoS2 nanogaps to act as all-electronic DNA sequencing devices. We carry out simulations based on density functional theory and the non-equilibrium Green's function formalism to investigate the electronic transport across the device. Our results suggest that the 1T'-MoS2 nanogap structure is energetically more favorable than its 2H counterpart. At zero bias, the changes in the conductance of the 1T'-MoS2 device can be well distinguished, making possible the selectivity of the DNA nucleobases. Although the conductance fluctuates around the resonances, the overall results suggest that it is possible to distinguish the four DNA bases for energies close to the Fermi level.

Electrically sensing Hachimoji DNA nucleotides through a hybrid graphene/h-BN nanopore.

The feasibility of synthesizing unnatural DNA/RNA has recently been demonstrated, giving rise to new perspectives and challenges in the emerging field of synthetic biology, DNA data storage, and even the search for extraterrestrial life in the universe. In line with this outstanding potential, solid-state nanopores have been extensively explored as promising candidates to pave the way for the next generation of label-free, fast, and low-cost DNA sequencing. In this work, we explore the sensitivity and selectivity of a graphene/h-BN based nanopore architecture towards detection and distinction of synthetic Hachimoji nucleobases. The study is based on a combination of density functional theory and the non-equilibrium Green's function formalism. Our findings show that the artificial nucleobases are weakly binding to the device, indicating a short residence time in the nanopore during translocation. Significant changes in the electron transmission properties of the device are noted depending on which artificial nucleobase resides in the nanopore, leading to a sensitivity in distinction of up to 80%. Our results thus indicate that the proposed nanopore device setup can qualitatively discriminate synthetic nucleobases, thereby opening up the feasibility of sequencing even unnatural DNA/RNA.

Embedded carbon nanowire in black phosphorene and C-doping: the rule to control electronic properties.

Tuning the properties of black phosphorene such as structural, electronic and transport are explored via substitutional C-doping. We employed density functional theory calculations in combination with the non-equilibrium Green's function for modeling the systems. Our results revealed that substitutional C-doped phosphorene is energetically favorable and ruled by the exothermic process. We also found that C-doping induces a change of the electric properties, such as a semiconductor-to-metal transition for the most lower concentration and zig-zag C-wire. Furthermore, for an armchair C-wire at the highest concentration, the semiconductor character is kept, meanwhile direct-to-indirect transitions are observed in the band gap nature. The band structures show that there exists a dependence of the electronic charge transport with the directional character of the C-doped configuration. The findings demonstrate that the directional doping could play a key role for the conductance of a 2D platform.

Controlled current confinement in interfaced 2D nanosensor for electrical identification of DNA.

The controlled synthesis of hybrid two-dimensional (2D) materials and the development of atomically precise nanopore fabrication techniques have opened up entirely new possibilities for sensing applications via nanoelectronics. Here, we investigate the electronic transport properties of an in-plane hybrid graphene/h-BN device, containing a graphene nanopore, to assess its feasibility to act as a molecular sensor. The results from our calculations based on density functional theory and the non-equilibrium Green's function formalism reveal the capability to confine the electric current pathways to the two carbon wires lining either edge of the nanopore, thereby creating conditions in which the conductance is highly sensitive to any changes in the electrical potential inside the nanopore. We apply this setup to assess whether it is possible to electrically determine the base sequence in a DNA molecule. Indeed, the modulation of the device conductance reveals a characteristic fingerprint of each nucleotide, which manifests itself in a pronounced difference in the sensitivity of the four different nucleotides, thereby allowing electrical discrimination. These findings lead us to propose this device architecture as a promising nanobiosensor. While fabrication in the lab may represent a profound experimental challenge, it should nevertheless in principle be feasible with existing contemporary techniques of hybrid 2D material synthesis, in conjunction with approaches for highly controlled nanopore creation.

Interplay of non-uniform charge distribution on the electrochemical modification of graphene.

Graphene is considered a model material for surfaces because it is stable despite being composed of a single layer of carbon atoms. Although the thermal and electronic properties of graphene are well reported, the behavior of graphene sheets with the addition of charges to the structure is not well understood. Combining infrared spectroscopy, electrochemical analysis, and computational simulations, we report the effect of an electrochemically induced covalent anchoring of 4-carboxyphenyl (4-CP) units on the optical and electronic properties of graphene. Charges in graphene become concentrated at specific sites of the sheet when electrochemically perturbed and the functionalization occurs inhomogeneously along the graphene sheet. We observed that, when graphene is covalently functionalized, the resistance to heterogeneous electron transfer is increased by a factor of 1.4. Furthermore, scattering-type scanning near-field optical microscopy and atomic force microscopy show that the covalent functionalization affects drastically the optical and physical properties of the graphene/SiO2 system, especially the plasmon-phonon coupling after the functionalization. In addition, from these we infer that a comparatively higher degree of functionalization occurs near the electrode edges. These results are supported by computational simulations, which show that the covalent anchoring of 4-CP units weakens electron transfer because the charges are retained on the sp3-hybridized carbon atoms generated upon functionalization, suggesting that graphene properties are deeply influenced by the way the molecules are immobilized on its structure.

Controlling the orientation of nucleobases by dipole moment interaction with graphene/h-BN interfaces.

The interfaces in 2D hybrids of graphene and h-BN provide interesting possibilities of adsorbing and manipulating atomic and molecular entities. In this paper, with the aid of density functional theory, we demonstrate the adsorption characteristics of DNA nucleobases at different interfaces of 2D hybrid nanoflakes of graphene and h-BN. The interfaces provide stronger binding to the nucleobases in comparison to pure graphene and h-BN nanoflakes. It is also revealed that the individual dipole moments of the nucleobases and nanoflakes dictate the orientation of the nucleobases at the interfaces of the hybrid structures. The results of our study point towards a possible route to selectively control the orientation of individual molecules in biosensors.

Treating High-Caries Risk Occlusal Surfaces in First Permanent Molars through Sealants and Supervised Toothbrushing: A 3-Year Cost-Effective Analysis.

We conducted a 3-year cost-effectiveness analysis on the cavitated dentine carious lesion preventive capabilities of composite resin (CR) (reference group) and atraumatic restorative treatment (ART) high-viscosity glass-ionomer cement (HVGIC) sealants compared to supervised toothbrushing (STB) in high-risk first permanent molars. School children aged 6-7 years in 6 schools (2 per group) received CR and ART/HVGIC sealants or STB daily for 180 days each school year. Data were collected prospectively and cost estimates were made for sample data and a projection of 1,000 sealants/STB high-risk permanent molars. Although STB had the best outcome, its high implementation cost (95% of cost for supervisors visiting schools 180 days/school year) affected the results. ART/HVGIC was cost-effective compared to CR for the sample data (savings of USD 37 per cavitated dentine carious lesion prevented), while CR was cost-effective compared to ART/HVGIC for the projection (savings of USD 17 per cavitated dentine carious lesion prevented), and both were cost-saving compared to STB. Two STB scenarios were tested in sensitivity analyses with variations in caries incidence and number of supervision days; results showed STB had lower costs and higher savings per cavitated dentine carious lesion prevented than CR and ART/HVGIC. A major assumption is that both scenarios have the same high effectiveness rate experienced by STB under study conditions; however, they point to the value of further research on the benefits of adopting STB as a long-term venture in a general population of school children.

Electrical detection of nucleotides via nanopores in a hybrid graphene/h-BN sheet.

Designing the next generation of solid-state biosensors requires developing detectors which can operate with high precision at the single-molecule level. Nano-scaled architectures created in two-dimensional hybrid materials offer unprecedented advantages in this regard. Here, we propose and explore a novel system comprising a nanopore formed within a hybrid sheet composed of a graphene nanoroad embedded in a sheet of hexagonal boron nitride (h-BN). The sensitive element of this setup is comprised of an electrically conducting carbon chain forming one edge of the nanopore. This design allows detection of DNA nucleotides translocating through the nanopore based on the current modulation signatures induced in the carbon chain. In order to assess whether this approach is feasible to distinguish the four different nucleotides electrically, we have employed density functional theory combined with the non-equilibrium Green's function method. Our findings show that the current localized in the carbon chain running between the nanopore and h-BN is characteristically modulated by the unique dipole moment of each molecule upon insertion into the pore. Through the analysis of a simple model based on the dipole properties of the hydrogen fluoride molecule we are able to explain the obtained findings.

Benchmark investigation of diamondoid-functionalized electrodes for nanopore DNA sequencing.

Small diamond-like particles, diamondoids, have been shown to effectively functionalize gold electrodes in order to sense DNA units passing between the nanopore-embedded electrodes. In this work, we present a comparative study of Au(111) electrodes functionalized with different derivatives of lower diamondoids. Focus is put on the electronic and transport properties of such electrodes for different DNA nucleotides placed within the electrode gap. The functionalization promotes a specific binding to DNA leading to different properties for the system, which provides a tool set to systematically improve the signal-to-noise ratio of the electronic measurements across the electrodes. Using quantum transport calculations, we compare the effectiveness of the different functionalized electrodes in distinguishing the four DNA nucleotides. Our results point to the most effective diamondoid functionalization of gold electrodes in view of biosensing applications.

Nano-structured interface of graphene and h-BN for sensing applications.

The atomically-precise controlled synthesis of graphene stripes embedded in hexagonal boron nitride opens up new possibilities for the construction of nanodevices with applications in sensing. Here, we explore properties related to the electronic structure and quantum transport of a graphene nanoroad embedded in hexagonal boron nitride, using a combination of density functional theory and the non-equilibrium Green's functions method to calculate the electric conductance. We find that the graphene nanoribbon signature is preserved in the transmission spectra and that the local current is mainly confined to the graphene domain. When a properly sized nanopore is created in the graphene part of the system, the electronic current becomes restricted to a carbon chain running along the border with hexagonal boron nitride. This circumstance could allow the hypothetical nanodevice to become highly sensitive to the electronic nature of molecules passing through the nanopore, thus opening up ways to detect gas molecules, amino acids, or even DNA sequences based on a measurement of the real-time conductance modulation in the graphene nanoroad.

Diamondoid-functionalized gold nanogaps as sensors for natural, mutated, and epigenetically modified DNA nucleotides.

Modified tiny hydrogen-terminated diamond structures, known as diamondoids, show a high efficiency in sensing DNA molecules. These diamond cages, as recently proposed, could offer functionalization possibilities for gold junction electrodes. In this investigation, we report on diamondoid-functionalized electrodes, showing that such a device would have a high potential in sensing and sequencing DNA. The smallest diamondoid including an amine modification was chosen for the functionalization. Here, we report on the quantum tunneling signals across diamondoid-functionalized Au(111) electrodes. Our work is based on quantum-transport calculations and predicts the expected signals arising from different DNA units within the break junctions. Different gating voltages are proposed in order to tune the sensitivity of the functionalized electrodes with respect to specific nucleotides. The relation of this sensitivity to the coupling or decoupling of the electrodes is discussed. Our results also shed light on the sensing capability of such a device in distinguishing the DNA nucleotides, in their natural and mutated forms.

Switching Behaviors of Graphene-Boron Nitride Nanotube Heterojunctions.

High electron mobility of graphene has enabled their application in high-frequency analogue devices but their gapless nature has hindered their use in digital switches. In contrast, the structural analogous, h-BN sheets and BN nanotubes (BNNTs) are wide band gap insulators. Here we show that the growth of electrically insulating BNNTs on graphene can enable the use of graphene as effective digital switches. These graphene-BNNT heterojunctions were characterized at room temperature by four-probe scanning tunneling microscopy (4-probe STM) under real-time monitoring of scanning electron microscopy (SEM). A switching ratio as high as 10(5) at a turn-on voltage as low as 0.5 V were recorded. Simulation by density functional theory (DFT) suggests that mismatch of the density of states (DOS) is responsible for these novel switching behaviors.

Silicene as a new potential DNA sequencing device.

Silicene, a hexagonal buckled 2D 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 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 Green's function method. Intriguingly, despite the relatively weak interaction between nucleobases and silicene, significant changes in the transmittance at zero bias are predicted by us, in particular for the two nucleobases cytosine and guanine. Our findings suggest that silicene could be utilized as an integrated-circuit biosensor as part of a lab-on-a-chip device for DNA sequencing.

Exfoliation rates of primary molars submitted to three treatment protocols after 3.5 years.

OBJECTIVE: The aim of the study was to evaluate the exfoliation pattern of primary molars treated according to three treatment protocols. The hypothesis tested was that there is no difference in the exfoliation pattern of primary molars treated according to conventional restorative treatment using amalgam (CRT), atraumatic restorative treatment using high­viscosity glass­ionomer (ART), and ultraconservative treatment (UCT). The latter consisted of restoring small cavities with ART and cleaning medium/large nonrestored cavities daily with toothpaste/toothbrush under supervision. METHODS: A sample of 302 children aged 6­7 years from a suburban area of Brasilia was followed up for 3.5 years. The numbers of treated molars were 341 (CRT), 244 (ART), and 275 (UCT). Exfoliation rates were obtained using the PHREG procedure. Differences between the three treatment protocol groups were tested using the Wald test. RESULTS: After 3.5 years, there was no difference over the exfoliation rates of all primary molars as 51.0% (CRT), 48.7% (ART), and 59.3% (UCT) had exfoliated at the overall period (P = 0.34). CONCLUSION: The three treatment protocols led to similar exfoliation patterns of all primary molars after 3.5 years.