Large-Area Graphene Nanodot Array for Plasmon-Enhanced Infrared Spectroscopy.

Graphene nanodot arrays (GNDAs) are fabricated by block copolymer lithography in a high-throughput manner. The GNDA shows strong broadband plasmonic resonances in the mid-IR region with high localized field enhancement, thus allowing plasmon-enhanced infrared spectroscopy with reliable sensitivity and selectivity to be performed.

Large-scale production of graphene nanoribbons from electrospun polymers.

Graphene nanoribbons (GNRs) are promising building blocks for high-performance electronics due to their high electron mobility and dimensionality-induced bandgap. Despite many past efforts, direct synthesis of GNRs with controlled dimensions and scalability remains challenging. Here we report the scalable synthesis of GNRs using electrospun polymer nanofiber templates. Palladium-incorporated poly(4-vinylphenol) nanofibers were prepared by electrospinning with controlled diameter and orientation. Highly graphitized GNRs as narrow as 10 nm were then synthesized from these templates by chemical vapor deposition. A transport gap can be observed in 30 nm-wide GNRs, enabling them to function as field-effect transistors at room temperature. Our results represent the first success on the scalable synthesis of highly graphitized GNRs from polymer templates. Furthermore, the generality of this method allows various polymers to be explored, which will lead to understanding of growth mechanism and rational control over crystallinity, feature size and bandgap to enable a new pathway for graphene electronics.

Repair of Osteochondral Defects With Predifferentiated Mesenchymal Stem Cells of Distinct Phenotypic Character Derived From a Nanotopographic Platform.

BACKGROUND: Articular cartilage has a zonal architecture and biphasic mechanical properties. The recapitulation of surface lubrication properties with high compressibility of the deeper layers of articular cartilage during regeneration is essential in achieving long-term cartilage integrity. Current clinical approaches for cartilage repair, especially with the use of mesenchymal stem cells (MSCs), have yet to restore the hierarchically organized architecture of articular cartilage. HYPOTHESIS: MSCs predifferentiated on surfaces with specific nanotopographic patterns can provide phenotypically stable and defined chondrogenic cells and, when delivered as a bilayered stratified construct at the cartilage defect site, will facilitate the formation of functionally superior cartilage tissue in vivo. STUDY DESIGN: Controlled laboratory study. METHODS: MSCs were subjected to chondrogenic differentiation on specific nanopatterned surfaces. The phenotype of the differentiated cells was assessed by the expression of cartilage markers. The ability of the 2-dimensional nanopattern-generated chondrogenic cells to retain their phenotypic characteristics after removal from the patterned surface was tested by subjecting the enzymatically harvested cells to 3-dimensional fibrin hydrogel culture. The in vivo efficacy in cartilage repair was demonstrated in an osteochondral rabbit defect model. Repair by bilayered construct with specific nanopattern predifferentiated cells was compared with implantation with cell-free fibrin hydrogel, undifferentiated MSCs, and mixed-phenotype nanopattern predifferentiated MSCs. Cartilage repair was evaluated at 12 weeks after implantation. RESULTS: Three weeks of predifferentiation on 2-dimensional nanotopographic patterns was able to generate phenotypically stable chondrogenic cells. Implantation of nanopatterned differentiated MSCs as stratified bilayered hydrogel constructs improved the repair quality of cartilage defects, as indicated by histological scoring, mechanical properties, and polarized microscopy analysis. CONCLUSION: Our results indicate that with an appropriate period of differentiation, 2-dimensional nanotopographic patterns can be employed to generate phenotypically stable chondrogenic cells, which, when implanted as stratified bilayered hydrogel constructs, were able to form functionally superior cartilage tissue. CLINICAL RELEVANCE: Our approach provides a relatively straightforward method of obtaining large quantities of zone-specific chondrocytes from MSCs to engineer a stratified cartilage construct that could recapitulate the zonal architecture of hyaline cartilage, and it represents a significant improvement in current MSC-based cartilage regeneration.

Assembly of polystyrene microspheres and its application in cell micropatterning.

Cell micropatterning has important applications in the development of biosensors and lab-on-a-chip devices, tissue engineering and fundamental cell biology studies. The conventional micropatterning techniques involve patterning of cells over a planar substrate. In this paper, we propose the introduction of topographical features on cell adhesive regions to enhance cell adhesion and function. The textured surface is created by assembly of polystyrene microspheres and the topographical parameters can be varied systematically by changing the size and density of the particles. A technique of generating spatial arrangement of microspheres on a non fouling background is developed. This is achieved by using a bi-functional template which has a patterned hydrophobic parylene film to facilitate self-assembly of particles; after assembly, the film is lift off, revealing a cell resistance background which is compatible with cell micropatterning. Particles were assembled by selective wetting of the hydrophobic-hydrophilic template. A fluidic chamber was designed to control the movement of the particle suspension across the template so as to attain uniform particle array over large area. This method of cell micropatterning can improve the efficiency and functionality of cell-based devices. It can also be used for examining the effects of topographical cues on cell-substrate adhesion which can provide valuable insights into cell biology and design of biomaterials.

Micropatterning of polystyrene nanoparticles and its bioapplications.

Micropatterning of biomolecules forms the basis of cell culture, biosensor and microarray technology. Currently, the most widely used techniques are photoresist lithography, soft lithography or using robots which all involve multi-step surface modification directly on a planar substrate. Here we report a method to pattern biomolecules through self-assembling polystyrene nanoparticles in arrayed microwells on a solid surface to form well-ordered patterning, followed by attaching biomolecules to the assembled nanoparticles. The formation of colloidal patterns depends on capillary force, surface wettability and physical confinement. This method can be used for micropatterning a variety of biomolecules such as protein and antibody.

Hierarchically built gold nanoparticle supercluster arrays as charge storage centers for enhancing the performance of flash memory devices.

Flash memory devices with high-performance levels exhibiting high charge storage capacity, good charge retention, and high write/erase speeds with lower operating voltages are widely in demand. In this direction, we demonstrate hierarchical self-assembly of gold nanoparticles based on block copolymer templates as a promising route to engineer nanoparticle assemblies with high nanoparticle densities for application in nanocrystal flash memories. The hierarchical self-assembly process allows systematic multiplication of nanoparticle densities with minimal increase in footprint, thereby increasing the charge storage density without an increase in operating voltage. The protocol involves creation of a parent template composed of gold nanoclusters that guides the self-assembly of diblock copolymer reverse micelles which in turn directs electrostatic assembly of gold nanoparticles resulting in a three-level hierarchical system. Capacitance-voltage (C-V) measurements of the hierarchical nanopatterns with a metal-insulator-semiconductor capacitor configuration reveal promising enhancement in memory window as compared to nonhierarchical nanoparticle controls. Capacitance-time (C-t) measurements show that over half the stored charges were retained when extrapolated to 10 years. The fabrication route can be readily extended to programmed density multiplication of features made of other potential charge storage materials such as platinum, palladium, or hybrid metal/metal oxides for next generation, solution-processable flash memory devices.

Direct growth of aligned graphitic nanoribbons from a DNA template by chemical vapour deposition.

Graphene, laterally confined within narrow ribbons, exhibits a bandgap and is envisioned as a next-generation material for high-performance electronics. To take advantage of this phenomenon, there is a critical need to develop methodologies that result in graphene ribbons <10 nm in width. Here we report the use of metal salts infused within stretched DNA as catalysts to grow nanoscopic graphitic nanoribbons. The nanoribbons are termed graphitic as they have been determined to consist of regions of sp(2) and sp(3) character. The nanoscopic graphitic nanoribbons are micrometres in length, <10 nm in width, and take on the shape of the DNA template. The DNA strand is converted to a graphitic nanoribbon by utilizing chemical vapour deposition conditions. Depending on the growth conditions, metallic or semiconducting graphitic nanoribbons are formed. Improvements in the growth method have potential to lead to bottom-up synthesis of pristine single-layer graphene nanoribbons.

Nanoparticle cluster arrays for high-performance SERS through directed self-assembly on flat substrates and on optical fibers.

We demonstrate template-guided self-assembly of gold nanoparticles into ordered arrays of uniform clusters suitable for high-performance SERS on both flat (silicon or glass) chips and an optical fiber faucet. Cluster formation is driven by electrostatic self-assembly of anionic citrate-stabilized gold nanoparticles (~11.6 nm diameter) onto two-dimensionally ordered polyelectrolyte templates realized by self-assembly of polystyrene-block-poly(2-vinylpyridine). A systematic variation is demonstrated for the number of particles (N ≈ 5, 8, 13, or 18) per cluster as well as intercluster separations (S(c) ≈ 37-10 nm). Minimum interparticle separations of <5 nm, intercluster separations of ~10 nm, and nanoparticle densities on surfaces as high as ~7 × 10(11)/in.(2) are demonstrated. Geometric modeling is used to support experimental data toward estimation of interparticle and intercluster separations in cluster arrays. Optical modeling and simulations using the finite difference time domain method are used to establish the influence of cluster size, shape, and intercluster separations on the optical properties of the cluster arrays in relation to their SERS performance. Excellent SERS performance, as evidenced by a high enhancement factor, >10(8) on flat chips and >10(7) for remote sensing, using SERS-enabled optical fibers is demonstrated. The best performing cluster arrays in both cases are achievable without the use of any expensive equipment or clean room processing. The demonstrated approach paves the way to significantly low-cost and high-throughput production of sensor chips or 3D-configured surfaces for remote sensing applications.

Protein micropatterning using surfaces modified by self-assembled polystyrene microspheres.

A technique for micropatterning of proteins on a nonplanar surface to improve the coverage and functionality of biomolecules is demonstrated. A nonplanar microstructure is created by the self-assembly of polystyrene microspheres into an array of microwells on a silicon wafer to allow the integration of a nonplanar spot on a planar chip. After the microspheres were deposited into the microwells, they were conjugated with proteins. The curve surfaces of the microspheres present more surface area for attaching biomolecules which will increase the density of biomolecules and, hence, the sensitivity for detection. Moreover, proteins immobilized on a curved surface can retain their native structures and function better than on a planar surface because of a smaller area of interaction between the protein and the substrate. Patterning of biomolecules was tested with two model fluorescent proteins. The results show that precise patterning of biomolecules on a nonplanar spot can be achieved with this technique.