Plasmonic nano surface for neuronal differentiation and manipulation.

Neurodegenerative diseases and traumatic brain injuries can destroy neurons, resulting in sensory and motor function loss. Transplantation of differentiated neurons from stem cells could help restore such lost functions. Plasmonic gold nanorods (AuNR) were integrated in growth surfaces to stimulate and modulate neural cells in order to tune cell physiology. An AuNR nanocomposite system was fabricated, characterized, and then utilized to study the differentiation of embryonic rat neural stem cells (NSCs). Results demonstrated that this plasmonic surface 1) accelerated differentiation, yielding almost twice as many differentiated neural cells as a traditional NSC culture surface coated with poly-D-lysine and laminin for the same time period; and 2) promoted differentiation of NSCs into neurons and astrocytes in a 2:1 ratio, as evidenced by the expression of relevant marker proteins. These results indicate that the design and properties of this AuNR plasmonic surface would be advantageous for tissue engineering to address neural degeneration.

The role of surface chemistry in the cytotoxicity profile of graphene.

Graphene and its derivative, because of their unique physical, electrical and chemical properties, are an important class of nanomaterials being proposed as foundational materials in nanomedicine as well as for a variety of industrial applications. A major limitation for graphene, when used in biomedical applications, is its poor solubility due to its rather hydrophobic nature. Therefore, chemical functionalities are commonly introduced to alter both its surface chemistry and biochemical activity. Here, we show that surface chemistry plays a major role in the toxicological profile of the graphene structures. To demonstrate this, we chemically increased the oxidation level of the pristine graphene and compared the corresponding toxicological effects along with those for the graphene oxide. X-ray photoelectron spectroscopy revealed that pristine graphene had the lowest amount of surface oxygen, while graphene oxide had the highest at 2.5% and 31%, respectively. Low and high oxygen functionalized graphene samples were found to have 6.6% and 24% surface oxygen, respectively. Our results showed a dose-dependent trend in the cytotoxicity profile, where pristine graphene was the most cytotoxic, with decreasing toxicity observed with increasing oxygen content. Increased surface oxygen also played a role in nanomaterial dispersion in water or cell culture medium over longer periods. It is likely that higher dispersity might result in graphene entering into cells as individual flakes ~1 nm thick rather than as more cytotoxic aggregates. In conclusion, changes in graphene's surface chemistry resulted in altered solubility and toxicity, suggesting that a generalized toxicity profile would be rather misleading. Copyright © 2016 John Wiley & Sons, Ltd.

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.

Quantification of cellular associated graphene and induced surface receptor responses.

The use of graphene for biomedical and other applications involving humans is growing and shows practical promise. However, quantifying the graphitic nanomaterials that interact with cells and assessing any corresponding cellular response is extremely challenging. Here, we report an effective approach to quantify graphene interacting with single cells that utilizes combined multimodal-Raman and photoacoustic spectroscopy. This approach correlates the spectroscopic signature of graphene with the measurement of its mass using a quartz crystal microbalance resonator. Using this technique, we demonstrate single cell noninvasive quantification and multidimensional mapping of graphene with a detection limit of as low as 200 femtograms. Our investigation also revealed previously unseen graphene-induced changes in surface receptor expression in dendritic cells of the immune system. This tool integrates high-sensitivity real-time detection and monitoring of nanoscale materials inside single cells with the measurement of induced simultaneous biological cell responses, providing a powerful method to study the impact of nanomaterials on living systems and as a result, the toxicology of nanoscale materials.

CO2 enhanced carbon nanotube synthesis from pyrolysis of hydrocarbons.

We report on the role of CO(2) in improving carbon nanotube yield and crystallinity from catalytic chemical vapor deposition of hydrocarbons.

Effects of the Fe-Co interaction on the growth of multiwall carbon nanotubes.

The influences of active species Fe-Co composition on the growth of carbon nanotubes (CNTs) were systemically investigated. CNTs were grown from the pyrolytic decomposition of C(2)H(2) over Fe-Co/CaCO(3) catalysts by radio frequency chemical vapor deposition (CVD). The catalyst stoichiometry was found to strongly influence the carbon deposition rate as well as the nanotube crystallinity characteristics. Compared to the CNTs synthesized over the Co/CaCO(3) catalyst, those produced by Fe-containing catalysts have less amorphous carbon. The maximum yield of high-quality CNTs was achieved at the Fe/Co atomic ratio of 2:1 due to a suitable concentration of benzene generated from acetylene CVD on such catalytic system. Fe and Co can form alloy and therefore the d-electron interaction between Fe and Co was believed to play an important role in the CNT growth.

Nanocrystalline Cellulose-Derived Doped Carbonaceous Material for Rapid Mineralization of Nitrophenols under Visible Light.

Nitrophenols (NPs) and related derivatives are industrially important chemicals, used notably to synthesize pharmaceuticals, insecticides, herbicides, and pesticides. However, NPs and their metabolites are highly toxic and mutagenic. They pose a serious threat to human health and ecosystem. Current work was undertaken to develop a suitable visible-light active catalyst for the sustainable and efficient mineralization of NPs in an aqueous environment. Nanocrystalline cellulose (NCs)-based nitrogen-doped titanium dioxide and carbonaceous material (N-TiO2/C) was synthesized by pyrolysis and sol-gel methods using NCs, polydopamine, and TiO2. The synthesized N-TiO2/C was characterized using different analytical techniques. Photocatalytic degradation of NPs under visible light indicated that acidic pH (3) was most suitable for the optimal degradation. 4-NP degradation followed both pseudo-first-order (R 2 = 0.9985) and Langmuir-Hinshelwood adsorption kinetic models (adsorption constant, K LH = 1.13 L mg-1). Gas chromatography-mass spectrometry and ion chromatography analysis confirmed the total mineralization of 4-NP into smaller molecular fragments such as acids, alcohols, and nitrates. The total organic carbon showed that 67% of total carbon present in 4-NP was mineralized into CO2 and CO. The catalyst was recycled for five consecutive cycles without losing its catalytic activities. The degradation mechanism of NPs with N-TiO2/C was also explored.

Comparative Aging Study of Organic Solar Cells Utilizing Polyaniline and PEDOT:PSS as Hole Transport Layers.

The aging effect on P3HT:PCBM organic solar cells was investigated with camphorsulfonic doped polyaniline (PANI:CSA) or poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) used as the hole transport layer (HTL). The cells were encapsulated and exposed to a continuous normal atmosphere on a dark shelf and then characterized intermittently for more than two years. The photovoltaic results revealed that the cells with PEDOT: PSS HTL showed better initial results than the cells with PANI:CSA HTL. Over time, PEDOT: PSS-based cells exhibited faster degradation than PANI:CSA-based cells, where the average efficiency of six cells dropped to zero in less than one and a half years. On the other hand, PANI:CSA-based cells exhibited a much more stable performance with an average efficiency drop of only 15% of their initial values after one and a half years and 63% after two years. A single-diode model was utilized to fit the experimental data with the theoretical curve to extract the diode parameters, such as the ideality factor, to explain the effect of aging on the diode's performance.

Photovoltaic device performance of single-walled carbon nanotube and polyaniline films on n-Si: device structure analysis.

In this paper, we explore the use of two organic materials that have been touted for use as photovoltaic (PV) materials: inherently conducting polymers (ICPs) and carbon nanotubes (CNTs). Due to these materials' attractive features, such as environmental stability and tunable electrical properties, our focus here is to evaluate the use of polyaniline (PANI) and single wall carbon nanotube (SWNT) films in heterojunction diode devices. The devices are characterized by electron microscopy (film morphology), current-voltage characteristics (photovoltaic behavior), and UV/visible/NIR spectroscopy (light absorption). We have found that both PANI and SWNT can be utilized as photovoltaic materials in a simple bilayer configuration with n-type Silicon: n-Si/PANI and n-Si/SWNT. It was our aim to determine how photovoltaic performance was affected utilizing both PANI and SWNT layers in multilayer devices: n-Si/PANI/SWNT and n-Si/SWNT/PANI. The short-circuit current density increased from 4.91 mA/cm(2) (n-Si/PANI) to 12.41 mA/cm(2) (n-Si/PANI/SWNT), while an increase in power conversion efficiency by ~91% was also observed. In the case of n-Si/SWNT/PANI and its corresponding device control (n-Si/SWNT), the short-circuit current density was decreased by an order of magnitude. The characteristics of the device were affected by the architecture and the findings have been attributed to the more effective transport of holes from the PANI to SWNT and less effective transport of holes from PANI to SWNT in the respective multilayer devices.

Catalytic conversion of graphene into carbon nanotubes via gold nanoclusters at low temperatures.

Here, we present the catalytic conversion of graphene layers into carbon nanotubes (CNTs), in the presence of Au nanoparticles (AuNPs) without the need for an additional carbon source. We have demonstrated that this catalytic process takes place at temperatures as low as 500 °C. No other oxide supports decorated with AuNPs were found to grow CNTs at this temperature. These findings highlight the high activity of graphene when used as a support for catalytic reactions.

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.

Cobalt nanoparticles coated with graphitic shells as localized radio frequency absorbers for cancer therapy.

Graphitic carbon-coated ferromagnetic cobalt nanoparticles (C-Co-NPs) with diameters of around 7 nm and cubic crystalline structures were synthesized by catalytic chemical vapor deposition. X-ray diffraction and x-ray photoelectron spectroscopy analysis indicated that the cobalt nanoparticles inside the carbon shells were preserved in the metallic state. Fluorescence microscopy images and Raman spectroscopy revealed effective penetrations of the C-Co-NPs through the cellular plasma membrane of the cultured HeLa cells, both inside the cytoplasm and in the nucleus. Low radio frequency (RF) radiation of 350 kHz induced localized heat into the metallic nanoparticles, which triggered the killing of the cells, a process that was found to be dependent on the RF application time and nanoparticle concentration. When compared to carbon nanostructures such as single-wall carbon nanotubes, these coated magnetic cobalt nanoparticles demonstrated higher specificity for RF absorption and heating. DNA gel electrophoresis assays of the HeLa cells after the RF treatment showed a strong broadening of the DNA fragmentation spectrum, which further proved the intense localized thermally induced damages such as DNA and nucleus membrane disintegration, under RF exposure in the presence of C-Co-NPs. The data presented in this report indicate a great potential of this new process for in vivo tumor thermal ablation, bacteria killing, and various other biomedical applications.

Influence of impurities on the x-ray photoelectron spectroscopy and Raman spectra of single-wall carbon nanotubes.

The effect of impurities on the properties of single-wall carbon nanotubes (SWNTs) was investigated with multiple analytical techniques. Charge transfer is believed to occur between the impurities and the SWNTs as observed by combining the Raman scattering and x-ray photoelectron measurements. The impurity condition (type and level) was found to strongly affect the electronic and vibrational properties of the SWNT. The metal catalysts in the impurity usually behave as electron donors, which can downshift the graphitic (G) band as well as the radial breathing mode frequencies. The low temperature air oxidation of as-prepared SWNT material usually upshifts the radial breathing mode Raman peaks to higher frequencies.