Effects Of Single-walled Carbon Nanotubes Research Articles

Choking Effect of Single-Wall Carbon Nanotubes on Solvent Adsorption in Radial Breathing Mode

The radial breathing mode (RBM) frequency in Raman spectra of single-wall carbon nanotubes (SWNTs) is upshifted (3−9 cm-1) by immersion of the SWNTs in various alcohols and water. However, the immersion in the solvents does not cause any visible variation in the tangential mode frequency. The degree of this RBM frequency upshift induced by the solvent adsorption corresponds to that caused by applying a high pressure of 1 GPa (6−10 cm-1/GPa) in the literature. The degree of the RBM frequency upshift increases with increases in the molecular weight of the solvents. RBM frequency upshift caused by immersion of SWNTs in water is much larger than that by the molecular weight of alcohols, indicating the cluster formation of water molecules.

Analysis of Stress Responsive Genes Induced by Single-Walled Carbon Nanotubes in BJ Foreskin Cells

Nanotechnology is finding its use as a potential technology in consumer products, defense, electronics, and medical applications by exploiting the properties of nanomaterials. Single-walled carbon nanotubes are novel forms of these nanomaterials with potential for large applications. However, the toxicity studies on this material are not explored in detail and therefore limiting its use. It has been earlier reported that single-walled carbon nanotubes induces oxidative stress and also dictates activation of specific signaling pathway in keratinocytes. The present study explores the effect of single-walled carbon nanotubes on stress genes in human BJ Foreskin cells. The results show induction of oxidative stress in BJ Foreskin cells by single-walled carbon nanotubes and increase in stress responsive genes. The genes included inducible genes like HMOX1, HMOX2, and Cyp1B1. In addition we validated increase for four genes by SWCNT, namely ATM, CCNC, DNAJB4, and GADD45A by RT-PCR. Moreover results of the altered stress related genes have been discussed and that partially explains some of the toxic responses induced by single-walled carbon nanotubes.

Analysis of Stress Responsive Genes Induced by Single-Walled Carbon Nanotubes in BJ Foreskin Cells

Nanotechnology is finding its use as a potential technology in consumer products, defense, electronics, and medical applications by exploiting the properties of nanomaterials. Single-walled carbon nanotubes are novel forms of these nanomaterials with potential for large applications. However, the toxicity studies on this material are not explored in detail and therefore limiting its use. It has been earlier reported that single-walled carbon nanotubes induces oxidative stress and also dictates activation of specific signaling pathway in keratinocytes. The present study explores the effect of single-walled carbon nanotubes on stress genes in human BJ Foreskin cells. The results show induction of oxidative stress in BJ Foreskin cells by single-walled carbon nanotubes and increase in stress responsive genes. The genes included inducible genes like HMOX1, HMOX2, and Cyp1B1. In addition we validated increase for four genes by SWCNT, namely ATM, CCNC, DNAJB4, and GADD45A by RT-PCR. Moreover results of the altered stress related genes have been discussed and that partially explains some of the toxic responses induced by single-walled carbon nanotubes.

Stabilization Effect of Single-Walled Carbon Nanotubes on the Functioning of Photosynthetic Reaction Centers

The interaction between single-walled carbon nanotubes and photosynthetic reaction centers purified from purple bacterium Rhodobacter sphaeroides R-26 has been investigated. Atomic force microscopy studies provide evidence that reaction center protein can be attached effectively to the nanotubes. The typical diameter of the nanotube is 1-4 nm and 15 +/- 2 nm without and with the reaction centers, respectively. Light-induced absorption change measurements indicate the stabilization of the P+(Q(A)Q(B))- charge pair, which is formed after single saturating light excitation after the attachment to nanotubes. The separation of light-induced charges is followed by slow reorganization of the protein structure. The stabilization effect of light-initiated charges by the carbon nanotubes opens a possible direction of several applications, the most promising being in energy conversion and storage devices.

Enhancement of in-field Jc in MgB2∕Fe wire using single- and multiwalled carbon nanotubes

The authors investigated the doping effects of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) on the Tc, lattice parameters, Jc(B), microstructure, and Hc2 of MgB2∕Fe wire. These effects systematically showed the following sequence for Tc and the a axis: the SWCNT doped wire<the MWshortCNT doped wire<the MWlongCNT doped wire<undoped wire, while Jc(B) followed the sequence of the SWCNT doped wire>the MWshortCNT doped wire>the MWlongCNT doped wire>undoped wire. A dominating mechanism behind all these findings is the level of C substitution for B in the lattice.

Interactions of Carbon Nanomaterials With Mammalian Cells

ABSTRACTDespite their diverse application potential, carbon nanotubes (CNT) have adverse effects in vitro, and in vivo. Previous research has focused on the in vitro cytotoxic impact of CNT aggregates and associated nanoparticulate impurities. In this study, we compared the single-walled carbon nanotube (SWNT) aggregates, and their associated finely dispersed, non-aggregated carbon nanomaterials on rat aortic smooth muscle cells (SMC), through filtration of the aggregates from the CNT-treated cell culture media. In general, our research shows that the removal of single-walled carbon nanotube (SWNT) aggregates from cell culture test media inhibited the growth in SMC to a lower extent than the corresponding unfiltered media at pre-filtered SWNT dosages below 0.10 mg/ml. We also found suspended nanoparticles (likely amorphous and graphitic carbon associated with the SWNT) and a small quantity of SWNT in the filtered media may have contributed to the observed cell growth inhibition by the filtered media. In addition, we compared the effect of SWNT, a nano-sized material, with activated carbon (AC), a nanoporous, microparticulate material, on SMC growth. AC (0.1 mg/ml) was found to be less inhibitory to SMC growth than the SWNT aggregates and suspended matter (0.1 mg/ml), potentially implying an inverse proportionality between carbon nanomaterial size regimes and cell growth inhibition.

Effects of SWNT and Metallic Catalyst on Hydrogen Absorption/Desorption Performance of MgH2

The microstructure and absorption/desorption characteristics of composite MgH2 and 5 wt % as-prepared single-walled carbon nanotubes (MgH2-5ap) obtained by the mechanical grinding method were investigated. Experimental results show that the MgH2-5ap sample exhibits faster absorption kinetics and relatively lower desorption temperature than pure MgH2 or MgH2-purified single-walled carbon nanotube composite. Storage capacities of 6.0 and 4.2 wt % hydrogen for the MgH2-5ap composite were achieved in 60 min at 423 and 373 K, respectively. Furthermore, its desorption temperature was reduced by 70 K due to the introduction of as-prepared single-walled carbon nanotubes (SWNTs). In addition, the different effects of SWNTs and metallic catalysts contained in the as-prepared SWNTs were also investigated and a hydrogenation mechanism was proposed. It is suggested that metallic particles may be mainly responsible for the improvement of the hydrogen absorption kinetics, and SWNTs for the enhancement of hydrogen absorption capacity of MgH2.

Effects of single-walled carbon nanotubes on the functions of plasma proteins and potentials in vascular prostheses

Background Nonwoven single-walled nanotubes (SWNTs) are novel materials with a nanotopography macroscopic surface and pure-carbon composition, which may serve as coatings on implants in blood-contact environments. Methods The adsorption behavior of albumin, fibrinogen, and fresh plasma on SWNT membranes was studied using scanning electron microscopy (SEM), energy-dispersive x-ray, and direct enzyme-linked immunosorbent assay, respectively. Platelet adhesion and activation were investigated in vitro using SEM observation, and via flow cytometry analysis by PAC-1, which binds to GPIIb/IIIa expressed on activated platelets. Results Nonwoven SWNTs clearly displayed greater adsorption preference for fibrinogen than for albumin. However, adhered platelets were not observed by SEM. Results obtained from flow cytometry analysis further proved very low expression of GPIIb/IIIa on platelets caused by nonwoven SWNTs. Conclusion The function of adsorbed fibrinogen to mediate platelet recognition, adhesion, activation, and aggregation was significantly suppressed, which induced extremely low levels of platelet adhesion and activation.

The catalytic effect of single-wall carbon nanotubes on the hydrogen sorption properties ofsodium alanates

Single-wall carbon nanotubes (SWNTs) were examined as catalysts forimproving the hydrogen absorption and desorption properties of Ti/Zr-dopedNaAlH4 hydride, proposed as a reversible hydrogen storage material. We studied the hydrogencharge and discharge characteristics and stability of sodium aluminium composites ballmilled with carbon additives such as SWNTs, graphite or activated carbon (AX-21). TheSWNT–NaAlH4 systemwas tested at 160 °C for up to 200 cycles, and the sorption kinetics were enhanced by a factor of four. Also, the catalyzedNaAlH4 hydride with graphite and activated carbon additives shows fast absorption and desorptionkinetics. Our results indicate that by creating new hydrogen transition sites, the structureof carbon in the composites plays an important role in enhancing the hydrogen absorptionand release rates.

Chiral and quantum size effects of single-wall carbon nanotubes on field emission

The emission current of a single-wall carbon nanotube (SWNT) in field emission is studied by the tunneling theory with the tight-binding approach. The emission current is almost independent of the chiral angle of SWNT in low fields, but increases with increase of chiral angles in very high fields. We found a room-temperature quantum size effect of SWNT on field emission. As the diameters of SWNTs increase, the current densities decrease for metallic tubes, but increase for semiconducting tubes. When the diameters of SWNTs are larger than 2nm the current densities of metallic and semiconducting tubes are very close. These chiral and quantum size effects are originated from the energy band structure of nanotubes.

New oscillation in terahertz magneto-optical effect of single-walled carbon nanotubes film

The magneto-optical Kerr effect of single-walled carbon nanotubes (SWNTs) film in the Terahertz region is theoretically studied by means of the Drude model. The calculation shows a new oscillation occurring near the plasma frequency as the origin of the magneto-optical Kerr effect for the single-walled nanotubes film. We propose that the amplitude of this near plasma frequency oscillation is directly proportional to the external magnetic field and its period increases with increasing cyclotron frequency. We consider these features of this oscillation of SWNTs are related to the Landau energy of SWNTs. The reflectivity and figure of merit (FOM) spectrum also reveal that this oscillation is the dominant mechanism for the magneto-optical Kerr effect of SWNTs film. Meanwhile, the shift and large enhancement of Kerr rotation under different external magnetic fields is explained.

Effects of single-walled carbon nanotubes on the polymerase chain reaction

The effects of single-walled carbon nanotubes on the polymerase chain reaction(PCR) were investigated via quantitative PCR product measurements, scanningelectron microscopy (SEM), high-resolution transmission electron microscopy(TEM) and x-ray photoelectron spectroscopy (XPS). The results showed thatadding single-walled carbon nanotubes (SWCNTs) into the reaction liquidincreases the amount of PCR product at SWCNT concentrations below3 µg µl−1,but this effect is reversed at higher SWCNT concentrations.Similar effects were observed in PCR reactions with or withoutMg2+.Both SEM and HRTEM results showed that the DNA templates and Taq enzymes areattached to bundles of SWCNTs in PCR products. XPS results showed that the C 1sbinding energy in PCR products increased after reaction, with the emergence of two newpeaks beside the main peak compared with carbon nanotubes before reaction, suggestingthat there might be a chemical reaction between SWCNTs and PCR components. Inconclusion, SWCNTs may increase the PCR efficiency at a concentration range of less than3 µg µl−1 in the reaction liquid and have the potential to act as catalysts in a variety of biochemicalreactions.

Chirality effect of single-wall carbon nanotubes on field emission

The chirality effect of an opened-end single-wall carbon nanotube on field emission is studied by using the tunneling theory with the tight-binding approximation. The characteristic of the emission-current line density versus field is found to be dependence on the chirality of nanotubes. A metallic tube has a line density higher than that of a semiconducting one. Also, for semiconducting tubes, a tube of larger chiral angle has a line density higher than that of smaller chiral angle; a zigzag semiconducting tube has a smallest line density among the others. Further, the Fowler–Nordheim plots may have a nonlinear behavior in high current region. Finally, at temperature T<1000 K, the emission current is almost independent of temperature. Our results are explained by the energy band structure of nanotubes.

Exposure to Carbon Nanotube Material: Assessment of Nanotube Cytotoxicity using Human Keratinocyte Cells

Carbon nanotubes are new members of carbon allotropes similar to fullerenes and graphite. Because of their unique electrical, mechanical, and thermal properties, carbon nanotubes are important for novel applications in the electronics, aerospace, and computer industries. Exposure to graphite and carbon materials has been associated with increased incidence of skin diseases, such as carbon fiber dermatitis, hyperkeratosis, and naevi. We investigated adverse effects of single-wall carbon nanotubes (SWCNT) using a cell culture of immortalized human epidermal keratinocytes (HaCaT). After 18 h of exposure of HaCaT to SWCNT, oxidative stress and cellular toxicity were indicated by formation of free radicals, accumulation of peroxidative products, antioxidant depletion, and loss of cell viability. Exposure to SWCNT also resulted in ultrastructural and morphological changes in cultured skin cells. These data indicate that dermal exposure to unrefined SWCNT may lead to dermal toxicity due to accelerated oxidative stress in the skin of exposed workers.

Current Chemistry: Electronic Properties of Single-Walled Carbon Nanotubes

This communication describes scanning tunnelling microscopy investigations of the electronic properties of singlewalled carbon nanotubes (SWNTs). First, the unique relationship between the atomic structure and electronic properties of SWNTs is presented. Second, structural defects in nanotubes are addressed, and quantum size effects in SWNTs are discussed. Lastly, the effects of magnetic impurities on the low-energy properties of metallic SWNTs are discussed. Applications and prospects for future research directions are considered. Manuscript received: 9 October 2001. Accepted without change.

Correlation effects of single-wall carbon nanotubes in weak coupling

Single-wall carbon nanotubes with on-site interaction $U\ensuremath{\ll}t$ are studied by a controlled renormalization group method. When formulated as a system of ${N}_{f}$ flavors of interacting Dirac fermions, the effective model at generic filling resembles a set of quasi-1D Hubbard chains. For the undoped ${(N}_{y}{,N}_{y})$ armchair and the ${(N}_{x},\ensuremath{-}{N}_{x})$ zigzag with ${N}_{x}=3n,$ specific mappings to the two-chain Hubbard model at half filling with effective interaction ${u}_{\mathrm{eff}}{=U/N}_{y}$ and ${2U/N}_{x}$ are found from this more general equivalence. The phase diagrams of the (3,3) armchair and the $(6,\ensuremath{-}6)$ zigzag at generic fillings are studied and compared as an example.