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With its diversity of signaling modalities: electrical, chemical and mechanical, nervous system poses demands of multimodality on neural interface technologies. Multimaterial fiber technology may enable minimally invasive multifunctional probing of the complexity of neural circuits.

In this paper we propose a new and cost-effective fabrication scheme for porous polymer optical fibers. Different porous polymer fibers made from polycarbonate (PC) and poly(methyl methacrylate) (PMMA) using this method have been thermally drawn and characterized. Porosity in the fiber cladding is introduced by the absorbed water in one layer of the polymer fiber preforms under heat treatment and/or thermal drawing, and can be controlled by adjusting the water concentration. In addition, we have shown that the fabricated porous polymer fibers have the potential application in localized drug delivery for cancer treatment.

Due to the limited regenerative ability of neural tissue, a diverse set of biochemical and biophysical cues for increasing nerve growth has been investigated, including neurotrophic factors, topography, and electrical stimulation. In this report, we explore optogenetic control of neurite growth as a cell-specific alternative to electrical stimulation. By investigating a broad range of optical stimulation parameters on dorsal root ganglia (DRGs) expressing channelrhodopsin 2 (ChR2), we identified conditions that enhance neurite outgrowth by three-fold as compared to unstimulated or wild-type (WT) controls. Furthermore, optogenetic stimulation of ChR2 expressing DRGs induces directional outgrowth in WT DRGs co-cultured within a 10 mm vicinity of the optically sensitive ganglia. This observed enhancement and polarization of neurite growth was accompanied by an increased expression of neural growth and brain derived neurotrophic factors (NGF, BDNF). This work highlights the potential for implementing optogenetics to drive nerve growth in specific cell populations., Charles Stark Draper Laboratory (University Research and Development Grant), National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (Award DMR-0819762), National Science Foundation (U.S.) (CAREER Award CBET-1253890), Simons Foundation, Korean Government Scholarship Program for Study Overseas

Carbon forms one of nature's strongest chemical bonds; its allotropes having provided some of the most exciting scientific discoveries in recent times. The possibility of inter-allotropic transformations/hybridization of carbon is hence a topic of immense fundamental and technological interest. Such modifications usually require extreme conditions (high temperature, pressure and/or high-energy irradiations), and are usually not well controlled. Here we demonstrate inter-allotropic transformations/hybridizations of specific types that appear uniformly across large-area carbon networks, using moderate alternating voltage pulses. By controlling the pulse magnitude, small-diameter single-walled carbon nanotubes can be transformed predominantly into larger-diameter single-walled carbon nanotubes, multi-walled carbon nanotubes of different morphologies, multi-layered graphene nanoribbons or structures with sp(3) bonds. This re-engineering of carbon bonds evolves via a coalescence-induced reconfiguration of sp(2) hybridization, terminates with negligible introduction of defects and demonstrates remarkable reproducibility. This reflects a potential step forward for large-scale engineering of nanocarbon allotropes and their junctions.

The ability to produce small scale, crystalline silicon spheres is of significant technological and scientific importance, yet scalable methods for doing so have remained elusive. Here we demonstrate a silicon nanosphere fabrication process based on an optical fibre drawing technique. A silica-cladded silicon-core fibre with diameters down to 340 nm is continuously fed into a flame defining an axial thermal gradient and the continuous formation of spheres whose size is controlled by the feed speed is demonstrated. In particular, spheres of diameter o500 nm smaller than those produced under isothermal heating conditions are shown and analysed. A fibre with dual cores, p-type and n-type silicon, is drawn and processed into spheres. Spatially coherent break-up leads to the joining of the spheres into a bispherical silicon ‘p–n molecule’. The resulting device is measured to reveal a rectifying I–V curve consistent with the formation of a p–n junction.

Multimaterial fiber devices share the basic functional attributes of their traditional electronic counterparts, yet are fabricated from metals, insulators and semiconductors using scalable preform-to-fiber processing methods, yielding kilometers of functional fibers. New discoveries extend the field of opportunities to nanofabrication and chemistry.

Nitrogen-doped graphitic nanoribbons (Nx-GNRs), synthesized by chemical vapor deposition (CVD) using pyrazine as a nitrogen precursor, are reported for the first time. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) reveal that the synthesized materials are formed by multilayered corrugated GNRs, which in most cases exhibit the formation of curved graphene edges (loops). This suggests that during growth, nitrogen atoms promote loop formation; undoped GNRs do not form loops at their edges. Transport measurements on individual pure GNRs exhibit a linear I–V (current-voltage) behavior, whereas Nx-GNRs show reduced current responses following a semiconducting-like behavior, which becomes more prominent for high nitrogen concentrations. To better understand the experimental findings, electron density of states (DOS), quantum conductance for nitrogen-doped zigzag and armchair single-layer GNRs are calculated for different N doping concentrations using density functional theory (DFT) and non-equilibrium Green functions. These calculations confirm the crucial role of nitrogen atoms in the transport properties, confirming that the nonlinear I–V curves are due to the presence of nitrogen atoms within the Nx-GNRs lattice that act as scattering sites. These characteristic Nx-GNRs transport properties could be advantageous in the fabrication of electronic devices including sensors in which metal-like undoped GNRs are unsuitable., M.T. thanks JST-Japan for funding the Research Center for Exotic NanoCarbons, under the Japanese regional Innovation Strategy Program by the Excellence. M.T. is grateful to the Penn State Center for Nanoscale Science (MRSEC; NSF grant number DMR-0820404), for a seed grant on “Defect Engineering in Layered Materials”. H.T. acknowledges support of CAPES, Brazil, through its Foreign Scientist Invited program. F.J.R.M., F.L.U., and E.M.S. acknowledge CONACYT (México) grants CB-2008-SEP-107082, 60218-F1 and 48300 S-3907, respectively. X.J. and M.S.D. acknowledge the MURI grant ONR-N00014-09-1-1063. R.M.G. was supported by MCINN, project number FIS2009-12721-C04-01 and scholarship AGAUR “FI-DGR 2011”. This work was supported by CONACYT Ph.D. scholarships 223807 (J.O.M.) and 223824 (M.L.G.B.), as well as financial research support from PSU. J.O.M. thanks complementary support from the Graduate Complementary Scholarship program (DGRI-SEP, México). B.G.S. was supported by the Center for Nanophase Materials Sciences (CNMS), sponsored at Oak Ridge National Laboratory by the Division of Scientifi c User Facilities, U.S. Department of Energy.

The polycomb group transcriptional modifier Bmi1 is often upregulated in numerous cancers and is intensely involved in normal and cancer stem cells, and importantly is as a prognostic indicator for some cancers, but its role in breast cancer remains unclear. Here, we found Bmi1 overexpression in 5-Fu (5-fluorouracil)-resistant MCF-7 cells (MCF-7/5-Fu) derived from MCF-7 breast cancer cells, MDA-MB-231 and MDA-MB-453 breast cancer cells compared to MCF-7 cells, was related with 5-Fu resistance and enrichment of CD44(+)/CD24(-) stem cell subpopulation. Bmi1 knockdown enhanced the sensitivity of breast cancer cells to 5-Fu and 5-Fu induced apoptosis via mitochondrial apoptotic pathway, and decreased the fraction of CD44(+)/CD24(-) subpopulation. In addition, our analysis showed inverse expression pattern between Bmi1 and miR-200c and miR-203 in selected breast cancer cell lines, and miR-200c and miR-203 directly repressed Bmi1 expression in protein level confirmed by luciferase reporter assay. MiR-200c and miR-203 overexpression in breast cancer cells downregulated Bmi1 expression accompanied with reversion of resistance to 5-Fu mediated by Bmi1. Inversely, Bmi1 overexpression inhibited miR-200c expression in MCF-7 cells, but not miR-203, however ectopic wild-type p53 expression reversed Bmi1 mediated miR-200c downregulation, suggesting the repressive effect of Bmi1 on miR-200c maybe depend on p53. Thus, our study suggests a cross-talk between Bmi1 and miR-200c mediated by p53, and Bmi1 interference would improve chemotherapy efficiency in breast cancer via susceptive apoptosis induction and cancer stem cell enrichment inhibition.

We demonstrate a high-throughput method for synthesizing zinc selenide (ZnSe) in situ during fiber drawing. Direct atomic-level compositional and structural analysis of the produced compound is performed, and a ZnSe-based in-fiber heterojunction device is achieved.

Hexagonal boron nitride (h-BN) is a promising material as a dielectric layer or substrate for two-dimensional electronic devices. In this work, we report the synthesis of large-area h-BN film using atmospheric pressure chemical vapor deposition on a copper foil, followed by Cu etching and transfer to a target substrate. The growth rate of h-BN film at a constant temperature is strongly affected by the concentration of borazine as a precursor and the ambient gas condition such as the ratio of hydrogen and nitrogen. h-BN films with different thicknesses can be achieved by controlling the growth time or tuning the growth conditions. Transmission electron microscope characterization reveals that these h-BN films are polycrystalline, and the c-axis of the crystallites points to different directions. The stoichiometry ratio of boron and nitrogen is close to 1:1, obtained by electron energy loss spectroscopy. The dielectric constant of h-BN film obtained by parallel capacitance measurements (25 μm(2) large areas) is 2-4. These CVD-grown h-BN films were integrated as a dielectric layer in top-gated CVD graphene devices, and the mobility of the CVD graphene device (in the few thousands cm(2)/(V·s) range) remains the same before and after device integration.

In this article, the role of kinetics, in particular, the pressure of the reaction chamber in the chemical vapor deposition (CVD) synthesis of graphene using low carbon solid solubility catalysts (Cu), on both the large area thickness uniformity and the defect density are presented. Although the thermodynamics of the synthesis system remains the same, based on whether the process is performed at atmospheric pressure (AP), low pressure (LP) (0.1-1 Torr) or under ultrahigh vacuum (UHV) conditions, the kinetics of the growth phenomenon are different, leading to a variation in the uniformity of the resulting graphene growth over large areas (wafer scale). The kinetic models for APCVD and LPCVD are discussed, thereby providing insight for understanding the differences between APCVD vs LPCVD/UHVCVD graphene syntheses. Interestingly, graphene syntheses using a Cu catalyst in APCVD processes at higher methane concentrations revealed that the growth is not self-limiting, which is in contrast to previous observations for the LPCVD case. Additionally, nanoribbons and nanostrips with widths ranging from 20 to 100 nm were also observed on the APCVD grown graphene. Interactions between graphene nanofeatures (edges, folds) and the contaminant metal nanoparticles from the Cu etchant were observed, suggesting that these samples could potentially be employed to investigate the chemical reactivity of single molecules, DNA, and nanoparticles with monolayer graphene.

Recent experimental reports indicate that Joule heating can atomically sharpen the edges of chemical vapor deposition grown graphitic nanoribbons. The absence or presence of loops between adjacent layers in the annealed materials is the topic of a growing debate that this Letter aims to put to rest. We offer a rationale explaining why loops do form if Joule heating is used alone, and why adjacent nanoribbon layers do not coalesce when Joule heating is applied after high-energy electrons first irradiate the sample. Our work, based on large-scale quantum molecular dynamics and electronic-transport calculations, shows that vacancies on adjacent graphene sheets, created by electron irradiation, inhibit the formation of edge loops.

Structural and compositional studies of nanomaterials of technological importance have been carried out using advanced electron microscopy methods, including aberration-corrected transmission electron microscopy (AC-TEM), AC-high angle annular dark field scanning TEM (AC-HAADF-STEM), AC-energy filtered TEM, electron-stimulated energy dispersive spectroscopy in the AC-(S)TEM and high-resolution TEM (HRTEM) with scanning tunneling microscopy (STM) holder. The AC-EM data reveal improvements in resolution and minimization in image delocalization. A JEOL 2200FS double-AC field emission gun TEM/STEM operating at 200 kV in the Nanocentre at the University of York has been used to image single metal atoms on crystalline supports in catalysts, grain boundaries in nanotwinned metals, and nanostructures of tetrapods. Joule heating studies using HRTEM integrated with an STM holder reveal in situ crystallization and edge reconstruction in graphene. Real-time in situ AC-HAADF-STEM studies at elevated temperatures are described. Dynamic in-column energy filtering in an AC environment provides an integral new approach to perform dynamic in situ studies with aberration correction. The new results presented here open up striking new opportunities for atomic scale studies of nanomaterials and indicate future development directions. Microsc. Res. Tech., 2011. © 2010 Wiley-Liss, Inc.

We report graphene films composed mostly of one or two layers of graphene grown by controlled carbon precipitation on the surface of polycrystalline Ni thin films during atmospheric chemical vapor deposition (CVD). Controlling both the methane concentration during CVD and the substrate cooling rate during graphene growth can significantly improve the thickness uniformity. As a result, one- or two- layer graphene regions occupy up to 87% of the film area. Single layer coverage accounts for 5%–11% of the overall film. These regions expand across multiple grain boundaries of the underlying polycrystalline Ni film. The number density of sites with multilayer graphene/graphite (>2 layers) is reduced as the cooling rate decreases. These films can also be transferred to other substrates and their sizes are only limited by the sizes of the Ni film and the CVD chamber. Here, we demonstrate the formation of films as large as 1 in2. These findings represent an important step towards the fabrication of large-scale high-quality graphene samples., National Science Foundation (U.S.) (CTS 05-06830), National Science Foundation (U.S.) (DMR07-04197)

A new and general approach to achieving efficient electrically driven light emission from a Si-based nano p-n junction array is introduced. A wafer-scale array of p-type silicon nanotips were formed by a single-step self-masked dry etching process, which is compatible with current semiconductor technologies. On top of the silicon nanotip array, a layer of n-type ZnO film was grown by pulsed laser deposition. Both the narrow line width of 10 nm in cathodoluminescence spectra and the appearance of multiphonon Raman spectra up to the fourth order indicate the excellent quality of the ZnO film. The turn-on voltage of our ZnO/Si nanotip array is found to be approximately 2.4 V, which is 2 times smaller than its thin film counterpart. Moreover, electroluminescence (EL) from our ZnO/Si nanotips array light-emitting diode (LED) has been demonstrated. Our results could open up new possibilities to integrate silicon-based optoelectronic devices, such as highly efficient LEDs, with standard Si ultralarge-scale integrated technology.

In this work we present a low cost and scalable technique, via ambient pressure chemical vapor deposition (CVD) on polycrystalline Ni films, to fabricate large area ( approximately cm2) films of single- to few-layer graphene and to transfer the films to nonspecific substrates. These films consist of regions of 1 to approximately 12 graphene layers. Single- or bilayer regions can be up to 20 mum in lateral size. The films are continuous over the entire area and can be patterned lithographically or by prepatterning the underlying Ni film. The transparency, conductivity, and ambipolar transfer characteristics of the films suggest their potential as another materials candidate for electronics and opto-electronic applications.

We report the use of chemical vapor deposition (CVD) for the bulk production (grams per day) of long, thin, and highly crystalline graphene ribbons (20-30 microm in length) exhibiting widths of 20-300 nm and small thicknesses (2-40 layers). These layers usually exhibit perfect ABAB... stacking as in graphite crystals. The structure of the ribbons has been carefully characterized by several techniques and the electronic transport and gas adsorption properties have been measured. With this material available to researchers, it should be possible to develop new applications and physicochemical phenomena associated with layered graphene.

Nanostructured thermoelectric materials have attracted lots of interest in recent years, due to their enhanced performance determined by their thermoelectric dimensionless figure of merit. However, because of equipment limitations, not much work has been done on combining simultaneous transport measurements and structural characterization on individual nanostructured thermoelectric materials. With an integrated TEM-STM system, we studied the structural behavior and electrical properties of bismuth (Bi) nanobelts and nanoparticles. Results showed that clean Bi nanostructures free of oxides can be produced by in-situ high temperature electro-migration and Joule annealing processes occurring within the electron microscope. Preliminary electrical measurements indicate a conductivity of two orders of magnitude lower for Bi nanoparticles than that for bulk Bi. Such in-situ studies are highly advantageous for studying the semimetal-semiconductor transition and how this transition could enhance thermoelectric properties.

Carrot-like defects in a 7 off-cut (from [0001] toward direction) 4H-SiC wafer with a 36μm thick 4H-SiC epilayer have been investigated using Nomarski optical microscopy, synchrotron white beam x-ray topography (SWBXT), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray topographs confirm that threading screw dislocations are often associated with the carrots. Cross-sectional TEM observation confirms that a prismatic stacking fault exists below the carrot. This fault was found to show contrast in all observed diffraction geometries except for g=0004. A model for the mechanism of formation of this type of defect during epitaxial growth is proposed.

The role of TGFβ in chemoresponse and progression of breast cancer (BC) remains unclarified, here we investigated the role of TGFβ2 in BC by taking into account BC heterogeneity. mRNA microarray identified TGFβ2 was upregulated in 5-Fu resistant MCF-7 BC cells (MCF-7/5-Fu) with EMT phenotype. TGFβ2 in mRNA and protein from MCF-7/5-Fu and triple-negative BC (TN-BC) cell lines MDA-MB-231, HCC38 and BT-549 with mesenchymal morphology was higher than luminal BC cell lines MCF-7, T47D, BT-474 and SKBR3. TGFβ signal was more active in mesenchymal BC cells than luminal BC cells charactered by p-smad2, p-smad3 and snial1 upregulated. TGFβ signal inhibition with TGFβ receptor (TGFβR) inhibitor SD208 or TGFβRI targeted shRNA reversed the mesenchymal phenotype accompanied with invasion inhibition, BC stem cell (BCSC) traits measured by CD44+CD24- subpopulation analysis and mammosphere assay, and resistance to 5-Fu and Paclitaxel, but played limited effect on MCF-7/5-Fu cells. As the same, TGFβ2 only partially induced EMT phenotype in MCF-7, T47D, BT474 and SKBR3 cells. miRNA microarray indentified downregulation of miR-141, miR-145 and miR-200a (Tβ2-miRNAs) in mesenchymal BC cells compared to lumial BC cells. Lentivirus system with two pre-miRNA units enhanced Tβ2-miRNAs expression accompanied with TGFβ2 downregulation and reversion of mesenchymal phenotype and drug resistance in mesenchymal BC cells. Luciferase activity assay also strongly suggested Tβ2-miRNAs directly target TGFβ2 synergistically. TGFβ signal inhibition and snail1 knockdown upregulated Tβ2-miRNAs in mesenchymal BC cells. ChIP assay showed snail1 bound to promoters of Tβ2-miRNAs, combined with promoter luciferase assay suggested snail1 transcriptionaly repress Tβ2-miRNAs expression in mesenchymal BC cells. However, DKK1 upregulated Tβ2-miRNAs expression in mesenchymal BC cells, but with limited effect in snail1 knockdown cells, suggesting DKK1 could reverse the repressive effect of snail1 on miRNAs expression. TGFβ2 upregulated Tβ2-miRNAs expression in MCF-7 and T47D cells with normal DKK1 expression, and snail1 konckdown abolished the effect of TGFβ2. In addition, using a tissue microarray of 93 BC biopsies containing 42 TN-BC, we found TGFβ2 and snail1 protein were present at higher levels in TN-BC than in luminal BC, and miRNAs measured by ISH and DKK1 protein were present at lower levels. Furthermore, the result of Tβ2-miRNAs detection in the serum samples from 76 BC patients including 34 TN-BC showed Tβ2-miRNAs abundance in serum samples from TN-BC was much lower. In conclusion, the role of TGFβ in BC is cell type dependent and our findings suggest TGFβ2 protein and Tβ2-miRNAs levels in serum will be valuable prognostic biomarkers and therapeutic strategies for mesenchymal BC. Note: This abstract was not presented at the meeting. Citation Format: Guopei Zheng, Xiaoting Jia, Zijuan Zhang, Zhijie Zhang, Chen Qu, Jiang Yin, Zhimin He. A DKK1 dependent crosstalk between TGFβ2-snail1 and miRNAs contributes to chemoresistance in mesenchymal-like breast cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4872. doi:10.1158/1538-7445.AM2014-4872

In this work, electrostatic spray assisted chemical vapor deposition is used to directly deposit single-walled carbon nanotube (SWNT) thin films on a substrate. The catalyst solution was finely dispersed by a strong electrical field and injected into the heated reaction zone (950-1100 degrees C) during the growth. It was found that under optimized growth conditions, the deposited material consists of SWNTs while only small amounts of impurities are observed. The growth at different temperatures results in nanotubes of different length and morphology. The location at which the SWNTs deposit at the downstream end of the growth chamber is found to be affected by the nanotube length and the growth temperature, which can be understood by considering different forces acting on the floating aerosol particles inside the furnace. These results suggest a potential for in situ separation of the SWNTs by applying different forces to the floating SWNTs.

Here the authors report the use of either furnace heating or Joule heating to pacify the exposed graphene edges by loop formation in a novel graphitic nanoribbon material, grown by chemical vapor deposition. The edge energy minimization process involves the formation of loops between adjacent graphene layers within the nanoribbons. A comparison is made of the similarities and differences between the loop structures formed using these two methods. An estimation of the temperature of these graphitic nanoribbons during Joule heating is also reported based on the melting and evaporation of Pt nanoparticles.