Single-walled carbon nanotubes based chemicapacitive sensors

Carboxylated single-walled carbon nanotubes (SWNTs) based chemicapacitive gas sensors were fabricated by AC dielectrophoretically aligning SWNTs across microfabricated gold electrodes with controlled density/device resistance. Two different sensing configurations (i.e., horizontal/in-plane and vertical/out-of-plane) were utilized to compare their sensing performance. Upon exposure to water vapor at room temperature, the response (R = [(C--C0)/C0] x 100%) increased with an increase in water vapor concentration similar to that of resistance response. In horizontal configuration, the response was increased with an increase in device resistance which might be attributed to preferentially alignment of semiconducting SWNTs during initial phase of alignment. However, the response was independent of device resistance in vertical/out-of-plane configuration which indicated that the sensing mechanism is based on the change of dielectric constant of gate and atmosphere.     

Single-walled carbon nanotubes as excitonic optical wires

Although metallic nanostructures are useful for nanoscale optics, all of their key optical properties are determined by their geometry. This makes it difficult to adjust these properties independently, and can restrict applications. Here we use the absolute intensity of Rayleigh scattering to show that single-walled carbon nanotubes can form ideal optical wires. The spatial distribution of the radiation scattered by the nanotubes is determined by their shape, but the intensity and spectrum of the scattered radiation are determined by exciton dynamics, quantum-dot-like optical resonances and other intrinsic properties. Moreover, the nanotubes display a uniform peak optical conductivity of approximately 8 e(2)/h, which we derive using an exciton model, suggesting universal behaviour similar to that observed in nanotube conductance. We further demonstrate a radiative coupling between two distant nanotubes, with potential applications in metamaterials and optical antennas.     

Single-walled carbon nanotubes used as stationary phase in GC

Single-walled carbon nanotubes (SWNTs) have high surface area, high adsorption ability, and nanoscale interactions. In this study, capillary columns including SWNTs, ionic liquid (IL), and IL + SWNTs for GC were prepared. The separation results showed that SWNTs possessed a wide selectivity toward alkanes, alcohols, aromatic compounds, and ketones, and a SWNT capillary column was a very useful GC column for the separation of gas samples. Coating the IL stationary phase on the SWNT capillary column, the SWNTs were able to improve chromatographic characteristic of ionic liquid. Comparing the IL coated on three graphite carbon black capillary columns, which were prepared by dynamic coating, static coating, and chemical bonding the Carbopack C with on SWNTs capillary column, the capacity factors were much higher on the SWNT column. The SEM showed that SWNTs could be bonded to the inner surface of capillary tubing, and most of them were linked end-to-end to form a layer of network structure of skeletons resulting in a high surface area, which increased the interactions between stationary phase and analytes. This is the first single-wall carbon nanotubes bonded to the fused-silica capillary tubing. In the first approach, SWNTs assist ionic liquid with enhanced chromatographic characteristic in GC. This work indicates that SWNTs make it possible to extend the application range on the newly prepared chromatographic stationary phases for GC.     

Single-walled carbon nanotubes nanocomposite microacoustic organic vapor sensors

We have developed highly sensitive microacoustic vapor sensors based on surface acoustic waves (SAWs) configured as oscillators using a two-port resonator 315, 433 and 915 MHz device. A nanocomposite film of single-walled carbon nanotubes (SWCNTs) embedded in a cadmium arachidate (CdA) amphiphilic organic matrix was prepared by Langmuir–Blodgett technique with a different SWCNTs weight filler content onto SAW transducers as nanosensing interface for vapor detection, at room temperature. The structural properties and surface morphology of the nanocomposite have been examined by X-ray diffraction, transmission and scanning electron microscopy, respectively. The sensing properties of SWCNTs nanocomposite LB films consisting of tangled nanotubules have been also investigated by using Quartz Crystal Microbalance 10 MHz AT-cut quartz resonators. The measured acoustic sensing characteristics indicate that the room-temperature SAW sensitivity to polar and nonpolar tested organic molecules (ethanol, ethylacetate, toluene) of the SWCNTs-in-CdA nanocomposite increases with the filler content of SWCNTs incorporated in the nanocomposite; also the SWCNTs-in-CdA nanocomposite vapor sensitivity results significantly enhanced with respect to traditional organic molecular cavities materials with a linearity in the frequency change response for a given nanocomposite weight composition and a very low sub-ppm limit of detection.     

Single-walled carbon nanotubes induces oxidative stress in rat lung epithelial cells

Single-walled carbon nanotubes (SWCNT) show unique properties find applications in micro devices; electronics to biological systems specially drug delivery and gene therapy. However the manufacture and extensive use of nanotubes raises concern about its safe use and human health. Very few studies have been carried out on toxicity of carbon nanotubes in experimental animals and humans, thus resulted in limiting their use. The extensive toxicological studies using in vitro and in vivo models are necessary and are required to establish safe manufacturing guidelines and also the use of SWCNT. These studies also help the chemists to prepare derivative of SWCNT with less or no toxicity. The present study was undertaken to determine the toxicity exhibited by SWCNT in rat lung epithelial cells as a model system. Lung epithelial cells (LE cells) were cultured with or without SWCNT and reactive oxygen species (ROS) produced were measured by change in fluorescence using dichloro fluorescein (DCF). The results show increased ROS on exposure to SWCNT in a dose and time dependent manner. The decrease in glutathione content suggested the depletion and loss of protective mechanism against ROS in SWCNT treated cells. Use of rotenone, the inhibitor of mitochondrial function have no effect on ROS levels suggested that mitochondria is not involved in SWCNT induced ROS production. Studies carried out on the effect of SWCNT on superoxide dismutase (SOD-1 and SOD-2) levels in LE cells, indicates that these enzyme levels decreased by 24 hours. The increased ROS induced by SWCNT on LE cells decreased by treating the cells with 1 mM of glutathione, N-Acetyl Cysteine, and Vitamin C. These results further prove that SWCNT induces oxidative stress in LE cells and shows loss of antioxidants.     

Single-walled carbon nanotubes modified carbon ionic liquid electrode for sensitive electrochemical detection of rutin

The single-walled carbon nanotubes (SWCNTs) modified carbon ionic liquid electrode (CILE) was designed and further used for the voltammetric detection of rutin in this paper. CILE was prepared by mixing graphite powder with ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate and liquid paraffin together. Based on the interaction of SWCNTs with IL present on the electrode surface, a stable SWCNTs film was formed on the CILE to get a modified electrode denoted as SWCNTs/CILE. The characteristics of SWCNTs/CILE were recorded by different methods including cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy. The electrochemical behaviors of rutin on the SWCNTs/CILE were investigated by cyclic voltammetry and differential pulse voltammetry. Due to the specific interface provided by the SWCNTs-IL film, the electrochemical response of rutin was greatly enhanced with a pair of well-defined redox peaks appeared in pH 2.5 phosphate buffer solution. The oxidation peak currents showed good linear relationship with the rutin concentration in the range from 1.0 × 10^− 7 to 8.0 × 10^− 4 mol/L with the detection limit as 7.0 × 10^− 8 mol/L (3σ). The SWCNTs/CILE showed the advantages such as excellent selectivity, improved performance, good stability and it was further applied to the rutin tablets sample detection with satisfactory results.     

Single-walled carbon nanotubes modified by ionic liquid as antiwear additives of thermoplastics

Pristine single-walled carbon nanotubes (CNTs) were dispersed in the room-temperature ionic liquid (IL) 1-octyl, 3-methylimidazolium tetrafluoroborate ([OMIM]BF₄) by grinding and ultrasounds. Excess IL was removed to obtain single-walled carbon nanotubes modified by [OMIM]BF₄ (mCNTs). mCNTs were added in a 1 wt.% to polystyrene (PS), polymethylmethacrylate (PMMA) and polycarbonate (PC) to obtain PS + mCNT, PMMA + mCNT and PC + mCNT. The dry tribological performance of the new nanocomposites was studied against AISI 316L stainless steel pins and compared with that of the neat polymers and with the nanocomposites containing pristine carbon nanotubes without IL (PS + CNT; PMMA + CNT and PC + CNT). The maximum wear rate and friction coefficient reduction is obtained for PS + mCNT. Results are discussed upon the basis of optical, SEM and TEM microscopy, thermogravimetric analysis (TGA), Raman spectroscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).     

Single-walled carbon nanotubes under the influence of dynamic coordination and supramolecular chemistry

A dynamic coordinative-directed solubilization of single-walled carbon nanotubes (SWNTs) in aqueous solutions has been achieved through a combination of a Zn(II) metalloporphyrin complex and a cis-protected Pd(II) complex, which are believed to form charged acyclic and/or cyclic adducts on or around the side walls of SWNTs. The solubilization of SWNTs in aqueous solution only occurs when these acyclic and/or cyclic complexes are allowed to enter simultaneously into a self-assembly process with SWNTs under mild conditions. The aqueous solubility properties that these dynamic complexes confer upon SWNTs are believed to involve noncovalent bonding interactions between the two entities. They have been probed in solution using ultraviolet and visible absorption spectroscopy and in thin films using high-resolution transmission electron microscopy. The supramolecular electronic effects that the individual components of their acyclic and/or cyclic complexes impart upon a single semiconducting SWNT have been probed within a nanotube field-effect transistor device.     

Nitrogen beam bombardment induce polarity of carbon nanotubes

The multiwalled carbon nanotubes (MWCNTs) were prepared on SiO₂ substrates using chemical vapor deposition (CVD). N ion beam bombardment to MWCNTs was performed at different beam currents of 5–15 mA in an ion-beam-assisted deposition (IBAD) system. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) proved no significant crack and surface morphological change for MWCNTs after N ion beam bombardment. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometry (FTIR), and Raman studies indicated that higher N ion beam current (15 mA) or N atomic concentration (8.6%) induced formation of polar N-containing functional groups of N–C and N–H bonds on the surfaces of MWCNTs. The content of N–C and N–H bonds increased with N ion beam current.     

Single-walled carbon nanotubes in the intact organism: near-IR imaging and biocompatibility studies in Drosophila

The ability of near-infrared fluorescence imaging to detect single-walled carbon nanotubes (SWNTs) in organisms and biological tissues has been explored using Drosophila melanogaster (fruit flies). Drosophila larvae were raised on food containing approximately 10 ppm of disaggregated SWNTs. Their viability and growth were not reduced by nanotube ingestion. Near-IR nanotube fluorescence was imaged from intact living larvae, and individual nanotubes in dissected tissue specimens were imaged, structurally identified, and counted to estimate a biodistribution.     

Amine-modified single-walled carbon nanotubes protect neurons from injury in a rat stroke model

Stroke results in the disruption of tissue architecture and is the third leading cause of death in the United States. Transplanting scaffolds containing stem cells into the injured areas of the brain has been proposed as a treatment strategy, and carbon nanotubes show promise in this regard, with positive outcomes when used as scaffolds in neural cells and brain tissues. Here, we show that pretreating rats with amine-modified single-walled carbon nanotubes can protect neurons and enhance the recovery of behavioural functions in rats with induced stroke. Treated rats showed less tissue damage than controls and took longer to fall from a rotating rod, suggesting better motor functions after injury. Low levels of apoptotic, angiogenic and inflammation markers indicated that amine-modified single-walled carbon nanotubes protected the brains of treated rats from ischaemic injury.     

A progressive fracture model for carbon nanotubes

An atomistic-based progressive fracture model for simulating the mechanical performance of carbon nanotubes by taking into account initial topological and vacancy defects is proposed. The concept of the model is based on the assumption that carbon nanotubes, when loaded, behave like space-frame structures. The finite element method is used to analyze the nanotube structure and the modified Morse interatomic potential to simulate the non-linear force field of the C–C bonds. The model has been applied to defected single-walled zigzag, armchair and chiral nanotubes subjected to axial tension. The defects considered were: 10% weakening of a single bond and one missing atom at the middle of the nanotube. The predicted fracture evolution, failure stresses and failure strains of the nanotubes correlate very well with molecular mechanics simulations from the literature.     

An RF circuit model for carbon nanotubes

We develop an RF circuit model for single walled carbon nanotubes for both dc and capacitively contacted geometries. By modeling the nanotube as a nanotransmission line with distributed kinetic and magnetic inductance as well as distributed quantum and electrostatic capacitance, we calculate the complex, frequency dependent impedance for a variety of measurement geometries. Exciting voltage waves on the nanotransmission line is equivalent to directly exciting the yet-to-be observed one dimensional plasmons, the low energy excitation of a Luttinger liquid.     

Multi-walled carbon nanotubes induce apoptosis in RAW 264.7 cell-derived osteoclasts through mitochondria-mediated death pathway

Carbon nanotubes (CNTs) have attracted great interest with respect to biomaterials, particularly for use as an implant material in bone-tissue engineering. Accordingly, the bone-tissue compatibility of CNTs and their influence on new bone formation are important issues. In the present study, we examined the effects of multi-wall carbon nanotubes (MWCNTs) on the receptor activator of nuclear factor kappaB ligand (RANKL)-supported osteoclastogenesis using a murine monocytic cell line RAW 264.7. MWCNTs significantly suppressed the differentiation of RAW 264.7 cells into osteoclasts. Treatment with MWCNTs induced apoptosis in osteoclasts as characterized by nuclear condensation, DNA fragmentation, caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage, but did not decrease the cell viability of the osteoblast-like cell line MC3T3-E1. MWCNTs also induced loss of the mitochondrial membrane potential (deltapsim) by regulating expression of Bcl-2 family proteins and caused release of cytochrome c from mitochondria to cytosol. MWCNTs-induced apoptosis in osteoclasts was inhibited both by cyclosporin A, a blocker of the mitochondrial permeability transition pore, and by DEVD-CHO, a cell-permeable inhibitor of caspase-3. The present study suggests that MWCNTs suppresse osteoclastogenesis via the inhibition of osteoclast differentiation and the induction of apoptosis in osteoclasts, rendering them promising candidate for the treatment of osteoclast-related diseases.     

DNA damage induced by multiwalled carbon nanotubes in mouse embryonic stem cells

Carbon nanotubes (CNTs) have shown promise as an important new class of multifunctional building blocks and innovative tools in a large variety of applications, ranging from nanocomposite materials through nanoelectronics to biomedical devices. Because of their unusual one-dimensional hollow nanostructure and unique physicochemical properties, CNTs are particularly useful as novel drug delivery tools and imaging agents. However, such biomedical applications will not be realized if there is no proper assessment of the potential hazards of CNTs to humans and other biological systems. Although a few reports on the cytotoxicity of CNTs have been published, very little is known about the toxicity at the molecular level, or genotoxicity, of CNTs in mammalian cells. We have for the first time assessed the DNA damage response to multiwalled carbon nanotubes (MWNTs) in mouse embryonic stem (ES) cells. We found that MWNTs can accumulate and induce apoptosis in mouse ES cells and activate the tumor suppressor protein p53 within 2 h of exposure. Furthermore, we also observed increased expression of two isoforms of base excision repair protein 8-oxoguanine-DNA glycosylase 1 (OGG1), double strand break repair protein Rad 51, phosphorylation of H2AX histone at serine 139, and SUMO modification of XRCC4 following the treatment with MWNTs. A mutagenesis study using an endogenous molecular marker, adenine phosphoribosyltransferase (Aprt), showed that MWNTs increased the mutation frequency by 2-fold compared with the spontaneous mutation frequency in mouse ES cells. These results suggest that careful scrutiny of the genotoxicity of nanomaterials is needed even for those materials, like multiwalled carbon nanotubes, that have been previously demonstrated to have limited or no toxicity at the cellular level.     

An elastic shell model for characterizing single-walled carbon nanotubes

This paper proposes a two-dimensional elastic shell model to characterize the deformation of single-walled carbon nanotubes using the in-plane rigidity, Poisson ratio, bending rigidity and off-plane torsion rigidity as independent elastic constants. It was found that the off-plane torsion rigidity of a single-walled carbon nanotube is not zero due to the off-plane change in the π-orbital electron density on both sides of the nanotube. It was concluded that a three-dimensional elastic shell model of single-walled carbon nanotubes can be established with well-defined effective thickness.     

Percolation model of reinforcement efficiency for carbon nanotubes dispersed in thermoplastics

Considerable experimental work on carbon nanotube-reinforced composites has shown that the reinforcement efficiency of carbon nanotubes (CNTs) becomes lower than the theoretical expectation when CNT content reaches a critical value. This critical volume fraction (percolation threshold) is considered related to the formation of percolating network. In this work, a percolation model is proposed to describe the observed sharp decrease in the reinforcement efficiency of multiwalled CNTs (MWCNTs) dispersed in thermoplastics when the CNT content exceeds the percolation threshold. The percolation threshold is estimated via a numerical simulation of randomly curved CNTs according to the statistics on geometrical features of real CNTs. The percolation model, integrated into the Halpin–Tsai equations, is verified using the experimental data of various thermoplastic composites reinforced with MWCNTs. The developed mechanical model achieves a good agreement with the measured moduli of nanocomposites, and demonstrates an excellent prediction capability over a wide range of CNT content.     

A structure model and growth mechanism for novel carbon nanotubes

The growth of carbon nanotubes from catalytic thermal decomposition of acetylene on fine iron particles has been studied. Electron microscopic images of the carbon nanotubes as formed and after annealing treatment are presented. Besides the ordinary carbon nanotubes which have been reported (S. Iijima, Nature, 354 (1991) 56), we have found, at first time, two other new kinds of carbon nanotubes: one is straight or curved nanotube with many irregular multi-layered diaphragms in the hollow core, in particular, the fringes of the wall of the tubes are not parallel to the axis of the tube; another one has many regular diaphragms (bamboo-like) which keep almost constant distance with each other. A model that postulates two steps growth of nanotubes from catalyst particles is proposed to explain the microstructure of the novel carbon nanotubes.     

Ferroelectric ordering in ice nanotubes confined in carbon nanotubes

The ice nanotubes with odd number of side faces formed inside carbon nanotubes (CNTs) are found to exhibit spontaneous electric polarizations along their tube axes by means of molecular dynamics simulations. The physical mechanism underlying the quasi-one-dimensional (Q1D) ferroelectricity is an interplay between the Q1D geometrical confinement of CNTs and the distinct orientational ordering of the hydrogen bonds dictated by the "ice rule". This mechanism is fundamentally different from the conventional one seen in three-dimensional ferroelectric (FE) materials or in two-dimensional FE ice films. In addition, it is found that vacancies in the ice nanotubes can induce a net polarization normal to the tube axis.