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The behavior of mammalian cells on vertical nanowire (NW) arrays, including cell spreading and the dynamic distribution of focal adhesions and cytoskeletal proteins, has been intensively studied to extend the implications for cellular manipulations in vitro. Prompted by the result that cells on silicon (Si) NWs showed morphological changes and reduced migration rates, we have explored the transition of mesenchymal stem cells into a neuronal lineage by using SiNWs with varying lengths. When human mesenchymal stem cells (hMSCs) were cultured on the longest SiNWs for 3 days, most of the cells exhibited elongated shapes with neurite-like extensions and dot-like focal adhesions that were prominently observed along with actin filaments. Under these circumstances, the cell motility analyzed by live cell imaging was found to decrease due to the presence of SiNWs. In addition, the slowed growth rate, as well as the reduced population of S phase cells, suggested that the cell cycle was likely arrested in response to the differentiation process. Furthermore, we measured the mRNA levels of several lineage-specific markers to confirm that the SiNWs actually induced neuron-like differentiation of the hMSCs while hampering their osteogenic differentiation. Taken together, our results implied that SiNWs were capable of inducing active reorganization of cellular behaviors, collectively guiding the fate of hMSCs into the neural lineage even in the absence of any inducing reagent.

Understanding how living cells interact with nanostructures is integral to a better understanding of the fundamental principles of biology and the development of next-generation biomedical/bioenergy devices. Recent studies have demonstrated that mammalian cells can recognize nanoscale topographies and respond to these structures. From this perspective, there is a growing recognition that nanostructures, along with their specific physicochemical properties, can also be used to regulate the responses and motions of bacterial cells. Here, by utilizing a well-defined silicon nanowire array platform and single-cell imaging, we present direct evidence that Shewanella oneidensis MR-1 can recognize nanoscale structures and that their swimming patterns and initial attachment locations are strongly influenced by the presence of nanowires on a surface. Analyses of bacterial trajectories revealed that MR-1 cells exhibited a confined diffusion mode in the presence of nanowires and showed preferential attachment to the nanowires, whereas a superdiffusion mode was observed in the absence of nanowires. These results demonstrate that nanoscale topography can affect bacterial movement and attachment and play an important role during the early stages of biofilm formation.

Semiconductors doped with magnetic ion, the so-called diluted magnetic semiconductors, are promising candidates for spintronics. Herein, we report on magnetic anisotropy in Mn:Ge diluted magnetic semiconductor nanowires. We grew single crystal Mn:Ge nanowires vertically on a Ge substrate and found the anisotropy in ratios of orbital to spin magnetic moments in the angle-dependent x-ray magnetic circular dichroism measurements. Our further characterization indicates that this anisotropy comes from the unique characteristics of nanowires, i.e., very high aspect ratio in their shape and tensile stress along the longitudinal direction, which confine the spins along the longitudinal direction and make an easy axis in that direction. [ABSTRACT FROM AUTHOR]

The single living cell action potential was measured in an intracellular mode by using a vertical nanoelectrode. For intracellular interfacing, Si nanowires were vertically grown in a controlled manner, and optimum conditions, such as diameter, length, and nanowire density, were determined by culturing cells on the nanowires. Vertical nanowire probes were then fabricated with a complimentary metal-oxide-semiconductor (CMOS) process including sequential deposition of the passivation and electrode layers on the nanowires, and a subsequent partial etching process. The fabricated nanowire probes had an approximately 60-nm diameter and were intracellular. These probes interfaced with a GH cell and measured the spontaneous action potential. It successfully measured the action potential, which rapidly reached a steady state with average peak amplitude of approximately 10 mV, duration of approximately 140 ms, and period of 0.9 Hz. [ABSTRACT FROM AUTHOR]

The recent demonstration of thermal conductivity of rough electrolessly etched Si nanowire (Hochbaum et al., Nature, 451:163, ) attracted a lot of interest, because it could not be explained by the existing theory; thermal conductivity of rough Si nanowires falls below the boundary scattering of the thermal conductivity. However, nanoscale pores presented in the nanowires (Hochbaum et al., Nano Letters, 9:3550-3554, ) hinder one to be fully convinced that the surface roughness solely made a contribution to the significant reduction in thermal conductivity. In this study, we synthesized vapor-liquid-solid (VLS) grown rough SiGe nanowire and measured and theoretically simulated thermal conductivity of the nanowire. The thermal conductivity of rough SiGe nanowire is an order of magnitude lower than that of bulk SiGe and around a factor of four times lower than that of smooth SiGe nanowire. This significant reduction could be explained by the fact that the surface roughness scatters medium-wavelength phonons, whereas the long-wavelength phonons are scattered by phonon boundary scattering, and the short-wavelength phonons are scattered by alloy scattering. [ABSTRACT FROM AUTHOR]

In this paper, we synthesize VLS-grown rough Si nanowires using Mn as a catalyst with various surface roughnesses and diameters and measured their thermal conductivities. We grew the nanowires by a combination vapor-liquid-solid and vapor-solid mechanism for longitudinal and radial growth, respectively. The surface roughness was controlled from smooth up to about 37 nm by the radial growth. Our measurements showed that the thermal conductivity of rough surface Si nanowires is significantly lower than that of smooth surface nanowires and decreased with increasing surface roughness even though the diameter of the smooth nanowire was lower than that of the rough nanowires. Considering both nanowires were grown via the same growth mechanism, these outcomes clearly demonstrate that the rough surface induces phonon scattering and reduces thermal conductivity with this nanoscale-hole-free nanowires. Control of roughness induced phonon scattering in Si nanowires holds promise for novel thermoelectric devices with high figures of merit. [ABSTRACT FROM AUTHOR]

We report on bifurcate reactions on the surface of well-aligned SiGe nanowires that enable fabrication of two different coaxial heterostructure nanowires. The SiGe nanowires were grown in a chemical vapor transport process using SiCl gas and Ge powder as a source. After the growth of nanowires, SiCl flow was terminated while O gas flow was introduced under vacuum. On the surface of nanowires was deposited Ge by the vapor from the Ge powder or oxidized into SiO by the O gas. The transition from deposition to oxidation occurred abruptly at 2 torr of O pressure without any intermediate region and enables selectively fabricated Ge/SiGe or SiO/SiGe coaxial heterostructure nanowires. The rate of deposition and oxidation was dominated by interfacial reaction and diffusion of oxygen through the oxide layer, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Silicon nanowires were grown on a stainless steel substrate using a vapor–liquid–solid mechanism in self-catalytic mode. The multi-component Fe–Cr–Ni–Mn–Si catalyst that was formed from the substrate leads the growth of single-crystal Si nanowires with lengths of several micrometers and diameters ranging from 100 to 150nm. A systematic investigation of the processing parameters revealed that the hydrogen flow rate is critical to the growth of the nanowires. At a high flow rate that exceeds 1000sccm, the substrate is embrittled by H2, and liquid droplets, which lead the growth of nanowires by the vapor–liquid–solid mechanism, are formed on the substrate. Electrical transport measurements indicated that the nanowires grown with the multi-component catalyst have electrical properties comparable to those grown by a single-component Ti catalyst. [Copyright &y& Elsevier]