Articles in 2012

The key factor and mechanism for reported toxicity of CNTs are unclear. Here we firstly quantify the contribution of metal residues and fiber structure to the toxicity of CNTs. Significant quantities of metal can be mobilized from CNTs into surrounding fluids, depending on the properties and constituent of biological microenvironment and metal particles. Hydroxyl radicals were generated by CNT containing metal impurities and leachable metal, while several inherent biomolecules facilitate the generation of free radical. Cell viability is highly dependent on the amount of metal residues and iron in particular but not tube structure, while the negative effect of CNT was limited in a certain concentration range below 80 μg ml⁻¹.

Graphene, owing to its remarkable electronic and structural properties, has attracted considerable attention in both science and technology communities. However, a major roadblock to the realization of graphene-based field-effect transistors is the fact that large-area graphene behaves like a semimetal with zero bandgap, making it unsuitable for real applications in sensing, detecting and switching systems. Surface functionalization could result in the construction of periodic micro/nanostructures by breaking sp² bonds and forming sp³ bonds. Therefore, direct chemical grafting might provide a useful way to covalently modify graphene for tailoring its properties. Owing to the inert reactivity of its surface, however, up to date only few chemical reactions were used to modify its atomic structure. Here, we demonstrate a controllable and efficient means of mild plasma methylation to manipulate the reversible interconversion of two distinct species of graphene (one crystalline and the other methylated). The strategy of incorporating diverse functional substituents (methyl group and hydrogen atoms here) into graphene instead of a single type of chemical groups could provide a useful route for the development of different applications, such as chemical/biosensors and multifunctional electrical circuits. Moreover, the methylated graphene with fine tunability is stable at room temperature, which suggests the intrinsic potential of novel applications in graphene-based optoelectronic devices that invites further studies.

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.

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.

Increasing the Seebeck coefficient has long been pursued for increasing thermoelectric efficiency, but other changes in transport properties may compensate this effect and ultimately lead to no improvement in figure of merit. The Seebeck coefficient can be enhanced by either the addition of resonant states or the involvement of multiple band conduction. This work demonstrates the beneficial effect of multiple band conduction for highefficiency thermoelectrics.

We report a microfluidic chip integrated with a bioengineered membrane for two-dimensional (2D) and three-dimensional (3D) spheroid tissue cultures to achieve deterministic patterning of cells. The cell-supporting membrane was selectively deposited with extracellular matrix molecules. Results show cell-trapping rate attains 97%. Tuning of the surface enables not only highly controlled geometry of the monolayer (2D) cell mass but also 3D culture of uniformly sized multicellular spheroids. The 3D spheroids of human ovarian epithelial cancer cells acquired mesenchymal traits—increased expressions of N-cadherin, vimentin and fibronectin—and lowered expression of epithelial marker (CD326/epithelial cell adhesion molecule) compared with that in 2D cultures, indicative of epithelial–mesenchymal transition. These results offer new opportunities to achieve active control of 2D cellular patterns and 3D multicellular spheroids on demand, and may be amenable toward study of the metastatic process in vitro.

We report the first attempt of magnetic manipulation of photoresponse in an one-dimensional device, in which a highly sensitive photodetector in the UV region composed of tin oxide nanowire and ferromagnetic nickel electrodes have been fabricated and characterized. Surprisingly, as the Nickel electrodes were magnetized, the photocurrent gain can be greatly enhanced by up to 20 times. The underlying mechanism is attributed to both oxygen molecules adsorbed and surface band bending effects due to the migration of electrons to the surface of tin oxide nanowire caused by the magnetic field of ferromagnetic electrodes.

Barcodes that composed of multiple colloidal crystal or magnetic-tagged ETPTA cores and PEG hydrogel shells were developed by using microfluidics. As the cores are with distinct reflection peaks, the barcodes allow for substantial number of coding levels for multiplexing. The hydrogel shells surrounding the barcodes enable the creation of three-dimensional scaffolds for immobilizing probes. Moreover, the presence of magnetism in the barcodes confer them controllable movement under magnetic fields, which could significantly increase the sensitivity and simplify the processing of the bioassays.

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.

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.

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.

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.

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.

Nonvolatile memory devices based on hybrid inorganic/organic nanocomposites have emerged as excellent candidates for promising applications in next-generation electronic and optoelectronic devices because of their advantages of high-mechanical flexibility, simple fabrication and low cost. As shown in the figure, the resistive switching of a nanocomposite sandwiched between two electrodes enables the cross-point where A and B cross to work as a memory cell for data storage. To date, various nanomaterials and device structures have been developed to optimize the memory properties of hybrid nanocomposites.

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.

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.

Regular microhelics on a heterogenous spindle knot are obtained by controlled biaxial stresses in three dimensions. The spindle knot has a tough core and a brittle shell, resulting in biaxial stresses that arise from a thermal expansion mismatch during a heating process. Surface cleavage and interface delamination are harmonized due to the special spindle geometry and cooperate to 3D helical crack. This study not only widens our understanding of the cracking phenomena, but also sheds light on the control and design of regular cracks in arbitrary dimensions. It holds promise for applications in eliminating or controlling cracks for manufacturing process, especially at micro/nanosales, which domains are difficult to be generated by routine methods.

Recent developments in advanced semiconductor nanomaterials and methods for their assembly establish new, important capabilities in flexible and stretchable electronics and optoelectronics. This review describes the most successful materials, mechanics and manufacturing strategies, and illustrates their use in bio-integrated devices designed for basic measurements of cellular electrophysiology and multimodal sensing suitable for clinical applications. Opportunities span a variety of biomedical applications including skin-based, neural, and cardiovascular monitoring and therapy.

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.