Showing papers on "Nanoparticle published in 2009"
TL;DR: Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility, according to a review of their radiative and nonradiative properties.
Abstract: Noble metal nanoparticles are capable of confining resonant photons in such a manner as to induce coherent surface plasmon oscillation of their conduction band electrons, a phenomenon leading to two important properties. Firstly, the confinement of the photon to the nanoparticle's dimensions leads to a large increase in its electromagnetic field and consequently great enhancement of all the nanoparticle's radiative properties, such as absorption and scattering. Moreover, by confining the photon's wavelength to the nanoparticle's small dimensions, there exists enhanced imaging resolving powers, which extend well below the diffraction limit, a property of considerable importance in potential device applications. Secondly, the strongly absorbed light by the nanoparticles is followed by a rapid dephasing of the coherent electron motion in tandem with an equally rapid energy transfer to the lattice, a process integral to the technologically relevant photothermal properties of plasmonic nanoparticles. Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility. We begin this review of gold nanorods by summarizing their radiative and nonradiative properties. Their various synthetic methods are then outlined with an emphasis on the seed-mediated chemical growth. In particular, we describe nanorod spontaneous self-assembly, chemically driven assembly, and polymer-based alignment. The final section details current studies aimed at applications in the biological and biomedical fields.
1,713 citations
TL;DR: The role of important factors such as solution ionic strength, pH, and particle surface chemistry that control nanoparticle dispersion was examined in this article, where the size and zeta potential of four TiO2 and three quantum dot samples dispersed in different solutions (including one physiological medium) were characterized.
Abstract: Characterizing the state of nanoparticles (such as size, surface charge, and degree of agglomeration) in aqueous suspensions and understanding the parameters that affect this state are imperative for toxicity investigations. In this study, the role of important factors such as solution ionic strength, pH, and particle surface chemistry that control nanoparticle dispersion was examined. The size and zeta potential of four TiO2 and three quantum dot samples dispersed in different solutions (including one physiological medium) were characterized. For 15 nm TiO2 dispersions, the increase of ionic strength from 0.001 M to 0.1 M led to a 50-fold increase in the hydrodynamic diameter, and the variation of pH resulted in significant change of particle surface charge and the hydrodynamic size. It was shown that both adsorbing multiply charged ions (e.g., pyrophosphate ions) onto the TiO2 nanoparticle surface and coating quantum dot nanocrystals with polymers (e.g., polyethylene glycol) suppressed agglomeration and stabilized the dispersions. DLVO theory was used to qualitatively understand nanoparticle dispersion stability. A methodology using different ultrasonication techniques (bath and probe) was developed to distinguish agglomerates from aggregates (strong bonds), and to estimate the extent of particle agglomeration. Probe ultrasonication performed better than bath ultrasonication in dispersing TiO2 agglomerates when the stabilizing agent sodium pyrophosphate was used. Commercially available Degussa P25 and in-house synthesized TiO2 nanoparticles were used to demonstrate identification of aggregated and agglomerated samples.
1,519 citations
TL;DR: The design of a high-temperature-stable model catalytic system that consists of a Pt metal core coated with a mesoporous silica shell and the design concept used in the Pt@mSiO(2) core-shell catalyst can be extended to other metal/metal oxide compositions.
Abstract: Recent advances in colloidal synthesis enabled the precise control of the size, shape and composition of catalytic metal nanoparticles, enabling their use as model catalysts for systematic investigations of the atomic-scale properties affecting catalytic activity and selectivity. The organic capping agents stabilizing colloidal nanoparticles, however, often limit their application in high-temperature catalytic reactions. Here, we report the design of a high-temperature-stable model catalytic system that consists of a Pt metal core coated with a mesoporous silica shell (Pt@mSiO2). Inorganic silica shells encaged the Pt cores up to 750 ∘C in air and the mesopores providing direct access to the Pt core made the Pt@mSiO2 nanoparticles as catalytically active as bare Pt metal for ethylene hydrogenation and CO oxidation. The high thermal stability of Pt@mSiO2 nanoparticles enabled high-temperature CO oxidation studies, including ignition behaviour, which was not possible for bare Pt nanoparticles because of their deformation or aggregation. The results suggest that the Pt@mSiO2 nanoparticles are excellent nanocatalytic systems for high-temperature catalytic reactions or surface chemical processes, and the design concept used in the Pt@mSiO2 core–shell catalyst can be extended to other metal/metal oxide compositions. Colloidal synthesis can help to precisely control the shape and composition of catalytic metal nanoparticles, but it has so far proved difficult to use these particles in high-temperature reactions. Core–shell structures capable of isolating Pt-mesoporous silica nanoparticles have now been shown to be catalytically active for ethylene hydrogenation and CO oxidation at high temperature.
1,344 citations
TL;DR: The ability of CuO nanoparticles to reduce bacterial populations to zero was enhanced in the presence of sub-MBC concentrations of silver nanoparticles, suggesting release of ions may be required for optimum killing.
1,273 citations
TL;DR: In this article, the properties, applications, and syntheses of three magnetic iron oxides (hematite, magnetite, and maghemite) are discussed and methods of preparation that allow control over the size, morphology, surface treatment and magnetic properties of their nanoparticles.
1,206 citations
TL;DR: An overview of the cosmetic products currently on the market is given and the improvement of the benefit/risk ratio of the topical therapy is shown and the lipid nanoparticles are a "nanosafe" carrier.
1,186 citations
01 Jan 2009
TL;DR: In this paper, the magnetic properties of magnetic nanoparticles have been investigated and a number of methods for nanoparticle synthesis including the preparation of metallic magnetic particles have been described in the literature, including the control of particle size, shape, and monodispersity as well as their stability towards oxidation.
Abstract: As compared to bulk materials, magnetic nanoparticles possess distinct magnetic properties and attempts have been made to exploit their beneficial properties for technical and biomedical applications, e.g. for magnetic fluids, high-density magnetic recording, or biomedical diagnosis and therapy. Early magnetic fluids (MFs) were produced by grinding magnetite with heptane or long chain hydrocarbon and a grinding agent, e.g. oleic acid [152]. Later procedures for MFs precipitated Fe 3+/Fe 2+ of an aqueous solution with a base, coated the particles by oleic acid, and dispersed them in carrier liquid [161]. However, besides the elemental composition and crystal structure of the applied magnetic particles, particle size and particle size distribution determine the properties of the resulting MF. Many methods for nanoparticle synthesis including the preparation of metallic magnetic particles have been described in the literature. However, there still remain important questions, e.g. concerning control of particle size, shape, and monodispersity as well as their stability towards oxidation. Moreover, peptization by suitable surfactants or polymers into stable MFs is an important issue since each application in engineering or biomedicine needs special MFs with properties adjusted to the requirements of the system.
980 citations
TL;DR: It is demonstrated that spherical nanoparticles uniformly grafted with macromolecules ('nanoparticle amphiphiles') robustly self-assemble into a variety of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix.
Abstract: It is easy to understand the self-assembly of particles with anisotropic shapes or interactions (for example, cobalt nanoparticles or proteins) into highly extended structures. However, there is no experimentally established strategy for creating a range of anisotropic structures from common spherical nanoparticles. We demonstrate that spherical nanoparticles uniformly grafted with macromolecules ('nanoparticle amphiphiles') robustly self-assemble into a variety of anisotropic superstructures when they are dispersed in the corresponding homopolymer matrix. Theory and simulations suggest that this self-assembly reflects a balance between the energy gain when particle cores approach and the entropy of distorting the grafted polymers. The effectively directional nature of the particle interactions is thus a many-body emergent property. Our experiments demonstrate that this approach to nanoparticle self-assembly enables considerable control for the creation of polymer nanocomposites with enhanced mechanical properties. Grafted nanoparticles are thus versatile building blocks for creating tunable and functional particle superstructures with significant practical applications.
942 citations
TL;DR: This perspective reviews recent developments in the synthesis, electrochemistry, and optical properties of gold nanoparticles, with emphasis on papers initiating the developments and with an eye to their consequences.
Abstract: This perspective reviews recent developments in the synthesis, electrochemistry, and optical properties of gold nanoparticles, with emphasis on papers initiating the developments and with an eye to their consequences. Key aspects of Au nanoparticle synthesis have included the two-phase synthesis of thiolated nanoparticles, the sequestration and reduction of Au salts within dendrimers, the controlled growth of larger particles of well-defined shapes via the seeded approach, and the assembling of a variety of nanoparticle networks and nanostructures. The electrochemistry of thiolated Au nanoparticles is systemized as regions of bulk-continuum voltammetry, voltammetry reflective of quantized double-layer charging, and molecule-like voltammetry reflective of molecular energy gaps. These features are principally determined by the nanoparticle core. Interesting multielectron Au nanoparticle voltammetry is observed when the thiolate ligand shell has been decorated with redox groupings. Another development is that Au nanoparticles were discovered to exhibit unanticipated properties as heterogeneous catalysts, starting with the low-temperature oxidation of CO. Substantial progress has also been made in understanding the surface plasmon spectroscopy of Au nanoparticles and nanorods. The need to investigate the optical properties of metal particles of a single, well-defined shape and size has motivated the development of a number of new techniques, leading to the study of electron transfer and redox catalysis on single nanoparticles.
940 citations
TL;DR: The investigation of particle size effects will impact on all applications of nanoparticles in biomedicine because it determines the mechanism and rate of cell uptake of ananoparticle and its ability to permeate through tissue.
Abstract: because itdetermines the mechanism and rate of cell uptake of ananoparticle and its ability to permeate through tissue. Theinvestigation of particle size effects will impact on allapplications of nanoparticles in biomedicine. It has beenfoundthatparticlesizecanaffecttheefficiencyandpathwayofcellularuptakebyinfluencingtheadhesionoftheparticlesandtheir interaction with cells.
915 citations
TL;DR: It is demonstrated that high-quality nanofibers can be readily produced in bulk quantity using the conventional chemical oxidative polymerization of aniline, and a range of new useful functionalities are developed.
Abstract: Known for more than 150 years, polyaniline is the oldest and potentially one of the most useful conducting polymers because of its facile synthesis, environmental stability, and simple acid/base doping/dedoping chemistry. Because a nanoform of this polymer could offer new properties or enhanced performance, nanostructured polyaniline has attracted a great deal of interest during the past few years. This Account summarizes our recent research on the syntheses, processing, properties, and applications of polyaniline nanofibers. By monitoring the nucleation behavior of polyaniline, we demonstrate that high-quality nanofibers can be readily produced in bulk quantity using the conventional chemical oxidative polymerization of aniline. The polyaniline nanostructures formed using this simple method have led to a number of exciting discoveries. For example, we can readily prepare aqueous polyaniline colloids by purifying polyaniline nanofibers and controlling the pH. The colloids formed are self-stabilized via el...
TL;DR: In this article, the authors synthesize silver nanoparticles from AgNO3 through a simple green route using the latex of Jatropha curcas as reducing as well as capping agent.
TL;DR: The bark extract and powder of novel Cinnamon zeylanicum are a good bio-resource/biomaterial for the synthesis of Ag nanoparticles with antimicrobial activity and the surface charge of the formed nanoparticles was highly negative.
TL;DR: N nanoparticles are not always more toxic than micrometer particles, but the high toxicity of CuO nanoparticles shows that the nanolevel gives rise to specific concern.
TL;DR: It is apparent that the unique properties of small size and corresponding large specific surface area of small nanometer‐scale ZnO particles impose several effects that govern its antibacterial action that do not exist in the range of microscale particles.
Abstract: An innovative study aimed at understanding the influence of the particle size of ZnO (from the microscale down to the nanoscale) on its antibacterial effect is reported herein. The antibacterial activity of ZnO has been found to be due to a reaction of the ZnO surface with water. Electron-spin resonance measurements reveal that aqueous suspensions of small nanoparticles of ZnO produce increased levels of reactive oxygen species, namely hydroxyl radicals. Interestingly, a remarkable enhancement of the oxidative stress, beyond the level yielded by the ZnO itself, is detected following the antibacterial treatment. Likewise, an exposure of bacteria to the small ZnO nanoparticles results in an increased cellular internalization of the nanoparticles and bacterial cell damage. An examination of the antibacterial effect is performed on two bacterial species: Escherichia coli (Gram negative) and Staphylococcus aureus (Gram positive). The nanocrystalline particles of ZnO are synthesized using ultrasonic irradiation, and the particle sizes are controlled using different solvents during the sonication process. Taken as a whole, it is apparent that the unique properties (i.e., small size and corresponding large specific surface area) of small nanometer-scale ZnO particles impose several effects that govern its antibacterial action. These effects are size dependent and do not exist in the range of microscale particles.
TL;DR: The evaluation of targeted nanoparticles in the treatment of cancers and diseases of the central nervous system, such as glioblastoma multiforme, neurovascular disorders, and neurodegenerative diseases, is discussed.
TL;DR: The surface-passivated carbon dots show good biocompatibility as potential bioimaging agents offering nanometer-scale resolution.
Abstract: Carbon lights up: A facile chemical method yields multicolor photoluminescent carbon dots derived from polymer/silica nanocomposites, which were prepared using surfactant-modified silica spheres as carriers and resols (phenol/formaldehyde resins) as carbon precursor (see picture). The surface-passivated carbon dots show good biocompatibility as potential bioimaging agents offering nanometer-scale resolution.
TL;DR: Comparisons with model calculations indicate the important roles of nanoparticle percolation and porosity of the nanocomposites on the dielectric properties, and the calculated maximum energy densities indicate maximal extractable energy for two different particle volume fractions.
Abstract: The dielectric permittivity and electric breakdown strength of nanocomposites comprising poly(vinylidene fluoride-co-hexafluoro propylene) and phosphonic acid surface-modified BaTiO3 nanoparticles have been investigated as a function of the volume fraction of nanoparticles. The mode of binding of pentafluorobenzylphosphonic acid on the BaTiO3 particles was investigated using infrared and 31P solid-state nuclear magnetic resonance spectroscopy, and the phosphonic acid was found to form well ordered, tightly bound monolayers. The effective permittivity of nanocomposites with low volume fractions (<50%) was in good agreement with standard theoretical models, with a maximum relative permittivity of 35. However, for nanoparticle volume fractions of greater than 50%, the effective permittivity was observed to decrease with increasing nanoparticle volume fraction, and this was correlated with an increase in porosity of the spin-coated nanocomposite films. The dielectric breakdown strength was also found to decre...
TL;DR: It was proved that the chemical treatment clearly improves the ultimate properties of the nanocomposites and significant differences were reported according to the nature of the nanoparticle and amount of nanofillers used as reinforcement.
TL;DR: The fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 microm using a novel electrochemistry approach is reported.
Abstract: Dye-sensitized solar cells consist of a random network of titania nanoparticles that serve both as a high-surface-area support for dye molecules and as an electron-transporting medium. Despite achieving high power conversion efficiencies, their performance is limited by electron trapping in the nanoparticle film. Electron diffusion lengths can be increased by transporting charge through highly ordered nanostructures such as titania nanotube arrays. Although titania nanotube array films have been shown to enhance the efficiencies of both charge collection and light harvesting, it has not been possible to grow them on transparent conducting oxide glass with the lengths needed for high-efficiency device applications (tens of micrometres). Here, we report the fabrication of transparent titania nanotube array films on transparent conducting oxide glass with lengths between 0.3 and 33.0 µm using a novel electrochemistry approach. Dye-sensitized solar cells containing these arrays yielded a power conversion efficiency of 6.9%. The incident photon-to-current conversion efficiency ranged from 70 to 80% for wavelengths between 450 and 650 nm. Transparent films of titania nanotubes up to 30-μm long are fabricated on transparent conducting oxide glass, and used to make dye-sensitized solar cells.
TL;DR: This report is a report on extracellular synthesis method for the preparation of Au, Ag and Au-Ag nanoparticles in water, using the extract of Volvariella volvacea, a naturally occurring edible mushroom, as reducing and protecting agents.
01 Jan 2009
TL;DR: A brief review of the classifications of metal combustion based on thermodynamic considerations and the different types of combustion regimes of metal particles (diffusion vs. kinetic control) is presented in this article.
Abstract: Metal combustion has received renewed interest largely as a result of the ability to produce and characterize metallic nanoparticles. Much of the highly desirable traits of nanosized metal powders in combustion systems have been attributed to their high specific surface area (high reactivity) and potential ability to store energy in surfaces. In addition, nanosized powders are known to display increased catalytic activity, superparamagnetic behavior, superplasticity, lower melting temperatures, lower sintering temperatures, and higher theoretical densities compared to micron and larger sized materials. The lower melting temperatures can result in lower ignition temperatures of metals. The combustion rates of materials with nanopowders have been observed to increase significantly over similar materials with micron sized particles. A lower limit in size of nanoenergetic metallic powders in some cases may result from the presence of their passivating oxide coating. Consequently, coatings, self-assembled monolayers (SAMs), and the development of composite materials that limit the volume of non-energetic material in the powders have been under development in recent years. After a brief review of the classifications of metal combustion based on thermodynamic considerations and the different types of combustion regimes of metal particles (diffusion vs. kinetic control), an overview of the combustion of aluminum nanoparticles, their applications, and their synthesis and assembly is presented.
TL;DR: The optimal conditions for maximum synthesis of silver nanoparticles (AgNPs) through reduction of Ag(+) ions by the culture supernatant of Escherichia coli are reported and it is demonstrated that particle size could be controlled by varying the parameters such as temperature, pH and concentration of AgNO(3).
TL;DR: In this paper, two plants, Magnolia kobus and Diopyros kaki, were used for ecofriendly extracellular synthesis of metallic gold nanoparticles, which were formed by treating an aqueous HAuCl 4 solution using the plant leaf extracts as reducing agents.
TL;DR: The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell.
Abstract: The miniemulsion process allows the formation of complex structured polymeric nanoparticles and the encapsulation of a solid or liquid, an inorganic or organic, or a hydrophobic or hydrophilic material into a polymer shell. Many different materials, ranging from organic and inorganic pigments, magnetite, or other solid nanoparticles, to hydrophobic and hydrophilic liquids, such as fragrances, drugs, or photoinitators, can be encapsulated. Functionalization of the nanoparticles can also be easily obtained. Compared to polymerization processes in organic solvents, polymerization to obtain polymeric nanoparticles can be performed in environmentally friendly solvents, usually water.
TL;DR: Electron tomography revealed a left-handed chirality in the spiral tubes, double-wall tube features, and conformational transitions between tubes.
Abstract: The assembly of nanoparticles into three-dimensional (3D) architectures could allow for greater control of the interactions between these particles or with molecules. DNA tubes are known to form through either self-association of multi-helix DNA bundle structures or closing up of 2D DNA tile lattices. By the attachment of single-stranded DNA to gold nanoparticles, nanotubes of various 3D architectures can form, ranging in shape from stacked rings to single spirals, double spirals, and nested spirals. The nanoparticles are active elements that control the preference for specific tube conformations through size-dependent steric repulsion effects. For example, we can control the tube assembly to favor stacked-ring structures using 10-nanometer gold nanoparticles. Electron tomography revealed a left-handed chirality in the spiral tubes, double-wall tube features, and conformational transitions between tubes.
TL;DR: The state of the art with respect to the preparation and use of supported metal nanoparticles in catalysis is described, the main groups of such nanoparticles (noble and transitionMetal nanoparticles) are highlighted and future prospects are discussed.
Abstract: Metal nanoparticles have attracted much attention over the last decade owing to their unique properties as compared to their bulk metal equivalents, including a large surface-to-volume ratio and tunable shapes. To control the properties of nanoparticles with particular respect to shape, size and dispersity is imperative, as these will determine the activity in the desired application. Supported metal nanoparticles are widely employed in catalysis. Recent advances in controlling the shape and size of nanoparticles have opened the possibility to optimise the particle geometry for enhanced catalytic activity, providing the optimum size and surface properties for specific applications. This Review describes the state of the art with respect to the preparation and use of supported metal nanoparticles in catalysis. The main groups of such nanoparticles (noble and transition metal nanoparticles) are highlighted and future prospects are discussed.
TL;DR: This work illustrates how oxidative etching and kinetic control can be employed to manipulate the shapes and optical responses of plasmonic nanoparticles made of either Ag or Pd.
Abstract: Under the irradiation of light, the free electrons in a plasmonic nanoparticle are driven by the alternating electric field to collectively oscillate at a resonant frequency in a phenomenon known as surface plasmon resonance. Both calculations and measurements have shown that the frequency and amplitude of the resonance are sensitive to particle shape, which determines how the free electrons are polarized and distributed on the surface. As a result, controlling the shape of a plasmonic nanoparticle represents the most powerful means of tailoring and fine-tuning its optical resonance properties. In a solution-phase synthesis, the shape displayed by a nanoparticle is determined by the crystalline structure of the initial seed produced and the interaction of different seed facets with capping agents. Using polyol synthesis as a typical example, we illustrate how oxidative etching and kinetic control can be employed to manipulate the shapes and optical responses of plasmonic nanoparticles made of either Ag or Pd. We conclude by highlighting a few fundamental studies and applications enabled by plasmonic nanoparticles having well-defined and controllable shapes.
TL;DR: Effect of protein binding on the nanoparticle hydrodynamic size, elements of coagulation, and the complement system have been investigated and the difference in size measurements obtained from dynamic light scattering, electron microscopy, and scanning probe microscopy are discussed.
TL;DR: Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution and played an important role as connectors to assemble these active amino groups of poly- Llysine, which provided a very biOCompatible environment for further functionalization, such as attaching bioactive molecules.
Abstract: Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution. PLL-functionalized graphene is water-soluble and biocompatible, which makes it a novel material promising for biological applications. Graphene sheets played an important role as connectors to assemble these active amino groups of poly-l-lysine, which provided a very biocompatible environment for further functionalization, such as attaching bioactive molecules. As an example, an amplified biosensor toward H2O2 based on linking peroxidase onto PLL-functionalized graphene was investigated.