Selective Sensing of DNA Nucleobases with Angular Discrimination.

The fast and precise selective sensing of DNA nucleobases is a long-pursued method that can lead to huge advances in the field of genomics and have an impact on aspects such as the prevention of diseases, health enhancement, and, in general, all types of medical treatments. We present here a new type of nanoscale sensor based on carbon nanotubes with a specific geometry that can discriminate the type of nucleobase and also its angle of orientation. The proper differentiation of nucleobases is essential to clearly sequence DNA chains, while angular discrimination is key to improving the sensing selectivity. We perform first-principle and quantum transport simulations to calculate the transmission, conductance, and current of the nanotube-based nanoscale sensor in the presence of the four nucleotides (A, C, G, and T), each of them rotated 0, 90, 180, or 270°. Our results show that this system is able to effectively discriminate between the four nucleotides and their angle of orientation. We explain these findings in terms of the interaction between the phosphate group of the nucleotide and the nanotube wall. The phosphate specifically distorts the electronic structure of the nanotube depending on the distance and the orientation and leads to nontrivial changes in the transmission. This work provides a method for finer and more precise sequential DNA chains.

Towards nanotube-based sensors for discrimination of drug molecules.

The proper detection of drug molecules is key for applications that have an impact in several fields, ranging from medical treatments to industrial applications. In case of illegal drugs, their correct and fast detection has important implications that affect different parts of society such as security or public health. Here we present a method based on nanoscale sensors made of carbon nanotubes modified with dopants that can detect three types of drug molecules: mephedrone, methamphetamine and heroin. We show that each molecule produces a distinctive feature in the density of states that can be used to detect it and distinguish it from other types of molecules. In particular, we show that for semiconducting nanotubes the inclusion of molecules reduces the gap around the Fermi energy and produces peaks in the density of states below the Fermi energy at positions that are different for each molecule. These results prove that it is possible to design nanoscale sensors based on carbon nanotubes tailored with dopants, in such a way that they might be able to discriminate between different types of compounds and, especially, drug molecules whose proper recognition has important consequences in different fields.

Defect-Induced Transport Enhancement in Carbon-Boron Nitride-Carbon Heteronanotube Junctions.

New heteromaterials, particularly those involving nanoscale elements such as nanotubes, have opened a wide window for the next generation of materials and devices. Here, we perform density functional theory (DFT) simulations combined with a Green's function (GF) scattering approach to investigate the electronic transport properties of defective heteronanotube junctions (hNTJs) made of (6,6) carbon nanotubes (CNT) with a boron nitride nanotube (BNNT) as scatterer. We used the sculpturene method to form different heteronanotube junctions with various types of defects in the boron nitride part. Our results show that the defects and the curvature induced by them have a nontrivial impact on the transport properties and, interestingly, lead to an increase of the conductance of the heteronanotube junctions compared to the free-defect junction. We also show that narrowing the BNNTs region leads to a large decrease of the conductance, an effect that is opposite to that of the defects.

Discriminating sensing of explosive molecules using graphene-boron nitride-graphene heteronanosheets.

Since the synthesis of graphene-boron nitride heterostructures, their interesting electronic properties have attracted huge attention for real-world nanodevice applications. In this work, we combined density functional theory (DFT) with a Green's function approach to examine the potential of graphene-boron nitride-graphene heteronanosheets (h-NSHs) for discriminating single molecule sensing. Our result demonstrates that the graphene-boron nitride-graphene (h-NSHs) can be used for discriminate sensing of the 2,4-dinitrotoluene (DNT), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), pentaerythritol tetranitrate (PENT), and 2,4,6-trinitrotoluene (TNT) molecules. We demonstrate that as the length of the BN region increases, the sensitivity of the heteronanosheets to the presence of these explosive substances increases.

Tuning the thermoelectric properties of metallo-porphyrins.

We investigated the thermoelectric properties of metalloporphyrins connected by thiol anchor groups to gold electrodes. By varying the transition metal-centre over the family Mn, Co, Ni, Cu, Fe, and Zn we are able to tune the molecular energy levels relative to the Fermi energy of the electrodes. The resulting single-molecule room-temperature thermopowers range from almost zero for Co and Cu centres, to +80 µV K(-1) and +230 µV K(-1) for Ni and Zn respectively. In contrast, the thermopowers with Mn(II) or Fe(II) metal centres are negative and lie in the range -280 to -260 µV K(-1). Complexing these with a counter anion to form Fe(III) and Mn(III) changes both the sign and magnitude of their thermopowers to +218 and +95 respectively. The room-temperature power factors of Mn(II), Mn(III), Fe(III), Zn and Fe(II) porphyrins are predicted to be 5.9 × 10(-5) W m(-1) K(-2), 5.4 × 10(-4) W m(-1) K(-2), 9.5 × 10(-4) W m(-1) K(-2), 1.6 × 10(-4) W m(-1) K(-2) and 2.3 × 10(-4) W m(-1) K(-2) respectively, which makes these attractive materials for molecular-scale thermoelectric devices.

Tuning thermoelectric properties of graphene/boron nitride heterostructures.

Using density functional theory combined with a Green's function scattering approach, we examine the thermoelectric properties of hetero-nanoribbons formed from alternating lengths of graphene and boron nitride. In such structures, the boron nitride acts as a tunnel barrier, which weakly couples states in the graphene, to form mini-bands. In un-doped nanoribbons, the mini bands are symmetrically positioned relative to the Fermi energy and do not enhance thermoelectric performance significantly. In contrast, when the ribbons are doped by electron donating or electron accepting adsorbates, the thermopower S and electronic figure of merit are enhanced and either positive or negative thermopowers can be obtained. In the most favourable case, doping with the electron donor tetrathiafulvalene increases the room-temperature thermopower to -284 µv K(-1) and doping by the electron acceptor tetracyanoethylene increases S to 210 µv K(-1). After including both electron and phonon contributions to the thermal conductance, figures of merit ZT up to of order 0.9 are obtained.