Multiwall carbon nanotubes from pyrolysis of tetrahydrofuran

Multiwalled carbon nanotubes have been prepared by pyrolysing tetrahydrofuran (THF) in the presence of nickelocene. Pyrolysis of the precursor mixture has been achieved at temperature as low as 600 °C. In this simple approach no carrier gas has been used. The yield of purified carbon nanotubes is found to be more than 65%. Characterization of the as-prepared and purified nanotubes are done by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and Raman spectra.     

Amphiphilic polymer-coated hybrid nanoparticles as CT/MRI dual contrast agents

We describe hybrid nanoparticles, composed of iron oxide and gold nanoparticles, as potential dual contrast agents for both computed tomography (CT) and magnetic resonance imaging (MRI). The hybrid nanoparticles are synthesized by thermal decomposition of mixtures of Fe-oleate and Au-oleylamine complexes. Using a nano-emulsion method, the nanoparticles are coated with amphiphilic poly(DMA-r-mPEGMA-r-MA) to impart water-dispersity and antibiofouling properties. An in?vitro phantom study shows that the hybrid nanoparticles have high CT attenuation, because of the constituent gold nanoparticles, and afford a good MR signal, attributable to the contained iron oxide nanoparticles. Intravenous injection of the hybrid nanoparticles into hepatoma-bearing mice results in high contrast between the hepatoma and normal hepatic parenchyma in both CT and MRI. These results suggest that the hybrid nanoparticles may be useful as CT/MRI dual contrast agents for in?vivo hepatoma imaging.     

Single-wall carbon nanotubes as attractive toughening agents in alumina-based nanocomposites

The extraordinary mechanical, thermal and electrical properties of carbon nanotubes have prompted intense research into a wide range of applications in structural materials, electronics, chemical processing and energy management. Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful; for example, in alumina-based systems only a 24% increase in toughness has been obtained so far. Here we demonstrate their potential use in reinforcing nanocrystalline ceramics. We have fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 degrees C by spark-plasma sintering. A fracture toughness of 9.7 MPa m 1/2, nearly three times that of pure nanocrystalline alumina, can be achieved.     

Noncovalent functionalization of carbon nanotubes with amphiphilic gd3+ chelates: toward powerful t1 and t2 MRI contrast agents

An amphiphilic gadolinium (III) chelate (GdL) was synthesized from commercially available stearic acid. Aqueous solutions of the complex at different concentrations (from 1 mM to 1 microM) were prepared and adsorbed on multiwalled carbon nanotubes. The resulting suspensions were stable for several days and have been characterized with regard to magnetic resonance imaging (MRI) contrast agent applications. Longitudinal water proton relaxivities, r1, have been measured at 20, 300, and 500 MHz. The r1 values show a strong dependence on the GdL concentration, particularly at low field. The relaxivities decrease with increasing field as it is predicted by the Solomon-Bloembergen-Morgan theory. Transverse water proton relaxation times, T2, have also been measured and are practically independent of both the frequency and the GdL concentration. An in vivo feasibility MRI study has been performed at 300 MHz in mice. A negative contrast could be well observed after injection of a suspension of functionalized nanotubes into the muscle of the leg of the mouse.     

A generally adoptable radiotracing method for tracking carbon nanotubes in animals

Carbon nanotube (CNT) mediated drug delivery systems have currently aroused a great deal of interest. Such delivery systems for drugs, proteins and genes have been preliminarily studied using cellular and animal models. For the further study of the pharmacokinetics and related biological behaviours of CNTs in vivo, a fast and convenient tracing method is particularly demanded. In this paper, we developed a generally adoptable tracing method for the biodistribution study of functionalized CNTs in vivo. Taurine covalently functionalized multi-walled carbon nanotubes (tau-MWNTs) and Tween-80 wrapped MWNTs (Tween-MWNTs) were labelled with (125)I, and then their distribution in mice was determined. It is interesting that Tween-80 can reduce the RES uptake of MWNTs remarkably. The resulting distribution of (125)I-tau-MWNTs was very consistent with that using (14)C-taurine-MWNTs as the CNTs tracer, which means the easy (125)I labelling method is reliable and effective.     

Multi-walled carbon nanotubes as a new counter electrode for dye-sensitized solar cells

Airbrushed multi-walled carbon nanotube (MWNT) networks were investigated as a new counter electrode for dye-sensitized TiO2 photoelectrochemical solar cells. The structural and physical properties of the MWNTs were studied by various techniques including SEM, TEM, Raman, optical absorption, and electrochemical impedance spectroscopy (EIS). The MWNTs exhibited catalytic activity for the reduction of triiodide in the electrolyte as studied by EIS measurements. The performance of the dye-sensitized solar cells was improved by using MWNTs as counter electrodes. This observation is explained by the significantly increased contact area between the MWNT counter electrode and the electrolyte which facilitates efficient charge transportation in the solar cell. We demonstrated that the MWNTs are suitable for replacing expensive Pt electrodes for fabricating high efficiency dye-sensitized solar cells. The process used in this study is also technically attractive for large scale and economic production.     

Mass-produced multi-walled carbon nanotubes as catalyst supports for direct methanol fuel cells

Commercially mass-produced multi-walled carbon nanotubes, i.e., VGNF (Showa Denko Co.), were applied to support materials for platinum-ruthenium (PtRu) nanoparticles as anode catalysts for direct methanol fuel cells. The original VGNFs are composed of high-crystalline graphitic shells, which hinder the favorable surface deposition of the PtRu nanoparticles that are formed via borohydride reduction. The chemical treatment of VGNFs with potassium hydroxide (KOH), however, enables highly dispersed and dense deposition of PtRu nanoparticles on the VGNF surface. This capability becomes more remarkable depending on the KOH amount. The electrochemical evaluation of the PtRu-deposited VGNF catalysts showed enhanced active surface areas and methanol oxidation, due to the high dispersion and dense deposition of the PtRu nanoparticles. The improvement of the surface deposition states of the PtRu nanoparticles was significantly due to the high surface area and mesorporous surface structure of the KOH-activated VGNFs.     

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.     

Self-assembled peptide amphiphile nanofibers conjugated to MRI contrast agents

Self-assembled peptide amphiphile nanofibers have been investigated for their potential use as in vivo scaffolds for tissue engineering and drug delivery applications. We report here the synthesis of magnetic resonance (MR) active peptide amphiphile molecules that self-assemble into spherical and fiber-like nanostructures, enhancing T(1) relaxation time. This new class of MR contrast agents can potentially be used to combine high-resolution three-dimensional MR fate mapping of tissue-engineered scaffolds with targeting of specific cellular receptors.     

Safety assessment of nanoparamagnetic contrast agents with different coatings for molecular MRI

Despite the wide application of gadolinium as a contrast agent for magnetic resonance imaging (MRI), there is a serious lack of information on its toxicity. Gadolinium and gadolinium oxide (Gd-oxide) are used as contrast agents for magnetic resonance imaging (MRI). There are methods for reducing toxicity of these materials, such as core nanoparticles coating or conjugating. Therefore, for toxicity evaluation, we compared the viability of commercial contrast agents in MRI (Gd-DTPA) and three nanoparticles with the same core Gd₂O₃ and small particulate gadolinium oxide or SPGO (< 40 nm) but different coatings of diethyleneglycol (DEG) as Gd₂O₃-DEG and methoxy polyethylene glycol-silane (mPEG-silane: 550 and 2000 Dalton) as SPGO-mPEG-silane550 and SPGO-mPEG-silane2000, respectively, in the SK-MEL3 cell line, by light microscopy, MTT assay using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide, and the LDH assay detecting lactate dehydrogenase activity. The viability values were not statistically different between the three nanoparticles and Gd-DTPA. The MTT and LDH assay results showed that Gd₂O₃-DEG nanoparticles were more toxic than Gd-DTPA and other nanoparticles. Also, SPGO-mPEG-silane2000 was more biocompatible than other nanoparticles. The obtained results did not show any significant increase in cytotoxicity of the nanoparticles and Gd-DTPA, neither dose-dependent nor time-dependent. Therefore, DEG and PEG, due to their considerable properties and irregular sizes (different molecular weights), were selected as the useful surface covering materials of nanomagnetic particles that could reveal noticeable relaxivity and biocompatibility characteristics.     

Adhesion, proliferation and differentiation of pluripotent stem cells on multi-walled carbon nanotubes

This article studies the adhesion, growth and differentiation of stem cells on carbon nanotube matrices. Glass coverslips were coated with multi-walled carbon nanotube (MWNT) thin films using layer-by-layer self-assembling techniques. Pluripotent P19 mouse embryonal carcinoma stem cells were seeded onto uncoated or MWNT-coated glass coverslips and either maintained in an undifferentiated state or induced to differentiate by the addition of retinoic acid. The authors found that cell adhesion was increased on the MWNT-coated glass surfaces, and that the expression patterns of some differentiation markers were altered in cells grown on MWNTs. The results suggest that MWNTs will be useful in directing pluripotent stem cell differentiation for tissue engineering purposes.     

Individual single-walled carbon nanotubes as nanoelectrodes for electrochemistry

We demonstrate the use of individual single-walled carbon nanotubes (SWNTs) as nanoelectrodes for electrochemistry. SWNTs were contacted by nanolithography, and cyclic voltammetry was performed in aqueous solutions. Interestingly, metallic and semiconducting SWNTs yielded similar steady-state voltammetric curves. We clarify this behavior through a model that considers the electronic structure of the SWNTs. Interfacial electron transfer to the SWNTs is observed to be very fast but can nonetheless be resolved due to the nanometer critical dimension of SWNTs. These studies demonstrate the potential of using a SWNT as a model carbon nanoelectrode for electrochemistry.     

Single-particle tracking of endocytosis and exocytosis of single-walled carbon nanotubes in NIH-3T3 cells

Over 10000 individual trajectories of nonphotobleaching single-walled carbon nanotubes (SWNT) were tracked as they are incorporated into and expelled from NIH-3T3 cells in real time on a perfusion microscope stage. An analysis of mean square displacement allows the complete construction of the mechanistic steps involved from single duration experiments. We observe the first conclusive evidence of SWNT exocytosis and show that the rate closely matches the endocytosis rate with negligible temporal offset. We identify and study the endocytosis and exocytosis pathway that leads to the previously observed aggregation and accumulation of SWNT within the cells.     

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.     

Magnetite-loaded carrier erythrocytes as contrast agents for magnetic resonance imaging

Superparamagnetic iron oxide nanoparticles (SPIONs) are commonly used in magnetic resonance imaging (MRI), but their fast phagocytosis makes them less than ideal for this application. To circumvent the lymphocyte-macrophage system, we encapsulated SPIONs into red blood cells (RBCs). For loading, the RBC's membrane was opened by swelling under hypoosmotic conditions and subsequently resealed. In this work, we demonstrate that SPIONs can be loaded into RBCs in a concentration sufficient to obtain strong contrast enhancement in MRI.     

Highly conductive polymer materials based multi-walled carbon nanotubes as counter electrodes for dye-sensitized solar cells

Poly(3,4-ethylenedioxxythiophene) (PEDOT), polyaniline (PANI) and polythiophene (PTh) based multi-walled carbon nanotube (MWCNT) composites were successfully prepared using RF-rotating plasma grafting method. Morphological characterizations of composites were determined using scanning electron microscopy (SEM), which showed that conducting polymers (CPs) of PEDOT, PANI and PTh were coated on the surface of CNTs. The surface properties of the Carbon Nanotube (CNT) composites were also determined by using Infrared Spectra (FT-IR), X-ray Photon Spectra (XPS), and Scanning Electron Microscopy-Energy Dispersive X-ray Spectra (SEM-EDX) analysis. X-ray photon spectra results confirmed the formation of the composites. Composites of MWCNT were used in dye-sensitized solar cells (DSSCs) as counter electrodes and exhibited short-circuit photocurrent densities of 11.19, 10.70 and 8.54 mA/cm² for PANI/MWCNT, PTh/MWCNT and PEDOT/CNT, respectively.