Zhongrui Li

Cytotoxicity Effects of Graphene and Single-Wall Carbon Nanotubes in Neural Phaeochromocytoma-Derived PC12 Cells

Graphitic nanomaterials such as graphene layers (G) and single-wall carbon nanotubes (SWCNT) are potential candidates in a large number of biomedical applications. However, little is known about the effects of these nanomaterials on biological systems. Here we show that the shape of these materials is directly related to their induced cellular toxicity. Both G and SWCNT induce cytotoxic effects, and these effects are concentration- and shape-dependent. Interestingly, at low concentrations, G induced stronger metabolic activity than SWCNT, a trend that reversed at higher concentrations. Lactate dehydrogenase levels were found to be significantly higher for SWCNT as compared to the G samples. Moreover, reactive oxygen species were generated in a concentration- and time-dependent manner after exposure to G, indicating an oxidative stress mechanism. Furthermore, time-dependent caspase 3 activation after exposure to G (10 microg/mL) shows evidence of apoptosis. Altogether these studies suggest different biological activities of the graphitic nanomaterials, with the shape playing a primary role.

Carbon Nanotubes Are Able To Penetrate Plant Seed Coat and Dramatically Affect Seed Germination and Plant Growth

Carbon nanotubes (CNTs) were found to penetrate tomato seeds and affect their germination and growth rates. The germination was found to be dramatically higher for seeds that germinated on medium containing CNTs (10-40 mug/mL) compared to control. Analytical methods indicated that the CNTs are able to penetrate the thick seed coat and support water uptake inside seeds, a process which can affect seed germination and growth of tomato seedlings.

Light-harvesting using high density p-type single wall carbon nanotube/n-type silicon heterojunctions.

Photovoltaic conversion was achieved from high-density p-n heterojunctions between single-wall carbon nanotubes (SWNTs) and n-type crystalline silicon produced with a simple airbrushing technique. The semitransparent SWNT network coating on n-type silicon substrate forms p-n heterojunctions and exhibits rectifying behavior. Under illumination the numerous heterojunctions formed between substrate generate electron-hole pairs, which are then split and transported through SWNTs (holes) and n-Si (electrons), respectively. The nanotubes serve as both photogeneration sites and a charge carriers collecting and transport layer. Chemical modification by thionyl chloride of the SWNT coating films was found to significantly increase the conversion efficiency by more than 50% through adjusting the Fermi level and increasing the carrier concentration and mobility. Initial tests have shown a power conversion efficiency of above 4%, proving that SOCl(2) treated-SWNT/n-Si configuration is suitable for light-harvesting at relatively low cost.

Comparative study on different carbon nanotube materials in terms of transparent conductive coatings

We compared conductive transparent carbon nanotube coatings on glass substrates made of differently produced single-wall (SWNT), double-wall, and multiwall carbon nanotubes. The airbrushing approach and the vacuum filtration method were utilized for the fabrication of carbon nanotube films. The optoelectronic performance of the carbon nanotube film was found to strongly depend on many effects including the ratio of metallic-to-semiconducting tubes, dispersion, length, diameter, chirality, wall number, structural defects, and the properties of substrates. The electronic transportability and optical properties of the SWNT network can be significantly altered by chemical doping with thionyl chloride. Hall effect measurements revealed that all of these thin carbon nanotube films are of p-type probably due to the acid reflux-based purification and atmospheric impurities. The competition between variable-range hoping and fluctuation-assisted tunneling in the functionized carbon nanotube system could lead to a crossover behavior in the temperature dependence of the network resistance.

Carbon Nanotubes: Synthesis, Properties, and Applications

This brief review presents a comprehensive outline of the present research status on the fast moving carbon nanotube (CNT) field. It covers a short introduction to the relation between carbon nanotubes, graphite, and other forms of carbon and explains in detail the structure of CNTs. The electronic, electrical, and mechanical properties of CNTs, as well as the most widely used methods for CNT production such as electric arc discharge, laser ablation, and chemical vapor deposition (CVD), are discussed. Some of the CNT applications covered in this review article are: field emission, hydrogen storage, carbon nanotube-based solar cells, and CNT composite materials.

Large-scale graphene production by RF-cCVD method

In this work, we report a low-cost facile method for the production of few-layer graphene sheets in large quantities through radio-frequency chemical vapor deposition.

Cytotoxicity and biological effects of functional nanomaterials delivered to various cell lines.

Functional nanomaterials that included gold, silver nanoparticles and single wall carbon nanotubes were delivered to two cell lines (MLO‐Y4 osteocytic cells and HeLa cervical cancer cells) in various concentrations. The cells were found to uptake the nanomaterials in a relatively short time, a process that significantly affected the shape and the size of the cells. The percentage of cellular death, due to the delivery of these nanomaterials, was found to be the highest for carbon nanotubes and increased gradually with the concentration of these nanostructures. Moreover, when the nanomaterials were delivered to the cells combined with commonly used chemotherapeutic agents such as etoposide or dexamethasone, the number of the cells that died increased significantly (100–300%) as compared with the case when only the nanomaterials or the chemotherapeutic agents were delivered. The experimental results were confirmed by Caspase 3 studies, indicating a strong interaction between the nanomaterials used in this study and the protein structure of the cells, which allowed a more effective action of the apoptotic agents. These findings could be the foundation of a new class of cancer therapies that are composed of both chemotherapeutic agents and nanomaterials. Copyright

Does the wall number of carbon nanotubes matter as conductive transparent material

As electrically conductive and optically transparent thin coating material, double-wall carbon nanotube network was found to have better transparency-conductance performance as compared with single-wall carbon nanotube (SWNT) and multiwall carbon nanotube (MWNT). The electronic transportability and optical properties of the SWNT films can be altered by chemical modification of thionyl chloride. Additionally, the conductance-temperature dependence analysis revealed that variable-range hopping mechanism dominates the conductance of few wall nanotube mats while fluctuation-assisted tunneling plays a more important role in that of MWNT films.

SOCl2 enhanced photovoltaic conversion of single wall carbon nanotube/n-silicon heterojunctions

We report solar cells based on high-density p-n heterojunctions between single wall carbon nanotubes (SWCNTs) and a n-type silicon wafer. Chemical modification by thionyl chloride of the SWCNT coating films was found to significantly increase the conversion efficiency by more than 45% through adjusting the Fermi level and increasing the carrier concentration and mobility. Electron-hole pairs are optically excited in the numerous heterojunctions formed between SOCl2-treated SWCNTs thin coating and n-type silicon substrate, and then split and transported through SWCNTs (holes) and n-Si (electrons), respectively.

Synergistic enhancement of cancer therapy using a combination of carbon nanotubes and anti-tumor drug

AIM In previous pharmacological applications, single-wall carbon nanotubes (CNTs) have primarily been explored as potential drug carriers and delivery vehicles. Here, we investigate and demonstrate for the first time, that CNTs can be considered as anti-tumor agents and, when in combination with conventional drugs, can significantly enhance their chemotherapeutic effects. METHOD & MATERIALS HeLa and human Panc1 cancer cells were treated with CNTs (24 h, 10 and 20 microg/ml), etoposide (6 h, 75 x 10(-6) M) and their combination. The cell viability was controlled by flow cytometry, caspase-3 assay and trypan blue dye. RESULTS A highly increased anti-tumor activity of the combination of etoposide and CNTs against cancer cells, compared with the administration of etoposide and CNTs alone, is reported. Data provided by viability assays suggest a strong interaction between CNTs and the cellular structures, thereby improving the effectiveness of conventional chemotherapeutic agents. CONCLUSION We believe this finding could lead to the development of new cancer therapies by carefully selecting the cytostatic drugs and nanostructural materials that, in combination, may provide synergistic curative rates.