Concentration control of carbon nanotubes in aqueous solution and its influence on the growth behavior of fibroblasts

Green Synthesis, Spectroscopic Characterization and Biomedical Applications of Carbon Nanotubes

Carbon nanotubes are nano-sized cylindrical chicken wire-like structures made of carbon atoms. Carbon nanotubes have applications in electronics, energy storage, electromagnetic devices, environmental remediation and medicine as well. The biomedical applications of carbon nanotubes can be owed to features like low toxicity, non-immunogenicity, high in vivo stability and rapid cell entry. Carbon nanotubes have a great prospect in the treatment of diseases through diagnostic as well as therapeutic approaches. These nanostructures are interesting carriers for delivery and translocation of therapeutic molecules e.g. proteins, peptides, nucleic acids, drugs, etc. to various organs like the brain, lungs, liver, and pancreas. Commonly used methods to synthesize carbon nanotubes are arc discharge, chemical vapor deposition, pyrolysis, laser ablation etc. These methods have many disadvantages such as operation at high temperature, use of chemical catalysts, prolonged synthesis time and inclusion of toxic metallic particles in the final product requiring additional purification processes. In order to avoid these setbacks, various green chemistry-based synthetic methods have been devised, e.g., those involving interfacial polymerization, supercritical carbon dioxide drying, plant extract assisted synthesis, water- assisted synthesis, etc. This review will provide a thorough outlook of the eco-friendly synthesis of carbon nanotubes reported in the literature and their biomedical applications. Besides, the most commonly used spectroscopic techniques used for the characterization of carbon nanotubes are also discussed.

CVD Conditions for MWCNTs Production and Their Effects on the Optical and Electrical Properties of PPy/MWCNTs, PANI/MWCNTs Nanocomposites by In Situ Electropolymerization

In this work, the optimal conditions of synthesizing and purifying carbon nanotubes (CNTs) from ferrocene were selected at the first stage, where decomposition time, argon fluxes, precursor amounts, decomposition temperature (at 1023 K and 1123 K), and purification process (HNO₃ + H₂SO₄ or HCl + H₂O₂), were modulated through chemical vapor deposition (CVD) and compared to commercial CNTs. The processing temperature at 1123 K and the treatment with HCl + H₂O₂ were key parameters influencing the purity, crystallinity, stability, and optical/electrical properties of bamboo-like morphology CNTs. Selected multiwalled CNTs (MWCNTs), from 1 to 20 wt%, were electropolymerized through in-situ polarization with conductive polymers (CPs), poly(aniline) (PANI) and poly(pyrrole) (PPy), for obtaining composites. In terms of structural stability and electrical properties, MWCNTs obtained by CVD were found to be better than commercial ones for producing CPs composites. The CNTs addition in both polymeric matrixes was of 6.5 wt%. In both systems, crystallinity degree, related to the alignment of PC chains on MWCNTs surface, was improved. Electrical conductivity, in terms of the carrier density and mobility, was adequately enhanced with CVD CNTs, which were even better than the evaluated commercial CNTs. The findings of this study demonstrate that synergistic effects among the hydrogen bonds, stability, and conductivity are better in PANI/MWCNTs than in PPy/MWCNTs composites, which open a promissory route to prepare materials for different technological applications.

Selective binding of single-stranded DNA-binding proteins onto DNA molecules adsorbed on single-walled carbon nanotubes

Single-stranded DNA-binding (SSB) proteins were treated with hybrids of DNA and single-walled carbon nanotubes (SWNTs) to examine the biological function of the DNA molecules adsorbed on the SWNT surface. When single-stranded DNA (ssDNA) was used for the hybridization, significant binding of the SSB molecules to the ssDNA-SWNT hybrids was observed by using atomic force microscopy (AFM) and agarose gel electrophoresis. When double-stranded DNA (dsDNA) was used, the SSB molecules did not bind to the dsDNA-SWNT hybrids in most of the conditions that we evaluated. A specifically modified electrophoresis procedure was used to monitor the locations of the DNA, SSB, and SWNT molecules. Our results clearly showed that ssDNA/dsDNA molecules on the SWNT surfaces retained their single-stranded/double-stranded structures.

Long-term effects of carbon containing engineered nanomaterials and asbestos in the lung: one year postexposure comparisons

The hallmark geometric feature of single-walled carbon nanotubes (SWCNT) and carbon nanofibers (CNF), high length to width ratio, makes them similar to a hazardous agent, asbestos. Very limited data are available concerning long-term effects of pulmonary exposure to SWCNT or CNF. Here, we compared inflammatory, fibrogenic, and genotoxic effects of CNF, SWCNT, or asbestos in mice 1 yr after pharyngeal aspiration. In addition, we compared pulmonary responses to SWCNT by bolus dosing through pharyngeal aspiration and inhalation 5 h/day for 4 days, to evaluate the effect of dose rate. The aspiration studies showed that these particles can be visualized in the lung at 1 yr postexposure, whereas some translocate to lymphatics. All these particles induced chronic bronchopneumonia and lymphadenitis, accompanied by pulmonary fibrosis. CNF and asbestos were found to promote the greatest degree of inflammation, followed by SWCNT, whereas SWCNT were the most fibrogenic of these three particles. Furthermore, SWCNT induced cytogenetic alterations seen as micronuclei formation and nuclear protrusions in vivo. Importantly, inhalation exposure to SWCNT showed significantly greater inflammatory, fibrotic, and genotoxic effects than bolus pharyngeal aspiration. Finally, SWCNT and CNF, but not asbestos exposures, increased the incidence of K-ras oncogene mutations in the lung. No increased lung tumor incidence occurred after 1 yr postexposure to SWCNT, CNF, and asbestos. Overall, our data suggest that long-term pulmonary toxicity of SWCNT, CNF, and asbestos is defined, not only by their chemical composition, but also by the specific surface area and type of exposure.

Surface morphology of hybrids of double-stranded DNA and single-walled carbon nanotubes studied by atomic force microscopy

We examined the formation of hybrids of double-stranded DNA (dsDNA) and single-walled carbon nanotubes (SWNTs), which has not been well investigated yet. In particular, the adsorption of dsDNA onto SWNT produced by chemical vapor deposition (CVD) was examined for the first time. When small amount of dsDNA was mixed with CVD SWNT, well dispersed hybrids with smooth surfaces were observed by atomic force microscopy (AFM). Through a comparison of dsDNA, single-stranded DNA (ssDNA), CVD SWNT, and high-pressure carbon monoxide process (HiPco) SWNT, we found that the surface morphology of the hybrids was independent of the DNA type. Even when sonicated salmon testes DNA, which has a random sequence and length, was employed, smooth surfaces were obtained on the dsDNA-CVD hybrids as well as on the ssDNA-CVD hybrids. The ratio of monodispersed SWNT and bundled SWNT in a dispersion solution was also not affected by the DNA type. In contrast, the quantity of the fabricated hybrids was affected by the types of DNA especially when HiPco SWNT was used. Our results indicated that characteristic features of the dsDNA-CVD hybrids and provide an enhanced understanding of the adsorption mechanism of dsDNA onto SWNTs.

Cellular response of RAW 264.7 to spray-coated multi-walled carbon nanotube films with various surfactants

The increasing role of carbon nanotubes (CNTs) in various biological applications has led to a number of studies on the cytotoxicity of solution-phase CNTs, but few studies are available concerning the cytotoxicity of CNT films. Herein, we studied the potential health effect of CNT films fabricated with three commercial surfactants (sodium cholate, sodium dodecyl sulfate, and triton X-100). Multi-walled carbon nanotube-surfactant dispersions were coated onto substrates through air-spray technique. Cellular morphology, MTT assays, as well as the expression of TNF-α and IL-1β of RAW 264.7 cells cultured on the spray-coated CNT films were evaluated for cytotoxicity. It was found that the cytotoxicity of the CNT films was largely dependent on the type of surfactant used and could be significantly reduced by mild washing steps.

The influence of natural organic matter on the toxicity of multiwalled carbon nanotubes

Engineered carbon nanostructures, such as multiwalled carbon nanotubes (MWNTs), are inherently hydrophobic and are not readily stable in aqueous media. However, the aqueous stability and bioavailability of these nanotubes may be influenced by the water quality parameters such as ionic strength, pH, and natural organic matter (NOM). Natural organic matter adsorbs onto the surface of MWNTs, effectively covering the hydrophobic surface and resulting in increased aqueous stability. This enhanced stability is likely to lead to an increased residence time in the water column and increased exposure times for pelagic organisms. In the current study, NOM from three different river systems in the southeast United States increased the stability of MWNT suspensions. The effects of these suspensions were evaluated using acute and chronic bioassays with Daphnia magna and Ceriodaphnia dubia. The 96-h LC50 for D. magna exposed to MWNTs suspended in Suwannee River (USA) NOM was approximately 2.0 mg/L and was not significantly influenced by NOM concentrations ranging from 1.79 to 18.5 mg/L DOC. However, there were differences in 96-h LC50 values among different sources of NOM (Suwannee, Black, and Edisto Rivers, USA). Daphnid growth was reduced in both D. magna and C. dubia, whereas reproduction was reduced in C. dubia. Characterization of the different NOM sources and MWNT suspensions was conducted. Visual inspection using transmission electron microscopy (TEM) and gut elimination observations suggested that the toxicity was attributable to ingested MWNTs clogging the gut tract of D. magna. The TEM micrographs indicated that MWNTs can disaggregate within the gut tract, but single MWNTs are unable to absorb across the gut lumen.

Subcutaneous injection of water-soluble multi-walled carbon nanotubes in tumor-bearing mice boosts the host immune activity

The immunological responses induced by oxidized water-soluble multi-walled carbon nanotubes on a hepatocarcinoma tumor-bearing mice model via a local administration of subcutaneous injection were investigated. Experimental results show that the subcutaneously injected carbon nanotubes induced significant activation of the complement system, promoted inflammatory cytokines' production and stimulated macrophages' phagocytosis and activation. All of these responses increased the general activity of the host immune system and inhibited the progression of tumor growth.