Fabricating and aligning pi-conjugated polymer-functionalized DNA nanowires: atomic force microscopic and scanning near-field optical microscopic studies

We report a simple method to functionalize DNA with pi-conjugated polymer, forming highly aligned and integrated arrays of pi-conjugated polymer nanowires of a few nanometers diameter. pi-conjugated polymer, polyphenazasiline, having alkylammonium salts on the N atom (PPhenaz-TMA), synthesized in this study can be directly attached to DNA, which can be organized along stretched and aligned DNA molecules on surfaces as a template. Furthermore, PPhenaz-TMA/DNA nanowires were stretched and aligned on surfaces, even when PPhenaz-TMA/DNA complexes formed in solutions. The resulting PPhenaz-TMA/DNA nanowires could be easily converted to oxidized states or metallic nanowires by using adequate oxidant or metal salts. The direct visualization of PPhenaz-TMA/DNA nanowires and its structural changes have been studied by atomic force microscopy and scanning near-field optical microscopy.     

Ag核Au壳双金属复合纳米线的制备及其表面增强拉曼光谱研究

采用氧化铝模板结合交流电沉积技术制备纯银纳米线, 然后通过化学还原方法, 并控制加入的金盐的量, 在已制备好的银线表面包裹不同厚度的金壳层, 得到具有核壳结构的Ag_核Au_壳复合纳米线. 采用电子显微镜(SEM, TEM)和表面增强拉曼光谱对该复合结构纳米线进行相关表征, 纳米线的表面形貌与加入的金盐的量有关. 以苯硫酚(TP)和对巯基苯胺(PATP)为探针分子, 研究了此类复合纳米线的表面增强拉曼散射效应. 并以PATP在金银纳米线表面吸附的表面增强拉曼光谱的差别为探针, 表征了复合纳米线表面金的包裹程度, 结果表明一定厚度的包裹程度可制备无针孔效应的核壳结构金银复合纳米线.     

Flow‐Enabled Self‐Assembly of Large‐Scale Aligned Nanowires

One‐dimensional nanowires enable the realization of optical and electronic nanodevices that may find applications in energy conversion and storage systems. Herein, large‐scale aligned DNA nanowires were crafted by flow‐enabled self‐assembly (FESA). The highly oriented and continuous DNA nanowires were then capitalized on either as a template to form metallic nanowires by exposing DNA nanowires that had been preloaded with metal salts to an oxygen plasma or as a scaffold to direct the positioning and alignment of metal nanoparticles and nanorods. The FESA strategy is simple and easy to implement and thus a promising new method for the low‐cost synthesis of large‐scale one‐dimensional nanostructures for nanodevices.     

Metallization of dna on the surface

A method to develop DNA fibrils with a length more than a few tens of micrometers, oriented in one direction on the n- and p-type silicon surface is described. A new simple and effective technique is proposed to produce silver nanowires by electrochemical reduction of silver ions bound to DNA using the obtained fibrils as a template, as a result of which DNA molecules fixed on the surface of the n-type silicon single crystal are uniformly covered by silver clusters with a size of about 30 nm. The proposed metallization procedure of DNA on the n-type silicon surface has an advantage in comparison with a similar one for macromolecules fixed on freshly cleaved mica, glass surface, and p-type silicon. n-Type silicon is not only a substrate, but also a source of electrons for silver reduction. The absence of an additional chemical component (reducer) principally distinguishes the proposed method from the others currently known. Atomic force microscopic images of fixed DNA molecules and prepared nanowires are obtained.     

基于银增强金标记物的阳极溶出伏安免疫分析用于补体第三成分的测定

分子印迹是制备对特定分子具有专一性结合能力的聚合物的技术,所制备的聚合物被称为分子印迹聚合物（Molecularly imprinted polymers,MIPs）,此类聚合物在分离提纯、模拟酶和传感器等方面均显示出广阔的应用前景,迄今,小分子化合物的印迹技术已经十分成熟。     

Photoresponsive monolayers on water and solid surfaces

Organic photochromic units and molecules can be regarded as light-driven nano molecular machines. Once such molecules are aligned at a surface, the supramolecular organization provides an efficient macroscopic mechanical response in a collective way. Amphiphilic polymers having an azobenzene (Az) side chain are the favorable materials for observation of such effects since they show marked photomechanical response with essentially full reversibility. An in situ Brewster angle microscopic observation showed marked morphological and rheological photoinduced changes in the molecular films. Moreover, we have newly found that the identical photosensitive molecular film transferred on to a solid mica surface shows large morphological changes under highly humid conditions as proven by atomic force microscopy (AFM). It is supposed that the molecular film is driven in the same mechanism both on water and water-adsorbed mica surfaces. These microscopic observations provide new insights of the photomechanical response in photochromic monolayers.     

表面分子印迹聚合物纳米线用于蛋白质的特异性识别

手性配体交换色谱是拆分手性化合物,特别是氨基酸和羟基酸对映体的一种有效方法,通常以光活性氨基酸或其衍生物为手性选择子,可通过键合及涂渍制备手性固定相,也可作为流动相添加剂来实现手性配体交换色谱分离分析,配体交换键合固定相需要完成载体和手性选择子之间的偶联,键合量因受到载体和制备条件的影响而较难控制,且柱效较低。     

Circular Dichroism Study of the Mechanism of Formation of DNA Templated Nanowires

In order to control the fabrication method, the mechanism used in the formation of DNA templated nanowires is investigated through circular dichroism (CD) spectroscopy. Metallic (Au) and magnetic (Fe₂O₃ and CoFe₂O₄) nanoparticles (NP) are aligned along the DNA strand at various mass ratios. The DNA templated nanowires are compared to the structure of B‐form dsDNA through CD experiments. Absorbance and thermal melting tests are performed to verify the structural changes of DNA templated nanowires. Low concentrations of nanoparticles preserve the DNA B‐form through electrostatic interactions. Conversely, at higher concentrations of nanoparticles aligned along the DNA strand, the template is denatured. Information on the mode of nanoparticle binding and DNA helix alterations are explored for metallic and magnetic nanowires based upon the results.     

Aligned Pt-diamond core-shell nanowires for electrochemical catalysis

Heavily boron-doped diamond electrode has been applied as a robust substrate for Pt based catalyst. However, by simply applying a planar electrode the effective surface area of the catalyst is limited. In this article we for the first time prepared vertically aligned Pt-diamond core-shell nanowires electrode in a convenient and scalable method (up to 6-inch wafer size). The diamond nanowires are first fabricated with reactive ion etching with metal nanoparticles as etching masks. The following Pt deposition was achieved by DC sputtering. Different amounts of Pt were coated on to the nanowires and the morphology of the core-shell wires is characterized by SEM and TEM. The catalytic oxygen/hydrogen adsorption/desorption response are characterized by cyclic voltammetry. The results show that the active Pt surface area is 23 times higher than a planar Pt electrode, and 4.3 times higher than previously reported on Pt nanoparticles on diamond by electro-deposition. Moreover, this highly active surface is stable even after 1000 full surface oxidation and reduction cycles.     

Selective formation of a latticed nanostructure with the precise alignment of DNA-templated gold nanowires

A very efficient method is introduced to selectively align and uniformly separate λ-DNA molecules and thus DNA-templated gold nanowires (AuNW's) using a combination of molecular combing and surface-patterning techniques. By the method presented in this work, it is possible to obtain parallel and latticed nanostructures consisting of DNA molecules and thus DNA-templated AuNW's aligned at 400 nm intervals. DNA-templated AuNW's are uniformly formed with an average height of 2.5 nm. This method is expected to hold potential for the integration of nanosized building blocks applicable to nanodevice construction.     

DNA Assisted Assembly of Multisegmented Nanowires

This work demonstrates a highly specific and selective assembly of multisegmented nanowires on prepatterned gold electrodes using DNA hybridization. Multisegmented Au/Pd/Au nanowires were synthesized using template‐directed electrodeposition. Two complementary single‐stranded DNAs modified with thiol tags adsorb on gold electrodes and gold segments of nanowires, and enable the nanowires to assemble across electrodes. The assembled nanowires show ohmic contact with minimum contact resistance. Using these nanowires, the temperature dependent electrical resistance and the sensing performance toward hydrogen were investigated. The temperature coefficient of resistance of nanowires was lower than bulk polycrystalline counterpart, because of higher electron scattering at the surface and grain boundaries of nanowires. The nanowires were sensitive toward hydrogen gas at room temperature with a detection limit of 0.5%.     

Investigation of microstructures of ZnCo_2O_4 on bare Ni foam and Ni foam coated with graphene and their supercapacitors performance

The graphene coating was deposited on the surface of Ni foam using the chemical vapor deposition process. A large amount of flower-like ZnCo_2O_4 microspheres with short nanowires were formed on bare Ni foam by hydrothermal method, while large-scale ZnCo_2O_4 nanowires arrays homogeneously aligned and separated adequately on Ni foam coated with graphene. This ZnCo_2O_4 nanowire structure exhibited superior supercapacitors properties. The excellent supercapacitors were mainly attributed to the large specific surface and the porosity on the nanowires which promoted the electrons and ions transportation. In addition, graphene improved conductivity of substrate for current collecting.     

Microwave synthesis of electrically conductive gold nanowires on DNA scaffolds

Biological molecules, in particular DNA, have shown great potential to be used as interconnects of nanodevices and computational elements. In this research, we synthesized electrically conductive gold nanowires for the first time exploiting an electroless and microwave heating method for 120-180 s. Our results indicate that DNA serves as a reducing and nonspecific capping agent for the growth of nanowires. The current voltage ( I- V) characteristics of the Au nanowires are continuous, exhibiting Ohmic behavior having low contact resistance with the gold electrodes. The nanowires have a diameter of 10-15 nm in solution and of 20-30 nm in immobilized DNA with resistivity comparable to pure metals. The method is highly selective with deposition confined to the DNA itself. The nanowires we fabricated can be used as building blocks for functional nanodevices, sensors, and optoelectronics.     

Molten gallium as a catalyst for the large-scale growth of highly aligned silica nanowires

The vapor-liquid-solid (VLS) process is a fundamental mechanism for the growth of nanowires, in which a small size (5-100 nm in diameter), high melting point metal (such as gold and iron) catalyst particle directs the nanowire's growth direction and defines the diameter of the crystalline nanowire. In this article, we show that the large size (5-50 microm in diameter), low melting point gallium droplets can be used as an effective catalyst for the large-scale growth of highly aligned, closely packed silica nanowire bunches. Unlike any previously observed results using gold or iron as catalyst, the gallium-catalyzed VLS growth exhibits many amazing growth phenomena. The silica nanowires tend to grow batch by batch. For each batch, numerous nanowires simultaneously nucleate, grow at nearly the same rate and direction, and simultaneously stop growing. The force between the batches periodically lifts the gallium catalyst upward, forming two different kinds of products on a silicon wafer and alumina substrate. On the silicon wafer, carrot-shaped tubes whose walls are composed of highly aligned silica nanowires with diameters of 15-30 nm and length of 10-40 microm were obtained. On the alumina substrate, cometlike structures composed of highly oriented silica nanowires with diameters of 50-100 nm and length of 10-50 microm were formed. A growth model was proposed. The experimental results expand the VLS mechanism to a broader range.     

Highly efficient dye-sensitized solar cells with a titania thin-film electrode composed of a network structure of single-crystal-like TiO2 nanowires made by the "oriented attachment" mechanism

In this study, single-crystal-like anatase TiO(2) nanowires were formed in a network structure by surfactant-assisted self-assembling processes at low temperature. The crystal lattice planes of the nanowires and networks of such wires composed of many nanoparticles were almost perfectly aligned with each other due to the "oriented attachment" mechanism, resulting in the high rate of electron transfer through the TiO(2) nanonetwork with single-crystal-like anatase nanowires. The direction of crystal growth of oriented attachment was controlled by changing the mole ratio of acetylacetone to Ti, that is, regulating both the adsorption of surfactant molecules via control of the reaction rate and the surface energy. A single-crystalline anatase exposing mainly the [101] plane has been prepared, which adsorbed ruthenium dye over 4 times higher as compared to P-25. A high light-to-electricity conversion yield of 9.3% was achieved by applying the titania nanomaterials with network structure as the titania thin film of dye-sensitized solar cells.     

模板法合成金银核壳纳米线及电化学表征

采用氧化铝模板由交流电沉积制备纯银纳米线.然后借助化学还原法,在已制备好的银线表面包裹不同厚度的金壳层,得到具有核壳结构的AgcoreAushell复合纳米线.电子显微镜(SEM,TEM)显示该复合结构纳米线表面形貌与加入的金盐量有关,而且包裹层较薄的复合纳米线表面存在大量的孔洞.循环伏安测试表明,具有孔洞效应的复合纳米线经多次循环扫描后即可过渡到无孔洞效应的表面.以对巯基苯胺(PATP)作为探针分子的表面增强拉曼光谱,可用于表征纳米材料的表面结构.     

Growth of large-area aligned molybdenum nanowires by high temperature chemical vapor deposition: synthesis, growth mechanism, and device application

Large-area aligned Mo nanowires have been grown on stainless steel substrates by high-temperature chemical vapor deposition with the use of Mo metal. The detailed physical and chemical growth processes regarding the formation of the nanowires have been investigated using mass spectroscopy, thermogravimetry, and differential scanning calorimetry analysis, as well as structure analysis by electron microscopy. In reference to Gibbs energy calculation, our study reveals that the growth relies on the decomposition of MoO2 vapors through condensation of its vapor at high substrate temperatures. The aligned growth is a result of competing growth with the nanowires normal to the substrate surface reaching the final growth front. The field emission measurement and the vacuum luminescent tube study show that the Mo nanowires have potential application as electron emitters.     

Template-free preparation of bunches of aligned boehmite nanowires

A simple method based on a hydrothermal process using alkali salts as mineralizers is proposed for the synthesis of aligned bunches of boehmite (gamma-AlOOH) nanowires without a template's assistance. Most bunches of aligned boehmite nanowires are constructed by two separated shorter bundles with widths of 700 to approximately 800 nm and lengths of about 1 microm. XRD patterns, FTIR spectra, and SEM and TEM images were used to characterize the products. The specific surface area and pore-size distribution of the obtained product as determined by gas-sorption measurements show that the boehmite bundles possess a high BET surface area and porosity properties. The importance of adding Na2B4O7 salts for the formation of bundle morphologies has been discussed.     

Synthesis, manipulation and conductivity of supramolecular polymer nanowires

The synthesis of supramolecular conducting nanowires can be achieved by using DNA and pyrrole. Oxidation of pyrrole in DNA-containing solutions yields a material that contains both the cationic polypyrrole (PPy) and the anionic DNA polymers. Intimate interaction of the two polymer chains in the self-assembled nanowires is indicated by FTIR spectroscopy. AFM imaging shows individual nanowires to be continuous, approximately 5 nm high and conformationally flexible. This feature allows them to be aligned by molecular combing in a similar manner to bare DNA and provides a convenient method for fabricating a simple electrical device by stretching DNA/PPy strands across an electrode gap. Current-voltage measurements confirm that the nanowires are conducting, with values typical for a polypyrrole-based material. In contrast to polymerisation of pyrrole on a DNA template in bulk solution, attempts to form similar wires by polymerisation at surface-immobilised DNA do not give a continuous coverage; instead, a beads-on-a-string appearance is observed suggesting that immobilisation inhibits the assembly process.     

DNA-templated assembly and electropolymerization of aniline on gold surface

Biomolecule template gives new opportunities for the fabrication of novel materials with special features. Here we report a route to the formation of DNA–polyaniline (PAn) complex, using immobilized DNA as a template. A gold electrode was first modified with monolayer of 2-aminoethanethiol by self-assembly. Thereafter, by simply immersing the gold electrode into DNA solution, DNA molecules can be attached onto the gold surface, followed by the DNA-templated assembly and electropolymerization of protonated aniline. The electrostatic interactions between DNA and aniline can keep the aniline monomers aligning along the DNA strands. Investigations by surface plasmon resonance (SPR), electrochemistry and reflection–absorption UV/Vis–Near IR spectroscopy substantially convince that PAn can be electrochemically grown around DNA template on gold surface. This work may be provides fundamental aspects for building PAn nanowires with DNA as template on solid surface if DNA molecules can be individually separated and stretched.