Nanopore Diameter Research Articles

Fabrication of cobalt-nickel binary nanowires in a highly ordered alumina template via AC electrodeposition

Cobalt-nickel (Co-Ni) binary alloy nanowires of different compositions were co-deposited in the nanopores of highly ordered anodic aluminum oxide (AAO) templates from a single sulfate bath using alternating current (AC) electrodeposition. AC electrodeposition was accomplished without modifying or removing the barrier layer. Field emission scanning electron microscope was used to study the morphology of templates and alloy nanowires. Energy-dispersive X-ray analysis confirmed the deposition of Co-Ni alloy nanowires in the AAO templates. Average diameter of the alloy nanowires was approximately 40 nm which is equal to the diameter of nanopore. X-ray diffraction analysis showed that the alloy nanowires consisted of both hexagonal close-packed and face-centered cubic phases. Magnetic measurements showed that the easy x-axis of magnetization is parallel to the nanowires with coercivity of approximately 706 Oe. AC electrodeposition is very simple, fast, and is useful for the homogenous deposition of various secondary nanostuctured materials into the nanopores of AAO.

Enhanced Ionic Transport Mechanism by Gramicidin A Confined Inside Nanopores Tuned by Atomic Layer Deposition

The confinement and the understanding of ion transport through ionic channels when they are confined inside solid-state nanopores smaller than 10 nm remains a challenge. Here we report on the fabrication of biomimetic nanopores with high length (5 μm)/diameter (smaller than 10 nm) ratio obtained using both a track-etched technique and atomic layer deposition on flexible membranes. These membranes present uniform hydrophobic nanopores with a low roughness inside the pores. Gramicidin A is then confined inside nanopores (diameter 10.6, 5.7, and ∼2 nm) leading to the NaCl ionic transport mechanism through a hybrid nanopore similar to the biological ones especially for small diameter (5.7 and ∼2 nm).

Uniform contraction of high-aspect-ratio nanochannels in hexagonally patterned anodic alumina films by pulsed voltage oxidation

Nanopore diameters in porous anodic alumina films were uniformly reduced via facile pulsed voltage anodization method. Spontaneous self-ordering into hexagonal pattern was maintained at pulse frequencies of 0.5–1Hz in both 0.3M oxalic (long-range ordered domains) and 10wt.% sulphuric (incipient short range ordering) acids, and yielded smooth uniform nanochannels of 19±2nm and 8±1nm diameters correspondingly.

Solution-processable graphene nanomeshes with controlled pore structures.

Graphene nanomeshes (GNMs) which can be cheaply produced on a large scale and processed through wet approaches are important materials for various applications, including catalysis, composites, sensors and energy related systems. Here, we report a method for large scale preparation of GNMs by refluxing reduced graphene oxide sheets in concentrated nitric acid solution (e.g., 8 moles per liter). The diameters of nanopores in GNM sheets can be readily modulated from several to hundreds nanometers by varying the time of acid treatment. The porous structure increased the specific surface areas of GNMs and the transmittances of GNM-based thin films. Furthermore, GNMs have large number of carboxyl groups at the edges of their nanopores, leading to good dispersibility in aqueous media and strong peroxidase-like catalytic activity.

What Happens to Polymer Chains Confined in Rigid Cylindrical Inorganic (AAO) Nanopores

Nanoconfinement can profoundly change the bulk characteristics. The question of conformational changes under one-dimensional confinement is recurrent in polymer physics. Very few works addresses this question because of the hard experimental challenge and the complex analysis of the signal. Here, the conformation of polystyrene chains shaped by wetting, in nanotubes or nanorods is for the first time determined at 3 dimensions. Polystyrene chains (molecular weight samples from 38 kDa to 310 kDa) confined in AAO nanopores as large as the size of the pore diameters (from 35 to 180 nm) are probed, revealing the invariance with respect to the bulk-like conformation for polystyrene chains up to 301 kDa confined down to 35 nm diameter nanopores.

Surface-enhanced Raman spectroscopy scattering from gold-coated ceramic nanopore substrates: effect of nanopore size

The dependence of magnitude of the electric near-field on the separation between metal nanoparticles for surface-enhanced Raman spectroscopy (SERS) substrates was experimentally verified. Diameters of gold-coated nanopores in a ceramic alumina substrate were varied to study the charge buildup near interparticle junctions and its effect on the enhancement factor due to SERS. The substrates were characterized by sensing a Rhodamine dye and calculating the associated Raman enhancement factors. Decreasing Au interparticle distance increases the electric near-field and shifts the plasmon resonance peak accordingly.

Modeling Ring/Chain Equilibrium in Nanoconfined Sulfur

The effect of nanoconfinement on the thermodynamics of free radical polymerization of sulfur is examined. We extend Tobolsky and Eisenberg's model of bulk sulfur polymerization to nanopores accounting for the confinement entropy of the chains and ring using scaling reported in literature. The model quantitatively captures literature data from Yannopoulos and co-workers for the extent of polymerization versus temperature for bulk sulfur polymerization and for polymerization in 20, 7.5, and 2.5 nm diameter Gelsil nanopores, assuming that the change of entropy of nanoconfined chains scales with molecular size to the second power and with nanopore diameter to either the -3.0 or -3.8 power, the former of which fits slightly better. The scaling, which is valid for strong confinement in spherical pores, predicts that the propagation equilibrium constant will depend on both nanopore size and chain length, such that the average chain length decreases significantly upon confinement.

Frictionless nanoscale plastic flows of soft solid He-4

Possible onset of the quantum plasticity in soft–solid He-4 was discovered recently in 7 nm diameter (Vycor glass) nanopores. Here, by using the transition-state model together with the specific activation energy and activation volume, we investigated the possible frictionless plastic flows of soft–solid He-4 under high pressure in confined nanodomains and we observed a series of sudden changes in the shearing stresses at corresponding very high shear strain rates of (locally amorphous) soft–solid He-4 for different activation volumes considering the role of He-3 impurities. Our calculated critical velocity for a fixed concentration of He-3 quantitatively agrees with recent reported values.

Synthesis and Characterization of ZnAPSO-34 Membrane on Porous α- Al<sub>2</sub>O<sub>3</sub> Support

Zeolites and other inorganic molecular sieve membranes have shown potential for separation based on molecular size and shape because of their small pore sized, typically less than 1nm, and their narrow pore size distribution. The in situ synthesis of ZnAPSO-34 films supported on alumina substrates is reported in this paper. Organic and water contents, alumina source, and supports have important roles in the syntheses of ZnAPSO-34 film. Traditionally, the role of organic molecules in the synthesis of these materials has been associated to their structure-directing and their protonation abilities. In our work, we were interested in a new family of materials; the alumino-phosphate, which are similar to zeolites. This work concerns the in-situ preparation of films of ZnAPSO-34 on porous α -alumina tubes. These films of ZnAPSO-34 corresponding to the structure Chabazite (CHA) have an effective intracrystal nanopore diameter of 0.38 nm. The hydrothermal synthesis was made in an autoclave under autogenous pressure. The membrane used was characterized by thermo-gravimetric analysis (TGA) and differential thermal analysis, X-ray diffraction and scanning electron microscopy after calcination.

Single-molecule DNA digestion in various alkanethiol-functionalized gold nanopores

This paper presents the alkanethiol-functionalized environmental effects of individual DNA molecules in nanopores on enzyme digestion at the single-molecule level. A template consisting of gold deposited within a solid-state nanoporous polycarbonate membrane was used to trap individual λ-DNA and enzyme molecules. The gold surfaces were modified with various functional groups (–OH, –COOH, –NH3). The enzyme digestion rates of single DNA molecules increased with decreasing nanopore diameters. Surprisingly, the digestion rates in the l-cysteine chemisorbed nanopores were 2.1–2.6 times faster than in the mercaptoethanol chemisorbed gold nanopores, even though these nanopores had equivalent interspacial areas. In addition, the membrane of chemisorbed cysteamine with ionized functional groups of H3N+ at pH 8.2 had a greater positive influence on the enzyme digestion rate than the membrane of chemisorbed mercaptoproponic acid with ionized carboxyl groups (COO-). These results suggest that the three-dimensional environment effect is strongly correlated with the functional group in confined nanopores and can significantly change the enzyme digestion rates for nanopores with different internal areas.

Precise Control of Solid-State Nanopore Device Properties for Single-Molecule Detection Applications

Solid-state nanopores are an emerging technology for detection and analysis at the single-molecule level. Here, we discuss fabrication and characterization of nanopores and nanopore arrays using Helium Ion Milling. We investigate nanopore dimensions using atomic force microscopy and transmission electron microscopy. We demonstrate that nanopore diameter and local membrane thickness are controlled precisely through ion beam dose, achieving pore diameters below 3 nm and device thickness below 5 nm. The technique is high-throughput and lithographic patterning can be used to form arrays of arbitrary size. The resulting devices are compatible with both electrokinetic and optical detection schemes for biodetection applications.

Effects of Polymeric Additives on the Crystallization and Release Behavior of Amorphous Ibuprofen

Some polymeric additives were studied to understand their effects on the amorphous phase of ibuprofen (IBU), used as a poorly water soluble pharmaceutical model compound. The amorphous IBU in bulk, as well as in nanopores (diameter ~24 nm) of anodic aluminum oxide, was examined with the addition of poly(acrylic acid), poly(N‐vinyl pyrrolidone), or poly(4‐vinylphenol). Results of bulk crystallization showed that they were effective in limiting the crystal growth, while the nucleation of the crystalline phase in contact with water was nearly instantaneous in all cases. Poly(N‐vinyl pyrrolidone), the most effective additive, was in specific interaction with IBU, as revealed by IR spectroscopy. The addition of the polymers was combined with the nanoscopic confinement to further stabilize the amorphous phase. Still, the IBU with addition of polymeric additives showed sustained release behavior. The current study suggested that the inhibition of the crystal nucleation was probably the most important factor to stabilize the amorphous phase and fully harness its high solubility.

Fabrication of Nanopores on Different Thickness Membranes

In recent years, solid-state nanopores have been widely used in biotechnology for detecting single molecules. Here, we studied the influence of membrane thickness and Focused Ion Beam action time on the diameter of silicon nitride nanppores. The results showed that on the 300 nm thick silicon nitride membrane, the minimum pore was 170 nm in diameter; while on thinner membranes with the thicknesses of 200nm and 100nm, the minimum pore diameters were 100nm and 30nm respectively. And on the membrane of a given thickness, the minimum diameter of nanopore is determined by the minimum action time. Therefore the 100 nm membrane thickness is ideal for milling small nanopores.

Insights into the Size and Geometry of a Robust Engineered Membrane Protein Nanopore

The maximum utility of protein nanopores in biotechnological applications is generally dictated by the size and internal geometry of the protein. The knowledge of these two parameters is imperative, particularly when extensive protein redesign is employed to produce task-specific proteins.Recently, we used ferric hydroxamate uptake component A (FhuA), a β-barrel bacterial outermembrane protein, as a protein-engineering template to produce an unusually-rigid, open nanopore (FhuA ΔC/Δ4L). This new nanopore maintains its stability under harsh experimental conditions. It was essential to couple comprehensive protein redesign with protein refolding protocols to obtain such a nanopore. With the radical revamp of the FhuA template, it was necessary to shed light on the overall structure of the new FhuA ΔC/Δ4L protein. Thus, we employed water-soluble, flexible poly(ethylene glycols) and dextran polymers to inspect the interior of FhuA ΔC/Δ4L during single-channel recordings.The addition of poly(ethylene glycols) to solution produced alterations in the single-channel conductance, allowing for the calculation of the nanopore diameter. We report that FhuA ΔC/Δ4L features an approximate conical internal geometry with the cis entrance (extracellular) smaller than the trans entrance (periplasmic). This finding is in accord with the asymmetric nature of the crystal structure of the wild-type FhuA protein. Additionally, experiments with impermeable dextran indicated an average internal diameter of ∼2.4 nm, an estimate based on the polymer-induced alteration of the access resistance contribution to the total resistance of the nanopore. The insights into size and geometry of FhuA ΔC/Δ4L deduced from these polymers experiments will aid in future protein engineering of FhuA, opening new engineering avenues for specific tasks in biotechnological applications.This work is funded in part by grants from the US National Science Foundation (DMR-1006332, L.M.) and the National Institutes of Health (R01 GM088403, L.M.).

Transition of dominative conduction mechanism caused by nanostructures on silicon surface

Nanopores on silicon surface are fabricated by metal-assisted etching process. Temperature coefficient of resistance (TCR) of silicon changes from positive value into negative value after nanostructuring, and the value increases with etching duration, indicating a competition between lattice-vibration scattering mechanism and hopping (thermionic emission) mechanism in carrier transport in silicon material. The capability of modulating TCR is one of the major advantages of nanostructured silicon. High TCR of −2.84%/°C is obtained after etching for 7min. This value is as large as that of some heat sensitive materials used for uncooled IR detectors. Both diameter and depth of nanopores increase with etching duration.

Theoretical study on key factors in DNA sequencing with graphene nanopores

Solid-state nanopores, in particular graphene nanopores, are believed to have promising applications in DNA sequencing. Many efforts have been made in this research area, the ultimate goal is to extend the DNA translocation time and to achieve single-base resolution. Unfortunately, several factors in DNA sequencing are still not well understood. In this paper, we report a study on the effects of two main factors, the salt concentration and the bias voltage, on the corresponding ionic current. We propose a theoretical model to explore the relationship between the occupied nanopore area and the current. We demonstrate that the DNA translocation time can be prolonged by decreasing the bias voltage and by properly narrowing the nanopore diameter. We find that the reduction of the blockade current depends on the ratio of the unoccupied nanopore area to the total nanopore area.

Fabrication, characterization, and application in nanoenergetic materials of uncracked nano porous silicon thick films

The porous silicon (PS) film has gained increasing attention in recent years as advanced nanoenergetic materials (nEMs). A simple fabrication method to prepare uncracked PS thick films was successfully realized with precisely controlled electrochemical etching, and the relationship between the current density and the concentration of electrolytes was found in its fabrication. Additionally, the capillary stresses resulted from the liquids in nanopores of PS films was another factor resulted in its crack. The nanopores composed of uncracked PS thick films distributed regularly and their diameters ranged from 2nm to 6nm. Its Sa (average roughness) of PS film surface was 6.53nm, and its thickness ranged from 102.41μm to 205.75μm. The specific surface area was 587m2/g and the average diameter of nanopores was 4.3nm. The PS film was found to be monocrystal and it was same as the substrate. The crack mechanism of PS films was discussed: the porous structure reduced the strength of PS films comparing the silicon bulk and the capillary effect hastened the crack of PS films. PS films filling with sodium percholorate in nanopores were ignited by laser and the stable combustion showed that they were advantageous to be applied as micro-electromechanical systems (MEMS) compatible devices, such as silicon-based chips of mircothruster and microigniter.

Inspection of the Engineered FhuA ΔC/Δ4L Protein Nanopore by Polymer Exclusion

Extensive engineering of protein nanopores for biotechnological applications using native scaffolds requires further inspection of their internal geometry and size. Recently, we redesigned ferric hydroxamate uptake component A (FhuA), a 22-β-stranded protein containing an N-terminal 160-residue cork domain (C). The cork domain and four large extracellular loops (4L) were deleted to obtain an unusually stiff engineered FhuA ΔC/Δ4L nanopore. We employed water-soluble poly(ethylene glycols) and dextran polymers to examine the interior of FhuA ΔC/Δ4L. When this nanopore was reconstituted into a synthetic planar lipid bilayer, addition of poly(ethylene glycols) produced modifications in the single-channel conductance, allowing for the evaluation of the nanopore diameter. Here, we report that FhuA ΔC/Δ4L features an approximate conical internal geometry with the cis entrance smaller than the trans entrance, in accord with the asymmetric nature of the crystal structure of the wild-type FhuA protein. Further experiments with impermeable dextran polymers indicated an average internal diameter of ∼2.4 nm, a conclusion we arrived at based upon the polymer-induced alteration of the access resistance contribution to the nanopore’s total resistance. Molecular insights inferred from this work represent a platform for future protein engineering of FhuA that will be employed for specific tasks in biotechnological applications.

Mesoporous Germanium formed by bipolar electrochemical etching

The formation of mesoporous Ge layers with different morphologies by bipolar electrochemical etching is reported for the first time. A detailed analysis of the effect of anodic/cathodic pulse duration on the mesoporous Ge formation is performed. It is shown that together with the applied current density and anodization time this parameter has the most important influence on porous Ge morphology. Six different types of porous morphologies were identified with the nanopore diameter being in the range from 5 to 15nm. Their crystalline nature has been confirmed by Raman spectroscopy. The diameters of the nanocrystallites of the porous Ge layers were extracted from Raman spectra by using the phonon-confinement model. Depending of the layer morphology their values varied between 4 and 10nm. A conceptual analysis of several aspects of the formation mechanisms of mesoporous Germanium based on the available information has allowed us to predict and create a new complex morphology.

Development of the Fibrillar and Microfibrillar Structure During Biomimetic Mineralization of Wood

AbstractWood is a hierarchical composite, consisting at its lowest hierarchy level of crystalline cellulose elementary fibrils with diameters of 2–4 nm embedded in a matrix of hemicelluloses and lignin. At the micrometer scale, it has a cellular architecture resembling a honeycomb structure. The transformation of the hierarchical wood structure into a silica replica has been reported recently. Its formation process and structural details are studied in this contribution. First, a silica/biopolymer composite is prepared by wood delignification and cell‐wall modification, followed by silica precursor infiltration and condensation. The calcination process is monitored to gain insight into the structure development upon decomposition of the biopolymers. The material changes its architecture gradually from fibrillar structures of 10–20 nm in diameter with homogeneous electron density, into fibrils of 8–10 nm in diameter with inhomogeneous electron density, exhibiting internal sub‐fibrillar structures of about 2 nm in diameter. The steps of the successful replication of the cellulose elementary fibrils into nanopores of similar diameter and orientation in a fibrillar silica matrix are demonstrated. These nanopore replicas of the original cellulose are wound in a steep helix within the macropore walls. These advanced materials may have lightweight structural applications and the nanopores may be advantageous for molecular separation.