Water-soluble organo-silica hybrid nanowires

There has been growing interest in the past decade in one-dimensional (1D) nanostructures, such as nanowires, nanotubes or nanorods, owing to their size-dependent optical and electronic properties and their potential application as building blocks, interconnects and functional components for assembling nanodevices. Significant progress has been made; however, the strict control of the distinctive geometry at extremely small size for 1D structures remains a great challenge in this field. The anisotropic nature of cylindrical polymer brushes has been applied to template 1D nanostructured materials, such as metal, semiconductor or magnetic nanowires. Here, by constructing the cylindrical polymer brushes themselves with a precursor-containing monomer, we successfully synthesized hybrid nanowires with a silsesquioxane core and a shell made up from oligo(ethylene glycol) methacrylate units, which are soluble in water and many organic solvents. The length and diameter of these rigid wires are tunable by the degrees of polymerization of both the backbone and the side chain. They show lyotropic liquid-crystalline behaviour and can be pyrolysed to silica nanowires. This approach provides a route to the controlled fabrication of inorganic or hybrid silica nanostructures by living polymerization techniques.     

DNA-directed synthesis of zinc oxide nanowires on carbon nanotube tips

This paper describes a class of three component hybrid nanowires templated by DNA directed self-assembly. Through the modification of carbon nanotube (CNT) termini with synthetic DNA oligonucleotides, gold nanoparticles are delivered, via DNA hybridization, to CNT tips that then serve as growth sites for zinc oxide (ZnO) nanowires. The structures we have generated using DNA templating represent an advance toward building higher order sequenced one dimensional nanostructures with rational control.     

Bimetallic Nanostructures as Active Raman Markers: Gold‐Nanoparticle Assembly on 1D and 2D Silver Nanostructure Surfaces

It is demonstrated that bimetallic silver–gold anisotropic nanostructures can be easily assembled from various nanoparticle building blocks with well‐defined geometries by means of electrostatic interactions. One‐dimensional (1D) silver nanowires, two‐dimensional (2D) silver nanoplates, and spherical gold nanoparticles are used as representative building blocks for bottom‐up assembly. The gold nanoparticles are electrostatically bound onto the 1D silver nanowires and the 2D silver nanoplates to give bimetallic nanostructures. The unique feature of the resulting nanostructures is the particle‐to‐particle interaction that subjects absorbed analytes to an enhanced electromagnetic field with strong polarization dependence. The Raman activity of the bimetallic nanostructures is compared with that of the individual nanoparticle blocks by using rhodamine 6G solution as the model analyte. The Raman intensity of the best‐performing silver–gold nanostructure is comparable with the dense array of silver nanowires and silver nanoplates that were prepared by means of the Langmuir–Blodgett technique. An optimized design of a single‐nanostructure substrate for surface‐enhanced Raman spectroscopy (SERS), based on a wet‐assembly technique proposed here, can serve as a compact and low‐cost alternative to fabricated nanoparticle arrays.     

A Nonconventional Approach to Patterned Nanoarrays of DNA Strands for Template‐Assisted Assembly of Polyfluorene Nanowires

DNA molecules have been widely recognized as promising building blocks for constructing functional nanostructures with two main features, that is, self‐assembly and rich chemical functionality. The intrinsic feature size of DNA makes it attractive for creating versatile nanostructures. Moreover, the ease of access to tune the surface of DNA by chemical functionalization offers numerous opportunities for many applications. Herein, a simple yet robust strategy is developed to yield the self‐assembly of DNA by exploiting controlled evaporative assembly of DNA solution in a unique confined geometry. Intriguingly, depending on the concentration of DNA solution, highly aligned nanostructured fibrillar‐like arrays and well‐positioned concentric ring‐like superstructures composed of DNAs are formed. Subsequently, the ring‐like negatively charged DNA superstructures are employed as template to produce conductive organic nanowires on a silicon substrate by complexing with a positively charged conjugated polyelectrolyte poly[9,9‐bis(6′‐N,N,N‐trimethylammoniumhexyl)fluorene dibromide] (PF2) through the strong electrostatic interaction. Finally, a monolithic integration of aligned arrays of DNA‐templated PF2 nanowires to yield two DNA/PF2‐based devices is demonstrated. It is envisioned that this strategy can be readily extended to pattern other biomolecules and may render a broad range of potential applications from the nucleotide sequence and hybridization as recognition events to transducing elements in chemical sensors.     

Nano-architectures by covalent assembly of molecular building blocks

The construction of electronic devices from single molecular building blocks, which possess certain functions such as switching or rectifying and are connected by atomic-scale wires on a supporting surface, is an essential goal of molecular electronics. A key challenge is the controlled assembly of molecules into desired architectures by strong, that is, covalent, intermolecular connections, enabling efficient electron transport between the molecules and providing high stability. However, no molecular networks on surfaces 'locked' by covalent interactions have been reported so far. Here, we show that such covalently bound molecular nanostructures can be formed on a gold surface upon thermal activation of porphyrin building blocks and their subsequent chemical reaction at predefined connection points. We demonstrate that the topology of these nanostructures can be precisely engineered by controlling the chemical structure of the building blocks. Our results represent a versatile route for future bottom-up construction of sophisticated electronic circuits and devices, based on individual functionalized molecules.     

Electrical nanowelding and bottom-up nano-construction together using nanoscale solder

A new bottom-up nanowelding technique enabling the welding of complex 3D nanoarchitectures assembled from individual building blocks using nanovolumes of metal solder is reported in this work. The building blocks of gold nanowires, (Co72Pt28/Pt)n multilayer nanowires, and nanosolder Sn99Au1 alloy nanowires were successfully fabricated by a template technique. Individual metallic nanowires dispersed on Si/SiO2(100 nm) wafers were manipulated and assembled together. Conductive nanostructures were then welded together by the new electrical nanowelding technique using nanovolumes of similar or dissimilar nanosolder. At the weld sites, nanoscale volumes of a chosen metal are deposited using nanosolder of a sacrificial nanowire, which ensures that the nanoobjects to be bonded retain their structural integrity. The whole nanowelding process is clean, controllable and reliable, and ensures both mechanically strong and electrically conductive contacts. The quality check of nanoweld achieve a resistance as low as 20 omega by using Sn99Au1 alloy solder. This technique should provide a promising way to conquer the challenge of the integration obstacle for bottom-up nanotechnology.     

Synthesis of Metal/Bimetal Nanowires and Their Applications as Flexible Transparent Electrodes

As a potential alternative to indium oxide (ITO), metal nanowire transparent conductive electrodes (TCEs) have attracted more and more attention. Here, a facile method that can be applied to the synthesis of a variety of metal/bimetallic nanowires has been proposed. Metal/bimetallic nanowires synthesized through this method show high aspect ratios and great dispersibility, which makes them ideal building blocks for transparent electrodes. The synthesis mechanism is discussed in‐depth to give a theoretical basis of morphology control of metal nanostructures in organic synthesizing systems. TCEs with high flexibility, excellent optical–electrical performance as well as outstanding anti‐thermal and anti‐moisture stability are constructed. To the best of our knowledge, this is the first work on synthesizing multiple metal/bimetallic nanowires through one method.     

Unconventional gallium oxide nanowires

Zigzag and helical beta-Ga(2)O(3) one-dimensional nanostructures were produced by thermal evaporation of gallium oxide in the presence of gallium nitride. High-resolution TEM analysis indicates that each individual zigzag nanostructure has a periodic arrangement of three distinct blocks: two structurally perfect blocks mirrored with respect to each other on the (002) plane, and one stacking-fault-rich block sandwiched between them. In a zigzag nanostructure, the growth orientation of a beta-Ga(2)O(3) crystal changes alternately in three blocks. The zigzag nanostructure as a whole has the [001] axial direction. In addition to zigzag nanostructures, single-crystalline helical nanowires were also obtained.     

Synthesis and Stretching of Rolling Circle Amplification Products in a Flow‐Through System

Enzymatic isothermal rolling circle amplification (RCA) produces long concatemeric single‐stranded DNA (ssDNA) molecules if a small circular ssDNA molecule is applied as the template. A method is presented here in which the RCA reaction is carried out in a flow‐through system, starting from isolated surface‐tethered DNA primers. This approach combines gentle fluidic handling of the single‐stranded RCA products, such as staining or stretching via a receding meniscus, with the option of simultaneous (fluorescence) microscopic observation. It is shown that the stretched and surface‐attached RCA products are accessible for hybridization of complementary oligonucleotides, which demonstrates their addressability by complementary base pairing. The long RCA products should be well suited to bridge the gap between biomolecular nanoscale building‐blocks and structures at the micro‐ and macroscale, especially at the single‐molecule level presented here.     

Circular Dichroism Studies on Plasmonic Nanostructures

In recent years, optical chirality of plasmonic nanostructures has aroused great interest because of innovative fundamental understanding as well as promising potential applications in optics, catalysis and sensing. Herein, state‐of‐the‐art studies on circular dichroism (CD) characteristics of plasmonic nanostructures are summarized. The hybrid of achiral plasmonic nanoparticles (NPs) and chiral molecules is explored to generate a new CD response at the plasmon resonance as well as the enhanced CD intensity of chiral molecules in the UV region, owing to the Coulomb static and dynamic dipole interactions between plasmonic NPs and chiral molecules. As for chiral assembly of plasmonic NPs, plasmon–plasmon interactions between the building blocks are found to induce generation of intense CD response at the plasmon resonance. Three‐dimensional periodical arrangement of plasmonic NPs into macroscale chiral metamaterials is further introduced from the perspective of negative refraction and photonic bandgap. A strong CD signal is also discerned in achiral planar plasmonic nanostructures under illumination of circular polarized plane wave at oblique incidence or input vortex beam at normal incidence. Finally perspectives, especially on future investigation of time‐resolved CD responses, are presented.     

生物分子模板法制备低维金属纳米材料研究进展（Ⅱ）

本文概述了蛋白质、DNA等生物分子模板表面化学沉积制备低维金属纳米材料的最新研究进展。蛋白质可自组装形成不同层次的纳米结构,而DNA分子可自组装形成纳米线和网状结构。这些不同的纳米结构可作为模板,化学沉积,制备金属纳米管、纳米线等一维或二维纳米材料。金属纳米管和纳米线具有导电、导热、磁性和具有特殊的量子效应,在电磁活性复合材料,可控缓释系统、纳米器件和纳米电路等领域有重要的应用前景。     

Self-assembly of luminescent twisted fibers based on achiral quinacridone derivatives

It is a great challenge to spontaneously assemble achiral molecules into twisted nanostructures in the absence of chiral substances. Here we show that two achiral centrosymmetric quinacridone (QA) derivatives, N,N′-di(n-hexyl)-1, 3, 8, 10-tetramethylquinacridone (C6TMQA) and N,N′-di(n-decyl)-1, 3, 8, 10-tetramethylquinac ridone (C10TMQA), can be employed as building blocks to fabricate well-defined twisted nanostructures by controlling the solvent composition and concentration. Bowknot-like bundles with twisted fiber arms were prepared from C6TMQA, whilst uniform twisted fibers were generated from C10TMQA in ethanol/THF solution. Spectroscopic characterization and molecular simulation calculations revealed that the introduction of ethanol into the solution could induce a staggered aggregation of C6TMQA (or C10TMQA) molecules and the formation of twisted nanostructures. Such twisted materials generated from achiral organic functional molecules may be valuable in the design and fabrication of new materials for optoelectronic applications. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users.     

Structures and electrical properties of Ag-tetracyanoquinodimethane organometallic nanowires

Ag-tetracyanoquinodimethane (Ag-TCNQ) nanostructures are synthesized using both solution reaction in acetonitrile and a novel vacuum-saturated vapor reaction method. Experiments show that the latter synthesis method produces Ag-TCNQ nanowires with better uniformity and higher aspect ratio. These nanowires, having diameters around 100 nm and lengths about 5 /spl mu/m, could serve as potential building blocks of nanoscale electronics. Nanodevices based on these nanowires are fabricated using the electron-beam lithography technique. Electrical transport study shows reproducible I--V hysteresis with a change in resistance of four orders of magnitude, demonstrating electrical memory effect. This electrical bistability makes Ag-TCNQ nanowires a promising candidate for future applications in ultrahigh-density information storage.     

Crystallographic alignment of high-density gallium nitride nanowire arrays

Single-crystalline, one-dimensional semiconductor nanostructures are considered to be one of the critical building blocks for nanoscale optoelectronics. Elucidation of the vapour-liquid-solid growth mechanism has already enabled precise control over nanowire position and size, yet to date, no reports have demonstrated the ability to choose from different crystallographic growth directions of a nanowire array. Control over the nanowire growth direction is extremely desirable, in that anisotropic parameters such as thermal and electrical conductivity, index of refraction, piezoelectric polarization, and bandgap may be used to tune the physical properties of nanowires made from a given material. Here we demonstrate the use of metal-organic chemical vapour deposition (MOCVD) and appropriate substrate selection to control the crystallographic growth directions of high-density arrays of gallium nitride nanowires with distinct geometric and physical properties. Epitaxial growth of wurtzite gallium nitride on (100) gamma-LiAlO(2) and (111) MgO single-crystal substrates resulted in the selective growth of nanowires in the orthogonal [1\[Evec]0] and [001] directions, exhibiting triangular and hexagonal cross-sections and drastically different optical emission. The MOCVD process is entirely compatible with the current GaN thin-film technology, which would lead to easy scale-up and device integration.     

应用DNA模版自组装CdS纳米线

近年来,由于具有双螺旋补偿结构,DNA分子作为智能模版被广泛应用于设计棒状或管状类的纳米结构.本文报道了应用DNA双螺旋模版将CdS纳米粒子自组装为CdS纳米线.制备的CdS纳米线由几根纳米线紧密缠绕在一起,也呈螺旋形结构,该结构在无机材料中是很少见的.该结构形成的主要原因归功于CdS纳米粒子和DNA分子间的强烈静电互作用,由于含自由基的CdS纳米粒子带负电荷,而氨基的DNA核酸根带正电荷.研究结果表明应用DNA模版制备纳米线是一种简便、高效的技术和方法.同时,DNA模版法也为从底上制备纳米级的材料和物体提供了广阔的空间.     

Dielectrophoretically controlled fabrication of single-crystal nickel silicide nanowire interconnects

We report here on applying electric fields and dielectric media to achieve controlled alignment of single-crystal nickel silicide nanowires between two electrodes. Depending on the concentration of nanowire suspension and the distribution of electrical field, various configurations of nanowire interconnects, such as single, chained, and branched nanowires were aligned between the electrodes. Several alignment mechanisms, including the induced charge layer on the electrode surface, nanowire dipole-dipole interactions, and an enhanced local electrical field surrounding the aligned nanowires are proposed to explain these novel dielectrophoretic phenomena of one-dimensional nanostructures. This study demonstrates the promising potential of dielectrophoresis for constructing nanoscale interconnects using metallic nanowires as building blocks.     

The emerging field of RNA nanotechnology

Like DNA, RNA can be designed and manipulated to produce a variety of different nanostructures. Moreover, RNA has a flexible structure and possesses catalytic functions that are similar to proteins. Although RNA nanotechnology resembles DNA nanotechnology in many ways, the base-pairing rules for constructing nanoparticles are different. The large variety of loops and motifs found in RNA allows it to fold into numerous complicated structures, and this diversity provides a platform for identifying viable building blocks for various applications. The thermal stability of RNA also allows the production of multivalent nanostructures with defined stoichiometry. Here we review techniques for constructing RNA nanoparticles from different building blocks, we describe the distinct attributes of RNA inside the body, and discuss potential applications of RNA nanostructures in medicine. We also offer some perspectives on the yield and cost of RNA production.     

Interfacially organized DNA/polycation complexes: a route to new planar polymeric and composite nanostructures

Effects of nano-scale supramolecular organization and patterning in amphiphilic polycation monolayer formed by poly-4-vinilpyridine with 16% cetylpyridinium groups and in novel planar DNA/amphiphilic polycation complexes formed at the air-aqueous DNA solution interface and deposited on the solid substrates have been studied using AFM. Stable ordered quasi-crystalline planar polymeric monolayer structures were formed by amphiphilic polycation molecules. Extended net-like and quasi-circular toroidal condensed conformations of deposited planar DNA/amphiphilic polycation complexes were obtained in dependence on the amphiphilic polycation Langmuir monolayer state during the DNA binding. Those monolayer and multilayer DNA/polycation complex Langmuir–Blodgett films were used as templates and nanoreactors for generation of inorganic nanostructures. As a result, ultrathin polymeric nanocomposite films with integrated DNA building blocks and inorganic semiconductor (CdS) and iron oxide nanoparticle quasi-linear arrays or aggregates (nanorods) were formed successfully and characterized by TEM. The data obtained give evidence for effectiveness of the monolayer techniques for study mechanisms of DNA structural transformations caused by complexation with cationic compounds and demonstrate its perspectives for creation of new planar DNA-based self-organized stable polymeric complex nanostructures and nanocomposites with nano-scale structural ordering.     

Coherent single charge transport in molecular-scale silicon nanowires

We report low-temperature electrical transport studies of chemically synthesized, molecular-scale silicon nanowires. Individual nanowires exhibit Coulomb blockade oscillations characteristic of charge addition to a single nanostructure on length scales up to at least 400 nm. Studies also demonstrate coherent charge transport through discrete single particle quantum levels extending across whole devices, and show that the ground-state spin configuration is consistent with the constant interaction model. In addition, depletion of nanowires suggests that phase coherent single-dot characteristics are accessible in the few-charge regime. These results differ from those for nanofabricated planar silicon devices, which show localization on much shorter length scales, and thus suggest potential for molecular-scale silicon nanowires as building blocks for quantum and conventional electronics.     

pH-sensitive morphological transition from nanowire to nanovesicle of a single amino acid-based water soluble molecule

Employment of single amino acid-based molecules for the construction of various nanostructures is a challenging issue. Moreover, it is fascinating to see the controlled fabrication of specific nanostructures from the self-assembly of molecular building blocks through the fine tuning of pH of the solution. The present study demonstrates pH-responsive nanostructural transformation of single amino acid-based nanostructures from nanowires to nanovesicles. The molecules have been developed by coupling the carboxyl group of natural amino acids with the amino group of unnatural m-aminobenzoic acid (m-ABA), such as NH₂–Xx–m-ABA–CO₂H, where Xx are amino acids Phe, Tyr, Gly, and Pro. The presence of m-aminobenzoic acid helps in self-assembly through insertion of conformational constraints in the peptide backbone and also through aromatic π–π interactions. The insertion of m-aminobenzoic acid also induces proteolytic stability in the nanostructures. The formation of nanowires has been observed at acidic pH (pH 4.2–6.0), while both nanowires and nanovesicles are formed simultaneously at nearly neutral pH (pH 6.4). With an increase in the pH of the solution, only one nanoscopic species, i.e., nanovesicles have been formed exclusively, and these nanovesicles are stable within the range of pH 7.0–9.1. A further increase in pH (pH 10) triggers the disruption of nanovesicular structures that starts at the peripheral wall of the vesicles and is completed after total disintegration at pH 11. Studies show that alkali metal salt KCl can also disrupt these nanovesicles efficiently. These peptide-based nanovesicles can encapsulate a potent drug curcumin, which can be effectively released through the disruption of the vesicles either in presence of KCl or alkaline pH. Single crystal X-ray diffraction analysis indicates the sheet-mediated self-assembly in the formation of different nanostructures. Studies also show that the tyrosine-based peptide nanovesicles are elegant hosts for in situ preparation and stabilization of silver nanoparticles.