One-step catalytic growth of carbon nanofiber arrays vertically aligned on carbon substrate

Vertically aligned carbon nanofiber (VA-CNF) arrays on carbon substrate have been synthesized via one-step chemical vapor deposition process on copper foil, by using acetylene as carbon resource. Three types of carbon nanostructures, viz. bare carbon films, CNFs and VA-CNFs grown on carbon substrate, could be selectively synthesized by only modulating the concentration of C₂H₂ and NH₃ in the feeding gases. It was found that NH₃ was a key factor in the growth of VA-CNF arrays, which could increase the diffusion capability of copper atoms in carbon materials, therefore promote forming larger spherical Cu NPs catalysts for the growth of VA-CNFs. Furthermore, a growth mechanism in different feeding gas compositions was proposed.     

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.     

Covalent immobilization of beta-galactosidase onto a gold-coated magnetoelastic transducer via a self-assembled monolayer: toward a magnetoelastic biosensor

The enzyme beta-galactosidase has been covalently immobilized onto a gold-coated magnetoelastic film via a self-assembled monolayer (SAM) of omega-carboxylic acid alkylthiol. Use of magnetoelastic transduction allows for the wireless monitoring of enzymatic activity through the associated change in the frequency and amplitude of magnetic fields. The formations of SAMs of 3-mercaptopropanoic acid and thioctic acid were monitored by magnetoelastic transduction. After coupling of beta-galactosidase to the SAMs, the enzyme activity was monitored by using a substrate that forms an insoluble product upon action of the enzyme. Specifically, an indolyl galactopyranoside substrate was employed in conjunction with an azo dye as the precipitating system. The immobilized enzyme was evaluated and found to have an apparent Michaelis-Menten constant (KM) of 1.2 mM for the indolyl galactopyranoside. Calibration plots for both substrates and inhibitors were generated to establish the versatility of this sensing system. Kinetic parameters for nonprecipitating substrates were determined in conjunction with a precipitating enzymatic substrate by way of a competitive inhibition study using beta-galactosidase attached to magnetoelastic strips. The methods developed within this work allow for the fabrication of wireless enzyme sensing systems, which can also be used as another means of screening for enzyme inhibitors.     

Spatial control of quantum sized nanocrystal arrays onto silicon wafers

Monolayer arrays of monodispersed nanocrystals (<10 nm) onto three dimensional (3D) substrates have considerable potential for various engineering applications such as highly integrated memory devices, solar cells, biosensors and photo and electro luminescent displays because of their highly integrated features with nanocrystal homogeneity. However, most reports on nanocrystal arrays have focused on two dimensional (2D) flat substrates, and the production of wafer-scale monolayer arrays is still challenging. Here we address the feasibility of arraying nanocrystal monolayers in wafer-scale onto 3D substrates. We present both metal (Pd) and semiconductor (CdSe) nanocrystals arrayed in monolayer onto trenched silicon wafers (4 inch diameter) using a facile electrostatic adsorption scheme. In particular, CdSe nanocrystal arrays in the trench well showed superior luminescent efficiency compared to those onto the protruded trench flat, due to the densely arrayed CdSe nanocrystals in the vertical direction. Furthermore, the surface coverage controllability was investigated using a 2D silicon substrate. Our approach can be applied to generate highly efficient displays, memory chips and integrated sensing devices.     

宏观超长定向碳纳米管阵列的制备

采用二甲苯和二茂铁作为碳源和催化剂的化学气相沉积法连续制备定向碳纳米管阵列,在反应6h内获得长度为6mm的宏观定向碳纳米管阵列。当反应时间超过6h后,定向碳纳米管阵列的生长速度明显下降,并有停止生长的趋势,反应16h,定向碳纳米管阵列的厚度仅为6．7mm。本文研究了采用多次连续进给碳源和催化剂的方式制备定向碳纳米管阵列,成功的制备了8．9mm厚的定向碳纳米管阵列,阵列中的碳纳米管具有高的定向性和良好的界面结合。     

Wettable arrays onto superhydrophobic surfaces for bioactivity testing of inorganic nanoparticles

Poly(l-lactic acid) superhydrophobic surfaces prepared by a phase-separation methodology were treated with 30 min exposition of UV/O₃ irradiation using hollowed masks in order to obtain patterned superhydrophilic squared-shaped areas. These wettable areas successfully confined bioactive glass nanoparticles (BG-NPs), by dispensing and drying individual droplets of BG-NPs suspensions. The obtained biomimetic chips were used to test the in vitro bioactivity of binary (SiO₂-CaO) and ternary (SiO₂-CaO-P₂O₅) nanoparticles produced using sol-gel chemistry by immersing such substrate in simulated body fluid (SBF). From SEM and EDX it was possible to conclude that the ternary system promoted an enhanced apatite deposition. This work shows the potential of using such flat disposable matrices in combinatory essays to easily evaluate the osteoconductive potential of biomaterials using small amounts of different samples.     

Direct observation of single flexible polymers using single stranded DNA()

Over the last 15 years, double stranded DNA (dsDNA) has been used as a model polymeric system for nearly all single polymer dynamics studies. However, dsDNA is a semiflexible polymer with markedly different molecular properties compared to flexible chains, including synthetic organic polymers. In this work, we report a new system for single polymer studies of flexible chains based on single stranded DNA (ssDNA). We developed a method to synthesize ssDNA for fluorescence microscopy based on rolling circle replication, which generates long strands (>65 kb) of ssDNA containing "designer" sequences, thereby preventing intramolecular base pair interactions. Polymers are synthesized to contain amine-modified bases randomly distributed along the backbone, which enables uniform labelling of polymer chains with a fluorescent dye to facilitate fluorescence microscopy and imaging. Using this approach, we synthesized ssDNA chains with long contour lengths (>30 μm) and relatively low dye loading ratios (~1 dye per 100 bases). In addition, we used epifluorescence microscopy to image single ssDNA polymer molecules stretching in flow in a microfluidic device. Overall, we anticipate that ssDNA will serve as a useful model system to probe the dynamics of polymeric materials at the molecular level.     

Control of the diffracted response of wire arrays with double periods

The possibility of controlling the diffracted response of a periodic structure is investigated by using dual-period arrays, i.e., periodic arrays with a compound unit cell. We consider wire gratings in which each period comprises several cylinders with circular cross sections and all the cylinder axes are contained in the same plane. It is shown that this kind of structure permits one to control the diffracted response, regardless of the cylinder material and the incident polarization. Our numerical results suggest that the effect produced by wire gratings with dual-period characteristics is basically a geometric effect, and it can be present for other shapes of individual scatterers within each subarray.     

Hydrodynamic micromanipulation of individual cells onto patterned attachment sites on biomicroelectromechanical system chips

We report on a simple methodology to move selected single live cells to a desired location on a flat substrate, such as a patterned biomicroelectromechanical system chip. A macroscopic syringe-and-tube-based hydrodynamic manipulation system is used to achieve controlled cell navigation onto hydrophilic sites for cell attachment. Centimeter-per-second flow velocities generated by the system get downgraded to micrometers-per-second flow at the height of settled cells as a result of viscous flow in the medium. By pushing/pulling two syringes that produce two orthogonal flows, fine manipulation in any horizontal direction is feasible. After attachment of the desired cell(s) onto the selected hydrophilic site, all other unwanted cells are washed away from the surrounding hydrophobic surface with faster flow. This simple methodology is applicable for rapid cell pattern formation with high precision.     

Controlled fabrication and electrical properties of long quasi-one-dimensional superconducting nanowire arrays

We report a general method for reliably fabricating quasi-one-dimensional superconducting nanowire arrays, with good control over nanowire cross section and length, and with full compatibility with device processing methods. We investigate Nb nanowires with individual nanowire cross sectional areas that range from bulklike to 10 x 11 nm, and with lengths from 1 to 100 microm. Nanowire size effects are systematically studied. In particular, a comprehensive investigation of influence of nanowire length on superconductivity is reported for the first time. All results are interpreted within the context of phase-slip models.     

Covalent attachment of gold nanoparticles to DNA templates

Functionalized gold nanoparticles have been covalently bound to internal, modified sites on double-stranded DNA. Gold nanoparticles coated with mercaptosuccinic acid or thioctic acid were bound to amino-modified thymine bases on double-stranded DNA. Visible absorption spectra, gel electrophoresis, and atomic force microscopy were used to analyze the products. Thiol groups were added to one end of the gold/nanoparticle product, which was then attached to a gold surface. This method has the potential to allow controlled placement of particles with subnanometer precision and to allow attachment of the product to fixed contacts for nanodevice fabrication.     

Electrical detection of viral DNA using ultramicroelectrode arrays

A fully electrical array for voltammetric detection of redox molecules produced by enzyme-labeled affinity binding complexes is shown. The electronic detection is based on ultramicroelectrode arrays manufactured in silicon technology. The 200-microm circular array positions have 800-nm-wide interdigitated gold ultramicroelectrodes embedded in silicon dioxide. Immobilization of oligonucleotide capture probes onto the gold electrodes surfaces is accomplished via thiol-gold self-assembling. Spatial separation of probes at different array positions is controlled by polymeric rings around each array position. The affinity bound complexes are labeled with alkaline phosphatase, which converts the electrochemically inactive substrate 4-aminophenyl phosphate into the active 4-hydroxyaniline (HA). The nanoscaled electrodes are used to perform a sensitive detection of enzyme activity by signal enhancing redox recycling of HA resulting in local and position-specific current signals. Multiplexing and serial readout is realized using a CMOS ASIC module and a computer-controlled multichannel potentiostat. The principle of the silicon-based electrical biochip array is shown for different experimental setups and for the detection of virus DNA in real unpurified multiplex PCR samples. The fast and quantitative electronic multicomponent analysis for all kinds of affinity assays is robust and particle tolerant.     

Silicon nanowire arrays for label-free detection of DNA

Arrays of highly ordered n-type silicon nanowires (SiNW) are fabricated using complementary metal-oxide semiconductor (CMOS) compatible technology, and their applications in biosensors are investigated. Peptide nucleic acid (PNA) capture probe-functionalized SiNW arrays show a concentration-dependent resistance change upon hybridization to complementary target DNA that is linear over a large dynamic range with a detection limit of 10 fM. As with other SiNW biosensing devices, the sensing mechanism can be understood in terms of the change in charge density at the SiNW surface after hybridization, the so-called "field effect". The SiNW array biosensor discriminates satisfactorily against mismatched target DNA. It is also able to monitor directly the DNA hybridization event in situ and in real time. The SiNW array biosensor described here is ultrasensitive, non-radioactive, and more importantly, label-free, and is of particular importance to the development of gene expression profiling tools and point-of-care applications.     

Synthesis of vertical arrays of ultra long ZnO nanowires on noncrystalline substrates

Vertically aligned arrays of ultralong ZnO nanowires were synthesized on SiO₂ substrates with carbothermal vapor phase transport method with Au seeding layer. High density of vertically aligned ZnO nanowires with lengths from a few to ∼300 μm could be grown by controlling growth conditions. Supply of high concentration of Zn vapor and control of the ratio between Zn vapor and oxygen are found to have the most significant effects on the growth of long ZnO nanowires in the vapor-solid growth mechanism. The nanowires are of high crystalline quality as confirmed by various structural, compositional, and luminescent measurements. Luminescent and electrical properties of ZnO nanowires with different growth conditions were also investigated.     

Magnetic assembly of high-density DNA arrays for genomic analyses

A method for rapidly assembling high-density DNA arrays with near-perfect order is described. Photolithography is used to generate a wafer-scale array of microwells in a layer of photoresist on a chemically functionalized glass coverslip. The array is enclosed within a microfluidic device, and a suspension of superparamagnetic microbeads conjugated to DNA molecules is introduced into the chamber. A permanent magnet is used to direct the rapid assembly of the beads into the wells, with each well containing a single bead. These beads are immobilized on the glass surface via affinity binding, and excess beads can be recycled or washed away. Nonspecifically bound beads are removed by dissolving the photoresist. The result is a high-density array of beads with virtually no background. This method can be used to produce protein arrays for chip-based assays and DNA arrays for genotyping or genome sequencing.     

A simple synthesis of long nanostructured arrays of crystalline strontium titanates at low-temperatures

Long aligned arrays of crystalline strontium titanate (SrTiO₃) nanostructures were synthesized by using simple low-temperature processes that incorporate strontium into titanium oxides. Tubular nanostructures are often confine energy carriers that result in extraordinary transport behaviors in various semiconductors including strontium titanates, which are promising for developing efficient thermoelectric energy conversion materials. However, synthesizing a micron-to-milimeter scale array of one-dimensional ternary nanostructures has been difficult. Moreover, ternary compounds are often obtained as disordered cubic-shape particles at the end of complicated and/or long reactions. In this study, a two-step process—anodization for preparing amorphous titanium oxides and a subsequent thermal annealing process in a mixture of strontium hydroxide, ammonia, and water—was employed. Typical diameter and length of the tubes are ~150 nm and ~160 μm, respectively. It has been found that the amorphous structure of titanium oxides plays an important role in obtaining high-purity long strontium titanate nanotubes at low temperatures (90 and 180 °C) with short reaction times. Comparative and systematic studies with different sample pre-treatments, etching times, temperatures, reaction times, and strontium concentrations revealed reaction mechanisms and key synthesis parameters, which may be utilized to obtain other ternary or quaternary nanostructured compounds such as barium or lead titanates.     

Entropic recoil separation of long DNA molecules

A novel technique that can rapidly separate long-strand polymers according to length is presented. The separation mechanism is mediated by a confinement-induced entropic force at the abrupt interface between regions of vastly different configuration entropy. To demonstrate this technique, DNA molecules were partially inserted into a dense array of nanopillars (an entropically unfavorable region) using a pulsed electric field and allowed to relax to their natural state by removal of the field. Molecules of dissimilar lengths (T2 and T7 coliphage DNA) were inserted into this region in such a way that shorter molecules were fully inserted in this region, while longer molecules remained partially across the interface. The longer T2 molecules were observed to recoil entirely out of the pillar array, leaving the shorter T7 molecules inserted, and effecting separation of the two species in a single step. To show how this method can be used for separation of unknown samples, the inserting electric field was pulsed for progressively longer times, allowing passage of progressively longer molecules and producing the equivalent of a conventional electropherogram. The effects limiting resolution in this device are discussed, and the expected separating power of a multistage device is reported. The extracted resolution and running separation time compare favorably with current conventional separation techniques.     

Synthesis of ZnTe nanowires onto TiO2 nanotubular arrays by pulse-reverse electrodeposition

Growth of ZnTe nanowires using a pulse-reverse electrodeposition technique from a non-aqueous solution is reported. ZnTe nanowires were grown on to an ordered nanotubular TiO₂ template in a propylene carbonate solution at 130 °C inside a controlled atmosphere glove box. The pulse-reverse electro deposition process consisted of a cathodic pulse at − 0.62 V and an anodic pulse at 0.75 V Vs Zn²⁺/Zn. Stoichiometry growth of crystalline ZnTe nanowires was observed in the as-deposited condition. The anodic pulse cycle of the pulse-reverse electrodeposition process presumably introduced zinc vacancies as deep level acceptors at an energy level of E_v + 0.47 eV. The resultant ZnTe nanowires showed p-type semiconductivity with a resistivity of 7.8 × 10⁴ Ω cm and a charge carrier density of 1.67 × 10¹⁴ cm^− 3. Annihilation of the defects occurred upon thermal annealing that resulted in marginal decrease in the defect density.     

Growth of ultra long multiwall carbon nanotube arrays by aerosol-assisted chemical vapor deposition

Using a home-made aerosol nebulizer, we developed a new aerosol-assisted chemical vapor deposition (AACVD) process that made it possible to synthesize vertically-aligned carbon nanotube (VACNT) arrays with heights over a few millimeters routinely. An essential part of this technique was in-situ formation of metal catalyst nanoparticles via pyrolysis of ferrocene-ethanol aerosol right before CNT synthesis. Through the optimization of aerosol supply and CVD process parameters, we were able to synthesize clean VACNT arrays as long as 4.38 mm with very low metal contents in 20 min. Furthermore, it is worthy noting that such an outstanding height is achieved very quickly without supporting materials and water-assistance. By taking advantage of almost complete inhibition of CNT growth on low melting-temperature metals, we were able to fabricate patterned VACNT arrays by combining AACVD process with a conventional photolithograpic patterning of gold lines. Characterizations of as-grown nanotubes such as morphology, purity, and metal contents are presented.