Flexible Gold Nanocone Array Surfaces as a Tool for Regulating Neuronal Behavior

Accelerated neurite outgrowth of rat cortical neurons on a flexible and inexpensive substrate functionalized with gold nanocone arrays is reported. The gold nanocone arrays are fabricated on Teflon films by a bottom‐up approach based on colloidal lithography followed by deposition of a thin gold layer. The geometry of nanocone arrays including height and pitch is controlled by the overall etching time and template polystyrene beads size. Fluorescence microscopy studies reveal high viability and significant morphological changes of the neurons on the structured surfaces. The elongation degree of neurite is maximized on the nanocone arrays created with 1 µm polystyrene beads by a factor of two with respect to the control. Furthermore, the interface between the neurons and the nanocones is investigated by scanning electron microscopy and focused ion beam cross‐sectioning. The detailed observation of the neuron/nanocone interfaces reveals the morphological similarity between the nanocone tips and the neuronal processes, the existence of interspace at the interface between the cell body and the nanocones, and neurite bridging among the neighboring structures, which may induce the acceleration of neurite outgrowth. The flexible gold nanocone arrays can be a good supporting substrate of neuron culture with noble electrical and optical properties.     

Interfacing Inorganic Nanowire Arrays and Living Cells for Cellular Function Analysis

Inorganic nanowires are among the most attractive functional materials, which have emerged in the past two decades. They have demonstrated applications in information technology and energy conversion, but their utility in biological or biomedical research remains relatively under‐explored. Although nanowire‐based sensors have been frequently reported for biomolecular detection, interfacing nanowire arrays and living mammalian cells for the direct analysis of cellular functions is a very recent endeavor. Cell‐penetrating nanowires enabled effective delivery of biomolecules, electrical and optical stimulation and recording of intracellular signals over a long period of time. Non‐penetrating, high‐density nanowire arrays display rich interactions between the nanostructured substrate and the micro/nanoscale features of cell surfaces. Such interactions enable efficient capture of rare cells including circulating tumor cells and trafficking leukocytes from complex biospecimens. It also serves as a platform for probing cell traction force and neuronal guidance. The most recent advances in the field that exploits nanowire arrays (both penetrating and non‐penetrating) to perform rapid analysis of cellular functions potentially for disease diagnosis and monitoring are reviewed.     

Synthesis of PbTe nanowire arrays using lithographically patterned nanowire electrodeposition

We describe the preparation by electrodeposition of arrays of lead telluride (PbTe) nanowires using the lithographically patterned nanowire electrodeposition (LPNE) method. PbTe nanowires had a rectangular cross-section with adjustable width and height ranging between 60-400 nm (w) and 20-100 nm (h). The characterization of these nanowire arrays using X-ray diffraction, transmission electron microscopy and electron diffraction, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy (XPS) is reported. PbTe nanowires were electrodeposited using a cyclic electrodeposition-stripping technique that produced polycrystalline, stoichiometric, face-centered cubic PbTe with a mean grain diameter of 10-20 nm. These nanowires were more than 1 mm in length and two additional processing steps permitted their suspension across 25 microm air gaps microfabricated on these surfaces. The LPNE synthesis of lithographically patterned PbTe nanowires was carried out in unfiltered laboratory air. Nanowires with lengths of 70-100 microm showed an electrical resistivity comparable to bulk PbTe. XPS reveals that exposure of PbTe nanowires to air causes the formation on the nanowire surface of approximately one monolayer of a mixed lead oxide and tellurium oxide within a few minutes.     

反应源温度对ZnO纳米线阵列定向性及发光性能的影响

以Au薄膜为催化剂、ZnO与碳混合粉末为反应源,采用碳热还原法在单晶Si衬底上制备了ZnO纳米线阵列.通过扫描电子显微镜( SEM)、X射线衍射仪(XRD)、荧光分光光度计对样品的表征,研究了反应源温度对ZnO纳米线阵列的定向性和光致发光性能的影响.样品在源温度920℃条件下沿(002)方向择优生长,定向性最好,温度过低不利于ZnO纳米线阵列密集生长,而温度过高导致Zn原子二次蒸发,因而也不利于纳米线阵列的定向和择优生长;样品在源温度880℃有最强的近紫外带边发射,表明温度过高和过低都不利于ZnO晶体结构的优化;由于ZnO纳米线在缺氧氛围下生长,氧空位是缺陷存在的主要形式,因此所有样品都有较强的绿光发射.温度升高导致纳米线生长速度提高而增加了氧空位缺陷数量,从而使样品绿峰强度增强并在源温度920℃时达最大值,但温度的进一步升高可导致ZnO纳米线表面Zn元素的蒸发而降低氧空位缺陷的数量,从而抑制绿峰强度.     

Synthesis of dense, single-crystalline CrO2 nanowire arrays using AAO template-assisted chemical vapor deposition

High-density, vertically aligned CrO(2) nanowire arrays were obtained via atmospheric-pressure CVD assisted by AAO templates. The CrO(2) nanowire arrays show remarkably enhanced coercivity compared with CrO(2) films or bulk. It was found that the length of the nanowires is greatly influenced by the pore diameter of the AAO template used. The growth mechanism and the pore size dependence of the CrO(2) nanowire arrays are discussed. The present method provides a useful approach for the synthesis of CrO(2) nanowire arrays. Such highly ordered nanowire arrays within an AAO template may have important applications in ultrahigh-density perpendicular magnetic recording devices and the mass production of spintronic nanodevices.     

Patterning to enhance activity of cultured neuronal networks

Embryonic rat hippocampal neurons were cultured in order to gain insights into how small networks of neurons interact. The principal observations are the electrical activities recorded with the electrode arrays, primarily action potentials both spontaneous and evoked. Several lithographic techniques were developed for controlling with micrometer precision the patterns of surface molecules in order to control neuronal attachment and growth. Cytophilic polylysine against protein repellent and hence cytophobic polyethylene glycol were used. By combining the cellular lithography with the microelectrode arrays it was possible to guide neurons preferentially to electrodes and to begin to investigate the question as to whether the geometric pattern of a neuronal network influences the patterns of its neuroelectric activity. It is clear that the techniques are adequate to ensure contact of neurons to electrodes but not to ensure the recording of signals, even when neurons lie directly on top of electrodes. The maturation of neuroelectric activity depends on the growth of glia within the culture, such that spontaneous activity appears to become robust when the number of glia is roughly the same as the number of neurons.     

Disposable biosensor based on Au nanoparticles-modified CdS nanorod arrays for detection cytochrome c

A novel disposable biosensor is developed based on gold nanoparticles modified CdS nanorod arrays. The ordered CdS nanorod arrays firstly have been synthesized by a simple hydrothermal method. Then, the CdS nanorod arrays are modified by gold nanoparticles, which are directly fabricated into an electrode for detection of cytochrome c (Cyc) in solution without any pretreatment. The modified CdS nanorod arrays biosensor with the immense surface area and high electrical conductivity shows a good sensitivity and linear range. This method may be used to construct other electrochemical biosensors using aligned nanorod/nanowire films.     

High-performance transparent conducting oxide nanowires

We report the growth and characterization of single-crystalline Sn-doped In2O3 (ITO) and Mo-doped In2O3 (IMO) nanowires. Epitaxial growth of vertically aligned ITO nanowire arrays was achieved on ITO/yttria-stabilized zirconia (YSZ) substrates. Optical transmittance and electrical transport measurements show that these nanowires are high-performance transparent metallic conductors with transmittance of approximately 85% in the visible range, resistivities as low as 6.29 x 10(-5) Omega x cm and failure-current densities as high as 3.1 x 10(7) A/cm2. Such nanowires will be suitable in a wide range of applications including organic light-emitting devices, solar cells, and field emitters. In addition, we demonstrate the growth of branched nanowire structures in which semiconducting In2O3 nanowire arrays with variable densities were grown epitaxially on metallic ITO nanowire backbones.     

Multiwalled carbon-nanotube-functionalized microelectrode arrays fabricated by microcontact printing: platform for studying chemical and electrical neuronal signaling

A facile method is proposed for the deposition of multiwalled carbon nanotube (MWCNT) layers onto microelectrode arrays by means of a microcontact printing technique, leading to the fabrication of MEAs characterized by well defined electrical and morphological properties. Using polydimethyl siloxane stamps, produced from different mold designs, a flexibility of printing is achieved that provides access to microscale, nanostructured electrodes. The thickness of MWCNT layers can be exactly predetermined by evaluating the concentration of the MWCNT solution employed in the process. The electrode morphology is further characterized using laser scanning and scanning electron microscopy. Next, by means of impedance spectroscopy analysis, the MWCNT-electrode contact resistance and MWCNT film resistance is measured, while electrochemical impedance spectroscopy is used to estimate the obtained electrode-electrolyte interface. Structural and electrochemical properties make these electrodes suitable for electrical stimulation and recording of neurons and electrochemical detection of dopamine. MWCNT-functionalized electrodes show the ability to detect micromolar amounts of dopamine with a sensitivity of 19 nA μm(-1) . In combination with their biosensing properties, preliminary electrophysiological measurements show that MWCNT microelectrodes have recording properties superior to those of commercial TiN microelectrodes when detecting neuronal electrical activity under long-term cell-culture conditions. MWCNT-functionalized microelectrode arrays fabricated by microcontact printing represent a versatile and multipurpose platform for cell-culture monitoring.     

高压PLD法生长p型钠掺杂氧化锌纳米线阵列

采用高压脉冲激光沉积法(HP-PLD)研究了压强、金催化层厚度对钠掺杂氧化锌纳米线(ZnO:Na)生长的影响, 并制备了ZnO:Al薄膜/ZnO:Na纳米线阵列同质pn结器件。实验发现, 当金膜厚度为4.2 nm, 生长压强为3.33×10⁴ Pa, 生长温度为875℃时, 可在单晶Si衬底上生长c轴取向性良好的ZnO纳米线阵列。X射线衍射和X射线光电子能谱综合分析证实了Na元素成功掺入ZnO纳米线晶格中。在低温(15 K)光致发光谱中, 观测到了一系列由Na掺杂ZnO产生引起的受主光谱指纹特征, 如中性受主束缚激子峰(3.356 eV, A0X)、导带电子到受主峰(3.312 eV, (e, A0))和施主受主对发光峰(3.233 eV, DAP)等。通过在ZnO:Al薄膜上生长ZnO:Na纳米线阵列形成同质结, 测得I-V曲线具有明显的整流特性, 证实了ZnO:Na纳米线具有良好的p型导电性能。     

Structure, photoluminescence and wettability properties of well arrayed ZnO nanowires grown by hydrothermal method

Well aligned ZnO nanowire arrays with high crystal quality were grown on Si substrates at a low temperature (50 degrees C) by hydrothermal method using a pre-formed ZnO seed layer. ZnO seeds were prepared via radio-frequency magnetron sputtering onto Si substrates. The morphologies of the ZnO nanowire arrays were shown by field emission scanning electron microscopy. X-ray diffraction spectra showed that the full width at the half maximum of the (0002) peak of the nanowire arrays without any heat treatment was only 0.07 degrees, indicating very high crystal quality. Furthermore, the room-temperature photoluminescence spectra of the ZnO nanowire arrays exhibited excellent UV emission. The special micro/nano surface structure of the ZnO nanowire arrays can enhance the dewettability for surfaces modified via low surface energy materials such as long chain fluorinated organic compounds. The surface of the ZnO nanowire arrays is also found to be superhydrophobic with a contact angle of 165 degrees +/- 1 degrees, while the sliding angle is 3 degrees.     

Vertical nanowire electrode arrays as a scalable platform for intracellular interfacing to neuronal circuits

Deciphering the neuronal code--the rules by which neuronal circuits store and process information--is a major scientific challenge. Currently, these efforts are impeded by a lack of experimental tools that are sensitive enough to quantify the strength of individual synaptic connections and also scalable enough to simultaneously measure and control a large number of mammalian neurons with single-cell resolution. Here, we report a scalable intracellular electrode platform based on vertical nanowires that allows parallel electrical interfacing to multiple mammalian neurons. Specifically, we show that our vertical nanowire electrode arrays can intracellularly record and stimulate neuronal activity in dissociated cultures of rat cortical neurons and can also be used to map multiple individual synaptic connections. The scalability of this platform, combined with its compatibility with silicon nanofabrication techniques, provides a clear path towards simultaneous, high-fidelity interfacing with hundreds of individual neurons.     

Metal Oxide Nanostructures from Simple Metal-oxygen Reaction in Air

Metal oxide nanostructures （CuO, Co3O4, ZnO and α-Fe2O3） have been successfully fabricated by a simple and efficient method： heating the appropriate metals in air at low temperatures ranging from 200 to 400℃. The chemical composition, morphology and crystallinity of the nanostructures have been characterized by micro-Raman spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Two mechanisms： vapor-solid and surface diffusion play dominant roles in the growth of metal oxide nanostructures starting with low melting point metals （Zn and Cu） and high melting point metals （Fe and Co）, respectively. With sharp ends and large aspect ratio, the metal oxide nanostructures exhibit impressive field-induced electron emission properties, indicating their potentials as future electron source and displays. The water wettability and anti-wettability properties of iron oxide nanoflakes were also discussed in this work.     

Manipulation of Crawling Growth for the Formation of Sub-millimeter Long ZnO Nanowalls

Vapor-phase growth of ZnO nanowires based on gold catalyst is usually accompanied with lateral crawling growth on the substrate surface. We present results from our systematic experiments where the growth temperature and catalyst size are controlled. The data corroborate that it is possible to obtain clean vertical nanowire arrays while avoiding the crawling growth. 0% the other hand, crawling growth can be manipulated to obtain root-interconnected nanowire arrays, which could be useful for certain applications. Our results also imply that the previously suggested growth mechanism for the wire-on-wall hybridstructure might be incorrect. Finally, we show the formation of sub-millimeter long, straight ZnO nanowalls by combining a gold-catalyzed epitaxial growth of vertical nanowires and their mergence due to a confined crawling growth. These unconventional nanostructures might have unique electric or optical transport properties.     

Neurite outgrowth on microstructured surfaces functionalized by a neural adhesion protein

Designed networks of neurons are potentially very useful to investigate neural activities. Using photolithography microgrooves suited in size for single neurons have been produced on glass chips. Two conducting gold lanes ending in each microgroove allow extracelluar stimulation of the neurons and recording of their activity. A cell adhesive surface was created by functionalization of glass with the adhesion peptide RGDC. In addition, in order to optimize the contact of the neuronal cell membrane to the electrode surface axonin-1, a specific neural adhesion protein was used. A recombinant form of axonin-1 was produced and immobilized in a correct orientation on protected gold surfaces through a C-terminal cysteine residue. Neurite outgrowth of neurons cultured on chips derivatized with RGDC or axonin-1 were compared. The developed materials and methods represent a first step towards establishing designed functionalized glass surfaces for neurophysiological investigations.     

The catalyst-free synthesis of large-area tungsten oxide nanowire arrays on ITO substrate and field emission properties

Tungsten oxide nanowire arrays have been grown on indium tin oxide coated glass substrate using tungsten trioxide powders as source by thermal evaporation approach without any catalysts. When the O₂/Ar flow rate ratio was 1/100, large-scale, high-density and uniformly distributed tungsten oxide nanowire arrays were obtained. The morphology and structure properties of the tungsten oxide nanowires were characterized by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The influences of the oxygen concentration on the growth, density, shape and structure of the nanowires were investigated. The possible growth mechanism which governs the various types of nanowire arrays as the O₂/Ar flow rate ratios changed is also discussed. Field emission properties of tungsten oxide nanowire arrays were studied at a poor vacuum condition. The remarkable performance reveals that the tungsten oxide nanowire arrays can be served as a good candidate for commercial application as electron emitters.     

Growth of TiO2 nanowire bundle arrays and their application in dye-sensitized solar cells

Highly oriented single-crystalline TiO₂ nanowire bundle arrays on transparent conductive fluorine-doped tin oxide substrates are prepared by hydrothermal method using the precursors of titanium butoxide, deionized water and hydrochloric acid. The structure and morphology characteristics of all the samples have been analyzed by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. Results show that the diameter, length, and density of the nanowire bundle arrays can be varied by changing the growth parameters, such as growth time, initial reactant concentration and acidity. The enhanced (002) peak in XRD patterns indicate that the nanowire is well crystallized and grow perpendicular to the substrate. The high resolution transmission electron microscope images and selected-area electron diffraction patterns confirm that there are approximately 10–30 nanowires in each bundle. The nanowire is single crystalline. Dye-sensitized solar cells assembled from oriented TiO₂ nanowire bundle arrays as the photoanode are studied. The light-to-electricity conversion efficiency is about 2.17 %.     

Influence of nanowire density on the shape and optical properties of ternary InGaAs nanowires

We have synthesized ternary InGaAs nanowires on (111)B GaAs surfaces by metal-organic chemical vapor deposition. Au colloidal nanoparticles were employed to catalyze nanowire growth. We observed the strong influence of nanowire density on nanowire height, tapering, and base shape specific to the nanowires with high In composition. This dependency was attributed to the large difference of diffusion length on (111)B surfaces between In and Ga reaction species, with In being the more mobile species. Energy dispersive X-ray spectroscopy analysis together with high-resolution electron microscopy study of individual InGaAs nanowires shows large In/Ga compositional variation along the nanowire supporting the present diffusion model. Photoluminescence spectra exhibit a red shift with decreasing nanowire density due to the higher degree of In incorporation in more sparsely distributed InGaAs nanowires.     

Bi-based Nanowire and Nanojunction Arrays： Fabrication and Physical Properties

This article reviews the recent developments in the fabrication and properties of one-dimensional （1D） Bi-based nanostructures, including Bi, Sb, BixSb1-x and Bi2Te3 nanowire arrays, and Bi-Bi and Bi-Sb nanojunction arrays. In this article, we present an efiective method to fabricate Bi nanowire arrays with difierent diameters in anodic alumina membrane （AAM） with a single pore size by the pulsed electrodeposition. The fabrication of the high-filling and ordered Bi1-xSbx and Bi2Te3 single crystalline nanowire arrays, the Bi nanowire metalsemiconductor homojunction and Bi-Sb nanowire metal-semiconductor heterojunction arrays by the pulsed electrodeposition are reported. The factors controlling the composition, diameter, growth rate and orientation of the nanowires are analyzed, and the growth mechanism of the nanowire and nanojunction arrays are discussed together with the study of the electrical and thermal properties of Bi-based nanowires and nanojunctions.Finally, this review is concluded with some perspectives on the research directions and focuses in the Bi-based nanomaterials fields.     

Real time atomic force microscopy imaging during nanogap formation by electromigration

We present real time atomic force microscopy imaging during nanogap fabrication by feedback controlled electromigration of a gold nanowire. The correlated measurements of electrical resistance and atomic force microscopy reveal that the major structural changes appear at the early stage of the process. Moreover, despite important morphological changes, the resistance of the nanowire shows a weak increase of just a few ohms. The detailed analysis of the atomic force microscopy images clearly shows that the electromigration process is strongly influenced by the initial microstructure of the nanowire.