Supported lipid bilayer/carbon nanotube hybrids

Carbon nanotube transistors combine molecular-scale dimensions with excellent electronic properties, offering unique opportunities for chemical and biological sensing. Here, we form supported lipid bilayers over single-walled carbon nanotube transistors. We first study the physical properties of the nanotube/supported lipid bilayer structure using fluorescence techniques. Whereas lipid molecules can diffuse freely across the nanotube, a membrane-bound protein (tetanus toxin) sees the nanotube as a barrier. Moreover, the size of the barrier depends on the diameter of the nanotube--with larger nanotubes presenting bigger obstacles to diffusion. We then demonstrate detection of protein binding (streptavidin) to the supported lipid bilayer using the nanotube transistor as a charge sensor. This system can be used as a platform to examine the interactions of single molecules with carbon nanotubes and has many potential applications for the study of molecular recognition and other biological processes occurring at cell membranes.     

Encapsulation of a benzene molecule into a carbon nanotube

Aromatic hydrocarbon molecules encapsulated in carbon nanotubes have been proposed for applications as semiconductors. They can be formed by exploiting the van der Waals interaction as a simple method to incorporate molecules into carbon nanotubes. However, the existence of energy barriers near the open ends of carbon nanotubes may be an obstacle for molecules entering carbon nanotubes. In this paper, we investigate the encapsulation mechanism of a typical aromatic hydrocarbon, namely a benzene molecule, into a carbon nanotube in order to determine the dependence on radius of the tube. A continuous approach which assumes that the molecular interactions can be approximated using average atomic densities together with the semi-empirical Lennard–Jones potential function is adopted, and an analytical expression for the interaction energy is obtained which may be readily evaluated by algebraic computer packages. In particular, we determine the threshold radius of the carbon nanotube for which the benzene molecule will enter the carbon nanotube. The analytical approach adopted here provides a computationally rapid procedure for the determination of critical numerical values.     

Oscillation of gas molecules in carbon nanotubes

The dynamics of N(2) molecules blocked in open single-walled carbon nanotubes is investigated using molecular dynamics simulations. It is found that periodic axial and radial oscillations with extremely high frequency exist widely among these molecules. Between the two nanotube ends, N(2) molecules oscillate along or parallel to the nanotube axis, and their frequencies show an inverse length dependence in the range of 22 to 64?GHz. Accompanying the axial oscillation, the molecules oscillate radially with small amplitudes in the lateral potential well. The corresponding frequencies have a magnitude of several hundred gigahertz, and the maximum exceeds 1800?GHz. These periodic oscillations contribute to the molecular blockage in nanotubes.     

Carbon nanotube/detergent interactions via coarse-grained molecular dynamics

Detergent interactions with carbon nanotubes are of potential importance in a number of bionanotechnology applications. We investigate the interaction of lysophospholipids with single-walled carbon nanotubes via coarse-grained molecular dynamics. We present compelling evidence that the mechanism of adsorption of these detergents onto a carbon nanotube is dependent upon detergent concentration. Furthermore, the chirality of the carbon nanotube influences the detergent wrapping angle for low detergent concentration. These findings advance our understanding of the mechanism of carbon nanotube solubilization via detergent molecules.     

Outside looking in: nanotube transistor intracellular sensors

Nanowire-based field-effect transistors, including devices with planar and three-dimensional configurations, are being actively explored as detectors for extra- and intracellular recording due to their small size and high sensitivities. Here we report the synthesis, fabrication, and characterization of a new needle-shaped nanoprobe based on an active silicon nanotube transistor, ANTT, that enables high-resolution intracellular recording. In the ANTT probe, the source/drain contacts to the silicon nanotube are fabricated on one end, passivated from external solution, and then time-dependent changes in potential can be recorded from the opposite nanotube end via the solution filling the tube. Measurements of conductance versus water-gate potential in aqueous solution show that the ANTT probe is selectively gated by potential changes within the nanotube, thus demonstrating the basic operating principle of the ANTT device. Studies interfacing the ANTT probe with spontaneously beating cardiomyocytes yielded stable intracellular action potentials similar to those reported by other electrophysiological techniques. In addition, the straightforward fabrication of ANTT devices was exploited to prepare multiple ANTT structures at the end of single probes, which enabled multiplexed recording of intracellular action potentials from single cells and multiplexed arrays of single ANTT device probes. These studies open up unique opportunities for multisite recordings from individual cells through cellular networks.     

New Light on Molecule–Nanotube Hybrids

Optoelectronics benefits from outstanding new nanomaterials that provide emission and detection in the visible and near‐infrared range, photoswitches, two level systems for single photon emission, etc. Among these, carbon nanotubes are envisioned as game changers despite difficult handling and control over chirality burdening their use. However, recent breakthroughs on hybrid carbon nanotubes have established nanotubes as pioneers for a new family of building blocks for optics and quantum optics. Functionalization of carbon nanotubes with molecules or polymers not only preserves the nanotube properties from the environment, but also promotes new performance abilities to the resulting hybrids. Photoluminescence and Raman signals are enhanced in the hybrids, which questions the nature of the electronic coupling between nanotube and molecules. Furthermore, coupling to optical cavities dramatically enhances single photon emission, which operates up to room temperature. This new light on nanotube hybrids shows their potential to push optoelectronics a step forward.     

Comparative MD simulation study on the mechanical properties of a zigzag single-walled carbon nanotube in the presence of Stone-Thrower-Wales defects

Using molecular dynamics simulation, we investigate the influence of Stone-Thrower-Wales defects in the mechanical behavior of a zigzag (5, 0) single-walled carbon nanotube considering two different interatomic potential functions, the Tersoff–Brenner bond order potential and the Tight-Binding potential. The nanotube is subjected to axial stretch and the potential energy is computed for gradually increasing values of strain. From the energy–strain curve the mechanical characteristics like Young’s modulus, tensile strength and ductility are computed using both the potentials, firstly with a perfect lattice and then by introducing an increasing number of Stone-Thrower-Wales defects. Significant reduction in the values of the mechanical properties is observed with changes in the plastic deformation pattern. Experimental data compares reasonably well with our calculated values of the mechanical constants. Such investigations will help designing carbon nanotube based composites.     

Active {010} facet-exposed Cu2MoS4 nanotube as high-efficiency photocatalyst

Rational design and facet-engineering of nanocrystal is an effective strategy to optimize the catalytic performance of abundant and economic semiconductorbased photocatalysts.In this study,we demonstrate a novel ternary Cu2MoS4 nanotube with the {010} facet exposed,synthesized via a hydrothermal method.Compared with two-dimensional Cu2MoS4 nanosheet with the {001} facet exposed,this one-dimensional nanotube exhibits highly enhanced performance of photodegradation and water splitting.Both theoretical calculations and experimental results suggest that the conduction band minimum (CBM) of the {010} facet crystal shows lower potential than that of the {001} facet.In particular,the up-shifted CBM in Cu2MoS4 nanotube is significantly beneficial for the absorption of dye molecules and reduction of H+ to H2.These results may open a new route for realizing high-efficiency photocatalysts based on Cu2MX4 by facet engineering.     

Effect of filling on the compressibility of carbon nanotubes: predictions from molecular dynamics simulations

The compressibility of filled and empty (10, 10) carbon nanotubes (CNTs) is examined using classical molecular dynamics simulations. The filled nanotubes contain C60, CH4, Ne, n-C4H10, and n-C4H7 molecules that are covalently cross-linked to the inner CNT walls. In addition, nanotubes filled with either a hydrogen-terminated carbon nanowire or a carbon nanotube of comparable diameter is also considered. The forces on the atoms are calculated using a many-body reactive empirical bond-order potential and the adaptive intermolecular reactive empirical bond-order potential for hydrocarbons. The butane-filled system shows a unique yielding behavior prior to buckling that has not been observed previously. Cross-linking the molecules to the inner CNT walls is not predicted to affect the stiffness of the filled nanotube systems and removes the yielding response. The mechanical response of the nanowire filled CNT is remarkably similar to the response of the similarly sized multiwalled CNT.     

Detecting mechanical resonance in carbon nanotubes via inter-tube electrical transport measurements

Detecting the mechanical resonance frequency of carbon nanotubes has strong potential applications that range from nano-scale balances to detect very small mass changes to ultra-sensitive bio-sensors. Detection of nanotube resonance requires elaborate and time-consuming techniques such as in-situ TEM, which limits the practical utility of this concept. In this paper we report a simple and accurate technique for detection of nanotube resonance by monitoring inter-tube electrical transport in a vibrating array of aligned multiwalled carbon nanotubes. The conductivity measurements are performed using a four-point probe in a direction perpendicular to the nanotube axis. We observe a dramatic decrease in the dc electrical resistance of the nanotube array at the mechanical resonance condition. We believe this is due to inter-tube impacts at resonance, which leads to an increase in the nanotube local temperature and hence increases the electron hopping rate. The impacting of the tubes could also enable localized tunneling of electrons through the nanotube array along with the hopping.     

Vibrating carbon nanotubes as water pumps

Nanopumps conducting fluids directionally through nanopores and nanochannels have attracted considerable interest for their potential applications in nanofiltration, water purification, and hydroelectric power generation. Here, we demonstrate by molecular dynamics simulations that an excited vibrating carbon nanotube (CNT) cantilever can act as an efficient and simple nanopump. Water molecules inside the vibrating cantilever are driven by centrifugal forces and can undergo a continuous flow from the fixed to free ends of the CNT. Further extensive simulations show that the pumping function holds good not only for a single-file water chain in a narrow (6,6) CNT, but also for bulk-like water columns inside wider CNTs, and that the water flux increases monotonically with increasing diameter of the nanotube.     

Salt Rejection and Water Transport Through Boron Nitride Nanotubes

Nanotube‐based water‐purification devices have the potential to transform the field of desalination and demineralization through their ability to remove salts and heavy metals without significantly affecting the fast flow of water molecules. Boron nitride nanotubes have shown superior water flow properties compared to carbon nanotubes, and are thus expected to provide a more efficient water purification device. Using molecular dynamics simulations it is shown that a (5, 5) boron nitride nanotube embedded in a silicon nitride membrane can, in principle, obtain 100% salt rejection at concentrations as high as 1 M owing to a high energy barrier while still allowing water molecules to flow at a rate as high as 10.7 water molecules per nanosecond (or 0.9268 L m^?2 h^?1). Furthermore, ions continue to be rejected under the influence of high hydrostatic pressures up to 612 MPa. When the nanotube radius is increased to 4.14 Å the tube becomes cation‐selective, and at 5.52 Å the tube becomes anion‐selective.     

Spectroscopic evidence and molecular simulation investigation of the pi-pi interaction between pyrene molecules and carbon nanotubes

The pi-pi interaction between pyrene molecules and single-walled carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs) was studied by fluorescence, FTIR, Raman spectroscopy and molecular simulation. The carbon nanotubes were incubated in pyrene solution and dried for characterization. A broadband fluorescence emission at 463 nm of the incubated samples was observed, which is similar to that of pyrene excimers but shifts to shorter wavelength. The typical FTIR bands of pyrene shift to lower wavenumbers in the incubated samples. D- and G-bands in Raman spectra of SWNTs also shift to low frequencies. All these spectroscopic evidences reveal the stronger pi-pi stacking interaction between the nanotubes and pyrene molecules over the pyrene dimers, which leads to the formation of pyrene-carbon nanotube complexes. The systems of SWNTs and pyrene molecules were also studied with molecular simulation. It was found from the binding energy calculation that a stronger interaction presents between the pyrene molecule and the nanotube. In addition, the simulation gives some structural information about the pyrene-nanotube complex, such as the staggered conformation of pyrene on nanotube. The effect of defects in carbon nanotube sidewall was also discussed.     

有限长开口单壁碳纳米管结构与非线性光学性质

利用ChemSketch10．0设计了一系列两端开口的有限长碳纳米管分子（n,0）（n=5-10）,使用量子化学半经验AM1方法研究了分子的电子结构,并使用有限场／AM1方法计算了分子的一阶极化率、非线性光学二阶和三阶极化率。研究结果表明,两端开口的有限长碳纳米管分子最高占据轨道（HOMO）与最低空轨道（LUMO）间的能隙Eg随着管径的增大而出现随奇偶n值的振荡变化,随着管长Ⅳ的增加呈单调减小的趋势。目标分子中,管长为N=3的分子系列具有较高的二阶、三阶非线性光学极化系数β,γ,而（8,0）N=3分子具有最大的β值,（7,0）N=3分子具有最大的γ值。     

Noise characteristics of single-walled carbon nanotube network transistors

The noise characteristics of randomly networked single-walled carbon nanotubes grown directly by plasma enhanced chemical vapor deposition (PECVD) are studied with field effect transistors (FETs). Due to the geometrical complexity of nanotube networks in the channel area and the large number of tube-tube/tube-metal junctions, the inverse frequency, 1/f, dependence of the noise shows a similar level to that of a single single-walled carbon nanotube transistor. Detailed analysis is performed with the parameters of number of mobile carriers and mobility in the different environment. This shows that the change in the number of mobile carriers resulting in the mobility change due to adsorption and desorption of gas molecules (mostly oxygen molecules) to the tube surface is a key factor in the 1/f noise level for carbon nanotube network transistors.     

Identifying the mechanism of biosensing with carbon nanotube transistors

Carbon nanotube transistors have outstanding potential for electronic detection of biomolecules in solution. The physical mechanism underlying sensing however remains controversial, which hampers full exploitation of these promising nanosensors. Previously suggested mechanisms are electrostatic gating, changes in gate coupling, carrier mobility changes, and Schottky barrier effects. We argue that each mechanism has its characteristic effect on the liquid gate potential dependence of the device conductance. By studying both the electron and hole conduction, the sensing mechanisms can be unambiguously identified. From extensive protein-adsorption experiments on such devices, we find that electrostatic gating and Schottky barrier effects are the two relevant mechanisms, with electrostatic gating being most reproducible. If the contact region is passivated, sensing is shown to be dominated by electrostatic gating, which demonstrates that the sensitive part of a nanotube transistor is not limited to the contact region, as previously suggested. Such a layout provides a reliable platform for biosensing with nanotubes.     

分散剂CTAB对碳纳米管悬浮液分散性能的影响

以十六烷基三甲基溴化铵(CTAB)为分散剂, 制备了分散性能良好的碳纳米管悬浮液. 通过测定等温吸附曲线和悬浮液的Zeta电位, 研究了CTAB对碳纳米管表面性质的影响. 结果表明, CTAB的加入使Zeta电位由-29mV变为65mV左右; 等温吸附曲线表明,CTAB在碳纳米管表面为“两阶段吸附”, CTAB浓度为9×10^-4 mol·L^-1时, 在碳纳米管表面达到饱和吸附. 通过悬浮碳纳米管浓度测定确定了所需最佳CTAB的用量为9×10^-4 mol·L^-1左右, 同时对CTAB的吸附分散机理进行了分析和讨论.     

Field emission properties of carbon nanotubes coated with boron nitride

Field emission properties of carbon nanotubes coated with a single layer of boron nitride are calculated using the first-principles pseudopotential method. At lower bias voltage, the emission current of the coated nanotube is comparable to that of the bare carbon nanotube and is dominated by the contribution from localized states at the tip of the tube. At higher voltage, newly generated hybridized states between the carbon nanotube tip and the even-membered boron nitride rings contribute significantly to the emission current because they experience a low tunneling barrier compared with the bare carbon nanotube case. Our results suggest that the insulator coating can, besides protecting the nanotube tip from the attack of gas molecules, substantially enhance the field emission current.     

Atomically resolved mechanical response of individual metallofullerene molecules confined inside carbon nanotubes

The hollow core inside a carbon nanotube can be used to confine single molecules and it is now possible to image the movement of such molecules inside nanotubes. To date, however, it has not been possible to control this motion, nor to detect the forces moving the molecules, despite experimental and theoretical evidence suggesting that almost friction-free motion might be possible inside the nanotubes. Here, we report on precise measurements of the mechanical responses of individual metallofullerene molecules (Dy@C82) confined inside single-walled carbon nanotubes to the atom at the tip of an atomic force microscope operated in dynamic mode. Using three-dimensional force mapping with atomic resolution, we addressed the molecules from the exterior of the nanotube and measured their elastic and inelastic behaviour by simultaneously detecting the attractive forces and energy losses with three-dimensional, atomic-scale resolution.     

Mono-dispersed single-wall carbon nanotubes formed in channels of zeolite crystal: Production, optical and electrical transport properties

Carbon nanotube materials can now be produced in macroscopic quantities. However, the raw material has a disordered structure and unsorted size, which restrict investigations of both the properties and applications of the nanotubes. In this paper, an alternative approach to the synthesis of mono-sized and parallel-aligned single wall carbon nanotubes (SWCNs) is reported. The SWCNs are formed in 1 nm-sized channels of aluminophosphate zeolite crystallites by pyrolysis of tripropylamine molecules. As verified by tunnel electron microscopy and micro-Raman scattering, the SWNT is of zigzag structure. Electrical transport properties of the SWNT are measured in the temperature range of 0·3K∼300K. The temperature-dependent dc conductivity shows that the SWNT is an intrinsic semiconductor with a narrow band-gap of 52 meV. The well-aligned and mono-sized SWCNs allow us to make more controlled characterization as well as open a door to potential nano-technological application for the novel electronic nanotube system.