Carbon nanofiber-based glucose biosensor

The use of highly activated carbon nanofibers for the design of catalytic electrochemical biosensors is demonstrated. The direct immobilization of enzymes onto the surface of carbon nanofibers is shown to be a highly efficient method for the development of a new class of very sensitive, stable, and reproducible electrochemical biosensors. These results establish the fact that the carbon nanofiber is the best matrix so far described for the development of biosensors, far superior to carbon nanotubes or graphite powder.     

Single DNA molecule patterning for high-throughput epigenetic mapping

We present a method for profiling the 5-methyl cytosine distribution on single DNA molecules. Our method combines soft-lithography and molecular elongation to form ordered arrays estimated to contain more than 250 000 individual DNA molecules immobilized on a solid substrate. The methylation state of the DNA is detected and mapped by binding of fluorescently labeled methyl-CpG binding domain peptides to the elongated dsDNA molecules and imaging of their distribution. The stretched molecules are fixed in their extended configuration by adsorption onto the substrate so analysis can be performed with high spatial resolution and signal averaging. We further prove this technique allows imaging of DNA molecules with different methylation states.     

H2O2活化聚酰亚胺碳纳米纤维无纺布及其储电性能

聚酰亚胺碳纳米纤维无纺布经双氧水在氮气氛中750℃活化,使其比表面积增大,从而改善其储电性能.通过透射电镜观察活性碳纳米纤维的尺寸、形貌和结构;采用次甲基蓝水溶液吸附法测定活化碳纳米纤维的比表面积;用CHI660B电化学工作站测定该活性碳纳米纤维电极的储电性能.结果显示：活化后碳纳米纤维具有更大的比表面积,表面粗糙,电极材料的储电性能随活化程度的提高而增大;聚酰亚胺碳纳米纤维电极具有良好的超级电容器特性,在1 mol/L的H2SO4电解液中,经6 h活化后的碳纳米纤维电极具有良好的电荷储存能力,比电容量达到174.2 F/g.     

Microspotting streptavidin and double-stranded DNA arrays on gold for high-throughput studies of protein-DNA interactions by surface plasmon resonance microscopy

We present two strategies for microspotting 10 x 12 arrays of double-stranded DNAs (dsDNAs) onto a gold-coated glass slide for high-throughput studies of protein-DNA interactions by surface plasmon resonance (SPR) microscopy. Both methods use streptavidin (SA) as a linker layer between a biotin-containing mixed self-assembled monolayer (SAM) and biotinylated dsDNAs to produce arrays with high packing density. The primary mixed SAM is produced from biotin- and oligo(ethylene glycol)-terminated thiols bonded as thiolates onto the gold surface. In the first method, a robotic microspotter is used to deliver nanoliter droplets of dsDNA solution onto a uniform layer of this SA ( approximately 2 x 10(12) SA/cm(2)). SPR microscopy shows a density of (5-6) x 10(11) dsDNA/cm(2) (0.2-0.3 dsDNA/SA) in the array elements. The second method uses instead a microspotted array of this SA linker layer, onto which the microspots of dsDNA are added with spatial registry. SPR microscopy before addition of the dsDNA shows a SA coverage of 2 x 10(12) SA/cm(2) within the spots and a dsDNA density of 8.5 +/- 3.5 x 10(11) dsDNA/cm(2) (0.3-0.7 dsDNA/SA, depending on the length of dsDNA) after dsDNA spotting. We demonstrate the ability to simultaneously monitor protein binding with the SPR microscope in many 200-microm spots with 1-s time resolution and sensitivity to <1 pg of protein.     

A novel nano-nonwoven fabric with three-dimensionally dispersed nanofibers: entrapment of carbon nanofibers within nonwovens using the wet-lay process

This study demonstrates, for the first time, the manufacturing of novel nano-nonwovens that are comprised of three-dimensionally distributed carbon nanofibers within the matrices of traditional wet-laid nonwovens. The preparation of these nano-nonwovens involves dispersing and flocking carbon nanofibers, and optimizing colloidal chemistry during wet-lay formation. The distribution of nanofibers within the nano-nonwoven was verified using polydispersed aerosol filtration testing, air permeability, low surface tension liquid capillary porometry, SEM and cyclic voltammetry. All these characterization techniques indicated that nanofiber flocks did not behave as large solid clumps, but retained the 'nanoporous' structure expected from nanofibers. These nano-nonwovens showed significant enhancements in aerosol filtration performance. The reduction-oxidation reactions of the functional groups on nanofibers and the linear variation of electric double-layer capacitance with nanofiber loading were measured using cyclic voltammetry. More than 65 m2 (700 ft2) of the composite were made during the demonstration of process scalability using a Fourdrinier-type continuous pilot papermaking machine. The scalability of the process with the control over pore size distribution makes these composites very promising for filtration and other nonwoven applications.     

Clumping Criteria of Vertical Nanofibers on Surfaces

The side–side, side–tip, and tip–tip clumping of nanofibers, including nanowires and nanotubes on surfaces, is a common problem that can diminish their optical, electrical, and mechanical performance. However, these different clumping configurations brought much complexity and confused researchers to predict or design the desired clumping or nonclumping. In this study, a universal model in the unified formula for the critical clumping criteria for three contact geometries of nanofiber arrays is derived in terms of two‐dimensionless geometric and mechanical parameters, based on the length, radius, spacing, Young's modulus, and adhesion energy of the nanofibers. The model provides an easy way to predict the sequences of the three clumping configurations, which are successfully verified by analyzing various clumping structures reported in the literatures. This study provides new insights into, and methods for, designing nanofiber arrays on surfaces to achieve desired clumping or nonclumping structures.     

Hollow carbon nanofiber-encapsulated sulfur cathodes for high specific capacity rechargeable lithium batteries

Sulfur has a high specific capacity of 1673 mAh/g as lithium battery cathodes, but its rapid capacity fading due to polysulfides dissolution presents a significant challenge for practical applications. Here we report a hollow carbon nanofiber-encapsulated sulfur cathode for effective trapping of polysulfides and demonstrate experimentally high specific capacity and excellent electrochemical cycling of the cells. The hollow carbon nanofiber arrays were fabricated using anodic aluminum oxide (AAO) templates, through thermal carbonization of polystyrene. The AAO template also facilitates sulfur infusion into the hollow fibers and prevents sulfur from coating onto the exterior carbon wall. The high aspect ratio of the carbon nanofibers provides an ideal structure for trapping polysulfides, and the thin carbon wall allows rapid transport of lithium ions. The small dimension of these nanofibers provides a large surface area per unit mass for Li(2)S deposition during cycling and reduces pulverization of electrode materials due to volumetric expansion. A high specific capacity of about 730 mAh/g was observed at C/5 rate after 150 cycles of charge/discharge. The introduction of LiNO(3) additive to the electrolyte was shown to improve the Coulombic efficiency to over 99% at C/5. The results show that the hollow carbon nanofiber-encapsulated sulfur structure could be a promising cathode design for rechargeable Li/S batteries with high specific energy.     

Nanosized-bismuth-embedded 1D carbon nanofibers as high-performance anodes for lithium-ion and sodium-ion batteries

Bi is a promising candidate for energy storage materials because of its high volumetric capacity,stability in moisture/air,and facile preparation.In this study,the electrochemical performance of nanosized-Bi-embedded one-dimensional (1D) carbon nanofibers (Bi/C nanofibers) as anodes for Li-ion batteries (LIBs) and Na-ion batteries (NIBs) was systematically investigated.The Bi/C nanofibers were prepared using a single-nozzle electrospinning method with a specified Bi source followed by carbothermal reduction.Abundant Bi nanoparticles with diameters of approximately 20 nm were homogeneously dispersed and embedded in the 1D carbon nanofibers,as confirmed by structural and morphological characterization.Electrochemical measurements indicate that the Bi/C nanofiber anodes could deliver a long cycle life for LIBs and a preferable rate performance for NIBs.The superior electrochemical performances of the Bi/C nanofiber anodes are attributed to the 1D carbon nanofiber structure and uniform distribution of Bi nanoparticles embedded in the carbon matrix.This unique embedded structure provides a favorable electron carrier and buffering matrix for the effective release of mechanical stress caused by volume change and prevents the aggregation of Bi nanoparticles.     

Effect of electrospinning parameters on the nanofiber diameter and length

Polymer nanofibers exhibit properties that make them a favorable material for the development of tissue engineering scaffolds, filtration devices, sensors, and high strength lightweight materials. Electrospinning is a versatile method commonly used to manufacture polymer nanofibers. Collection of electrospun nanofibers across two parallel plates is a technique useful for creating nanofiber structures because it allows for the collection of linearly oriented individual nanofiber arrays and these arrays can be easily transferred to other substrates or structures. It is of importance to have some understanding of the capabilities of this collection method, such as the maximum length of fibers that can be collected across two parallel plates. The effect of different electrospinning parameters on maximum fiber length, average fiber diameter, diameter uniformity, and fiber quality was explored. It was shown that relatively long continuous polycaprolactone (PCL) nanofibers with average diameters from approximately 350 nm to 1 μm could be collected across parallel plates at lengths up to 35-50 cm. Experimental results lead to the hypothesis that even longer continuous nanofibers over 50 cm could be collected if the size of the parallel plates were increased. Extending the maximum fiber length that can be collected across parallel plates could expand the applications of electrospinning. Polymer solution concentration, plate size, and applied voltage were all shown to have varying effects on maximum fiber length, fiber diameter, and fiber uniformity.     

Interactions of benzyl viologen with surface-bound single- and double-stranded DNA

The interactions of benzyl viologen (BV) with single- and double-stranded calf-thymus DNA immobilized onto gold electrodes have been studied by electrochemical methods. Benzyl viologen interacts electrostatically with both double-stranded (ds) and single-stranded (ss) DNA, and the strength of the interactions is dependent on ionic strength (mu). The dicationic form (BV2+) binds to dsDNA 9 times more strongly than the singly reduced form, BV*+, in a pH 7.4 Tris-HCl buffer solution at mu = 8.4 mM. BV2+ binds to ssDNA 5 times more strongly than the BV*+ form. From measurements at mu = 8.4 mM, a binding constant (K2+) of 2.0 (+/-0.2) x 10(4) M(-1) and a binding site size (s) of 1 base pair were obtained, respectively, for dsDNA. For ssDNA, at the same ionic strength, the values obtained for K and s were 3.6 (+/-0.4) x10(4) M(-1) and 2 nucleotides, respectively. The amount of BV bound, whether to dsDNA or ssDNA, decreased with increasing ionic strength. Whereas the binding rate of BV to both dsDNA and ssDNA immobilized onto gold electrodes is relatively low, once immobilized, it dissociates rapidly away from the electrode surface. The electron-transfer rate constant for BV is moderately fast at both dsDNA- and ssDNA-modified gold electrodes. The application of benzyl viologen as an electroactive indicator capable of differentiating between surface-immobilized single- and double-stranded DNA in denaturation/regeneration cycles has been explored.     

Electrospinning Nanofibers as Uniaxially Aligned Arrays and Layer‐by‐Layer Stacked Films

The conventional procedure for electrospinning has been modified to generate nanofibers as uniaxially aligned arrays over large areas. The key to the success of this method was the use of a collector composed of two conductive strips separated by an insulating gap of variable width. Directed by electrostatic interactions, the charged nanofibers were stretched to span across the gap and became uniaxially aligned arrays. Two types of gaps have been demonstrated: void gaps and gaps made of a highly insulating material. When a void gap was used, the nanofibers could readily be transferred onto the surfaces of other substrates for various applications. When an insulating substrate was involved, the electrodes could be patterned in various designs on the solid insulator. In both cases, the nanofibers could be conveniently stacked into multi‐layered architectures with controllable hierarchical structures. This new version of electrospinning has already been successfully applied to a range of different materials that include organic polymers, carbon, ceramics, and composites.     

Processing and characterization of carbon nanofiber/syndiotactic polystyrene composites in the absence and presence of liquid crystalline polymer

Syndiotactic polystyrene (s-PS)/carbon nanofiber (CNF) composites were developed through melt process in a brabender mixer and then compression moulded. Thermal properties were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while morphologies of the composites were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The degree of polymer and nanofiber alignment was assessed using X-ray diffraction. The resistivity reduced with increase in loading of carbon nanofibers. Surface modification of the carbon nanofiber resulted in improved properties compared to as-received carbon nanofiber composites.Blending of liquid crystalline polymer (LCP A950) with s-PS/CNFs developed composites results in improved electrical and thermal properties. This improvement is ascribed to the self reinforcing tendency of LCPs due to their rigid rod-like molecular structure, which helps to concentrate and align the carbon nanofibers.     

Nondestructive replication of self-ordered nanoporous alumina membranes via cross-linked polyacrylate nanofiber arrays

Ordered nanofiber arrays are a promising material platform for artificial adhesive structures, tissue engineering, wound dressing, sensor arrays, and self-cleaning surfaces. Their production via self-ordered porous alumina hard templates serving as shape-defining molds is well-established. However, their release requires the destruction of the hard templates, the fabrication of which is costly and time-consuming, by wet-chemical etching steps with acids or bases. We report the nondestructive mechanical extraction of arrays of cross-linked polyacrylate nanofibers from thus recyclable self-ordered nanoporous alumina hard templates. Silica replicas of the latter were synthesized using the extricated nanofiber arrays as secondary molds that could be mechanically detached from the molded material. The approach reported here, which can be combined with microstructuring, may pave the way for the high-throughput production of both functional nanofiber arrays and ordered nanoporous membranes consisting of a broad range of material systems.     

改性条件对半导体Ni片上电纺丝沉积碳纳米纤维结构和性能的影响

选择乙醇电纺丝工艺制备碳纳米纤维,优化了工艺条件,并制备得到结构均匀的碳纳米纤维。选择EP溶液与水蒸气作为碳纳米纤维的改性介质,分析不同方法对碳纳米纤维进行表面改性的差异性。研究结果表明：通过乙醇电纺丝方法制备碳纳米纤维的最优条件为：锂盐溶液质量分数为70%,镍片-电纺丝间距1.5 cm,烧制时间为9 min。通过电纺丝工艺制得了高碳含量的碳纳米纤维。通过DFT方法进行分析发现其孔径尺寸为9.2 nm,微孔与介孔的孔容依次为0.094与0.213,形成了大量的微孔与介孔。EP-CNFs、Na-CNFs与CNFs都跟水形成了均匀混合状态,未出现分层的情况,而Wc-CNFs混合液形成了澄清液,说明Wc-CNFs已出现沉降的情况。采用EP改性方法可以使EP活化基团和碳纳米纤维活性基团发生相互作用,增强碳纳米纤维表面极性,避免发生团聚,达到更稳定的分散状态。     

Transparent liquid-crystal-based microlens array using vertically aligned carbon nanofiber electrodes on quartz substrates

A novel transparent liquid-crystal-based microlens array has been fabricated using an array of vertically aligned multi-wall carbon nanofibers (MWCNFs) on a quartz substrate and its optical characteristics investigated. Electron beam lithography was used for the catalyst patterning on a quartz substrate to grow the MWCNF array of electrodes. The structure of the electrode array was determined through simulation to achieve the best optical performance. Both the patterned catalyst and growth parameters were optimized for optimal MWCNF properties. We report an in-depth optical characterization of these reconfigurable hybrid liquid crystal and nanofiber microlens arrays.     

Electrospun La₀.₈Sr₀.₂MnO₃ nanofibers for a high-temperature electrochemical carbon monoxide sensor

Lanthanum strontium manganite (La(0.8)Sr(0.2)MnO(3), LSM) nanofibers have been synthesized by the electrospinning method. The electrospun nanofibers are intact without morphological and structural changes after annealing at 1050?°C. The LSM nanofibers are employed as the sensing electrode of an electrochemical sensor with yttria-stabilized zirconia (YSZ) electrolyte for carbon monoxide detection at high temperatures over 500?°C. The electrospun nanofibers form a porous network electrode, which provides a continuous pathway for charge transport. In addition, the nanofibers possess a higher specific surface area than conventional micron-sized powders. As a result, the nanofiber electrode exhibits a higher electromotive force and better electro-catalytic activity toward CO oxidation. Therefore, the sensor with the nanofiber electrode shows a higher sensitivity, lower limit of detection and faster response to CO than a sensor with a powder electrode.     

Fabrication of Nanofiber Reinforced Protein Structures For Tissue Engineering

Extracellular matrices and degradable nanofibers are two very promising materials in the field of tissue engineering; however both of these structures face limitations as tissue engineering scaffolds. Extracellular matrices, such as collagen, gelatin, and laminin, have excellent biocompatibility and allow cell in growth and survival, but structural weakness makes them difficult to handle and greatly limits their uses. Degradable nanofibers support cell attachment and can provide structural support and directional guidance, but individual degradable nanofibers are fragile and have a tendency to form dense fiber bundles which limit cell penetration into the spaces between the nanofibers, especially in the case of aligned nanofibers. To overcome these difficulties, degradable loose nanofibers were embedded in protein matrix in an attempt to fabricate a hybrid scaffold with improved properties, such as improved strength, guidance, spacing among nanofibers, etc. Polycaprolactone (PCL) was used as a model material for degradable nanofibers. Gelatin was employed as a model protein for matrix structure formation. Thin hybrid films (average thickness = 2.78 um) were fabricated by wetting the loose aligned undirectional nanofiber arrays or loose aligned bi-directional nanofiber grids with a gelatin aqueous solution, which also allows for live cell loading into the nanofiber-protein composite if cell are premixed with protein solution or on the surface of the films. Gelatin film alone without nanofiber reinforcement is difficult to handle due to the weakness of the thin membrane. Gelatin films with a fiber density as low as 3% v/v were structurally robust enough for handling, and manipulation into complex shapes. Mechanical testing confirmed that the addition of nanofibers enhanced the strength of gelatin films, in both dry and hydrated state. In vitro testing confirmed that nanofiber reinforced films were biocompatible and provided cells with directional guidance. Results demonstrate the promise of gelatin/PCL nanofiber composites as a tissue scaffolding material.     

Stretching-induced crystallinity and orientation to improve the mechanical properties of electrospun PAN nanocomposites

Polyacrylonitrile-based carbon fibers, embedded with single-walled carbon nanotubes have been prepared by the electrospinning technique. The as-spun nanofibers were hot-stretched in an oven to enhance the orientation and crystallinity which has been confirmed by X-ray diffraction and DSC etc. With the hot-stretched process and the introduction of SWNTs, the mechanical properties of PAN nanofibers such as the modulus and tensile strength will be enhanced correspondingly. In addition, the electrical conductivities of the PAN/SWNTs nanofiber composites were also enhanced. It was concluded that the hot-stretched nanofibers and the PAN/SWNTs nanofiber composites can be used as a potential precursor to produce high-performance carbon nanocomposites.