The effect of environmental factors on the electrical conductivity of a single oligo-DNA molecule measured using single-walled carbon nanotube nanoelectrodes

Intra-strand phosphate-mediated pathways in microsolvated double-stranded DNA

We argue that dry DNA charge transport in molecular junctions, over distances of tens of nanometers, can take place via independent intra-strand pathways involving the phosphate groups. Such pathways explain recent single-molecule experiments that compare currents in intact and nicked 100 base-pair double-stranded DNA. We explore the conditions that favor independent intra-strand transport channels with the participation of the phosphate groups, as opposed to purely base-mediated transport involving the pi-stacked bases and inter-strand transitions. Our computations demonstrate how long-distance transport pathways in DNA are tuned by the degree of solvation, which affects the level of dynamic disorder in the pi-stacking, and the energies of phosphate-group molecular orbitals.

Tuning the Coupling in Single-Molecule Heterostructures: DNA-Programmed and Reconfigurable Carbon Nanotube-Based Nanohybrids

Herein a strategy is presented for the assembly of both static and stimuli-responsive single-molecule heterostructures, where the distance and electronic coupling between an individual functional nanomoiety and a carbon nanostructure are tuned via the use of DNA linkers. As proof of concept, the formation of 1:1 nanohybrids is controlled, where single quantum dots (QDs) are tethered to the ends of individual carbon nanotubes (CNTs) in solution with DNA interconnects of different lengths. Photoluminescence investigations-both in solution and at the single-hybrid level-demonstrate the electronic coupling between the two nanostructures; notably this is observed to progressively scale, with charge transfer becoming the dominant process as the linkers length is reduced. Additionally, stimuli-responsive CNT-QD nanohybrids are assembled, where the distance and hence the electronic coupling between an individual CNT and a single QD are dynamically modulated via the addition and removal of potassium (K+) cations; the system is further found to be sensitive to K+ concentrations from 1 pM to 25 × 10-3 m. The level of control demonstrated here in modulating the electronic coupling of reconfigurable single-molecule heterostructures, comprising an individual functional nanomoiety and a carbon nanoelectrode, is of importance for the development of tunable molecular optoelectronic systems and devices.

Site-Specific One-to-One Click Coupling of Single Proteins to Individual Carbon Nanotubes: A Single-Molecule Approach

We report the site-specific coupling of single proteins to individual carbon nanotubes (CNTs) in solution and with single-molecule control. Using an orthogonal Click reaction, Green Fluorescent Protein (GFP) was engineered to contain a genetically encoded azide group and then bound to CNT ends in different configurations: in close proximity or at longer distances from the GFP's functional center. Atomic force microscopy and fluorescence analysis in solution and on surfaces at the single-protein level confirmed the importance of bioengineering optimal protein attachment sites to achieve direct protein-nanotube communication and bridging.

Particle clustering during pearl chain formation in a conductive-island based dielectrophoretic assembly system

Particle clustering during pearl chain formation in a conductive-island based dielectrophoretic assembly system.

Enhancement of the thermoelectric figure of merit in DNA-like systems induced by Fano and Dicke effects

We report a theoretical study highlighting the thermoelectric properties of biological and synthetic DNA molecules.

Charge transport in desolvated DNA

The conductivity of DNA in molecular junctions is often probed experimentally under dry conditions, but it is unclear how much of the solvent remains attached to the DNA and how this impacts its structure, electronic states, and conductivity. Classical MD simulations show that DNA is unstable if the solvent is removed completely, while a micro-hydrated system with few water molecules shows similar charge transport properties as fully solvated DNA does. This surprising effect is analyzed in detail by mapping the density functional theory-based electronic structure to a tight-binding Hamiltonian, allowing for an estimate of conductivity of various DNA sequences with snapshot-averaged Landauer's approach. The characteristics of DNA charge transport turn out to be determined by the nearest hydration shell(s), and the removal of bulk solvent has little effect on the transport.

Influence of induced-charge electrokinetic phenomena on the dielectrophoretic assembly of gold nanoparticles in a conductive-island-based microelectrode system

Metal nanoparticles in a liquid suspension can be assembled dielectrophoretically (DEP) into nanoparticle chains, which can serve as electrical functional microwires connecting isolated and conductive elements to an electrode pair, as used in wet electronics, bioelectronics, and biochemical sensors. The frequency-dependent morphology of these nanoparticle chains assembled between an electrode pair has even been attributed to the decreasing magnitude of alternating current electroosmosis (ACEO) flow velocity with driving frequency. For instance, highly oriented nanoparticle nanowires can be generated by DEP assembly only at a high frequency, which induces a negligible small ACEO above the electrode surface, corresponding to fewer nanoparticles transported to the assembly region. In this study, attention is focused on the formation of nanoparticle chains in a conductive-island-based microelectrode system. It is worth noting that the intrusion of an island entity can bring about further double-layer polarization and induced charge electroosmosis flow (ICEO) around this conductive object, which exerts a significant influence on DEP assembly. In our experiments, the ends of nanoparticle chains are always extended onto the metal surfaces at 50 kHz, and their central parts become slender at 150 kHz. Meanwhile, wire-shaped particle clusters aligned along the direction of local field lines are more densely distributed at the island rims than that growing from the electrode edges. Consequently, a series of numerical modeling based on the theory of induced charge electrokinetic phenomena are introduced to account for these regular experimental results, including the double-layer charging effect at the metal/electrolyte interface, ACEO, ICEO, and electrothermal flow. Mutual DEP is also treated as an important factor affecting DEP behavior when neighboring particles are approaching one another. The results from the theoretical study are in good agreement with the experimental observations.

Dielectrophoresis at the nanoscale

Dielectrophoresis has become a powerful tool for manipulation of various materials, such as metal and semiconducting particles, DNA molecules, nanowires and graphene. This short review is intended to provide the reader with an overview of the recent advances of application of dielectrophoresis at the nanoscale.

Enhancement of transport in DNA-like systems induced by backbone disorder

We report a theoretical study highlighting the fundamental effects of backbone disorder which simulates the environmental complications on charge transport properties of biological and synthetic DNA molecules. Based on effective tight-binding models of duplex DNA, the Lyapunov coefficient and current-voltage characteristics are numerically calculated by varying the backbone disorder degree. In contrast to the localization picture that the conduction of duplex DNA becomes poorer when the backbone disorder degree is increased, we find that the backbone disorder can enhance the charge transport ability of the DNA molecules when the environment-induced disorder surpasses a critical value, giving rise to a semiconducting-metallic transition. The physical origin for this is traced back to the antiresonant effects. These results provide a scenario to interpret a variety of transport behaviors observed in DNA molecules and suggest perspectives for future experiments intending to control the charge transport through DNA-based nanodevices.