Low‐voltage efficient electroosmotic pumps with ultrathin silica nanoporous membrane

In this work, an efficient electroosmotic pump (EOP) based on the ultrathin silica nanoporous membrane (u‐SNM), which can drive the motion of fluid under the operating voltage as low as 0.2 V, has been fabricated. Thanks to the ultrathin thickness of u‐SNM (～75 nm), the effective electric field strength across u‐SNM could be as high as 8.27 × 10⁵ V m^?1 in 0.4 M KCl when 1.0 V of voltage was applied. The maximum normalized electroosmotic flow (EOF) rate was as high as 172.90 mL/min/cm²/V, which was larger than most of other nanoporous membrane based EOPs. In addition to the ultrathin thickness, the high porosity of this membrane (with a pore density of 4 × 10¹² cm^?2, corresponding to a porosity of 16.7%) also contribute to such a high EOF rate. Moreover, the EOF rate was found to be proportional to both the applied voltage and the electrolyte concentration. Because of small electrokinetic radius of u‐SNM arising from its ultrasmall pore size (ca. 2.3 nm in diameter), the EOF rate increased with increasing the electrolyte concentration and reached the maximum at a concentration of 0.4 M. This dependence was rationalized by the variations of both zeta potential and electrokinetic radius with the electrolyte concentration.     

On the capacitive behavior of silicon electrodes modified with ultrathin hydrophobic polymer brushes

Journal of Solid State Electrochemistry - The modification of a silicon surface with ultrathin poly(styrene) brushes, obtained by grafting-from, results in a dramatic increase in capacitance as...     

Thermally controlled wettability of a nanoporous membrane grafted with catechol-tethered poly(N-isopropylacrylamide)

A nanoporous membrane is coated with catechol-tethered poly(N-isopropylacrylamide). The thermosensitive variation of surface wettability determines the hindered diffusivity of dextran (40 kDa) through the nanopores.     

Capping agent replacement induced self-organization of ultrathin nanowires: a new and general approach for fabricating noble metal nanoporous films with small ligament sizes

Ultrafine ligament noble metal nanoporous films are successfully fabricated by self-organization of ultrathin nanowires. The replacement of weak binding capping agent Triton X-114, used for stabilizing nanowires, by Cl(-) is claimed for this self-organization. Our method is also applicable for synthesizing other hierarchical nanostructure-like hybrid nanoporous films.     

3D patterning of silicon by contact etching with anodically biased nanoporous gold electrodes

A novel strategy to achieve 3D pattern transfer into silicon in a single step without using lithography is presented. Etching is performed electrochemically in HF media by contacting silicon with a positively biased, patterned, metal electrode. Dissolution is localized at the Si/metal contacts and patterning is obtained as the electrode digs into the substrate. Previous attempts at imprinting Si using bulk metal electrodes have been limited by electrolyte blockage. Here, the problem is solved by using, for the first time, a nanoporous metal electrode that allows the electrolyte to access the entire Si/metal interface, irrespective of the electrode dimensions. As a proof of concept, imprinting of well-defined arrays of inverted pyramids has been performed with sub-micrometer spatial resolution over 1 mm² using a nanoporous gold electrode of the complementary shape. Under a polarization of + 0.3 V/SME in 5 M HF, the etch rate is ~ 0.5 μm min^− 1. The pyramidal pattern is imprinted independently of the Si crystallographic orientation. This maskless imprinting technique opens new opportunities in the fabrication of Si microstructures.     

Comparison of the major polypeptides of the erythrocyte nuclear envelope

The three most abundant nonhistone polypeptides (molecular weights 75,000, 71,000 and 61,000) of the avian erythrocyte nucleus have previously been isolated in the nuclear envelope fraction. They have been separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis and peptide-mapped after limited enzymatic digestion. Three enzymes -- chymotrypsin, papain and Staphylococcus aureus protease -- were used. Results obtained with each enzyme indicate strong similarities between the three nuclear envelope polypeptides. The amino acid compositions of the two most abundant polypeptides (P75 and P71) have been determined and found to be similar. Further, they readily yield large fragments upon brief alkaline hydrolysis. For both P75, and P71 the degree and the pattern of alkaline fragmentation are almost identical. A 61,000-dalton polypeptide which appears to be P61 is obtained from P75 and P71 by mild acid hydrolysis. These results establish the close chemical similarity of these predominant polypeptides in the erythrocyte nucleus and suggest that they serve related functions.     

Boundary effects of molecular diffusion in nanoporous materials: a pulsed field gradient nuclear magnetic resonance study

The boundary conditions of intraparticle diffusion in nanoporous materials may be chosen to approach the limiting cases of either absorbing or reflecting boundaries, depending on the host-guest system under study and the temperature of measurement. Pulsed field gradient nuclear magnetic resonance is applied to monitor molecular diffusion of n-hexane and of an n-hexane-tetrafluoromethane mixture adsorbed in zeolite crystallites of type NaX under either of these limiting conditions. Taking advantage of the thus-established peculiarities of mass transfer at the interface between the zeolite bulk phase and the surrounding atmosphere, three independent routes for probing the crystal size are compared. These techniques are based on (i) the measurement of the effective diffusivity under complete confinement, (ii) the application of the so-called NMR tracer desorption technique, and (iii) an analysis of the time dependence of the effective diffusivity in the short-time limit where, by an appropriate variation of the adsorbate and the measuring conditions, the limiting cases of reflecting and adsorbing boundaries could be considered. All these techniques are found to yield coinciding results, which are in excellent agreement with the crystal sizes determined by microscopy.     

Anisotropic and passivation-dependent quantum confinement effects in germanium nanowires: a comparison with silicon nanowires

Electronic structures of hydrogen-passivated germanium nanowires (GeNWs) along the [100], [110], [111], and [112] directions are studied by using the density functional theory within the generalized gradient approximation. The band gaps of the fully relaxed GeNWs along the [100], [110], and [111] directions are all direct at the smaller sizes, while those of the wires along the [112] direction remain indirect. The magnitude of the band gaps of the GeNWs for a given size approximately follows the order of E(g)[100] > E(g)[111] > E(g)[112] > E(g)[110]. Compared with silicon nanowires, GeNWs exhibit stronger quantum confinement effects. Replacement of H by the more stable ethine group is found to lead to a weakening of the quantum confinement effects of GeNWs.     

Performance of a biomimetic oxidation catalyst immobilized on silicon wafers: comparison with its gold congener

With the aim of extending the usefulness of an existing biomimetic catalytic system, cobalt porphyrin catalytic units with thiol linkers were heterogenized via chemical grafting to silicon wafers and utilized for the catalytic oxidation of hydroquinone to p-benzoquinone. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to analyze the morphology and composition of the heterogeneous catalyst. The results of the catalytic oxidation of hydroquinone obtained with porphyrins grafted on silicon were compared with those obtained earlier with the same catalyst in homogeneous phase and immobilized on gold. It was found that the catalysis could run over 400 h, without showing any sign of deactivation. The measured catalytic activity is at least 10 times higher than that measured under homogeneous conditions, but also 10 times lower than that observed with the catalytic unit immobilized on gold. The reasons of this discrepancy are discussed in term of substrate influence and overlayer organization. The silicon-immobilized catalyst has potential as an advanced functional material with applications in oxidative heterogeneous catalysis of organic reactions, as it combines long-term relatively high activity with low cost.     

Integrated multilayer microfluidic device with a nanoporous membrane interconnect for online coupling of solid-phase extraction to microchip electrophoresis

An integrated microfluidic device was developed for online coupling of solid-phase extraction to microchip electrophoresis (chip SPE-CE). With a nanoporous membrane sandwiched between two PDMS substrates, SPE preconcentration and electrophoretic separation can be carried out in upper and lower fluidic layers, separately and sequentially. During the SPE process, the thin membrane can act as a fluid isolator to prevent intermixing between two fluidic channels. However, when a pulse voltage is applied, the membrane becomes a gateable interconnect so that a small plug of concentrated analytes can be online injected into the lower channel for subsequent separations. This multilayer design provides a universal solution to online SPE-CE hyphenation. Both electroosmotic flow and hydrodynamic pumps have been adopted for SPE operation. SPE was performed on a 2.5 mm long microcolumn, with two weirs on both sides to retain the C(18)-coated silica beads. Rhodamine 123 and FITC-labelled ephedrine were used to test the operational performance of the hyphenation system. High separation efficiency and thousand-fold signal enhancement were achieved.     

A nanostructured skeleton catalyst: Suzuki-coupling with a reusable and sustainable nanoporous metallic glass Pd-catalyst

Nanoporous metallic glass Pd, which was fabricated by dealloying of a glassy metallic alloy Pd(30)Ni(50)P(20), exhibited a remarkable catalytic activity for the Suzuki-coupling reaction between iodoarenes and arylboronic acids under mild conditions. Moreover, the catalyst can be reused several times without a significant loss of catalytic activity.     

A 10,000-fold nuclear hyperpolarization of a membrane protein in the liquid phase via a solid-state mechanism

Several techniques rely on electron-nuclear interactions to boost the polarization of nuclear spins in the solid phase. Averaging out of anisotropic interactions as a result of molecular tumbling strongly reduces the applicability of such hyperpolarization approaches in liquids. Here we show for the first time that anisotropic electron-nuclear interactions in solution can survive sufficiently long to generate nuclear spin polarization by the solid-state photo-CIDNP mechanism. A 10,000-fold NMR signal increase in solution was observed for a giant biomolecular complex of a photosynthetic membrane protein with a tumbling correlation time in the submicrosecond regime, corresponding to a molecular weight close to 1 MDa.     

Effects of divalent-cation chelators and chloramphenicol on the spatial relationship of the nuclear envelope to chromatin in micronuclei of Chinese hamster cells.

In the presence of the spindle poison Colcemid in the culture medium to prevent anaphase, approximately 20% of Chinese hamster metaphase cell were converted to micronucleated cells during 7 h. In the micronuclei the chromosome had become enclosed by a nuclear envelope (NE). In the light-microscope the micronuclei were of two kinds: with either visible chromatids or with decondensed chromosomes. In the electron microscope (EM) the spatial relationship of the NE to the chromatin was of two kinds only in the presence of Colcemid. In about 90% of the micronucleated cells the spatial relationship was normal, ie, the NE was immediately adjacent to the chromatin. In the remaining cells, the NE was distended so that the outer NE was separated from the inner one. In the presence of the divalent cation chelator, (ethylenedinitrilo) tetraacetic acid (EDTA) or the Ca2+-chelator [ethylenebis (oxyethylenenitrilo)] tetraacetic acid (EGTA) in addition to Colcemid, the amount of cells with micronuclei increased to 40%. The light-microscope appearance was the same as that found in the absence of the chelating agents. However, after Colcemid plus EGTA, EM revealed that only about 50% of the micronucleated cells had NE that was immediately adjacent to the chromatin and about 10% of them had distended outer NE. In the remaining 40% a third kind of spatial relationship was seen: the NE was intact but most of it was not adjacent to the chromatin. Furthermore, this type of micronucleus often contained mitochondria within the confines of NE. Thus, Ca2+ and possibly Mg2+ may regulate the rate of formation of the NE and also its ultrastructural relation to the chromatin. Mitochondrial function also appears to be involved in this relationship. In the presence of chloramphenicol (CAP), an inhibitor of mitochondrial protein synthesis, in addition to Colcemid, only about 50% of the micronucleated cells exhibited the normal relationship. The outer NE was separated from the inner NE in about 46% of the micronucleated cells and the third kind of NE-chromatin relationship was observed only in 2%. In the case of the third kind of relationship produced by CAP, inclusion of mitochondria within the micronuclei was not observed, in contrast to the finding with EGTA.     

Measurement of apparent diffusion coefficients within ultrathin nafion Langmuir-Schaefer films: comparison of a novel scanning electrochemical microscopy approach with cyclic voltammetry

The use of scanning electrochemical microscopy (SECM) to evaluate the apparent diffusion coefficient, Dapp, of redox-active species in ultrathin Nafion films is described. In this technique, an ultramicroelectrode (UME) tip, positioned close to a film on a macroscopic electrode, is used to oxidize (or reduce) a species in bulk solution, causing the tip-generated oxidant (reductant) to diffuse to the film/solution interface. The oxidation (reduction) of film-confined species regenerates the reductant (oxidant) in solution, leading to feedback to the UME. A numerical model is developed that allows Dapp to be determined. For these studies, ultrathin films of Nafion were prepared using the Langmuir-Schaefer (LS) technique and loaded with an electroactive species, either the ferrocene derivative ferrocenyltrimethylammonium cation, FA+, or tris(2,2'-bipyridyl)ruthenium(II), Ru(bpy)32+. The morphology and the thickness of the Nafion LS films (1.5 +/- 0.2 nm per layer deposited) were evaluated using atomic force microscopy (AFM). For comparison with the SECM measurements, cyclic voltammetry (CV) was employed to evaluate the concentration of electroactive species within the Nafion LS films and to determine Dapp. The latter was found to be essentially invariant with film thickness, but the value for Ru(bpy)32+ was 1 order of magnitude larger than for FA+. CV and SECM measurements yield different values of Dapp, and the underlying reasons are discussed. In general, the Dapp values for these films are considerably smaller than for recast Nafion films, which can be attributed to the compactness of Nafion LS films. Nonetheless, the ultrathin nature of the films leads to fast response times, and we thus expect that these modified electrodes could find applications in sensing, electroanalysis, and electrocatalysis.     

Paired cell for the preparation of AgI nanowires using nanoporous alumina membrane templates

This communication describes a relatively new and simple method for the preparation of AgI nanowires using nanoporous alumina membrane templates which can be easily extended to prepare nanowires of many other materials.     

Development of a low flow‐resistive charged nanoporous membrane in a microchip for fast electropreconcentration

A nanoporous poly‐(styrene sulfonate) (poly‐SS) membrane was developed for fast and selective ion transport in a microfluidic chip. The poly‐SS membrane can be photopolymerized in‐situ at arbitrary location of a microchannel, enabling integrated fluidics design in the microfluidic chip. The membrane is characterized by a low hydraulic resistance and a high surface charge to maximize the electroosmotic flow and charge selectivity. The membrane characteristics were investigated by charge‐selective electropreconcentration method. Experimental results show membranes with various percentages of poly‐SS are able to concentrate anions (fluorescein and TRITC‐labeled BSA). The anion‐selective electropreconcentration process is stable and 26‐times faster than previously reported poly‐AMPS (2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) based system. The electropreconcentration was also demonstrated to depend on the sample valency and buffer concentration.     

Evaluation of a novel microextraction technique for aqueous samples: porous membrane envelope filled with multiwalled carbon nanotubes coated with molecularly imprinted polymer

A novel microextraction technique based on membrane-protected multiwalled carbon nanotubes coated with molecularly imprinted polymer (MWCNTs-MIP) was developed. In this technique, MWCNTs-MIP were packed inside a polypropylene membrane envelope, which was then clamped onto a paper clip. For extraction, the packed membrane envelope was first impregnated with toluene and then placed in sample solutions. Target analytes in the solutions were first extracted into toluene in the membrane envelope, and were then extracted specifically onto the MWCNTs-MIP. After the extraction, target analytes were desorbed in methanol for liquid chromatography analysis. MWCNTs-MIP of prometryn were used as a model to demonstrate the feasibility of this novel microextraction technique. Factors affecting the extraction including organic solvent, stirring rate, extraction time, salt concentration, and pH were investigated. Under the optimized conditions, the limits of detection (a signal-to-noise ratio of 3) for the selected triazine herbicides were 0.08-0.38 μg/L. The prepared membrane envelope could be used at least 50 times. The developed method was used for the analysis of the triazines spiked in river water, wastewater, and liquid milk, with recoveries ranging from 79.3-97.4, 58.9-110.3 and 76.2-104.9%, respectively.     

Fluorescence anisotropy imaging reveals localization of meso-tetrahydroxyphenyl chlorin in the nuclear envelope

We have measured the intrinsic fluorescence anisotropies of six photosensitizers in homogeneous solution, and we have imaged the anisotropies of these sensitizers in tumor cell monolayers using polarization-sensitive laser-scanning confocal microscopy. The intrinsic anisotropies are unremarkable and are within the approximate range of 0.2–0.27. In cells, however, very interesting behavior is exhibited by meso -tetrahydroxyphenyl chlorin (mTHPC). Polarization-sensitive images of mTHPC's fluorescence show a pronounced banding of alternating high and low anisotropy consistent with an ordering of the sensitizer in the nuclear envelope, indicating that this structure is a target of photodynamic damage with this sensitizer. None of the other sensitizers exhibits localization to the nuclear envelope. The frequency distributions of the intracellular anisotropies of the sensitizers exhibit variable peaks and widths. An unusual case is that of Photofrin, with a peak in its anisotropy frequency distribution of –0.12. The change from a positive intrinsic anisotropy in homogeneous solution to a negative value in cells suggests an environmentally induced change in the relative orientations of the absorption and emission dipole moments.