Precise Nanostructures Research Articles

Polymer Nanowires with Highly Precise Internal Morphology and Topography.

The construction of precise soft matter nanostructures in solution presents a challenge. A key focus remains on the rational design of functionalities to achieve the high morphological complexity typically found in biological systems. Advances in controlled polymerizations and self-assembly increasingly allow approaches toward complex hierarchical nanomaterials. By combining tailor-made cylindrical polymer brushes, block copolymers and interpolyelectrolyte complexation-driven self-assembly, we demonstrate a facile construction of uniformly compartmentalized and topographically structured polymeric nanowires in aqueous media. The approach offers a modular avenue in programming the internal morphology of polymer nanowires by varying the block copolymer composition and topology.

Near-field imaging of graphene triangles patterned by helium ion lithography

Plasmon nanoresonators in graphene have many applications in biosensing, photodetectors and modulators. As a result, an efficient and precise patterning technique for graphene is required. Helium ion lithography (HIL) emerges as a promising tool for direct writing fabrication because it owns improved fabrication precision compared to electron beam lithography and conventional gallium focused ion beam technique. In this paper, utilizing HIL, a set of graphene triangles are patterned and excellent plasmon response is detected. Particularly, the evolution of breathing mode in these structures is unveiled by scattering-type scanning near-field optical microscopy. Besides, the plasmon response of graphene structures can be efficiently tuned by adjusting the irradiated ion dose during the etching process, which can be explained by the phenomenal simulation model. Our work demonstrates that HIL is a feasible way for precise plasmonic nanostructure fabrication, and can be applied to graphene plasmon control at the nanoscale as well.

Protein Bricks: 2D and 3D Bio‐Nanostructures with Shape and Function on Demand

Precise patterning of polymer-based biomaterials for functional bio-nanostructures has extensive applications including biosensing, tissue engineering, and regenerative medicine. Remarkable progress is made in both top-down (based on lithographic methods) and bottom-up (via self-assembly) approaches with natural and synthetic biopolymers. However, most methods only yield 2D and pseudo-3D structures with restricted geometries and functionalities. Here, it is reported that precise nanostructuring on genetically engineered spider silk by accurately directing ion and electron beam interactions with the protein's matrix at the nanoscale to create well-defined 2D bionanopatterns and further assemble 3D bionanoarchitectures with shape and function on demand, termed "Protein Bricks." The added control over protein sequence and molecular weight of recombinant spider silk via genetic engineering provides unprecedented lithographic resolution (approaching the molecular limit), sharpness, and biological functions compared to natural proteins. This approach provides a facile method for patterning and immobilizing functional molecules within nanoscopic, hierarchical protein structures, which sheds light on a wide range of biomedical applications such as structure-enhanced fluorescence and biomimetic microenvironments for controlling cell fate.

Targeted drug delivery and vaccinology approaches using virus-like particles for cancer

Nanotechnology has the potential to make significant alterations in the treatment of diseases such as cancer through targeted drug delivery nanoparticles. Virus-like particles (VLPs) are composed of the capsid proteins that do not carry the viral genome and are also noninfectious. VLPs are self-assembling competent protein structures with identical or highly related structures to their corresponding native viruses. VLPs that have precise 3D nanostructures exhibit a notable diversity in shapes and structures. They can be produced in large quantities through biological amplification and growth. External protein inserts can be displayed through genetic methods or chemical modifications. Functionalized VLPs when used as delivery systems have the ability to target with specificity and can attract macrophages for the destruction of cancer cells. The capability to target tumors for the delivery of therapeutic agents is an important goal of the design approaches of VLPs. Against the current problems in cancer therapies, delivery systems using VLPs are an arising and promising field with the potential to exhibit solutions. Cancer therapies require specific targeting of the diagnostic element or the drug to tumor cells without binding to or affecting healthy cells and tissues. Specialization of the VLPs provides an opportunity for using them as site-specific drug delivery systems in cancer therapy while reducing the systemic toxicity and the overall damage to healthy cells. With fewer side effects, immunotherapy is also a promising alternative for cancer treatment by primarily activating the host’s immune system. Cancer vaccines are aimed at inducing an immune response in the host, thereby generating a defensive mechanism against tumor cells. VLPs can be used as a vaccine without the requirement of any adjuvant due to their naturally optimized particle size and their repetitive structural order. Therefore, the aim of this review is to provide basic information about VLPs and describe previous research on VLPs used as drug and vaccine delivery systems and their applications in different types of cancer.

General Oriented Synthesis of Precise Carbon-Confined Nanostructures by Low-Pressure Vapor Superassembly and Controlled Pyrolysis.

Earth-abundant metal-based nanostructured materials have been widely studied for potential energy conversion and storage. However, controlled synthesis of functional nanostructures with high electron conductivity, high reaction activity, and structural stability is still a formidable challenge for further practical applications. Herein, for the first time, we develop a facile, efficient, and general method for the oriented synthesis of precise carbon-confined nanostructures by low-pressure vapor superassembly of a thin metal-organic framework (MOF) shell and subsequent controlled pyrolysis. The selected nanostructured metal oxide precursors not only act as metal ion sources but also orient the superassembly of gaseous organic ligands through the coordination reactions under the low-pressure condition, resulting in the formation of a tunable MOF shell on their surfaces. This strategy is further successfully extended to obtain various precise carbon-confined nanostructures with diverse compositions and delicate morphologies. Notably, these as-prepared carbon-confined architectures exhibit outstanding electrochemical performances in water splitting and lithium storage. The remarkable performances are mainly attributed to the synergistic effect from appropriate chemical compositions and stable carbon-confined structures. This synthetic approach and proposed mechanism open new avenues for the development of functional nanostructured materials in many frontier fields.

Eco-friendly synthesis and morphology-dependent superior electrocatalytic properties of CuS nanostructures

Copper sulfide with desired structure is of special interest for electrocatalytical application due to their unique physicochemical properties, simple synthesis and less toxic in nature. In this study, simple and eco-friendly (without using any template or surfactant) route for the fabrication of copper sulfide nanostructure morphologies were tuned from cauliflower, microflower to nanoparticles inter-connected network-like structures by changing the polarity of solvent medium during solvothermal synthesis. However, to the best of our knowledge, no such kinds of special three types of CuS nanostructure with excellent electro-catalytic properties using only H2O and C2H5OH as the solvents have been reported in the literature. The as-prepared different CuS nanostructure was characterized using FE-SEM, HR-TEM, XRD, XPS and cyclic voltammetry. This morphological alteration able to produce several precise nanostructures with improved electrocatalytic properties that led to an excellent performance towards enzymeless glucose oxidation. The CuS inter-connected nanoparticles modified electrode displayed a synergistic effect towards the oxidation of glucose (ipa: 103±5μA) when compared to that of cauliflower (ipa: 68±3.7μA) and microflower (ipa: 60±2.4μA) modified electrode surfaces. Further, the CuS inter-connected nanoparticles modified electrode showed a wide linear range (2.0×10−5−2.5×10−3M), high sensitivity (1085μAmM−1cm−2), low detection limit (2μM), rapid response time (<3s), good stability, selectivity and reproducibility. The obtained sensing parameters based on CuS inter-connected nanoparticles modified electrode were superior with many reports and also comparable with few reports in the available literatures.

Preparation at the water–oil interface of Janus composite nanoparticles and their photoelectric properties

ABSTRACTA series of Janus composite poly(3‐hexyl thiophene)‐b‐poly(3‐thiophenehexanethiol)–gold nanoparticles were synthesized by self‐assembly at the water–oil interface, and their photoelectric performance was investigated. The results show that the precise Janus composite nanostructure could be controlled by the adjustment of the reaction temperature and stirring time. The UV–visible measurement revealed that the absorption maximum had an appreciable redshift, and the photoluminescence (PL) spectra indicated that the PL intensity of poly(3‐hexyl thiophene)‐b‐poly[3‐(6‐thiolhexyl thiophene)] decreased upon the addition of gold nanoparticles. In addition, compared to a common composite of poly(3‐hexyl thiophene), the conductivity properties of the Janus composite nanostructure increased remarkably. Therefore, the Janus composite nanoparticles have the potential for applications in photovoltaic devices. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45107.

Spray-evaporation assembled graphene oxide membranes for selective hydrogen transport

Abstract For gas separation through laminar-structured graphene oxide (GO) membranes, precise nanostructure manipulation is of critical significance for the acquirement of high performance. In this study, facile engineering of GO membranes is realized by combining spraying and solvent evaporation-induced assembly technique. Disordered-to-ordered and porous-to-compact GO membrane structures can be finely and conveniently manipulated via controlling the spraying times and evaporation rate during GO assembly. The as-fabricated GO membranes possess the optimal gas separation performance with H2/CO2 selectivity of 20.9 and H2 permeance of 2.7 × 10−8 mol Pa−1 m−2 s−1, which exceeds the upper bound of polymeric membranes. A probable transport mechanism for different gas molecules is applied to clarify the relationships between membrane structure and gas permeation. This study may explore an efficient and facile approach to fabricate defect-free GO membranes with high controllability and practicability.

Π Band Dispersion along Conjugated Organic Nanowires Synthesized on a Metal Oxide Semiconductor.

Surface-confined dehalogenation reactions are versatile bottom-up approaches for the synthesis of carbon-based nanostructures with predefined chemical properties. However, for devices generally requiring low-conductivity substrates, potential applications are so far severely hampered by the necessity of a metallic surface to catalyze the reactions. In this work we report the synthesis of ordered arrays of poly(p-phenylene) chains on the surface of semiconducting TiO2(110) via a dehalogenative homocoupling of 4,4″-dibromoterphenyl precursors. The supramolecular phase is clearly distinguished from the polymeric one using low-energy electron diffraction and scanning tunneling microscopy as the substrate temperature used for deposition is varied. X-ray photoelectron spectroscopy of C 1s and Br 3d core levels traces the temperature of the onset of dehalogenation to around 475 K. Moreover, angle-resolved photoemission spectroscopy and tight-binding calculations identify a highly dispersive band characteristic of a substantial overlap between the precursor’s π states along the polymer, considered as the fingerprint of a successful polymerization. Thus, these results establish the first spectroscopic evidence that atomically precise carbon-based nanostructures can readily be synthesized on top of a transition-metal oxide surface, opening the prospect for the bottom-up production of novel molecule–semiconductor devices.

Nano-photo-thermal energy drive MoS_2/ZnO nanoheterojunctions growing

The heterojunction of transition-metal dichalcogenides is an important task for their applications in optoelectronics and nanoelectronics owning to substantial enhancing and enticing the material, optical, and electronic properties. A precise and controllable nanostructure preparing method, although highly desired, remains quite challenging, especially for heterojunction growing. In this work, an inspiring strategy is first reported for the synthesis of the MoS2/ZnO composite structure through driving by the nano-photo-thermal energy. The ZnO NCs exhibit a 2D layer growth way on the surface of MoS2 nanosheets. MoS2/ZnO composite structures possess high quality optical properties for the application of heterojunction. The nano-photo-thermal energy drive nanoheterojunction growing technology is a promising strategy towards the facile and in situ controllable method of novel functional materials.

Structurally uniform and atomically precise carbon nanostructures

Nanometre-sized carbon materials consisting of benzene units oriented in unique geometric patterns, hereafter named nanocarbons, conduct electricity, absorb and emit light, and exhibit interesting magnetic properties. Spherical fullerene C60, cylindrical carbon nanotubes and sheet-like graphene are representative forms of nanocarbons, and theoretical simulations have predicted several exotic 3D nanocarbon structures. At present, synthetic routes to nanocarbons mainly lead to mixtures of molecules with a range of different structures and properties, which cannot be easily separated or refined into pure forms. Some researchers believe that it is impossible to synthesize these materials in a precise manner. Obtaining ‘pure’ nanocarbons is a great challenge in the field of nanocarbon science, and the construction of structurally uniform nanocarbons, ideally as single molecules, is crucial for the development of functional materials in nanotechnology, electronics, optics and biomedical applications. This Review highlights the organic chemistry approach — more specifically, bottom-up construction with atomic precision — that is currently the most promising strategy towards this end. Conventional synthesis of nanocarbons, such as graphene, fullerenes and carbon nanotubes, yields mixtures of molecules with varying structures. However, harnessing the full potential of these materials demands atomically precise synthesis methods. Recent advances using organic chemistry are discussed in this Review.

A new strategy for achieving vertically-erected and hierarchical TiO2 nanosheets array/carbon cloth as a binder-free electrode for protein impregnation, direct electrochemistry and mediator-free glucose sensing

We present a new approach to directly grow uniform and highly-ordered TiO2 nanosheets array (NSA) on a low-cost flexible carbon cloth substrate while simultaneously fulfill precise TiO2 nanostructure tailoring and crystal phase control. The unique vertically-erected TiO2 NSA/carbon cloth with hierarchical structures was directly explored as electrode for enzyme immobilization and biosensing applications without suffering any influences of insulating binders usually used to fix nanomaterials on conductive substrates during sensor fabrications. Efficient direct electron transfer was successfully achieved for glucose oxidase (GOx) immobilized on the TiO2 NSA/carbon cloth, which produces a stable, mediator-free glucose sensor with good selectivity, high-sensitivity (52μA mM−1cm−2), low response time (<5s) and low detection limit (23.4μM, S/N=3). The mechanism of the superior direct electrochemical properties and sensing performance was investigated in detail, and discussed from the aspects of material nanostructure and crystalline form of TiO2 NSA, and an intimate contact between TiO2 and carbon cloth resulted from direct crystallization and growth of TiO2 nanosheets on the substrate.

Shaping quaternary assemblies of water-soluble non-peptide helical foldamers by sequence manipulation.

The design and construction of biomimetic self-assembling systems is a challenging yet potentially highly rewarding endeavour that contributes to the development of new biomaterials, catalysts, drug-delivery systems and tools for the manipulation of biological processes. Significant progress has been achieved by engineering self-assembling DNA-, protein- and peptide-based building units. However, the design of entirely new, completely non-natural folded architectures that resemble biopolymers ('foldamers') and have the ability to self-assemble into atomically precise nanostructures in aqueous conditions has proved exceptionally challenging. Here we report the modular design, formation and structural elucidation at the atomic level of a series of diverse quaternary arrangements formed by the self-assembly of short amphiphilic α-helicomimetic foldamers that bear proteinaceous side chains. We show that the final quaternary assembly can be controlled at the sequence level, which permits the programmed formation of either discrete helical bundles that contain isolated cavities or pH-responsive water-filled channels with controllable pore diameters.

Self-assembly of diphenylalanine backbone homologues and their combination with functionalized carbon nanotubes.

The integration of carbon nanotubes (CNTs) into organized nanostructures is of great interest for applications in materials science and biomedicine. In this work we studied the self-assembly of β and γ homologues of diphenylalanine peptides under different solvent and pH conditions. We aimed to investigate the role of peptide backbone in tuning the formation of different types of nanostructures alone or in combination with carbon nanotubes. In spite of having the same side chain, β and γ peptides formed distinctively different nanofibers, a clear indication of the role played by the backbone homologation on the self-assembly. The variation of the pH allowed to transform the nanofibers into spherical structures. Moreover, the co-assembly of β and γ peptides with carbon nanotubes covalently functionalized with the same peptide generated unique dendritic assemblies. This comparative study on self-assembly using diphenylalanine backbone homologues and of the co-assembly with CNT covalent conjugates is the first example exploring the capacity of β and γ peptides to adopt precise nanostructures, particularly in combination with carbon nanotubes. The dendritic organization obtained by mixing carbon nanotubes and peptides might find interesting applications in tissue engineering and neuronal interfacing.

Aqueous self-assembly of chromophore-conjugated amphiphiles.

The self-assembly of π-conjugated building blocks has been a topic of interest in last few years owing to their close relevance to optoelectronic device applications. If such building blocks are made amphiphilic by appropriate derivatization, then the self-assembly can be realized in water by the strong hydrophobic repulsive forces between the polar medium and the rigid π-surface. On the other hand, as π-π interactions are directional, such self-assembly can produce structurally precise nano-structures, compared to classical surfactants. With these objectives, the self-assembly of several amphiphilic π-systems has been studied in the recent past and is described in this article. Examples include electron-deficient, electron-rich and also mixed assemblies of donor and acceptor type chromophores which produce many elegant soft structures such as micelles, vesicle, nanotubes and fibres etc.

Multi‐Site Functionalization of Protein Scaffolds for Bimetallic Nanoparticle Templating

The use of biological scaffolds to template inorganic material offers a strategy to synthesize precise composite nanostructures of different sizes and shapes. Proteins are unique biological scaffolds that consist of multiple binding regions or epitope sites that site‐specifically associate with conserved amino acid sequences within protein‐binding partners. These binding regions can be exploited as synthesis sites for multiple inorganic species within the same protein scaffold, resulting in bimetallic inorganic nanostructures. This strategy is demonstrated with the scaffold protein clathrin, which self‐assembles into spherical cages. Specifically, tether peptides that noncovalently associate with distinct clathrin epitope sites, while initiating simultaneous synthesis of two inorganic species within the assembled clathrin protein cage, are designed. The flexibility and diversity of this unique biotemplating strategy is demonstrated by synthesizing two types of composite structures (silver–gold mixed bimetallic and silver–gold core–shell nanostructures) from a single clathrin template. This noncovalent, Template Engineering Through Epitope Recognition, or TEThER, strategy can be readily applied to any protein system with known epitope sites to template a variety of bimetallic structures without the need for chemical or genetic mutations.

Growth of two-dimensional materials on non-catalytic substrates: h-BN/Au(111)

The growth of two-dimensional (2D) materials is a topic of very high scientific and technological interest. While chemical vapour deposition on catalytic metals has become a well developed approach for the growth of graphene and hexagonal boron nitride (BN), very few alternative approaches for synthesis on non-reactive supports have been explored so far. Here we report the growth of BN on gold, using magnetron sputtering of B in N2/Ar atmosphere, a scalable method using only non-toxic reagents. Scanning tunnelling microscopy at low coverage shows primarily triangular monolayer BN islands exhibiting two ‘magic’ orientations on the Au(111) surface. Such rotational alignment of BN on Au(111) is surprising, given the expected weak binding and the high lattice mismatch (∼14%) between BN and Au. Our observations are consistent with a strong coupling between the edges of BN flakes and the substrate, which leads to the selection of BN orientations that maximize the orbital overlap between edge atoms and Au surface atoms. Diverse flake morphologies resembling the shape of butterflies, six-apex stars and diamonds, implying alternating B- and N- terminated edges, are observed as well. Our results provide insight into the growth mechanisms of 2D materials on weakly interacting and chemically inert substrates, and provide the basis for integrating other 2D materials with atomically precise graphene nanostructures synthesized from molecular precursors on Au.

Advanced thermopower wave in novel ZnO nanostructures/fuel composite.

Thermopower wave is a new concept of energy conversion from chemical to thermal to electrical energy, produced from the chemical reaction in well-designed hybrid structures between nanomaterials and combustible fuels. The enhancement and optimization of energy generation is essential to make it useful for future applications. In this study, we demonstrate that simple solution-based synthesized zinc oxide (ZnO) nanostructures, such as nanorods and nanoparticles are capable of generating high output voltage from thermopower waves. In particular, an astonishing improvement in the output voltage (up to 3 V; average 2.3 V) was achieved in a ZnO nanorods-based composite film with a solid fuel (collodion, 5% nitrocellulose), which generated an exothermic chemical reaction. Detailed analyses of thermopower waves in ZnO nanorods- and cube-like nanoparticles-based hybrid composites have been reported in which nanostructures, output voltage profile, wave propagation velocities, and surface temperature have been characterized. The average combustion velocities for a ZnO nanorods/fuel and a ZnO cube-like nanoparticles/fuel composites were 40.3 and 30.0 mm/s, while the average output voltages for these composites were 2.3 and 1.73 V. The high output voltage was attributed to the amplified temperature in intermixed composite of ZnO nanostructures and fuel due to the confined diffusive heat transfer in nanostructures. Moreover, the extended interfacial areas between ZnO nanorods and fuel induced large amplification in the dynamic change of the chemical potential, and it resulted in the enhanced output voltage. The differences of reaction velocity and the output voltage between ZnO nanorods- and ZnO cube-like nanoparticles-based composites were attributed to variations in electron mobility and grain boundary, as well as thermal conductivities of ZnO nanorods and particles. Understanding this astonishing increase and the variation of the output voltage and reaction velocity, precise ZnO nanostructures, will help in formulating specific strategies for obtaining enhanced energy generation from thermopower waves.

Electric control of straight stripe conductive mixed-phase nanostructures in La-doped BiFeO3

This study examines the atomic force microscope (AFM) tip-based electrical formation of tens of microns long stripe (and ∼100 nm wide) inorganic one-dimensional nanostructures based on the morphotropic phase boundary of La-doped BiFeO3 epitaxial thin films. The substitution of Lanthanum into bismuth ferrite not only produces the formation of straight stripe mixed-phase patterns but also improves the spatial continuity drastically by two orders of magnitude. We create, switch and erase stripe nanostructures in a reversible and deterministic way. We demonstrate that electrically formed areas with a nearly single variant alignment can be overwritten with different alignments repeatedly, which reflects the reversible and nonvolatile nature of the switching process. In addition, we explore the functionality of the created nanostructures by clarifying ferroelectric polarizations and observing the improvement of the electronic conduction at the phase boundary. Our findings provide new pathways to one-dimensional rewritable nanostructures and inspire researchers to conceive various multifunctional devices by combining the superb electromechanical property with their unique interfacial electronic conduction properties at nanoscale phase boundaries. Scanning a La-doped BiFeO3 epitaxial thin film with a biased AFM tip, we produce straight stripe one-dimensional nanostructures in which two competing polymorphic ferroelectric phases appear alternately at the interval of ∼100 nm showing the enhancement of electronic conduction at the phase boundaries. We can create, switch and erase the eight-variant stripe nanostructures in a reversible and deterministic way by controlling the tip scanning direction and tip biased voltage. The findings provide a new pathway into one-dimensional nanostructures and versatile patterns of ferroelectric domains and interfaces. Some materials exhibit ‘morphotropic phase boundaries’ at which their crystal structure abruptly changes from a tetrahedral to a rhombohedral lattice. Such phase boundaries are created under high pressure or strain and are accompanied by a change in the material's characteristics. For example, there is great interest in controlling mixed-phase domains composed of ‘T’ and ‘R” phases in thin films of bismuth ferrite (BiFeO3, also known as BFO) for electromechanical applications. Now, a South Korea-Australia-based team led by Chan-Ho Yang has used an atomic force microscope tip to create - and further manipulate or erase - well-aligned, alternating straight stripes of the T and R' domains on a BFO thin film doped with lanthanum. In the absence of lanthanum, the stripes are curved rather than straight. The T-R' phase boundary shows enhanced electronic conduction compared to the bulk phases. These precise and rewritable nanostructures might serve to develop functional materials.

DNA Origami Compliant Nanostructures with Tunable Mechanical Properties

DNA origami enables fabrication of precise nanostructures by programming the self-assembly of DNA. While this approach has been used to make a variety of complex 2D and 3D objects, the mechanical functionality of these structures is limited due to their rigid nature. We explore the fabrication of deformable, or compliant, objects to establish a framework for mechanically functional nanostructures. This compliant design approach is used in macroscopic engineering to make devices including sensors, actuators, and robots. We build compliant nanostructures by utilizing the entropic elasticity of single-stranded DNA (ssDNA) to locally bend bundles of double-stranded DNA into bent geometries whose curvature and mechanical properties can be tuned by controlling the length of ssDNA strands. We demonstrate an ability to achieve a wide range of geometries by adjusting a few strands in the nanostructure design. We further developed a mechanical model to predict both geometry and mechanical properties of our compliant nanostructures that agrees well with experiments. Our results provide a basis for the design of mechanically functional DNA origami devices and materials.