Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Nanostructures”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed2005

Microwave-assisted synthesis of metallic nanostructures in solution.

Microwave (MW) rapid heating has received considerable attention as a new promising method for the one-pot synthesis of metallic nanostructures in solutions. In this concept, advantageous application of this method has been demonstrated by using some typical examples for the preparation of Ag, Au, Pt, and AuPd nanostructures. Not only spherical nanoparticles, but also single crystalline polygonal plates, sheets, rods, wires, tubes, and dendrites were prepared within a few minutes under MW heating. Morphologies and sizes of nanostructures could be controlled by changing various experimental parameters, such as the concentration of metallic salt and surfactant polymer, the chain length of the surfactant polymer, the solvent, and the reaction temperature. In general, nanostructures with smaller sizes, narrower size distributions, and a higher degree of crystallization were obtained under MW heating than those in conventional oil-bath heating. The origin of these characteristic features under MW irradiation is discussed in terms of thermal and non-thermal effects under MW irradiation.

Journal Article↗
PubMed2006

Systematic investigation of the formation of 1D alpha-Si(3)N(4) nanostructures by using a thermal-decomposition/nitridation process.

This article describes a simple thermal-decomposition/nitridation method for the large-scale synthesis of 1D alpha-Si(3)N(4) nanostructures, such as millimeter-scale microribbons, nanosaws, nanoribbons, and nanowires. These nanostructures are systematically investigated by checking the product deposited at different areas by using powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electron energy loss spectroscopy. Studies show that all these nanostructures have a single-crystalline nature and predominantely grow along the [011] direction. These 1D nanostructures are formed by thermal decomposition, followed by the nitridation of SiO.

Journal Article↗
PubMed2005

Nanomaterials and chip-based nanostructures for capillary electrophoretic separations of DNA.

Capillary electrophoresis (CE) and microchip capillary electrophoresis (MCE) using polymer solutions are two of the most powerful techniques for the analysis of DNA. Problems, such as the difficulty of filling polymer solution to small separation channels, recovering DNA, and narrow separation size ranges, have put a pressure on developing new techniques for DNA analysis. In this review, we deal with DNA separation using chip-based nanostructures and nanomaterials in CE and MCE. On the basis of the dependence of the mobility of DNA molecules on the size and shape of nanostructures, several unique chip-based devices have been developed for the separation of DNA, particularly for long DNA molecules. Unlike conventional CE and MCE methods, sieving matrices are not required when using nanostructures. Filling extremely low-viscosity nanomaterials in the presence and absence of polymer solutions to small separation channels is an alternative for the separations of DNA from several base pairs (bp) to tens kbp. The advantages and shortages of the use of nanostructured devices and nanomaterials for DNA separation are carefully addressed with respect to speed, resolution, reproducibility, costs, and operation.

DNA↗
PubMed2003

Nanostructure evolution studies of bulk polymer materials with synchrotron radiation: progress in method development.

The prospects of a modern analysis of nanostructure evolution during the processing of polymer materials by means of scattering from synchrotron radiation are demonstrated in examples. The beam sources have gained stability, shortages are located in beamline setups and in method development for the quantitative analysis of voluminous data sets. By using the proposed multidimensional chord distribution function (CDF) analysis method, nanostructure information from small-angle X-ray scattering (SAXS) data are extracted and visualised. The method can be automated if the beamline setup is able to deliver a full data set with simple constraints. In this case even a simultaneous data evaluation is possible (while one pattern is accumulated, the previous one is analysed). The advantages of the method are demonstrated in a study of the straining of a thermoplastic elastomer. The possibilities of an automated analysis are demonstrated in an investigation of the crystallisation behaviour of high-pressure injection-moulded polyethylene (HPIM-PE). The achievable results of nanostructure analysis of polymer materials are discussed. It is shown that the time-resolved SAXS of polymer materials studied during a transformation and analysed by the CDF method is not just a powerful tool to investigate the relationship between structure and properties of materials; the information that can be gained concerning the processes that control nanostructure evolution is equally important. In the future the enlightenment of such relationships may help to tailor polymer materials with respect to their properties and, beyond that, to improve assessments concerning their aging.

Journal Article↗
PubMed2004

Pt based enzyme electrode probes assembled with Prussian Blue and conducting polymer nanostructures.

Conductive polymer nanotubules of 1,2-diaminobenzene (1,2-DAB) were prepared using a porous polycarbonate membrane template, placed on a Pt foil and used to support the polymer, then, the electropolymerisation was performed by chronocoulometry. The obtained conductive polymer nanostructures were then placed on Pt electrode and used to support highly dispersed prussian blue (PB), which acts as the active component for H2O2 detection. The observed good stability of PB as catalyst of H2O2 was related to the presence of organic non-conventional conducting polymers in a composite nanostructured film. These nanostructured polymer/PB composite films were also characterised by scanning electron microscopy (SEM) and Raman spectroscopy. The non-conventional conducting polymer nanotubules/PB modified Pt electrodes were tested by cyclic voltammeter for stability at different pH values, then, by amperometry, for hydrogen peroxide, ascorbic acid, acetaminophen, uric acid and acetylcholine. Glucose oxidase (GOD), lactate oxidase (LOD), L-amino acid oxidase (L-AAOD), alcohol oxidase (AOD), glycerol-3-phosphate oxidase (GPO), lysine oxidase (LyOx), and choline oxidase (ChOx) were immobilised on PB layer supported on 1,2-diaminobenzene (1,2-DAB) nanotubules onto the Pt electrodes. Different strategies for enzyme immobilisation were performed and used. Analytical parameters such as reproducibility, interference rejection, response time, storage and operational stability of the sensors have been studied and optimised. Results provide a guide to design high sensitive, stable and interference-free biosensors. The glucose biosensors assembled with nanostructured poly(1,2-DAB) showed a detection limit of 5 x 10(-5) mol l(-1), a wide linearity range (5 x 10(-5) to 5 x 10(-3) mol l(-1)), a high selectivity, a stability of 3 months at 4 degrees C, and at least 4 weeks at room temperature. Similar analytical parameters and stability were also studied for L-(+)-lactic acid, L-leucine, ethanol, glycerol-3-phosphate, lysine, and choline biosensors.

Biosensing Techniques↗
PubMed2004

Nanostructured hybrid materials from aqueous polymer dispersions.

Organic-inorganic (O-I) hybrids with well-defined morphology and structure controlled at the nanometric scale represent a very interesting class of materials both for their use as biomimetic composites and because of their potential use in a wide range of technologically advanced as well as more conventional application fields. Their unique features can be exploited or their role envisaged as components of electronic and optoelectronic devices, in controlled release and bioencapsulation, as active substrates for chromatographic separation and catalysis, as nanofillers for composite films in packaging and coating, in nanowriting and nanolithography, etc. A synergistic combination or totally new properties with respect to the two components of the hybrid can arise from nanostructuration, achieved by surface modification of nanostructures, self-assembling or simply heterophase dispersion. In fact, owing to the extremely large total surface area associated with the resulting morphologies, the interfacial interactions can deeply modify the bulk properties of each component. A wide range of starting materials and of production processes have been studied in recent years for the controlled synthesis and characterization of hybrid nanostructures, from nanoparticle or lamellar dispersions to mesoporous materials obtained from templating nanoparticle dispersions in a continuous, e.g. ceramic precursor, matrix. This review is aimed at giving some basic definitions of what is intended as a hybrid (O-I) material and what are the main synthetic routes available. The various methods for preparing hybrid nanostructures and, among them, inorganic-organic or O-I core-shell nanoparticles, are critically analyzed and classified based on the reaction medium (aqueous, non-aqueous), and on the role it plays in directing the final morphology. Particular attention is devoted to aqueous systems and water-borne dispersions which, in addition to being environmentally more acceptable or even a mandatory choice for any future development of large output applications (e.g. in paint, ink and coating industry), can provide the thermodynamic drive for self-assembling of amphiphilics, adsorption onto colloidal particles or partitioning of the hybrid's precursors between dispersed nanosized reaction loci, as in emulsion or miniemulsion free-radical polymerization. While nanoencapsulation and self-assembling processes are already exploited as commercially viable fabrication methods, a newly developed technique based on two-stage sol-gel and free-radical emulsion polymerization is described, which can grant a versatile synthetic approach to hybrid O-I nanoparticles with tailor-made composition of both the organic core and the silica or organosilica shell, and good control on morphology, size and heterophase structure in the 50-500 nm range. Styrene or acrylate homo- and copolymer core latex particles need to be modified with a reactive comonomer, such as trimethoxysilylpropyl methacrylate, to achieve efficient interfacial coupling with the inorganic shell. Accurate control over pH and process conditions is required to avoid latex coagulation or, in case of organic particles with uniform composition, incipient intraparticle crosslinking.

Journal Article↗
PubMed2006

Determining molecule-carbon surface adsorption energies using molecular mechanics and graphene nanostructures.

Five model surfaces were developed using molecular mechanics with MM2 parameters. A smooth, flat model surface was constructed of three parallel graphene layers where each graphene layer contained 127 interconnected benzene rings. Four rough surfaces were constructed by varying the separation between a pair of graphene nanostructures placed on the topmost layer of graphene. Each nanostructure contained 17 benzene rings arranged in a linear strip. The parallel nanostructures were moved closer together to increase the surface roughness and to enhance the molecule-surface interaction. Experimental adsorption energy values from the temperature variation of second gas-solid virial coefficients values were available for 16 different alkanes, haloalkanes, and ether molecules adsorbed on Carbopack B (Supelco, 100 m(2)/g). For each of the five different surface models, sets of 16 calculated adsorption energies, E(cal)( *), were determined and compared to the available experimental adsorption energies, E( *). The best linear regression correlation between E( *) and E(cal)( *) was found for a 1.20 nm internuclei separation of the surface nanostructures, and for this surface model the calculated gas-solid interaction energies closely matched the experimental values (E( *)=1.018E(cal)( *), r(2)=0.964).

Journal Article↗
PubMed2006

Self-assembly of Co-based nanosheets into novel nest-shaped nanostructures: Synthesis and characterization.

We report the first observation of the formation of novel Co-based three-dimensional (3D) self-assembly hollow nanostructures, i.e., nest-shaped nanospheres composed of sheet-like particles, via reduction of cobalt salt with sodium tetrahydroboride in cetyltrimethylammonium bromide (CTAB)-cyclohexane-NH4F aqueous solutions. It was found that the cyclohexane has a significant influence on the formation of the nest-shaped Co-based nanospheres, because when the experiments are carried out in the absence of cyclohexane, only sheet-like particles are formed. NH4F plays also an important role in the formation of the hollow nanostructures because without this salt mainly solid spherical structures, composed of sheet-like particles, instead of nest-shaped structures are obtained. The nanostructures are mainly formed by Co, but also a minor amount (17%) of Co2B is present in the final compounds. The structures are characterized by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), and field-emission scanning electron microscopy (FESEM). A possible mechanism for the formation of the novel Co-based nanostructures is proposed.

Journal Article↗
PubMed2002

Spray-dried indomethacin-loaded polyester nanocapsules and nanospheres: development, stability evaluation and nanostructure models.

The industrial development of polymeric nanoparticle suspensions, as drug delivery systems, is limited due to the problems in maintaining stability of suspensions. In this work, a spray-drying technique was applied to dry nanocapsule and nanosphere suspensions prepared by nanoprecipitation of polyesters using SiO(2) as adjuvant. Powders obtained from nanocapsules presented stable drug recoveries and morphological characteristics after 5 months. For nanocapsules, nanostructures around 200 nm were observed by scanning electron microscopy (SEM) on the surface of microparticles of SiO(2), whereas for the nanosphere formulation, nanostructures with a reduced diameter (60-90 nm) were observed, despite the particle sizes of each original suspension being similar, when measured by photon correlation spectroscopy (PCS). In order to investigate the morphological aspects of nanocapsule and nanosphere powders, several nanosphere formulations were spray-dried using different concentrations of SiO(2) and a comparative study of the different colloidal systems (nanocapsules, nanospheres, nanoemulsion or nanodispersion) was carried out by PCS. SEM analyses showed that nanostructures with reduced diameter are formed independently of the adjuvant concentration. The dynamic properties of these systems allowed to suggest that the structure of the nanosphere particle (polymer, sorbitan monostearate and polysorbate 80) was a polymeric matrix dispersing the sorbitan monostearate which, when submitted to the spray-drying process in the presence of SiO(2), gave nanostructures presenting diameters around 80 nm covering the microparticles due to the release of lipophilic surfactant from the polymeric matrix.

Capsules↗
PubMed2001

Core-shell nanostructured nanoparticle films as chemically sensitive interfaces.

This paper reports the results of an investigation of vapor molecule sorption at different types of nanostructured nanoparticle films. Core-shell nanoparticles of two different core sizes, AU2-nm and Au5-nm, and molecular linkers of two different binding properties, 1,9-nonanedithiol and 11-mercaptoundecanoic acid, are utilized as building blocks for constructing chemically sensitive interfaces. The work couples measurements of two different transducers, interdigitated microelectrodes and quartz crystal microbalance, to determine the correlation of the electronic resistance change and the mass loading with vapor sorption. The responses to vapor sorption at these nanostructured interfaces are demonstrated to be dependent on the core size of nanoparticles and the chemical nature of linking molecules. The difference of molecular interactions of vapor molecules at the nanostructured interface is shown to have a significant impact on the response profile and sensitivity. For the tested vapor molecules, while there are small differences for the sorption of nonpolar and hydrophobic vapor molecules, there are striking differences for the sorption of polar and hydrophilic vapor molecules at these nanostructured interfacial materials. The implication of the findings to the delineation of design parameters for constructing core-shell nanoparticle assemblies as chemically sensitive interfacial materials is also discussed.

Journal Article↗
PubMed2006

Local feedback mode of scanning electrochemical microscopy for electrochemical characterization of one-dimensional nanostructure: theory and experiment with nanoband electrode as model substrate.

Local feedback mode is introduced as a novel operation mode of scanning electrochemical microscopy (SECM) for electrochemical characterization of a single one-dimensional (1D) nanostructure, for example, a wire, rod, band, and tube with 1-100-nm width and micrometer to centimeter length. To demonstrate the principle, SECM feedback effects under diffusion limitation were studied theoretically and experimentally with a disk probe brought near a semi-infinitely long band electrode as a geometrical model for a conductive 1D nanostructure. As the band becomes narrower than the disk diameter, the feedback mechanism for tip current enhancement is predicted to change from standard positive feedback mode, to positive local feedback mode, and then to negative local feedback mode. The negative local feedback effect is the only feedback effect that allows observation of a 1D nanostructure without serious limitations due to small lateral dimension, available tip size, or finite electron-transfer rate. In line-scan and approach-curve experiments, an unbiased Pt band electrode with 100-nm width and 2.6-cm length was detectable in negative local feedback mode, even using a 25-microm-diameter disk Pt electrode. Using a 2-microm-diameter probe, both well-defined and defected sites were observed in SECM imaging on the basis of local electrochemical activity of the nanoband electrode. Noncontact and spatially resolved measurement is an advantage of this novel SECM approach over standard electrochemical approaches using electrodes based on 1D nanostructure.

Journal Article↗
PubMed2006

Solution-based synthetic strategies for 1-D nanostructures.

One-dimensional (1-D) nanostructures of materials have received great research attention because of their unique photochemistry, photophysical, and electron-transport properties different from those of bulky or nanoparticle materials. One of the main challenges in this field is how to precisely control the sizes, dimensionalities, compositions, and crystal structures of materials in nanoscale. This review summarizes the recent progress in the solution-based routes to prepare 1-D nanostructures, highlighting the contribution from this laboratory. Crystal structure as one of the inherent factors that may determine the growth behavior of the nanocrystals is emphasized in this paper. Particularly compounds with layered structures or anistropic crystal structures are given special attention in the controlled growth of 1-D nanostructures. This review aims to present a relatively general understanding of the correlation between the crystal structure and growth behavior of materials under solution-based conditions and show how to choose appropriate conditions for the growth of 1-D nanostructures.

Journal Article↗
PubMed2004

Controlled synthesis of 2-D and 3-D dendritic platinum nanostructures.

Seeding and autocatalytic reduction of platinum salts in aqueous surfactant solution using ascorbic acid as the reductant leads to remarkable dendritic metal nanostructures. In micellar surfactant solutions, spherical dendritic metal nanostructures are obtained, and the smallest of these nanodendrites resemble assemblies of joined nanoparticles and the nanodendrites are single crystals. With liposomes as the template, dendritic platinum sheets in the form of thin circular disks or solid foamlike nanomaterials can be made. Synthetic control over the morphology of these nanodendrites, nanosheets, and nanostructured foams is realized by using a tin-porphyrin photocatalyst to conveniently and effectively produce a large initial population of catalytic growth centers. The concentration of seed particles determines the ultimate average size and uniformity of these novel two- and three-dimensional platinum nanostructures.

Journal Article↗
PubMed2006

Self-organization of rotaxane thin films into spatially correlated nanostructures: morphological and structural aspects.

The self-organization of rotaxane thin films into spatially correlated nanostructures is shown to occur upon a thermal stimulus. The mechanism of formation of nanostructures and their organization has been investigated using atomic force microscopy, bright field transmission electron microscopy, selected area electron diffraction, and molecular mechanics simulations. The evolution of the nanostructures follows a complex pathway, where a rotaxane thin film first dewets from the substrate to form nanosized droplets. Droplets coalesce by ripening, generating spatially correlated motifs. In a later stage, the larger droplets change shape, nucleate, and coalesce to yield crystallites that grow into larger crystals by incorporating the surrounding droplets. The results show the following: (i) the nanostructures represent a metastable state of a crystallization process; (ii) spatial correlations emerge during ripening, but they are destroyed as stable nuclei are formed and crystallization proceeds to completion; iii) crystallization, either on graphite or amorphous carbon films, leads to a precise basal plane, viz. (010), which has minimum surface energy. The inherent degrees of freedom permitted in the rotaxane architecture favors the re-organization and nucleation of the film in the solid state. Low-energy trajectories leading to crystallites with stable surfaces and minimum energy contact plane are found to occur via concerted, small amplitude, internal motions without disruption of packing and intermolecular contacts.

Journal Article↗
PubMed2005

Morphology-controllable synthesis of pyrene nanostructures and its morphology dependence of optical properties.

Morphology-controllable synthesis of various pyrene nanostructures from nanoparticles to short nanorods and nanowires (long nanorods) was achieved by a simple self-assembly method. In this approach, aqueous sodium dodecyl sulfate (SDS) micelles were used as templates to direct the self-assembly of the pyrene molecules into nanorods. It was found that changing the concentration ratio of the pyrene to SDS molecules could be employed to control the aspect ratio (length to diameter) of the pyrene nanostructures from 1 to 50 or higher. Moreover, the dimensional variation was accompanied by changes of their optical properties. With the increase of the aspect ratio, the characteristic fluorescence of the isolated pyrene molecules was suppressed and concurrently replaced by the excimer emission of the pyrene nanostructures. A blue-shift was observed in the excimer emission peaks as the length of the nanorods increased. The growth mechanism and the change in optical properties of these pyrene nanostructures were discussed in detail.

Journal Article↗
PubMed2006

Ordering of TiO2-based nanostructures on SrTiO3(001) surfaces.

A class of nanostructured surface phases on SrTiO3(001) is reported and characterized through atomic-resolution scanning tunneling microscopy and Auger electron spectroscopy. These surface phases are created via argon ion sputtering and UHV annealing and form close-packed domains of highly ordered nanostructures. Depending on the type of nanostructures present, the domain ordering exhibit either (6 x 2), (9 x 2), (12 x 2), (6 x 8), or (7 x 4) surface patterning. The nanostructures are composed of TiO2-derived complexes surrounded by a TiO2 surface termination. Such surface ordering phenomena introduce another level of complexity in the chemistry of perovskite oxide surfaces and provide a basis from which potential photocatalytic and molecular-ordering applications may be developed.

Journal Article↗
PubMed2006

Density functional theoretical investigations on various nanostructural zeolite surfaces.

Through density functional calculations, the Brønsted acidities on various nanostructural ZSM-5 zeolite surfaces were studied as well as the hydrogen exchanging processes with adsorbed H(2)O monomer or dimer. The Brønsted acidities on the four nanostructural surfaces show differences, although slightly, with their strengths increasing as (100) < (210) < (410) < (001). For hydrogen exchanging processes with H(2)O monomer or dimer, the reaction rate increases in the order (210) < (100) < (001) < (410) or (210) < (410) < (001). No transition-state structure is present on H(2)O dimer/(100) surface system. The introduction of a second H(2)O molecule accelerates the hydrogen exchanging processes and meanwhile influences the nanostructural geometries such that they are more evident. Besides the activation barrier, the adsorption energy and reaction heat display differences from one surface to another, which results in the preference of catalytic reactions to a specific nanostructural zeolite surface, such as the hydrogen exchanging processes studied in this paper.

Journal Article↗
PubMed2006

Shape-controlled electrodeposition of gold nanostructures.

A one-step, nontemplated, low-cost electrochemical method for the growth of gold nanostructures with different shapes is reported here. It is the first time that nanopyramidal, nanorod-like, and spherical gold nanostructures were fabricated on polycrystalline gold substrates through electrochemical overpotential deposition (OPD) by easily manipulating the deposited potentials and concentrations of HAuCl4. X-ray diffraction and electrochemical analyses revealed that the pyramidal structures are more extensively dominated by (111) facets in comparison with the other nanostructures. The nanopyramids, which have anisotropic structures, exhibited broad extinction over the visible region, most likely due to plasmon resonance. Oxygen reduction activity of a gold electrode with the pyramidal structures was lower than those of the electrodes with the other nanostructures since the activity at the gold (111) surface is lower than that at the (100) and (110) surfaces.

Journal Article↗