Suspended Single-walled Carbon Nanotubes Research Articles

Suspensions of single-wall carbon nanotubes stabilized by pluronic for biomedical applications

The optimal conditions of preparation of aqueous suspensions of individual single-wall carbon nanotubes with Pluronic F127 surfactant have been determined. The variable parameters are the surfactant concentration, the regimes of ultrasonication and ultracentrifuging. The stable suspensions of bio-molecules (such as albumin) and nanotubes dispersed with Pluronic have been demonstrated.

Exciton Transport in Suspended Single Carbon Nanotubes Studied by Photoluminescence Imaging Spectroscopy

We studied the spatial profiles and time traces of the photoluminescence (PL) intensity of suspended single-walled carbon nanotubes (SWNTs) using a microscopic PL imaging technique. These PL images, obtained in different gases, showed that adsorbed oxygen molecules act as PL quenchers in SWNTs. The exciton transport length of suspended SWNTs was estimated to be ∼200 nm at room temperature. We found that the exciton transport and its temperature dependence are dominated by the diffusive motion of a one-dimensional exciton in a single carbon nanotube.

Effect of deposition conditions on percolation in single‐walled carbon nanotube networks

AbstractMacroscopic networks of ordered single‐walled carbon nanotubes (SWNTs) have been formed using laminar‐flow deposition (LFD) at room temperature. This deposition method involves successive deposition cycles from aqueous suspensions of SWNTs. Each deposition cycle deposits a reproducible density of partially aligned SWNTs, which allows a great level of control over the network formation process. The macroscopic conductivity of these 2‐D thin‐films was observed to follow percolation theory throughout the network growth process. The ability of this deposition method to partially align SWNTs during deposition was investigated. Networks deposited with SWNTs having orthogonal directionality showed significantly greater precision and current capacity than networks composed of SWNTs that were partially aligned in only one direction. magnified image

Tailored dispersion of carbon nanotubes in water with pH-responsive polymers

In an effort to control the level of carbon nanotube exfoliation in water, pH-responsive polymers (i.e., weak polyelectrolytes) have been used as stabilizers in water. This noncovalent functionalization of single-walled carbon nanotubes (SWNTs) results in suspensions whose dispersion state can be altered by simply changing pH. In this study poly(acrylic acid), poly(methacrylic acid), poly(allylamine) and polyethyleneimine were used to stabilize aqueous SWNT suspensions. The results indicate that SWNTs stabilized with these polymers show a pH tailorable exfoliation and bundling in water, as evidenced by cryo-TEM images and shifts in suspension viscosity. Composite films prepared by drying these aqueous suspensions suggest that nanotube microstructure in the liquid state is largely preserved in the solid composites, with more bundled/networked structures showing higher electrical conductivity. A stabilization mechanism based upon the results obtained is proposed to explain the exfoliation and aggregation behavior of SWNTs. This method of controlling the microstructure of SWNTs in liquid state with pH could have a significant impact on the ability to tailor the microstructure and properties of composites.

Sorting single-walled carbon nanotubes by strain-based electrical burn-off

Armchair metallic single-walled carbon nanotubes (SWCNTs) retain their high symmetry under tensile stretching, and their electrical properties are the least sensitive to tensile strain. Other types of SWCNTs with lower symmetries, including quasi-metallic (or small band-gap semiconducting) and semiconducting SWCNTs, are more sensitive and can exhibit band-gap changes under tensile stretching. In this study, we demonstrate a simple and reliable method for selectively removing armchair metallic SWCNTs from suspended SWCNT arrays to tailor the strain property of these composite SWCNTs. Our method takes advantage of the band-gap changes of three SWCNT species with respect to strain. Proof of the effectiveness of selection is given by a comparative strain sensitivity study on the initial and treated SWCNT arrays.

Ensemble-averaged particle orientation and shear viscosity of single-wall-carbon-nanotube suspensions under shear and electric fields

The ensemble-averaged particle-orientation angles and apparent shear viscosities of dilute suspensions of single-wall carbon nanotubes (SWNTs) in a liquid solvent, α-terpineol, were experimentally studied under combined shear flow and electric fields. An optical polarization-modulation method was used to measure the orientation angles of individual and small bundles of SWNTs, while a modified concentric-cylinder viscometer was used to make simultaneous electrorheological measurements of the apparent viscosity. The particle-orientation response occurs on time scales one to two orders of magnitude faster than the macroscopic electrorheological response, and does not appear to directly affect the apparent viscosity at these low concentrations. Particle-orientation angles for various shear rates and electric fields are found to collapse when plotted against the parameter, f∼E2/γ̇, as predicted by the theory developed by Mason and co-workers for the equilibrium orientation angle of ellipsoids under electric fields and shear flow. However, comparison between measured and predicted particle-orientation angles shows poor agreement at intermediate values of f. Electrostatic interactions between large-aspect-ratio particles are shown to be significant, and may account for the discrepancy between the measurements and classical theory for even dilute suspensions of nanotubes under both shear and electric fields.

Transfer and Alignment of Random Single-Walled Carbon Nanotube Films by Contact Printing

We present a simple method to transfer large-area random single-walled carbon nanotube (SWCNT) films grown on SiO(2) substrates onto another surface through a simple contact printing process. The transferred random SWCNT films can be assembled into highly ordered, dense regular arrays with high uniformity and reproducibility by sliding the growth substrate during the transfer process. The position of the transferred SWCNT film can be controlled by predefined patterns on the receiver substrates. The process is compatible with a variety of substrates, and even metal meshes for transmission electron microscopy (TEM) can be used as receiver substrates. Thus, suspended web-like SWCNT networks and aligned SWCNT arrays can be formed over the grids of TEM meshes, so that the structures of the transferred SWCNTs can be directly observed by TEM. This simple technique can be used to controllably transfer SWCNTs for property studies, for the fabrication of devices, or even as support films for TEM meshes.

Large-Scale Aligned Carbon Nanotubes from Their Purified, Highly Concentrated Suspension

Large-scale aligned single-walled carbon nanotube (SWCNT) composite membranes have been successfully prepared from highly concentrated purified SWCNT suspensions. Biopolymer dispersant gellan gum was used to achieve aqueous dispersion of highly concentrated SWCNTs, which can be used to form the SWCNT liquid crystal phase. To achieve alignment of SWCNTs, purification of SWCNTs is found to be very important. Purification was achieved by a facile and nondestructive physical method that can prepare large volumes of SWCNTs in high yield for experimental use. Composite membranes of aligned SWCNTs could be obtained by simple evaporation SWCNT liquid crystal. The orientation direction of aligned SWCNTs was controlled by mechanical shearing of SWCNT liquid crystal. The aligned SWCNTs in the biopolymer matrix were observed by electron microscopy, and the anisotropic electrical performance of this composite thin film has been characterized.

Sequence-Specifically Addressable Hairpin DNA−Single-Walled Carbon Nanotube Complexes for Nanoconstruction

Single-walled carbon nanotubes (SWCNTs) are attractive building blocks for molecular electronics and novel materials. Generating functional architectures with SWCNTs requires methodologies for dispersing, purifying, and binding these highly insoluble quasi one-dimensional molecules. We have previously shown that unstructured DNA strands bind to carbon nanotubes so tightly that it is difficult to address them with complementary strands. Here we show that hairpin oligonucleotides give SWCNT suspensions more concentrated than those obtainable with previously optimized DNA sequences. Further, hairpin-forming oligonucleotides and (6,5)-SWCNTs form complexes that are addressable with complementary, triplex-forming oligonucleotides. As proof of principle, we show that DNA-SWCNT complexes can be bound sequence-specifically with oligonucleotides featuring fluorophores or quantum dots. The new method brings SWCNTs of exquisite purity into the realm of DNA-based nanostructuring.

Generation and size classification of single-walled carbon nanotube aerosol using atmospheric pressure pulsed laser ablation (AP-PLA)

Gas suspended single-walled carbon nanotubes (SWCNTs) with single tube diameter smaller than 2 nm and length of longer than 500 nm were generated by simple and continuous system using laser ablation technique under atmospheric conditions. Graphite target containing 0.5 wt%-nickel and 0.5 wt%-cobalt was ablated by Nd:YAG laser in an electrical furnace under atmospheric pressure of nitrogen flow that allowed one step and continuous synthesis of the SWCNTs. Size distribution of the gas suspended SWCNTs aerosol was measured using size-classification by a differential mobility analyzer (DMA) coupled with a condensation particle counter (CPC) used as a detector. Characteristics of SWCNT aerosol generated under the different temperature were also investigated using scanning and transmission electron microscopes and Raman scattering. Mono-mobility SWCNT aerosol with mobility diameter of 100 and 200 nm was successfully prepared after the size separation using a DMA.

Fabrication of Directionally Aligned Carbon Nanotube Thin Films on Solid Surfaces Using Chemical Patterns

We propose a simple fabrication process of directionally aligned single-walled carbon nanotube (SWCNT) thin films. This process consists of dropping of a highly dispersed SWCNT suspension followed by its drying. We used a substrate surface on which hydrophilic and hydrophobic patterns are formed by chemical processes. A SWCNT suspension dropped on the hydrophobic areas is transferred to the hydrophilic areas in the early stage of the drying. During the drying, the SWCNTs in the suspension are self-aligned by the surface tension. When the degree of hydrophilicity on the hydrophilic areas is too large, deposition of the SWCNTs on small hydrophilic areas is blocked by the repulsive force owing to hydration between the hydrophilic substrate and the SWCNT surfaces. We demonstrated that narrow line patterns of the SWCNT thin films can be fabricated by controlling the hydrophilicity on the hydrophilic areas on the substrate. [DOI: 10.1380/ejssnt.2010.207]

Stable and Responsive Fluorescent Carbon Nanotube Silica Gels

AbstractHere we report a general route to prepare silica nanocomposite gels doped with fluorescent single walled carbon nanotubes (SWNT). We show that tetramethylorthosilicate (TMOS) vapors can be used to gel an aqueous suspension of surfactant-wrapped SWNT while maintaining fluorescence from the semiconducting nanotubes. The vapor phase silica process is performed at room temperature and is simple, reproducible, relatively quick, and requires no dilution of SWNT dispersions. However, exposure of aqueous SWNT suspensions to TMOS vapors resulted in an acidification of the suspension prior to gelation that caused a decrease in the emission signal from sodium dodecylsulfate (SDS) wrapped SWNT. We also show that although the SWNT are encapsulated in silica the emission signal from the encapsulated SWNT may be attenuated by exposing the nanocomposites to small aromatic molecules known to mitigate SWNT emission. These results demonstrate a new route for the preparation of highly luminescent SWNT/silica composite materials that are potentially useful for future sensing applications.

High sensitivity temperature sensor based on a long, suspended single-walled carbon nanotube array

Considering the electron–phonon scattering mechanisms as well as the number of conduction channels, the long single-walled carbon nanotube (SWCNT) has larger temperature coefficient of resistivity than that of the short SWCNT or that of the multi-walled carbon nanotube (CNT). A tens of micrometres length, suspended SWCNT array-based temperature sensor was proposed, and its fabrication technique was presented. The theoretical analysis and the experimental results showed that the long SWCNT array device had high sensitivity and low power consumption than ordinary platinum thermal resistor. The long SWCNT array sensor also featured a simple and application-oriented process and was easier to use than a single CNT-based device. Thus, it has the potential to be applied in high sensitivity temperatures or flow measurements in an ultra small scale.

Force-sensitive Sensor Based on Single-walled Carbon Nanotube Array

Traditional silicon micro-machining technology is utilized to produce parallel micro-electrodes on silicon chips,and silicon chips are deeply etched to wear a rectangular hole between the parallel micro-electrodes.Next,ultra-long single-walled carbon nanotube(SWCNT) array is grown across micro-electrodes and rectangular hole to suspend well aligned between the parallel micro-electrodes by the method of large gas flow directional chemical vapor deposition(CVD).The Si chip attached with SWCNTs is then mounted onto a thin PVC base and the connections of Si island are cut by laser technology,so that the force acting on the PVC base can directly transfer to SWCNT array.After extraction of wires,the fabrication of micro-nano-force-sensing unit is finished.Later,the research is carried out mainly on strain sensing of suspended SWCNT array.High gauge factor and linearity are obtained.The experimental results show that this sensor unit is simple and low in cost,thus providing a new way of thinking upon the preparation for micro-nano integrated sensor unit based on carbon nanotubes.

Fabrication of single-walled carbon nanotube three-dimensional networks inside the pores of a porous silicon structure

Single-walled carbon nanotube (SWCNT) three-dimensional (3-D) networks were first fabricated in the pores of a porous silicon substrate using thermal decomposition of C2H2 at 800°C. Catalyst nanoparticles were uniformly distributed on the inner wall surfaces of the pores using a dipping method combined with ultrasonication. SWCNTs were synthesized along the inner wall surface of the pores, and spanned it. The suspended SWCNTs inside the pores formed 3-D networks in the results of the chaotic overgrowth of SWCNTs in a confined space under thermal vibration, and van der Waals interactions between SWCNTs.

Ultrafast vibrational motion of carbon nanotubes in different pH environments

We have used a femtosecond pump-probe impulsive Raman technique to explore the ultrafast dynamics of micelle suspended single walled carbon nanotubes (SWNTs) in various pH environments. The structures of coherent phonon spectra of the radial breathing modes (RBMs) exhibit significant pH dependence, to which we attribute the effect of the protonation at the surface of SWNTs, resulting in the modification of electronic properties of semiconductor SWNTs. Analysis of the time-domain data using a time-frequency transformation uncovers also a second transient longitudinal breathing mode, which vanishes after 1 ps of the photoexcitation.

Spectroscopic and Scanning Probe Studies of a Nondestructive Purification Method for SWNT Suspensions

A mild method for the bulk enrichment of high-aspect-ratio single-walled carbon nanotubes (SWNTs), while avoiding the damaging effects of acid purification methods, has been developed in this group. Various analytical techniques (atomic force microscopy, Raman microscopy, near IR, and UV−vis spectroscopy) have been used in order to attain a better understanding of the correlation between low-G centrifugation cycles and the quality of the SWNT suspension. Atomic force microscopy data of low-density SWNT networks formed from these suspensions indicate that the size and occurrence of globular impurities is lessened, while small bundles of high-aspect-ratio SWNTs remain. Raman spectroscopy is used to verify that this method produces suspensions of purified SWNTs without significantly damaging them. Near-infrared and UV−vis spectroscopy of these suspensions show prominent semiconducting and metallic interband transitions in the SWNTs and removal of impurities.

Abstract C142: Safety of single-walled carbon nanotubes for delivery of siRNA

Abstract siRNA is a leading potential new cancer therapy but currently lacks an adequate delivery mechanism. Ensysce has been exploring the use of single-walled carbon nanotubes (SWCNT) as delivery vehicles for siRNA delivery and has previously reported on the in vitro and in vivo efficacy of this platform. This study was conducted to determine what if any toxicities result from the use of SWCNT and identify toxicities that may be directly attributed to this delivery vehicle. For this application, it is not only necessary to determine the maximal load of SWCNT that can be tolerated, the dose limiting toxicities and the fate of the material in the body, but also to carefully prepare the SWCNT suspensions to ensure that contaminating metals, nanotube aggregates and other materials are not present when administered systemically. Ensysce Biosciences has been exploring the safe use of this material and here presents its latest findings from a toxicology study where the total dose of 50 and 100 g of fully suspended and individualized SWCNT were administered to groups of 3 mice. Mice were sacrificed at 12, 24, 48 hr and 1 week following i.v. administration. Blood chemistry and hematology were evaluated at each time point. Urine and feces were collected at 12, and 24 hr. Organs, including spleen, liver, kidney, heart, lung and brain were examined macroscopically and by near IR-fluorescence for the presence of SWCNT. The presence and persistence of SWCNT in the tissues was measured. Data to be presented will include details of the analytical characterization of the SWCNT preparations that were delivered, showing that the tubes were well dispersed and individualized. At both the 24 hr and 1 week timepoints, blood chemistry and hematology showed no evidence of toxicity, as values for all were within the normal ranges. Macroscopic examination of organs indicated that SWCNT were present in liver and spleen at 24 hr. Near IR-fluorescence spectroscopy demonstrated that the nanotube accumulation in the spleen decreased over a 1 week period. Data will be presented showing that a 100 g dose (equivalent to 30 mg in humans) was well tolerated and non-toxic. These studies have led to further work examining limits for use of SWCNT for siRNA delivery, including stability of the siRNA complexes in serum, siRNA loading efficiency and systemic efficacy. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C142.

Low frequency four-wave mixing spectroscopy of biopolymer hydration layers in aqueous solutions

Four-wave mixing (FWM) spectroscopy has been applied to detection of H2O2 molecules rotational resonances in both DNA and denatured DNA aqueous solutions in the range ±100 cm−1. A considerable growth of rotational lines intensity of H2O and H2O2 has been observed in comparison with distilled water. This fact was interpreted as an exhibition of specific property of a hydration layer formation at DNA/water and denatured DNA/water interfaces. The fitting of four-wave mixing spectra shows the increasing of the H2O2 rotational line’s amplitude by a factor of ∼3 in DNA solutions due to denaturizing. The shifting of FWM Brillouin resonances in opposite way in protein solution and SWNT (single wall carbon nanotube) suspension to comparison with water was observed and discussed.

Single‐walled carbon nanotubes modified by PFO: An optical absorption and Raman spectroscopic investigation

AbstractIn this contribution, we present preliminary results from an optical absorption and resonance Raman spectroscopic investigation on single‐walled carbon nanotubes (SWCNT) functionalized by poly(9,9‐dioctylfluorenyl‐2,7‐diyl)‐co‐bithiophene (PFO‐BTP). A route for a stable suspension of SWCNT in a solution of fluorine‐base copolymer is shown. Additionally, the detailed analysis of the supernatant and sediment after centrifugation of the functionalized sample is given. The resonance Raman and optical absorption spectroscopic data suggest that selective wrapping of the carbon nanotubes by PFO occurs. Additionally, one can see that the abundance of SWCNT in the supernatant in a bulk sample increased by a factor of 2.