Optimization of Parameters to Achieve High Yield and Purity Single-Walled Carbon Nanotube by Thermal and Chemical Oxidation and Its Effect on Conductivity.

Single wall carbon nanotubes due to their unique structural and electronic characteristics have revolutionized the field of nanotechnology and are widely used the field of transistors, drug delivery, and nanocomposities. For improved efficiency of these applications, the utilized tubes must of preeminent purity. Here, we report key parameters that are optimized to achieve their highest purity upto 98 wt%, and yield as high as 50 wt% by thermal and chemical oxidation. The as-produced SWCNT were heated in air at 470 °C, for 90 min, and later subjected to chemical oxidation. The chemical oxidation involved the treatment of thermally treated SWCNT with different concentrations of HCl (4N, 6N, 8N) and 30% H2O2, for different time periods (4 hr, 6 hr). This method does not cause damage to the walls of the tubes, observing no loss of nanotubes. The sheet resistance of as-produced and purified tubes was measured and the conductivity was calculated.

Toxicity of Raw and Purified Single-Walled Carbon Nanotubes in Rat's Lung Epithelial and Cervical Cancer Cells.

The increased applications of carbon nanotubes in the field of drug delivery, bioimaging and biosensors demand nanotubes to be of highest purity, free from metallic impurities and amorphous carbon. All of these sectors require a profound investigation about the toxic effects on human and the environment. Many attempts have been made to purify and surface modify the carbon nanotubes, however a detailed study on the raw and purified material has yet to be conducted. Here we present the toxicity studies of raw and the purified single-walled carbon nanotubes in rat's lung epithelial cell and cervical cancer cells (HeLa). These cells were treated with increasing concentration of 0.5 µg/mL to 50 µg/mL and the various biocompatibility assays were performed. The results showed an increased cell death with purified single-walled carbon nanotubes followed by the depletion of antioxidant levels and activation of the caspase cascade at a rapid rate compared to raw single-walled carbon nanotubes. This suggests that purified single walled carbon nanotubes are more toxic to the cells and exhibit ultra-fine particulate matter like toxicity.

Utilization of highly purified single wall carbon nanotubes dispersed in polymer thin films for an improved performance of an electrochemical glucose sensor.

In this work we report the improved performance an electrochemical glucose sensor based on a glassy carbon electrode (GCE) that has been modified with highly purified single wall carbon nanotubes (SWCNTs) dispersed in polyethyleneimine (PEI), polyethylene glycol (PEG) and polypyrrole (PPy). The single wall carbon nanotubes were purified by both thermal and chemical oxidation to achieve maximum purity of ~98% with no damage to the tubes. The SWCNTs were then dispersed by sonication in three different organic polymers (1.0mg/ml SWCNT in 1.0mg/ml of organic polymer). The stable suspension was coated onto the GCE and electrochemical characterization was performed by Cyclic Voltammetry (CV) and Amperometry. The electroactive enzyme glucose oxidase (GOx) was immobilized on the surface of the GCE/(organic polymer-SWCNT) electrode. The amperometric detection of glucose was carried out at 0.7 V versus Ag/AgCl. The GCE/(SWCNT-PEI, PEG, PPY) gave a detection limit of 0.2,633 µM, 0.434 µM, and 0.9,617 µM, and sensitivities of 0.2411 ± 0.0033 µA mM(-1), r(2)=0.9984, 0.08164 ± 0.001129 µA mM(-1), r(2)=0.9975, 0.04189 ± 0.00087 µA mM(-1), and r(2)=0.9944 respectively and a response time of less than 5s. The use of purified SWCNTs has several advantages, including fast electron transfer rate and stability in the immobilized enzyme. The significant enhancement of the SWCNT modified electrode as a glucose sensor can be attributed to the superior conductivity and large surface area of the well dispersed purified SWCNTs.

Agarose gel tailored calcium carbonate nanoparticles-synthesis and biocompatibility evaluation.

In this study, a novel approach to tailor the calcium carbonate nanoparticles was exploited based on agarose gel as polymer medium. The size of nanoparticles formed was governed by ionic diffusion and affected by weight percent of agarose and reaction temperature. The size, shape, purity, composition and allotropy of the synthesized nanoparticles were analyzed by different characterization techniques. Purity of nanoparticles as small as 37 nm demonstrates their suitability for broad range of industrial applications. The exposure of rat lung epithelial cells to these nanoparticles even at a higher concentration (50 microg/ml) did not induce considerable oxidative stress or cell death authenticating their fidelity to potential applications in the field of biotechnology and medicine. Through the simple and economic method of synthesis adopted in this study, separation of nanoparticles from the gel was easy, and process parameters could be optimized to control the particle size.

Optimization of process parameters of polymer solution mediated growth of calcium carbonate nanoparticles.

With the advent of nanotechnology, many methods of synthesis of nanoparticles have come into practice and the 'polymer mediated growth' technique is among them. In this route, ions of one of the reactants are allowed to diffuse from an external solution into a polymer matrix where the other reactant is complexed and bound. The exact role of ionic diffusion in the formation of nanoparticles was investigated in the current study by studying the patterns of kinetics of nanoparticle formation using UV vis spectroscopy. Typically, calcium carbonate nanoparticles were formed by the aforementioned technique using polyethylene glycol solution. The particle size was calculated using Scherrer's formula on x-ray diffraction plots and was reconfirmed with field emission scanning electron microscope and transmission electron microscope images. Energy-dispersive x-ray analysis was used to study the composition and purity of the nanoparticles formed. The reactant to polymer ratio, reaction temperature and molecular weight of polyethylene glycol affected the size of the particles formed. Through this knowledge we optimized these parameters to obtain particles as small as 20 nm and confirmed that this technique can be used to control the size of nanoparticles.

Magnetite induces oxidative stress and apoptosis in lung epithelial cells.

There is an ongoing concern regarding the biocompatibility of nanoparticles with sizes less than 100 nm as compared to larger particles of the same nominal substance. In this study, we investigated the toxic properties of magnetite stabilized with polyacrylate sodium. The magnetite was characterized by X-ray powder diffraction analysis, and the mean particle diameter was calculated using the Scherrer formula and was found to be 9.3 nm. In this study, we treated lung epithelial cells with different concentrations of magnetite and investigated their effects on oxidative stress and cell proliferation. Our data showed an inhibition of cell proliferation in magnetite-treated cells with a significant dose-dependent activation and induction of reactive oxygen species. Also, we observed a depletion of antioxidants, glutathione, and superoxide dismutase, respectively, as compared with control cells. In addition, apoptotic-related protease/enzyme such as caspase-3 and -8 activities, were increased in a dose-dependent manner with corresponding increased levels of DNA fragmentation in magnetite-treated cells compared to than control cells. Together, the present study reveals that magnetite exposure induces oxidative stress and depletes antioxidant levels in the cells to stimulate apoptotic pathway for cell death.

Calcium carbonate nanoparticles: synthesis, characterization and biocompatibility.

The synthesis of nanoparticles and their functionalization to effectively utilize them in biological applications including drug delivery is currently a challenge. Calcium carbonate among many other inorganic nanosized particles offers promising results for such applications. We have synthesized calcium carbonate nanoparticles using polymer mediated growth technique, where one of the ions bound within polymer matrix and the other diffuses and reacts to form desired compound. The synthesized nanoparticles are characterized using X-ray diffraction, Scanning Electron Microscopy and spectroscopic techniques such as Fourier-Transform Infra-red spectroscopy and UV-Vis spectroscopy. The diameter of the calcium carbonate nanoparticles is estimated to be 39.8 nm and their biocompatibility studies showed no significant induction of oxidative stress or cell death even at higher concentrations (50 microg) upon exposure to HeLa and LE cells. Here, we report that the synthesized calcium carbonate nanosized particles using polymer mediated growth technique are biocompatible and can be safely used for biomedical applications.

Epitaxial growth of the zinc oxide nanorods, their characterization and in vitro biocompatibility studies.

Here, we have synthesized Zinc Oxide (ZnO) nanorods at room temperature using zinc acetate and hexamethylenetetramine as precursors followed by characterization using X-ray diffraction (XRD), fourier transform infra red spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy. The growth of the synthesized ZnO was found to be very close to its hexagonal nature, which is confirmed by XRD. The nanorods were grown perpendicular to the long-axis and grew along the [001] direction, which is the nature of ZnO growth. The morphology of the synthesized ZnO nanorods was also confirmed by SEM. The size of the nanorod was estimated to be around 20-25 nm in diameter and approximately 50-60 nm in length. Our biocompatibility studies using synthesized ZnO showed no significant dose- or time-dependent increase in the formation of free radicals, accumulation of peroxidative products, antioxidant depletion or loss of cell viability on lung epithelial cells.

Pulmonary biocompatibility assessment of inhaled single-wall and multiwall carbon nanotubes in BALB/c mice.

With the widespread application of carbon nanotubes (CNTs) in diverse commercial processes, scientists are now concerned about the potential health risk of occupational exposures. In this study, CNT-induced pulmonary toxicity was investigated by exposing BALB/c mice to aerosolized single-wall (SW) CNT and multiwall (MW) CNT (5 µg/g of mice) for 7 consecutive days in a nose-only exposure system. Microscopic studies showed that inhaled CNTs were homogeneously distributed in the mouse lung. The total number of bronchoalveolar lavage polymorphonuclear leukocytes recovered from the mice exposed to SWCNT and MWCNT (1.2 × 10(6) ± 0.52 and 9.87 × 10(5) ± 1.45; respectively) was significantly greater than control mice (5.46 × 10(5) ± 0.78). Rapid development of pulmonary fibrosis in mice that inhaled CNT was also confirmed by significant increases in the collagen level. The lactate dehydrogenase levels were increased nearly 2- and 2.4-fold in mice that inhaled SWCNT and MWCNT, respectively, as compared with control mice. In addition, exposure of CNTs to mice showed a significant (p < 0.05) reduction of antioxidants (glutathione, superoxide dismutase, and catalase) and induction of oxidants (myloperoxidase, oxidative stress, and lipid peroxidation) compared with control. Apoptosis-related proteins such as caspase-3 and -8 activities were also significantly increased in mice that inhaled CNT than in control mice. Together, this study shows that inhaled CNTs induce inflammation, fibrosis, alteration of oxidant and antioxidant levels, and induction of apoptosis-related proteins in the lung tissues to trigger cell death.