Stability of the thin partitioned carbon nanotubes

We report on the research of the stability of partitioned (bamboo-like) carbon nanotubes with different diameters. The stability of the partitioned carbon nanotubes of the smallest diameter were determined by the tight-binding method. For the prediction of the destruction regions of the bamboo-like nanotubes atomic framework subjected to strain the new original method of the calculation of the local stress of atomic network was developed. Using this method it was shown that partitioned carbon nanotubes with a diameter of 2.02 nm are stable. These partitioned carbon nanotubes with chirality (15,15) are the most stable partitioned carbon nanotubes with the smallest diameter.     

High‐Performance Solution‐Processed Double‐Walled Carbon Nanotube Transparent Electrode for Perovskite Solar Cells

Double‐walled carbon nanotubes are between single‐walled carbon nanotubes and multiwalled carbon nanotubes. They are comparable to single‐walled carbon nanotubes with respect to the light optical density, but their mechanical stability and solubility are higher. Exploiting such advantages, solution‐processed transparent electrodes are demonstrated using double‐walled carbon nanotubes and their application to perovskite solar cells is also demonstrated. Perovskite solar cells which harvest clean solar power have attracted a lot of attention as a next‐generation renewable energy source. However, their eco‐friendliness, cost, and flexibility are limited by the use of transparent oxide conductors, which are inflexible, difficult to fabricate, and made up of expensive rare metals. Solution‐processed double‐walled carbon nanotubes can replace conventional transparent electrodes to resolve such issues. Perovskite solar cells using the double‐walled carbon nanotube transparent electrodes produce an operating power conversion efficiency of 17.2% without hysteresis. As the first solution‐processed electrode‐based perovskite solar cells, this work will pave the pathway to the large‐size, low‐cost, and eco‐friendly solar devices.     

Covalent functionalization of multiwalled carbon nanotubes with a low molecular weight chitosan

Covalent functionalization of shortened multiwalled carbon nanotubes (MWNTs) with a natural low molecular weight chitosan (LMCS) was accomplished by a nucleophilic substitution reaction. Amino and primary hydroxyl groups of the LMCS contributed mainly to the formation of MWNT-LMCS conjugates. The LMCS content in the MWNT-LMCS is approximately 58 wt %, and approximately four molecular chains of the LMCS are attached to 1000 carbon atoms of the nanotube sidewalls. Most interestingly, the amorphous packing structure of the LMCS changed dramatically when it attached to the MWNTs. The MWNTs might induce the crystalline character of the LMCS. As a novel derivative of MWNTs, the MWNT-LMCS is soluble in dimethylformamide, dimethyl acetamide, dimethylsulfoxide, and acetic acid aqueous solution. The confirmation of the chitosan-based covalent functionalization route might lead to further studies aiming for potential applications in catalysis and environmental protection.     

Applications of carbon nanotubes for cancer research

Carbon nanotubes have many unique properties such as high surface area, hollow cavities, and excellent mechanical and electrical properties. Interfacing carbon nanotubes with biological systems could lead to significant applications in various disease diagnoses. Significant progress in interfacing carbon nanotubes with biological materials has been made in key areas such as aqueous solubility, chemical and biological functionalization for biocompatibility and specificity, and electronic sensing of proteins. In addition, the bioconjugated nanotubes combined with the sensitive nanotube-based electronic devices would enable sensitive biosensors toward medical diagnostics. Furthermore, recent findings of improved cell membrane permeability for carbon nanotubes would also expand medical applications to therapeutics using carbon nanotubes as carriers in gene delivery systems. This article reviews the current trends in biological functionalization of carbon nanotubes and their potential applications for breast cancer diagnostics. The article also reports the applications of confocal microscopy for use in understanding the interactions of biological materials such as antibodies on carbon nanotubes that are specific to surface receptors in breast cancer cells. Furthermore, a nanotube-field-effect transistor is demonstrated for electronic sensing of antibodies that are specific to surface receptors in cancer cells.     

Carbon nanotube solar cells

We present proof-of-concept all-carbon solar cells. They are made of a photoactive side of predominantly semiconducting nanotubes for photoconversion and a counter electrode made of a natural mixture of carbon nanotubes or graphite, connected by a liquid electrolyte through a redox reaction. The cells do not require rare source materials such as In or Pt, nor high-grade semiconductor processing equipment, do not rely on dye for photoconversion and therefore do not bleach, and are easy to fabricate using a spray-paint technique. We observe that cells with a lower concentration of carbon nanotubes on the active semiconducting electrode perform better than cells with a higher concentration of nanotubes. This effect is contrary to the expectation that a larger number of nanotubes would lead to more photoconversion and therefore more power generation. We attribute this to the presence of metallic nanotubes that provide a short for photo-excited electrons, bypassing the load. We demonstrate optimization strategies that improve cell efficiency by orders of magnitude. Once it is possible to make semiconducting-only carbon nanotube films, that may provide the greatest efficiency improvement.     

On the elastic properties of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites using molecular dynamics simulations

Molecular dynamics simulations are used to study the physical and mechanical properties of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites. The effects of nanotube atomic structure, diameter, and volume fraction on the polymer density distribution, polymer atom distribution, stress–strain curves of nanocomposites and Young’s, and shear moduli of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites are explored. It is shown that the density of polymer, surrounding the nanotube surface, has a peak near the nanotube surface. However, increasing distance leads to dropping it to the value near the density of pure polymer. It is seen that for armchair nanotubes, the average polymer atoms distances from the single-walled carbon nanotubes are larger than the polymer atom distance from zigzag nanotubes. It further is shown that zigzag nanotubes are better candidates to reinforce poly (ethylene oxide) than their armchair counterparts.     

Ranking the affinity of aromatic residues for carbon nanotubes by using designed surfactant peptides.

A series of surfactant peptides were created to evaluate the affinity of aromatic AAs for single-walled carbon nanotubes in the absence of complications from peptide folding or self-association. Each surfactant peptide has a lipidlike architecture, with two Lys residues at the C-terminus as a hydrophilic head, five Val residues to form a hydrophobic tail, and the testing AA at the N-terminus. Raman and CD spectroscopic studies reveal that the surfactant peptides have a large unordered structural component which is independent of peptide concentration, suggesting that the peptides undergo minimal association under experimental conditions, thus removing this interference from interpretation of the peptide/carbon nanotube interactions. A lack of peptide self-association is also indicated by sedimentation equilibrium ultracentrifugation results. Optical spectroscopy of the peptide/carbon nanotube dispersions indicate that among the three aromatic AAs, tryptophan has the highest affinity for carbon nanotubes (both bundled and individual states) when incorporated into a surfactant peptide, while the Tyr-containing peptide is more selective for individual carbon nanotubes. Phe has the lowest overall affinity for carbon nanotubes. Raman spectra of dispersions made with SPF, SPY and SPW display similar types of nanotubes dispersed, although differences in the relative nanotube populations are observed by optical spectroscopy.     

Molecular dynamics simulation of the size effect of carbon nanotubes on the bulk modulus of a lipid bilayer

Due to their nanoscale size and special features, carbon nanotubes could enter the human body via certain way. The growing use of carbon nanotubes in practical applications, hence, prompts a necessity to study the potential health risks of carbon nanotubes. A numerical study is performed in this paper to investigate the size effect of carbon nanotubes on the bulk modulus of a lipid bilayer by using the constant surface tension molecular dynamics simulation procedure. It is found that the size effect is not monotonic with the increase of nanotube length. An explanation is given on the basis of the atomic interaction between the nanotube and bilayer involved in the model system.     

LyP-1-fMWNTs enhanced targeted delivery of MBD1siRNA to pancreatic cancer cells

Functionalized multi-walled carbon nanotubes have been extensively gained popularity in pancreatic cancer gene therapy. LyP-1, a peptide, has been proved to specifically bind pancreatic cancer cells. The potential therapeutic effect of LyP-1–conjugated functionalized multi-walled carbon nanotubes in treating pancreatic cancer is still unknown. In this study, LyP-1–conjugated functionalized multi-walled carbon nanotubes were successfully synthesized, characterized and showed satisfactory size distribution and zeta potential. Compared with functionalized multi-walled carbon nanotubes, cellular uptake of LyP-1–functionalized multi-walled carbon nanotubes was shown to be increased. Compound of LyP-1–functionalized multi-walled carbon nanotubes and MBD1siRNA showed superior gene transfection efficiency. Moreover, LyP-1-fMWNTs/MBD1siRNA complex could significantly decrease the viability and proliferation and promoted apoptosis of pancreatic cancer cells in vitro. Further xenograft assays revealed that the tumour burden in the nude mice injected with LyP-1–functionalized multi-walled carbon nanotubes/MBD1siRNA was significantly relieved. The study demonstrated that LyP-1–functionalized multi-walled carbon nanotubes/MBD1siRNA could be a promising candidate for tumour active targeting therapy in pancreatic cancer.     

Enzymes immobilized on carbon nanotubes

Enzyme immobilizations on carbon nanotubes for fabrication of biosensors and biofuel cells and for preparation of biocatalysts are rapidly emerging as new research areas. Various immobilization methods have been developed, and in particular, specific attachment of enzymes on carbon nanotubes has been an important focus of attention. The method of immobilization has an effect on the preservation of the enzyme structure and retention of the native biological function of the enzyme. In this review, we focus on recent advances in methodology for enzyme immobilization on carbon nanotubes.     

Adsorption mechanism of single guanine and thymine on single-walled carbon nanotubes

Bio-nano hybrids introduce magnificent applications of nanomaterials to various fields. The choice of carbon nanotube as well as sequence selection of the nucleic acid bases play a crucial role in shaping DNA–carbon nanotube hybrids. To come up with a clear vision for the choice of carbon nanotube and nucleic acid bases to create bio-nano hybrids, we studied the adsorption mechanism of the nucleic acid bases guanine and thymine on four different types of nanotubes based on density functional theory. Nucleic acid bases exhibit differential binding strengths according to their structural geometry, inter-molecular distances, the carbon nanotube diameter, and charge transfer. The π–π interaction mechanism between the adsorbent and adsorbate is discussed in terms of charge density profile and electronic band structure analysis.     

Carbon Nanotube‐Silicon Solar Cells

Due to the high cost of silicon photovoltaics there is currently great interest in finding alternative semiconductor materials for light harvesting devices. Single‐walled carbon nanotubes are an allotrope of carbon with unique electrical and optical properties and are promising as future photovoltaic materials. It is thus important to investigate the methods of exploiting their properties in photovoltaic devices. In addition to already extensive research using carbon nanotubes in organic photovoltaics and photoelectrochemical cells, another way to do this is to combine them with a relatively well understood model semiconductor such as silicon. Nanotube‐silicon heterojunction solar cells are a recent photovoltaic architecture with demonstrated power conversion efficiencies of up to ～14% that may in part exploit the photoactivity of carbon nanotubes.     

Carbon nanotube reinforced Bombyx mori silk nanofibers by the electrospinning process

Nanocomposite fibers of Bombyx mori silk and single wall carbon nanotubes (SWNT) were produced by the electrospinning process. Regenerated silk fibroin dissolved in a dispersion of carbon nanotubes in formic acid was electrospun into nanofibers. The morphology, structure, and mechanical properties of the electrospun nanofibers were examined by field emission environmental scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and microtensile testing. TEM of the reinforced fibers shows that the single wall carbon nanotubes are embedded in the fibers. The mechanical properties of the SWNT reinforced fiber show an increase in Young's modulus up to 460% in comparison with the un-reinforced aligned fiber, but at the expense of the strength and strain to failure.     

The solvation study of carbon, silicon and their mixed nanotubes in water solution

Nanotubes are believed to open the road toward different modern fields, either technological or biological. However, the applications of nanotubes have been badly impeded for the poor solubility in water which is especially essential for studies in the presence of living cells. Therefore, water soluble samples are in demand. Herein, the outcomes of Monte Carlo simulations of different sets of multiwall nanotubes immersed in water are reported. A number of multi wall nanotube samples, comprised of pure carbon, pure silicon and several mixtures of carbon and silicon are the subjects of study. The simulations are carried out in an (N,V,T) ensemble. The purpose of this report is to look at the effects of nanotube size (diameter) and nanotube type (pure carbon, pure silicon or a mixture of carbon and silicon) variation on solubility of multiwall nanotubes in terms of number of water molecules in shell volume. It is found that the solubility of the multi wall carbon nanotube samples is size independent, whereas multi wall silicon nanotube samples solubility varies with diameter of the inner tube. The higher solubility of samples containing silicon can be attributed to the larger atomic size of silicon atom which provides more direct contact with the water molecules. The other affecting factor is the bigger inter space (the space between inner and outer tube) in the case of silicon samples. Carbon type multi wall nanotubes appeared as better candidates for transporting water molecules through a multi wall nanotube structure, while in the case of water adsorption problems it is better to use multi wall silicon nanotubes or a mixture of multi wall carbon/ silicon nanotubes.     

Effect of the electric field of the anode sheath on the growth of aligned carbon nanotubes in a glow discharge

Arrays of aligned carbon nanotubes on silicon substrates were grown in the anode sheath of a dc glow discharge. In order to clarify the role of the electric field in the growth of nanotubes, numerical simulations of charged particle transport in the anode sheath were carried out in the drift-diffusion approximation. The distributions of the charged particle density and electric field are obtained. Possible mechanisms whereby the electric field influences the growth of aligned carbon nanotubes are analyzed. It is found that the nanotubes grow in the region in which the electric field is enhanced due to the depletion of positive ions in the anode sheath.     

Single-walled carbon nanotube induction of rat aortic endothelial cell apoptosis: Reactive oxygen species are involved in the mitochondrial pathway

The use of nano-sized materials offers exciting new options in technical and medical applications. Single-walled carbon nanotubes are emerging as technologically important in different industries. However, adverse effects on cells have been reported and this may limit their use. We previously found that 200μg/mL of single-walled carbon nanotubes induce apoptosis in rat aorta endothelial cells. The current study aimed to determine the signaling pathway involved in this process. We found that reactive oxygen species generation was involved in activation of the mitochondria-dependent apoptotic pathway. The finding of apoptosis was supported by a number of morphological and biochemical hallmarks, including chromatin condensation, internucleosomal DNA fragmentation, and caspase-3 activation. In conclusion, our results demonstrate that single-walled carbon nanotubes induce apoptosis in rat aorta endothelial cells and that reactive oxygen species are involved in the mitochondrial pathway.     

Biocatalysts for fuel cells: efficient hydrogenase orientation for H<Subscript>2</Subscript> oxidation at electrodes modified with carbon nanotubes

We report the modification of gold and graphite electrodes with commercially available carbon nanotubes for immobilization of Desulfovibrio fructosovorans [NiFe] hydrogenase, for hydrogen evolution or consumption. Multiwalled carbon nanotubes, single-walled carbon nanotubes (SWCNs), and amine-modified and carboxyl-functionalized SWCNs were used and compared throughout. Two separate methods were performed: covalent attachment of oriented hydrogenase by controlled architecture of carbon nanotubes at gold electrodes, and adsorption of hydrogenase at carbon-nanotube-coated pyrolytic graphite electrodes. In the case of self-assembled carbon nanotubes at gold electrodes, hydrogenase orientation based on electrostatic interaction with the electrode surface was found to control the electrocatalytic process for H₂ oxidation. In the case of carbon nanotube coatings on pyrolytic graphite electrodes, catalysis was controlled more by the geometry of the nanotubes than by the orientation of the enzyme. Noticeably, shortened SWCNs were demonstrated to allow direct electron transfer and generate high and quite stable current densities for H₂ oxidation via adsorbed hydrogenase, despite having many carboxylic surface functions that could yield unfavorable hydrogenase orientation for direct electron transfer. This result is attributable to the high degree of oxygenated surface functions in addition to the length of shortened SWCNs that yields highly divided materials. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

ROS induction and structural modification in human lymphocyte membrane under the influence of carbon nanotubes

To assess the potential risks of using the artificial nanostructures the structural state of the human lymphocyte membrane and lipid peroxidation under the influence of multi-walled carbon nanotubes with metal impurities was studied. The ability of carbon nanotubes to induce the formation of reactive oxygen species in cells was examined. A dose-dependent increase in reactive oxygen species formation in lymphocytes, which was not registered in cells pre-incubated with N-acetylcystein, after exposure to carbon nanotubes was shown. The addition of iron chelator deferoxamine to carbon nanotubes has also resulted in a decrease of reactive oxygen species. The mechanism of the activation of lipid peroxidation under the influence of carbon nanotubes and a structural modification of human lymphocyte membranes were discussed.     

ROS induction and structural modification in human lymphocyte membrane under the influence of carbon nanotubes

To assess the potential risks of using artificial nanostructures, the structural state of the human lymphocyte membrane and lipid peroxidation under the influence of multiwalled carbon nanotubes with metal impurities was studied. The ability of carbon nanotubes to induce the formation of reactive oxygen species in cells was examined. A dose-dependent increase in reactive oxygen species formation in lymphocytes, which was not registered in cells preincubated with N-acetylcysteine, after exposure to carbon nanotubes was shown. The addition of iron chelator deferoxamine to carbon nanotubes has also resulted in a decrease of reactive oxygen species. The mechanism of the activation of lipid peroxidation under the influence of carbon nanotubes and a structural modification of human lymphocyte membranes were discussed.     

Supramolecular conjugates of carbon nanotubes and DNA by a solid-state reaction

DNA-wrapped nanotubes of both multiwalled and single-walled carbon nanotubes were obtained by a solid-state mechanochemical reaction. Scanning electron microscopic images show that the nanotubes were cut into shorter lengths and were fully covered with DNA, which was further confirmed by fluorescence microscopy. This resulted in a high aqueous solubility of the products with a stability of >6 months. The results show that nanotubes were cut also with uniform distribution where >90% of the multiwalled products were 500 nm to 3 microm and 80% of the single-walled products were 250 nm to 1 microm in length, respectively. UV-vis spectra and gel electrophorosis show that the DNA in the product is intact. This facile technique for obtaining supramolecularly masked, water-soluble carbon nanotubes by a solid-state reaction has a great potential for both biological and nonbiological applications of nanotubes.