Showing papers in "Npg Asia Materials in 2012"
TL;DR: Wang et al. as mentioned in this paper used a polymer made of two flexible blocks with different properties, one block exhibits a high affinity to oil phases and low affinity to aqueous ones, while the other changes its wettability but also its shape through protonation, depending on the acidity of the aquequeous phase.
Abstract: Peng Wang and co-workers have devised smart surfaces that have switchable wettability – affinity to oil and water phases. Such materials are useful for applications that require oil/water separation, and might help clean up oil spills in future. The researchers have endowed materials with smart surfaces by decorating them with a polymer made of two flexible blocks with different properties. One block exhibits a high affinity to oil phases and low affinity to aqueous ones, while the other changes its wettability but also its shape through protonation, depending on the acidity of the aqueous phase. At different pHs, therefore, either one block or the other is predominantly exposed to the solution, endowing the surface with different wettability characteristics. These smart surfaces can be coated on commonly used materials such as textiles and sponges, and showed good properties for oil capture and release applications.
434 citations
TL;DR: In this paper, a review focuses on recent researches to develop functional materials by forming nanomaterials into organized structures, especially in well-ordered layered structural motifs, achieved by using the versatile technology of layer-by-layer assembly.
Abstract: Forming nanomaterials into hierarchic and organized structures is a rational way of preparing advanced functional materials. The term nanoarchitectonics can express this innovation. This review focuses on recent researches to develop functional materials by forming nanomaterials into organized structures, especially in well-ordered layered structural motifs. This layered nanoarchitectonics can be achieved by using the versatile technology of layer-by-layer assembly. Reassembly of bulk materials into novel layered structures through layered nanoarchitectonics has created many innovative functional materials in a wide variety of fields as can be seen in ferromagnetic nanosheets, sensors, flame-retardant coatings, transparent conductors, electrodes and transistors, walking devices, drug release surfaces, targeting drug carriers and cell culturing.
347 citations
TL;DR: In this paper, the authors investigate the characteristics that distinguish the resonant state mechanism from that due to multiple valence bands and their effect on the thermoelectric figure of merit, zT.
Abstract: The Seebeck coefficient of p-type PbTe can be enhanced at 300 K, either due to the addition of Tl-resonant states or by manipulation of the multiple valence bands by alloying with isovalent compounds, such as MgTe. PbTe alloyed with MnTe shows a similar thermopower enhancement that could be due to either mechanism. Here we investigate the characteristics that distinguish the resonant state mechanism from that due to multiple valence bands and their effect on the thermoelectric figure of merit, zT. Ultimately, we find that the transport properties of PbTe alloyed with MnTe can be explained by alloy scattering and multiple band model that result in a zT as high as 1.6 at 700 K, and additionally a ~30% enhancement of the average zT.
229 citations
TL;DR: Yu et al. as mentioned in this paper developed a simple and inexpensive method to fabricate highly conductive and stretchable composites using bacterial cellulose (BC) pellicles as starting materials, which can be produced in large amounts on an industrial scale via a microbial fermentation process.
Abstract: Advanced materials that can remain electrically conductive under substantial elastic stretch and bending have attracted extensive interest recently owing to their broad application potentials, particularly for flexible electronics. Here, we have developed a simple and inexpensive method to fabricate highly conductive and stretchable composites using bacterial cellulose (BC) pellicles as starting materials, which can be produced in large amounts on an industrial scale via a microbial fermentation process. The prepared pyrolyzed BC (p-BC)/polydimethylsiloxane (PDMS) composites exhibit a high electrical conductivity of 0.20–0.41 S cm−1, which is much higher than conventional carbon nanotubes and graphene-based composites. More importantly, the p-BC/PDMS composites that combine high stretchability with high conductivity show great electromechanical stability. Even after 1000 stretching cycles at the maximum strain of 80%, the resistance of the composites increased by only ∼10%. The resistance increased slightly (∼4%) after 5000 bending cycles with a maximum bending radius of 1.0 mm. Shu-Hong Yu and co-workers at the University of Science and Technology of China in Hefei have devised an easy and cost-effective approach to prepare flexible conductors. Increasingly, conducting materials are required to be stretchable and bendable - properties that are difficult to achieve with conventional conductors. Yu and colleagues have now turned to bacterial cellulose to get around this problem. Although cellulose is mostly known as a component of plants, it can be generated, in high purity, by some micro-organisms through fermentation - a facile process that can be carried out in large quantities. Bacterial cellulose pellicles were treated by freeze-drying and pyrolysis to give a robust aerogel composed of entangled nanofibres, which was then infiltrated with a polymer. The resulting composite material showed excellent electrical conductivity, which was maintained even under stretching and bending, and is thus very well suited to applications in flexible, foldable electronics. Highly conductive and stretchable conductors from bacterial cellulose (BC) can be fabricated through a simple and inexpensive method using bacterial cellulose pellicles as starting materials, which can be produced in large amounts on an industrial scale via a microbial fermentation process. The prepared pyrolyzed BC/polydimethylsiloxane composites exhibit highly stable electric conductivity even under high stretching and bending strain.
222 citations
TL;DR: Liu et al. as discussed by the authors reviewed recent progress in the rapidly developing area of biomolecular interaction detection using FET-based biosensors based on the carbon nanomaterials single-walled carbon nanotubes (SWNTs) and graphene.
Abstract: Carbon nanomaterials field-effect transistor (FET)-based electrical biosensors provide significant advantages over the current gold standards, holding great potential for realizing direct, label-free, real-time electrical detection of biomolecules in a multiplexed manner with ultrahigh sensitivity and excellent selectivity. The feasibility of integrating them with current complementary metal oxide semiconductor platform and a fluid handling module using standard microfabrication technology opens up new opportunities for the development of low-cost, low-noise, portable electrical biosensors for use in practical future devices. In this article, we review recent progress in the rapidly developing area of biomolecular interaction detection using FET-based biosensors based on the carbon nanomaterials single-walled carbon nanotubes (SWNTs) and graphene. Detection scenarios include DNA–DNA hybridization, DNA–protein interaction, protein function and cellular activity. In particular, we will highlight an amazing property of SWNT- or graphene-FETs in biosensing: their ability to detect biomolecules at the single-molecule level or at the single-cell level. This is due to the size comparability and the surface compatibility of the carbon nanomaterials with biological molecules. We also summarize some current challenges the scientific community is facing, including device-to-device heterogeneity and the lack of system integration for uniform device array mass production. The detection of biological events is crucial in many life science applications such as disease diagnosis and the analysis of biological systems. Song Liu and Xuefeng Guo from the Beijing National Laboratory for Molecular Sciences and Peking University now review the use of field-effect transistors (FET) based on carbon nanomaterials for biosensing applications. Biosensors made from graphene or carbon nanotubes-based FETs have several advantages. They are very sensitive to environmental parameters such as surface charges or pH values. Furthermore, these nanostructures are very good charge conductors, allowing for a fast response to external changes. In particular sensors based on transistor geometries are of benefit, as biological reactions taking place at their surface directly influence the charge transport through the device. Although reliability remains an issue, such carbon-derived biosensors have already shown protein reactions and detection down to the single molecule level, clearly establishing their potential for practical applications. In this article, we review recent progress in the rapidly developing area of biomolecular interaction detection with excellent selectivity and ultrahigh sensitivity, such as DNA-DNA hybridization, DNA-protein interaction, protein function, and cellular activity, using FET-based biosensors based on the carbon nanomaterials single-walled carbon nanotubes (SWNTs) and graphenes. We also summarize some current challenges the scientific community is facing, including device-to-device heterogeneity and the lack of system integration for uniform device array mass-production.
222 citations
TL;DR: Lu et al. as mentioned in this paper showed that the band gap of single-layer graphene (SLG) can be opened to 0.16 and 0.34 eV with a strong electric field when properly sandwiched between two hexagonal boron nitride single layers.
Abstract: Opening a tunable and sizable band gap in single-layer graphene (SLG) without degrading its structural integrity and carrier mobility is a significant challenge. Using density functional theory calculations, we show that the band gap of SLG can be opened to 0.16 eV (without an electric field) and 0.34 eV (with a strong electric field) when properly sandwiched between two hexagonal boron nitride single layers. The zero-field band gaps are increased by more than 50% when the many-body effects are included. The ab initio quantum transport simulation of a dual-gated field effect transistor (FET) made of such a sandwich structure reveals an electric-field-enhanced transport gap, and the on/off current ratio is increased by a factor of 8.0 compared with that of a pure SLG FET. The tunable and sizeable band gap and structural integrity render this sandwich structure a promising candidate for high-performance SLG FETs. Jing Lu and co-workers have revealed how to open up a tunable band gap in single-layer graphene, the one-atom-thick honeycomb carbon layer that has sparked much interest both in fundamental physics and in practical applications. Although graphene's excellent mechanical, thermal and electrical properties are very attractive, one major drawback is its lack of ‘band gap’ — the energy gap in the electronic structure of a material that enables to switch its conductivity on and off. Previous attempts to create such a gap in single-layer graphene have typically damaged its structure or conductivity. Through extensive calculations, the researchers have now examined the properties of single-layer graphene when sandwiched between two honeycomb boron nitride (BN) layers. They revealed that for a specific positioning of the layers, a sizable band gap can be opened and further tuned by applying an electric field without causing damage, making the sandwich structure a promising component for field-effect transistors. An electric field-enhanced transport gap is well established in a dual-gated field effect transistor (FET) based on the h-BN/single-layer graphene/h-BN sandwich structure, and the on/off current ratio is increased by a factor of 8.0 compared with pure single-layer graphene FET. The tunable and sizeable band gap and structural integrity render this sandwich structure a promising candidate for high-performance single-layer graphene FETs.
182 citations
TL;DR: In this article, the role of carbon doping at the microscopic scale on magnesium diboride (MgB2) was investigated and it was shown that carbon encapsulates boron powder, prevents agglomeration and as a result reduces void fraction.
Abstract: Increasing dissipation-free supercurrent has been the primary issue for practical application of superconducting wires. For magnesium diboride, MgB2, carbon is known to be the most effective dopant to enhance high-field properties. However, the critical role of carbon remains elusive, and also low-field critical current density has not been improved. Here, we have undertaken malic acid doping of MgB2 and find that the microscopic origin for the enhancement of high-field properties is due to boron vacancies and associated stacking faults, as observed by high-resolution transmission electron microscopy and electron energy loss spectroscopy. The carbon from the malic acid almost uniformly encapsulates boron, preventing boron agglomeration and reducing porosity, as observed by three-dimensional X-ray tomography. The critical current density either exceeds or matches that of niobium titanium at 4.2 K. Our findings provide atomic-level insights, which could pave the way to further enhancement of the critical current density of MgB2 up to the theoretical limit. Hiroaki Kumakura, Shi Xue Dou and co-workers have uncovered the role of carbon doping at the microscopic scale on magnesium diboride (MgB2). This inexpensive superconductor — a material with no electrical resistance below a certain temperature — is also sensitive to magnetic fields. The researchers show that incorporating an organic molecule into MgB2 (‘carbon doping’) improves its critical current density under low magnetic field — an effect previously known only for high fields. Detailed characterizations revealed that the number of voids within the material increased, yet their size decreased, so that MgB2 was denser after doping. The team suggests that a boron deficiency causes microscopic defects within the superconductor's structure, improving its properties, while a particular arrangement of the doping molecules can explain the increased density. These findings may lead to further enhancement of the properties of MgB2, which has recently attracted interest in various fields. In medical magnetic resonance imaging, for example, MgB2-based magnets are promising alternatives to the current NbTi-based technology that relies on expensive cooling with liquid helium. Where does carbon go when it is doped into magnesium diboride (MgB2) and why the superconducting properties are improved? In this work, malic acid-doped MgB2 was investigated and it was shown that carbon encapsulates boron powder, prevents agglomeration and as a result reduces void fraction as was confirmed by the first detailed X-ray tomogram analysis. It was also found that carbon induces a lot of stacking faults within MgB2 grains. The critical current density is now comparable to commercial niobium titanium (NbTi) wire and further improvements are expected.
180 citations
TL;DR: Kim et al. as discussed by the authors reviewed how nanocomposite materials that combine organic and inorganic materials are attractive for use in memory components and showed that hybrid organic-inorganic devices, such as a polymer matrix in which metal nanoparticles have been incorporated, are easy to make, cost-effective, mechanically flexible and efficient.
Abstract: Tae Whan Kim and co-workers review how nanocomposite materials that combine organic and inorganic materials are attractive for use in memory components. A wide variety of structures have been used to store information by switching between two states, making for either volatile or nonvolatile memory systems; well-known examples of both types are random access memory (RAM) and computer hard disks, respectively. Among those, hybrid organic-inorganic devices–such as a polymer matrix in which metal nanoparticles have been incorporated–are easy to make, cost-effective, mechanically flexible, and efficient. Further studies will endeavour to better understand the memories' mechanisms and improve their switching speed and reproducibility. These hybrid structures are particularly promising for the development of flexible memories required to construct the next generation of portable devices.
168 citations
TL;DR: Xia et al. as discussed by the authors proposed a method to convert biomolecular information (the presence or absence of DNA strands) into electronic currents by assembling electrochemical sensors, which can then be used as encoders and decoders, converting patterns that are encoded and decoded by the presence of specific DNA sequences into specific electronic outputs.
Abstract: We fabricated and tested encoders and decoders based on a multiplex, DNA-based electrochemical biosensor that uses electronic (electrochemical) signals as its readout. These devices use two or more sequence-specific DNA probes, with each being modified with a distinct redox reporter. These probes, when interrogated together, serve as encoders and decoders, converting patterns that are encoded and decoded by the presence or absence of specific DNA sequences into specific electronic outputs. We demonstrated these multifunctional, bio-electrochemical devices, for example, 4-to-2 and 8-to-3 encoders and 1-to-2 and 2-to-3 decoders. Accordingly, these devices bridge the division between DNA-based devices and silicon-based electronics. Fan Xia and co-workers have converted biomolecular information – the presence or absence of DNA strands – into electronic currents by assembling electrochemical sensors. Each sensor is composed of an electrode, a DNA strand and a redox reporter – such as anthraquinone, methylene blue or ferrocene – and responds to the presence of one particular DNA strand by a change in its redox current. A set of sensors were designed to respond to different DNA strands by emitting distinct currents, and combining these sensors in various ways led to a series of encoding and decoding devices. While systems previously developed had typically given fluorescent outputs, this electrochemical approach moves DNA-based devices a step closer to their silicon-based electronic counterparts, and could potentially become components in DNA-based data processors. We have fabricated and tested encoders and decoders based on a multiplex, DNA-based electrochemical biosensor that uses electronic (electrochemical) signals as its readout. We have demonstrated these multifunctional, bio-electrochemical devices, for example, 4-to-2 and 8-to-3 encoders and 1-to-2 and 2-to-3 decoders. In doing so, these devices bridge the barrier between DNA-based devices and silicon-based electronics.
142 citations
TL;DR: In this paper, the authors discuss recent advances that have made possible the preparation of inorganic semiconductors as nanowires or nanomembranes, their assembly together with organic components into hybrid materials, and their integration into devices.
Abstract: Semiconductors are materials — traditionally inorganic ones — that can act as either conductors or insulators under different conditions. They form the foundation of electronics and play a crucial role in many devices. John Rogers and co-workers discuss recent advances that have made possible the preparation of inorganic semiconductors as nanowires or nanomembranes, their assembly together with organic components into hybrid materials, and their integration into devices. These one- and two-dimensional structures allow for the construction of electronic or opto-electronic devices that are flexible and stretchable — properties that are particularly, albeit not exclusively, promising for biological applications. Systems capable of mapping the electrical activity of the heart and brain have been built, and assemblies whose characteristics mimic those of human skin have led to the construction of epidermal electronic devices. Such devices hold promise for monitoring functional activity and for therapeutic interventions.
141 citations
TL;DR: In this article, the authors demonstrate both theoretically and experimentally an effective method to break the dipole-forbidden rule in SnO2 via nano-engineering its crystalline structure.
Abstract: It is commonly believed that bulk SnO2 is not a suitable ultraviolet (UV) light emitter due to the dipole-forbidden nature of its band-edge states, which has hindered its potential use in optical applications. Here, we demonstrate both theoretically and experimentally an effective method to break the dipole-forbidden rule in SnO2 via nano-engineering its crystalline structure. Furthermore, we designed and fabricated a prototypical UV-light-emitting diode (LED) based on SnO2 thin films. Our methodology is transferable to other semiconductors with ‘forbidden’ energy gaps, offering a promising route toward adding new members to the family of light-emitting materials.
TL;DR: Gu et al. as discussed by the authors developed a barcode system based on photonic crystals, whose color reflection can be controlled during fabrication, with the help of a microfluidic system that also enables the simultaneous incorporation of biomolecules to be probed.
Abstract: Biological systems are often studied through the use of assays, in which different experimental parameters are varied systematically. One method uses so-called barcode particles to track different samples. However this approach is complicated by the difficulty of producing barcode systems that allow for a sufficient number of configurations. Zhongze Gu and colleagues from Southeast University in Nanjing, China, have now developed a barcode system based on photonic crystals. These crystals, whose color reflection can be controlled during fabrication, are prepared with the help of a microfluidic system that also enables the simultaneous incorporation of the biomolecules to be probed. The barcodes particles also contain a magnetic tagged component that allows them to be moved in a magnetic field for easier read-out. By combining several types of photonic crystals in one unit, up to 1.28 million marker combinations are possible.
TL;DR: Guo et al. as mentioned in this paper synthesized high-quality CZTSe nanocrystals with thermodynamically metastable wurtzite phase and optical band gap of 1.46
Abstract: Indium-free quaternary chalcogenide, Cu2ZnSnSe4 (CZTSe), has driven much attention for its potential application in photovoltaics and optoelectronics. It is well known that the composition and structure of nanocrystals (NCs) significantly affect their optical and electrical properties. Controllable synthesis of materials with new crystal structures, especially metastable structures, has given impetus to the development of nanomaterials with many new exciting properties and applications. High-quality CZTSe NCs with thermodynamically metastable wurtzite phase and optical band gap of 1.46 eV were herein synthesized via a facile, lost-cost and safe-solution method. The formation mechanism of the wurtzite CZTSe NCs was investigated in detail, which indicates high reaction rate and low surface energy are favorable for the formation of wurtzite structure. The promising application of as-synthesized NCs in photovoltaics and optoelectronics has been demonstrated by the high-performance hybrid photodetector made from CZTSe NCs and P3HT, with an on/off ratio larger than 150. Yu-Guo Guo, Li-Jun Wan and co-workers have prepared CZTSe nanocrystals with a ‘wurtzite’ structure in a simple, cost-effective synthesis at relatively low temperature. While there is currently an efficient component in photovoltaic and optoelectronic devices made of copper, indium and selenium, indium is in limited supply and there is a concerted effort to discover an alternative. By heating some precursors together in solution, cooling down the mixture and then adding a solvent, the team obtained the quarternary chalcogenide Cu2ZnSnSe4 (CZTSe) in a wurtzite form — a metastable structure which typically offers tunable properties that are well suited to photovoltaic applications. Indeed, when incorporated with poly(3-hexylthiophene) (P3HT) the new material showed a good photoresponse — a rapid, sensitive switch between ‘on’ and ‘off’ states - that subsequently served to construct a high-performance photodetector. Indium-free quaternary chalcogenide, Cu2ZnSnSe4 (CZTSe), has driven much attention for its potential application in photovoltaics and optoelectronics. High-quality CZTSe nanocrystals (NCs) with thermodynamically metastable wurtzite phase were herein synthesized via a facile, lost-cost and safe-solution method, in which high reaction rate and low surface energy are favorable for the formation of wurtzite structure. The promising application of the as-synthesized NCs in photovoltaics and optoelectronics has been demonstrated by the high-performance hybrid photodetector made from CZTSe NCs and P3HT.
TL;DR: Chen et al. as discussed by the authors found that metallic impurities readily leach out of the carbon nanotubes, including into simulated biological fluids mimicking those found in the lung, stomach and intestines.
Abstract: Carbon nanotubes (CNTs) are a class of materials that have stimulated a great deal of interest among researchers due to their unique chemical and electronic properties. However, the apparent toxicity of CNTs has raised concerns about their use in research and applications. Chunying Chen and Yuliang Zhao at the Chinese Academy of Sciences in Beijing and their co-workers have re-examined the safety profile of CNTs, highlighting the role that metallic impurities left over from nanotube synthesis play in their toxicity. The researchers found that these metallic particles readily leach out of the nanotubes, including into simulated biological fluids mimicking those found in the lung, stomach and intestines. Iron particles leached into acidic fluids caused particular safety concerns—electron-spin resonance analysis showed that leached iron particles were generating cytotoxic free radical species at levels much higher than the nanotubes themselves. Cell viability studies demonstrated a clear negative correlation between the amount of metal residue in the nanotube sample and the health of the cultured cells.
TL;DR: In this article, the growth of high-quality GaN films with flat surface and uniform morphology on large-scale polycrystalline chemical vapor-deposited graphene films was demonstrated.
Abstract: We demonstrate the growth of high-quality GaN films with flat surface and uniform morphology on large-scale polycrystalline chemical vapor-deposited graphene films. The films exhibit stimulated emission even at room temperature, a highly c-axis-oriented crystal structure, and a preferred in-plane orientation. Furthermore, the GaN films grown on the graphene films can be used for fabrication of blue and green light-emitting diodes.
TL;DR: In this paper, the ultralong LiV3O8 nanowire cathode materials synthesized by topotactic Li intercalation were demonstrated to have high-rate and long-life performance.
Abstract: High-power applications at fast charge and discharge rates are still great challenges in the development of rechargeable lithium batteries. Here, we demonstrate that ultralong LiV3O8 nanowire cathode materials synthesized by topotactic Li intercalation present excellent high-rate and long-life performance. At the current density of 2000, mA g−1, the initial and the six-hundredth discharge capacities can reach 137 and 120 mAh g−1, respectively, corresponding to a capacity fading of only 0.022% per cycle. Such performance indicates that the topotactically synthesized ultralong LiV3O8 nanowires are promising cathode materials for high-rate and long-life rechargeable lithium batteries.
TL;DR: Kimura et al. as discussed by the authors demonstrated the generation of giant pure spin currents at room temperature in lateral spin valve devices with a highly ordered Heusler-compound Co2FeSi (CFS) spin injector.
Abstract: The generation, manipulation and detection of a pure spin current (i.e., the flow of spin angular momentum without a charge current) are prospective approaches for realizing next-generation spintronic devices with ultra-low electric power consumption. Conventional ferromagnetic electrodes such as Co and NiFe have been utilized as spin injectors to generate pure spin currents in nonmagnetic channels. However, the generation efficiency of pure spin currents is extremely low at room temperature, giving rise to a serious obstacle for device applications. Here we demonstrate the generation of giant pure spin currents at room temperature in lateral spin valve devices with a highly ordered Heusler-compound Co2FeSi (CFS) spin injector. The generation efficiency of pure spin currents from the CFS spin injectors is 10 times greater than that of the NiFe injectors, indicating that Heusler compound spin injectors with high spin polarization enable us to materialize a high-performance lateral spin device. The present study is a technological jump in spintronics, and indicates the great potential of ferromagnetic Heusler compounds with half metallicity for generating pure spin currents. Takashi Kimura, Kohei Hamaya and co-workers have generated large pure spin currents at room temperature, with high efficiency. Spintronic devices, which use the spin of electrons as well as their charge, promise to be faster and less power-consuming than traditional charge-based electronic ones. A pure spin current — a flow that is not accompanied by charge current — seems to be a promising way to write information for such devices. However, although ‘spin injectors’ capable of creating such currents have been developed, their efficiency has generally remained too low for practical applications. Now, Kimura, Hamaya and colleagues have significantly improved this efficiency by using a highly ordered cobalt-iron-silicon ‘Heusler’ compound with high spin polarization. These findings highlight the potential of Heusler compounds as spin injectors, and move the construction of functional spintronic devices one step forward. Heusler compound spin injector with a high spin polarization dramatically improves the generation efficiency of the pure spin current compared with a conventional ferromagnetic metal.
TL;DR: In this article, a hybrid organic-inorganic single-layered film with a surface that responds selectively to external stimuli, resulting in mechanical strain and self-rolling in one-step fabrication is presented.
Abstract: Strain driven micro and nanoroll fabrication is generally restricted to multilayer and multiprocessing systems, limiting the ability to exploit self-organization at different length scales. We have designed a hybrid organic–inorganic single-layered film with a surface that responds selectively to external stimuli, resulting in mechanical strain and self-rolling in one-step fabrication. The scrolling is initiated by water and any aqueous solution of molecules or colloidal particles. During scrolling, the different species in solution remain entrapped in the rolls; the constrained environment at the interface of the roll walls pushes the particles to organize into ordered structures. We used this rolling process to create self-assembled hybrid films with well-ordered layers of gold nanoparticles and opals of polystyrene nanospheres. These films also respond selectively to solvents, allowing the easy release of molecules/particles entrapped at the interface. Researchers from Japan and Italy have devised a one-step strategy to roll single-layer films into microtubes. Films of materials ranging from metals to semiconductors to polymers have previously been rolled up. They typically consist of two or more mismatched layers, so that the scrolling process relies on the strain between layers. The researchers have now prepared a self-rolling single-layer film by ‘sol–gel’ synthesis of a glycidoxy-organosilane derivative in basic conditions, spin-coating of the product obtained on a silica substrate and subsequent drying. The bottom part of the film formed, less condensed than its upper counterpart, takes up water preferentially. Simply dipping it in water creates a strain that is sufficient to provoke scrolling. Species such as molecules or particles can be trapped within the resulting microtubes, whose diameters are controlled by adjusting the processing conditions. This simple and convenient method may facilitate preparation of rolls for functional materials. Strain-driven micro- and nanorolls fabrication is generally restricted to multilayer and multiprocessing systems, which limit the possibility of exploiting the self-organization at different length scales. We have designed a hybrid organic–inorganic film whose surface shows a selective response to external stimuli, which induces mechanical strain and self-rolling in one-step–one-layer fabrication. The scrolling is initiated by water and any aqueous solution that also contains molecules or colloidal particles. During scrolling, the different species in solution remain entrapped in the rolls, giving rise to functional microrolls.
TL;DR: In this article, a facile and reliable approach for the assembly of crack-free single-crystalline photonic crystals (PCs) with centimeter scale by the synergistic effects of substrate deformation and monomer infiltration/polymerization is presented.
Abstract: We present a facile and reliable approach for the assembly of crack-free single-crystalline photonic crystals (PCs) with centimeter scale by the synergistic effects of substrate deformation and monomer infiltration/polymerization. The critical thickness of crack-free PCs is ∼5.6 μm, below which crack-free PCs can be fabricated on proper substrate. The co-assembling monomer infiltrates and polymerizes in the interstices of the colloidal spheres to form an elastic polymer network, which could lower the tensile stress generated from colloid shrinkage and strengthen the long range interactions of the colloidal spheres. Otherwise, the timely transformation of the flexible substrate releases the residual stress. This approach to centimeter-scale crack-free single-crystalline PCs will not only prompt the practical applications of PCs in high-performance optic devices, but also have great implications for the fabrication of crack-free thin films in other fields, such as wet clays, coating and ceramic industry.
TL;DR: Yang et al. as mentioned in this paper used gold nanoparticles (AuNPs) to detect copper ions (Cu2+), whose accumulation in the body has been linked to several diseases.
Abstract: In this study, a novel method for the fast, sensitive and selective detection of Cu2+ using gold nanoparticles (AuNPs) was developed and used in immunoassays. In the presence of L-cysteine, L-cysteine can bind to the surface of citrate-stabilized AuNPs through Au-S bonds. As a result, aggregation of AuNPs occurs through electrostatic interactions between the cysteine-bound AuNPs. In contrast, in the presence of Cu2+, Cu2+ can catalyze O2 oxidation of cysteine, leading to the quick formation of disulfide cystine. An increase in the concentration of Cu2+ decreased L-cysteine-induced AuNPs aggregation by decreasing the number of free cysteine thiol groups, and the solution color changed from purple to red. Therefore, the concentration of Cu2+ can be detected with the naked eye or with ultraviolet–visible spectroscopy, and the detection limits of Cu2+ were 20 nM and 10 nM, respectively. This sensitivity was approximately three orders of magnitude higher than that of traditional AuNPs-based colorimetric Cu2+ detection methods. Because of the high sensitivity of the proposed method, we further used it with a labeled antibody in colorimetric immunoassays. The detection limit of the cancer biomarker α-fetoprotein was 2 ng ml−1, which is comparable to the detection limit of the enzyme-linked immunosorbent assay method. Huang-Hao Yang and co-workers at Fuzhou University have devised an ultra-sensitive method to detect copper ions (Cu2+), whose accumulation in the body has been linked to several diseases. The researchers' method relies on gold nanoparticles, popular in colourimetric sensing because they turn a solution from red to purple on aggregation. Here, however, instead of triggering the aggregation directly, the copper ions catalyse a ‘supporting reaction’ – the oxidation of a monomeric amino acid (cysteine) into a dimeric one (cystine). Only cysteine triggers the aggregation of the nanoparticles, which means the presence or absence of copper results in a red or purple solution, respectively. The method's sensitivity is very high because only catalytic quantities of copper are needed. The researchers further used this rapid, convenient, sensitive method in an immunoassay for a human protein. A novel method based on the AuNPs for fast, sensitive and selective detection of Cu2+ was developed and applied in immunoassays.
TL;DR: Choi et al. as discussed by the authors showed that zinc phthalocyanine (ZnPc) nanowires (NWs) directly grown from zinc powder by vaporization-condensation-recrystallization process show surprisingly increased water dispersibility without any functionalization.
Abstract: The phototherapy is one of the widely accepted noninvasive clinical methodologies to eradicate cancer cells owing to its minimal side effects and high selectivity to the light of specific wavelength. As represented by photodynamic (PD) and photothermal (PT) therapy, the phototherapy requires light and photosensitizer to generate reactive oxygen species and heat, respectively. Zinc phthalocyanine (ZnPc) is one of the promising photosensitizers as it has a strong absorption cross-section in the spectral range of 650–900 nm that guarantees maximum tissue penetration. One critical issue in using Pc molecule, including ZnPc as a biocompatible sensitizer is the poor water solubility. To increase water solubility, various chemical modifications inducing hydrophilicity have been widely attempted to introduce various functional groups in the ZnPc backbone. We report that ZnPc nanowires (NWs) directly grown from ZnPc powder by vaporization–condensation–recrystallization process show surprisingly increased water dispersibility without any functionalization. The ZnPc NW solution exhibits highly efficient dual PD and PT effects upon the irradiation of near infrared (808 nm) laser. The dual phototherapeutic effect of ZnPc NW is proven to enhance cytotoxic efficiency according to both in vitro and in vivo experimental results. Hee Cheul Choi, Sang Ho Lee and co-workers have devised a way to improve the dispersibility of light-sensitive molecules in water. Using light to treat medical conditions, including tumours, can be less invasive and toxic than other approaches. Such photodynamic and photothermal therapies rely on a light-sensitive molecule — a photo-sensitizer — that is excited under irradiation to release either reactive oxygen species or heat, respectively, which in turn can destroy targeted cells. Most photo-sensitizers, however, suffer from poor solubility in aqueous physiological media, which hinders their applications in the body. This is the case for zinc phthalocyanine, a macrocyclic compound hosting a zinc atom in its central cavity. Rather than trying to alter its chemical composition, the researchers have now observed that converting the powder form into crystalline nanowires significantly increased its dispersibility in water. Furthermore, the nanowires were found to be promising for both photothermal and photodynamic therapies. Water-dispersed nanowires for phototherapy: Without passivation of any water-friendly functional groups in its backbone, one-dimensional zinc phthalocyanine nanowires show remarkably increased dispersibility in water. Upon irradiation with near infrared light, the zinc phthalocyanine nanowires exhibit dual photodynamic and photothermal properties, which enhance the cytotoxic efficiency against tumor cells.
TL;DR: In this article, the authors review how chiral-responsive polymers can convey a signal from the molecular to the macroscopic level, which can be exploited to construct functional devices, such as for sensing or electronic applications, and to control the conformation of inherently chiral biosystems.
Abstract: Chirality – the ‘handedness’ of entities whose mirror images of each other are not superimposable, such as our left and right hands, or helices that twist in opposite directions – is a crucial concept in chemistry and biology: changing the handedness of chiral molecules has a profound impact on their properties. Guangyan Qing and Taolei Sun review how chiral-responsive polymers can convey a signal from the molecular to the macroscopic level. Two strategies can be adopted: incorporating chiral units into the structure of stimuli-responsive polymers, or altering interactions between polymers and chiral molecules. Specific triggers, such as chemical or thermal signals, alter the chirality of these systems, which in turn affect their macromolecular and materials properties. This can be exploited to construct functional devices, such as for sensing or electronic applications, and to control the conformation of inherently chiral biosystems.
TL;DR: Tissue cultures in a microfluidic chip that allows deterministic patterning of cells in 2D/3D offer new opportunities to achieve active control of 2D cellular patterns and 3D multicellular spheroids on demand, and may be amenable toward the study of the metastatic processes by in vitro modeling.
Abstract: A team of researchers based in Taiwan and Singapore, led by Andrew Wo, has constructed a microfluidic chip that enables cells to be cultured into either two-dimensional monolayer or three-dimensional spheroid geometries. Although methods for patterning tissue cultures are known, they typically require complex procedures or involve significant cell waste. The microfluidic chip devised by the researchers is comprised of two microchannels separated by a perforated membrane. Cells loaded onto the chip are efficiently trapped and cultured into specific patterns that are determined by judiciously chosen extracellular matrix molecules used to coat holes in the membrane. Use of a protein or a surfactant ‘Pluronic’ polymer coating led to the formation of a monolayer 2D cellular pattern or a 3D multicellular spheroid one, respectively. Furthermore, 3D patterning induced a change in the cells from ‘epithelial’ towards ‘mesenchymal’ characteristics. These chips may find applications in the study of biological processes.
TL;DR: Jung et al. as discussed by the authors proposed a method for liquid crystal alignment using nano-patterns of electrically conductive indium-tin oxide (ITO) layers with high resolution (ca < 20nm) and high aspect ratio (ca 10), fabricated based on the secondary sputtering phenomenon.
Abstract: We describe a novel method for liquid crystal (LC) alignment using nano-patterns of electrically conductive indium–tin oxide (ITO) layers with high resolution (ca< 20 nm) and high aspect ratio (ca 10), fabricated based on the secondary sputtering phenomenon. The ITO pattern developed in this manner not only provides high anchoring energy comparable to that of rubbed polyimides, but also maintains its low resistivity as an electrode. As a result, the patterned ITO can function as an electrode and alignment layer at the same time, which facilitates successful fabrication of bifunctional conductive alignment layer for LC devices. The LC cells fabricated using patterned ITO substrates show highly stable alignment of LCs over large area and good electro-optical responses. Moreover, systematic approach made by the precise control of pattern dimensions allows us to estimate a critical anchoring energy required for an effective LC alignment based on Berreman's theory. Hee-Tae Jung, Shin-Woong Kang and co-workers have devised an efficient way to prepare liquid-crystal devices. These devices comprise a layer of liquid crystals – molecules that flow as in a liquid state yet can be aligned over large areas in a crystalline manner – sandwiched between two electrodes. Controlling the orientation of the liquid crystals can be used to modulate light, but this is usually achieved through additional components or processing steps. Relying on a lithographic technique, the researchers have now used ion bombardment and a mould material to create stripes on the surface of an electrically conductive indium tin oxide surface. The resulting material is bifunctional, serving as both an electrode and a way to control the alignment of the liquid crystals over large domains. Devices constructed using indium tin oxide patterned in this way have shown good electro-optical properties, making this technique promising for practical applications. We describe a novel method for liquid crystal (LC) alignment using nano-patterns of electrically conductive indium–tin oxide (ITO) layers with high resolution (ca<20 nm) and high aspect ratio (ca 8), fabricated based on the secondary sputtering phenomenon. The ITO pattern developed in this manner can function as an electrode and alignment layer at the same time, which facilitates successful fabrication of bifunctional conductive alignment layer for LC devices.
TL;DR: Yang-Fang Chen et al. as mentioned in this paper used a tin oxide nanowire between two nickel "ferromagnetic" electrodes and the resulting device was subjected to a magnetic field.
Abstract: Yang-Fang Chen and co-workers from the National Taiwan University have dramatically enhanced the photoresponse of tin oxide semiconductor nanowires using a magnetic field. Tin oxide nanowires can produce a photocurrent under irradiation through the separation of electron–hole pairs at an irradiated location — an effect that makes the nanowires attractive components for a variety of devices including gas sensors and solar cells. The photoresponse depends on the nanowires' morphology, the presence of other ‘dopant’ species, and can be typically tuned through an electric field. The researchers have now devised a system in which the photocurrent can be amplified — by up to 20 times — using a magnetic field instead. A tin oxide nanowire is placed between two nickel ‘ferromagnetic’ electrodes and the resulting device subjected to a magnetic field. The high photoresponse observed is attributed to a migration of electrons towards the surface of the nanowires, induced by the electrodes' magnetization. This combination of nanowires with ferromagnetic materials may serve in future to fabricate efficient optoelectronic devices.
TL;DR: In this article, the conformational and structural details of peptide-mimic poly(n-hexyl isocyanate) (PHIC) are reported for the first time.
Abstract: We report for the first time the conformational and structural details of peptide-mimic poly(n-hexyl isocyanate) (PHIC). PHIC is a representative poly(n-alkyl isocyanate)s, which have received significant attention because of their unique stiff chain characteristics and potential applications in various fields. A well-ordered hexagonal close packing structure of PHIC with 83 helical conformation was clearly observed in the nanoscale thin films that were selectively annealed with carbon disulfide (CS2). A well-ordered multi-bilayer structure of the polymer with β-sheet conformation was also clearly formed in the films that were selectively annealed with toluene. In addition, a fully reversible transformation between these two self-assembled structures was demonstrated by consecutive annealings with CS2 and toluene. A family of peptide-mimic polymers — polyisocyanates with linear alkyl side groups — are known to have a stiff helical backbone. These structural features have garnered attention for the development of chiral recognition, optical switches, liquid crystals or degradable materials. Yet the exact conformation the chains adopt, and how they pack in the solid state, remains unclear. Through detailed characterization, Moonhor Ree, Jae-Suk Lee and co-workers in Korea have now confirmed that, in a thin film, the polymer ‘poly(n-hexyl isocyanate)’ forms one of two different, well-ordered structures. The two morphologies were obtained, and reversibly converted into each other, by annealing under different solvent vapours. In the presence of carbon disulfide, helical chains self-assembled into a hexagonal close packing structure, whereas the use of toluene yielded a multi-bilayer lamellar structure consisting of polymer chains in β-sheet conformation. This intriguing transformation arises from the solvent molecules' different affinities with the backbone and side groups of the polymer chain. Peptide-mimic poly(n-hexyl isocyanate) (PHIC) with stiff chain characteristics demonstrated to selectively form a well-ordered hexagonal close packing structure with 83 helical conformation in the nansocale thin films annealed with carbon disulfide. Moreover, this polymer showed to selectively form a well-ordered multi-bilayer structure with β-sheet conformation in the thin films annealed with toluene. These two self-assembled structures were reversibly transformed by consecutive annealing with carbon disulfide and toluene. These chain conformations and self-assembled structures were confirmed by synchrotron grazing incidence X-ray scattering analysis.
TL;DR: Guo et al. as discussed by the authors incorporated both methyl groups and hydrogen atoms to the sheet in a controlled, and reversible, manner, which may enable in future the preparation of advanced materials for applications in sensing or optoelectronic devices.
Abstract: The discovery of graphene — a sheet of graphite that is only one atom thick — has sparked much enthusiasm in the science and technology communities. Dubbed ‘wonder material’ owing to its intriguing and promising properties, graphene is poised to play a crucial role in applications that range from electronic to biomedical devices; however, tuning its properties remains challenging. Grafting methyl (–CH3) groups on its surface, for example, can open a band gap in its electronic structure, but too many functional groups will damage the original sheet. Xuefeng Guo and co-workers from Peking University have now described a route that circumvents previous issues. Through a mild gas-phase reaction between graphene and methane plasma, the researchers incorporated both methyl groups and hydrogen atoms to the sheet in a controlled, and reversible, manner. This process, which introduces two functional groups, may enable in future the preparation of advanced materials for applications in sensing or optoelectronic devices.
TL;DR: In this paper, Zhao et al. showed that the thermal expansion undergone by the tough core does not match that of the brittle shell, creating longitudinal and circumferential stresses, in turn causing the knots to crack into helical coils, whose shapes depend on the initial formation process.
Abstract: Materials are prone to crack under stress — this can either cause materials failure or, when deliberately induced, offer a useful manufacturing step. In both situations, knowing how to control and predict how materials crack will help in their design and synthesis. Yet exerting control is difficult — for example, we have all seen pottery cracked along random directions. Yong Zhao and co-workers have now prepared core–shell fibres that undergo helical cracking at specific positions. A tough glass fibre was dip-coated with a brittle metal oxide film featuring regular spindle knots. On calcination, the thermal expansion undergone by the tough core does not match that of the brittle shell, creating longitudinal and circumferential stresses. The stress lines in turn cause the knots to crack into helical coils, whose shapes depend on the initial formation process. These findings represent a step forward along the way of controllable fracture.
TL;DR: In this article, the volume number for the original PDF version of this article was incorrect, and the correct volume number is 4. The publisher would like to apologize for the mistake.
Abstract: Correction to: NPG Asia Materials 4, e9; doi:10.1038/am.2012.16; published online 9 March 2012 The volume number for the original PDF version of this article was incorrect. The correct volume number is 4. The publisher would like to apologize for the mistake.
TL;DR: In this paper, the authors have studied an unconventional polar switching associated with an electro-optical response in the columnar oblique phase of a dipeptide derivative, where the cross-section of the columns is birefringent, and the principal axis rotates about the column axis by applying an electric field parallel to the columnaxis, yielding the following characteristics: (1) the rotation angle exhibits linear dependence on an applied electric field; (2) the rotational sense is reversed by reversing the field direction; and (3) the optical isomers exhibit
Abstract: We studied unconventional polar switching associated with an electro–optical response in the columnar oblique phase of a dipeptide derivative. Slow and careful cooling allows us to obtain a large monodomain with the column axis perpendicular to the substrates. The cross-section of the columns is birefringent, and the principal axis rotates about the column axis by applying an electric field parallel to the column axis, yielding the following characteristics: (1) the rotation angle exhibits linear dependence on an applied electric field; (2) the rotational sense is reversed by reversing the field direction; and (3) the optical isomers exhibit opposite rotational sense. A second-harmonic generation (SHG) signal was observed only under an electric field. We observed a dependence of the SHG intensity and infrared (IR) absorption on the incidence angle. Asymmetric and symmetric variations were observed when the sample was rotated about the slow and fast in-plane optical axes, respectively. From these experimental results, we proposed a model of molecular packing in the columnar phase; the molecules stack with their molecular planes tilted from the column axis, and the polar order is cancelled within the neighboring columns. Hideo Takezoe and colleagues have described an unusual electro-optical behaviour of peptide derivatives. Studying biomolecules and their properties is important in order to gain better understanding of biosystems, as well as in the design of biomimetic materials for specific purposes. Some polypeptide derivatives are known to have the ability to form liquid crystalline columns. Studying such a dipeptide-based molecule, Takezoe and co-workers succeeded in forming a very large domain of columns ordered in two dimensions and observed that, under an external electric field judiciously chosen, the columns rotate around their long axis. Moreover, the angle and direction of the rotation depend on the strength and direction of the field. The phenomenon is accompanied by a change in optical properties and arises, as the researchers propose, through an interplay between polarity and chirality within the columns. We have studied an unconventional polar switching associated with an electro–optical response in the columnar oblique phase of a dipeptide derivative. Observations were made using a large monodomain with the column axis perpendicular to substrates, as shown here. The interplay between polarity and chirality was found as the rotation of columns about the column axis, that is, the rotation angle linearly depends on an applied electric field and the rotational sense is reversed by either reversing the field direction or using opposite isomers. On the basis of the detailed SHG and FT-IR measurements, molecular and polar structures are shown.