Showing papers in "Small in 2007"

Size-Dependent Cytotoxicity of Gold Nanoparticles

Abstract: Gold nanoparticles are widely used in biomedical imaging and diagnostic tests. Based on their established use in the laboratory and the chemical stability of Au(0), gold nanoparticles were expected to be safe. The recent literature, however, contains conflicting data regarding the cytotoxicity of gold nanoparticles. Against this background a systematic study of water-soluble gold nanoparticles stabilized by triphenylphosphine derivatives ranging in size from 0.8 to 15 nm is made. The cytotoxicity of these particles in four cell lines representing major functional cell types with barrier and phagocyte function are tested. Connective tissue fibroblasts, epithelial cells, macrophages, and melanoma cells prove most sensitive to gold particles 1.4 nm in size, which results in IC(50) values ranging from 30 to 56 microM depending on the particular 1.4-nm Au compound-cell line combination. In contrast, gold particles 15 nm in size and Tauredon (gold thiomalate) are nontoxic at up to 60-fold and 100-fold higher concentrations, respectively. The cellular response is size dependent, in that 1.4-nm particles cause predominantly rapid cell death by necrosis within 12 h while closely related particles 1.2 nm in diameter effect predominantly programmed cell death by apoptosis.

Mesoporous Silica Nanoparticles as a Delivery System for Hydrophobic Anticancer Drugs

Abstract: A critical obstacle and challenge for cancer therapy concerns the limited availability of effective biocompatible delivery systems for most hydrophobic therapeutic anticancer drugs. It is particularly important to improve the aqueous solubility of drugs, as low drug solubility in aqueous media hampers the ability of drugs to be administered through the intravenous route. Since many important anticancer agents have poor water solubility, the development of novel delivery systems for these molecules without the use of organic solvents has received significant attention. Nanoparticles offer great potential and a promising approach to deliver therapeutic agents into targeted organs or cells and they have been actively developed for application in cancer therapy. We have incorporated a representative hydrophobic anticancer drug, camptothecin (CPT), into the pores of fluorescent mesoporous silica nanoparticles (FMSNs) and delivered the drug into a variety of human cancer cells to induce cell death, a procedure suggesting that the mesoporous silica nanoparticles might be used as a vehicle to overcome the insolubility problem of many anticancer drugs. CPT and its derivatives are considered to be among the most promising anticancer drugs of the 21st century. Although studies have demonstrated their effectiveness against carcinomas of the stomach, colon, neck, and bladder, as well as breast and small-cell lung cancers, and leukemia, in vitro, clinical application of CPT in humans has not been achieved to date because the poor water solubility of the drug requires changes to the physicochemical characteristics. The need to formulate water-soluble salts of CPT (that is, alkaline solutions for intravenous injections) led to chemical modifications of the molecule with loss of antiACHTUNGTRENNUNGtumor activity and significant alterations in the toxicological profile of the drug. Although derivatives such as irinotecan have produced good clinical results, irinotecan was shown to have far lower cytotoxicity to cancer cells than CPT (10%), and CPT remains the most potent compound. Among a variety of drug-delivery systems, mesoporous silica materials have several attractive features for use in the delivery of water-insoluble drugs. These particles have large surface areas and porous interiors that can be used as reservoirs for storing hydrophobic drugs. The pore size and environment can be tailored to selectively store different molecules of interest, while the size and shape of the particles can be tuned to maximize cellular uptake. Unlike polymer-based nanoparticles, these robust inorganic materials can tolerate many organic solvents. Silica-based materials have been successfully used as drug-delivery vectors, gene transfection reagents, cell markers, and carriers of molecules. Here, we describe the preparation of fluorescent mesoporous silica nanoparticles that are highly stable in aqueous solution and their use for the delivery of the hydrophobic anticancer drug CPT. The FMSNs were prepared by using a base-catalyzed sol–gel process at high temperature with a modification of published procedures. 25,26] In a typical synthesis, fluorescein isothiocyanate (FITC) was first treated with 3-aminopropyltriethoxysilane (APTS) in ethanol. The mixture was then added, along with tetraethylorthosilicate, to cetyltriACHTUNGTRENNUNGmethylammonium bromide solution at 80 8C. The surfactants were removed from the pores by refluxing the nanoparticles in acidic methanol, the success of which was confirmed by Fourier transform infrared spectroscopy (FTIR; see Supporting Information). Electron microscopy and Xray diffraction (XRD) analysis showed that the particle shape and hexagonal arrays of the pores in the FMSNs remained intact after the surfactant-removal process (Figure 1). The nanoparticles were roughly spherical in shape and smaller than 130 nm in diameter. An average pore diameter of around 2 nm was observed by using transmission electron microscopy (TEM) and an interplanar spacing of dACHTUNGTRENNUNG(100) 4 nm was calculated from the XRD pattern. It is necessary for efficient cellular uptake of the particles that the FMSNs remain dispersed and do not aggregate in the buffer solution. The observed aggregation is caused by interparticle hydrogen-bonding interactions between the amine groups (from the unreacted APTS) and the silanols (Scheme 1A). By modifying only the surfaces of the FMSNs with trihydroxysilylpropyl methylphosphonate (THMP) after particle formation, we reduced the aggregation and increased the stability of the particles in aqueous solution (Scheme 1B, see Supporting Information). [*] Dr. J. Lu, Prof. F. Tamanoi Department of Microbiology, Immunology, and Molecular Genetics California NanoSystems Institute, JCCC University of California, Los Angeles 609 Charles E. Young Drive East, Los Angeles, CA 90095 (USA) Fax: (+1)310-206-5231 E-mail: fuyut@microbio.ucla.edu

Formation of nanotubes and hollow nanoparticles based on Kirkendall and diffusion processes: a review.

Abstract: The Kirkendall effect is a consequence of the different diffusivities of atoms in a diffusion couple causing a supersaturation of lattice vacancies. This supersaturation may lead to a condensation of extra vacancies in the form of so-called “Kirkendall voids” close to the interface. On the macroscopic and micrometer scale these Kirkendall voids are generally considered as a nuisance because they deteriorate the properties of the interface. In contrast, in the nanoworld the Kirkendall effect has been positively used as a new fabrication route to designed hollow nano-objects. In this Review we summarize and discuss the demonstrated examples of hollow nanoparticles and nanotubes induced by the Kirkendall effect. Merits of this route are compared with other general methods for nanotube fabrication. Theories of the kinetics and thermodynamics are also reviewed and evaluated in terms of their relevance to experiments. Moreover, nanotube fabrication by solid-state reactions and non-Kirkendall type diffusion processes are covered.

Bi2WO6 nano- and microstructures: shape control and associated visible-light-driven photocatalytic activities.

Abstract: The shape-controlled synthesis of nano- and microstructured materials has opened up new possibilities to improve their physical and chemical properties. In this work, new types of Bi(2)WO(6) with complex morphologies, namely, flowerlike, tyre- and helixlike, and platelike shapes, have been controllably synthesized by a facile hydrothermal process. The benefits of the present work also stem from the first report on the transformation of Bi(2)WO(6) from three-dimensional (3D) flowerlike superstructures to 2D platelike structures, and on the formation of tyre- and helixlike Bi(2)WO(6) superstructures. UV/Vis absorption spectra show that the optical properties of Bi(2)WO(6) samples are relevant to their size and shape. More importantly, the photocatalytic activities of Bi(2)WO(6) nano- and microstructures are strongly dependent on their shape, size, and structure for the degradation of Rhodamine B (RhB) under visible-light irradiation. The reasons for the differences in the photocatalytic activities of these Bi(2)WO(6) nano- and microstructures are further investigated.

Nanoplatforms for targeted molecular imaging in living subjects.

Abstract: Molecular or personalized medicine is the future of patient management and molecular imaging plays a key role towards this goal. Recently, nanoplatform-based molecular imaging has emerged as an interdisciplinary field, which involves chemistry, engineering, biology, and medicine. Possessing unprecedented potential for early detection, accurate diagnosis, and personalized treatment of diseases, nanoplatforms have been employed in every single biomedical imaging modality, namely, optical imaging, computed tomography, ultrasound, magnetic resonance imaging, single-photon-emission computed tomography, and positron emission tomography. Multifunctionality is the key advantage of nanoplatforms over traditional approaches. Targeting ligands, imaging labels, therapeutic drugs, and many other agents can all be integrated into the nanoplatform to allow for targeted molecular imaging and molecular therapy by encompassing many biological and biophysical barriers. In this Review, we will summarize the current state-of-the-art of nanoplatforms for targeted molecular imaging in living subjects.

Infrared-emitting colloidal nanocrystals: synthesis, assembly, spectroscopy, and applications.

Abstract: Semiconductor nanocrystals produced by means of colloidal chemistry in a solvent medium are an attractive class of nanometer-sized building blocks from which to create complex materials with unique properties for a variety of applications. Their optical and electronic properties can be tailored easily, both by their chemical composition and particle size. While colloidal nanocrystals emitting in the infrared region have seen a burst of attention during the last decade there is clearly a paucity of review articles covering their synthesis, assembly, spectroscopic characterization, and applications. This Review comprehensively addresses these topics for II-VI, III-V, and IV-VI nanocrystals, examples being HgTe and Cd(x)Hg(1-) (x)Te, InP and InAs, and PbS, PbSe, and PbTe, respectively. Among the applications discussed here are optical amplifier media for telecommunications systems, electroluminescence devices, and noninvasive optical imaging in biology.

Strong Carbon‐Nanotube Fibers Spun from Long Carbon‐Nanotube Arrays

Abstract: The superior mechanical properties of carbon nanotubes (CNTs) mean they have been regarded as a new material with the potential to revolutionize and enable many advanced technologies. CNTs have extremely high tensile strength ( 150 GPa), high modulus ( 1 TPa), large aspect ratio, low density, good chemical and environmental stability, and high thermal and electrical conductivity. These superior and unique properties make CNTs very attractive for many structural applications such as aerospace structures, body armors, and sporting goods. Early studies of CNT-reinforced nanocomposites showed that CNTs were effective fillers to enhance the mechanical properties of polymer matrices, but the reinforcement was limited by the quality of dispersion, CNT alignment, and load-transfer efficiency between the CNT and the matrix. The full reinforcement potential of CNTs has not yet been utilized in CNT composites. It has been a challenge to make macroscale CNT structures and to fully utilize the outstanding mechanical properties of CNTs. The first macroscale CNT structure was in the form of a film called buckypaper, which displayed relatively high electrical and thermal conductivity, but low mechanical properties. For the purpose of obtaining superior mechanical performance, researchers have recently focused on CNT fibers. The first CNT fiber was successfully prepared through spinning a CNT homogeneous dispersion into a polyvinyl alcohol (PVA) coagulation bath. This approach was modified by Baughman s group to make single-walled (SW) CNT composite fibers with very high strength. 8] The major issues with this approach include a relatively high fraction of remaining polymer volume and short individual CNTs, which limits the fiber s strength, electrical and thermal conductivity. Recently, new approaches have been reported in which pure CNT fibers were spun without a matrix. For example, pure CNT fibers were spun from a CNT-fuming sulfuric acid solution. A continuous multi-walled (MW) CNT yarn was pulled from a high-quality array without twisting. SWCNT fibers were spun from an aerogel in the chemical vapor deposition synthesis zone, and MWCNT fibers were spun from CNT arrays. 15] These CNT fibers usually have a strength of 1.5 GPa and a Young s modulus of 30 GPa. Here, we report the spinning of CNT fibers from relatively long CNT arrays (0.65 mm). The influence of post-spin twisting on the mechanical performance of these fibers is also discussed. Figure 1a shows a scanning electron microscopy (SEM) image of the 0.65-mm CNT array, which is synthesized by

Extremely high stability of glutathionate-protected Au25 clusters against core etching.

Abstract: It is well known that so-called magic-numbered clusters can be preferentially populated by dissociative excitation of larger precursors, because the energy required for removal of a single atom from a magic-numbered cluster is higher than from a neighbor. Thus, if the Au atoms can be removed sequentially from preformed thiolated-protected gold (Au:SR) clusters, one can anticipate a population growth of certain stable Aun:SR clusters. Chemical etching by free thiols is one feasible method for core size reduction of the Au:SR clusters. The etching rate of Aun:SR clusters must be determined as a function of core size, in order to provide a synthesis for welldefined Aun(SR)m clusters in large quantity, as well as to provide information regarding the stability of Aun(SR)m. In the present paper, we studied etching reactions of Aun(SG)m clusters with (n,m) = (10,10), (15,13), (18,14), (22,16), (25,18), (29,20), (33,22), (39,24) by free glutathione (GSH). It was found that Au25:SG clusters show higher stability against etching than the others and as a result two different reaction modes are operative depending on the core size. The Aun(SG)m (n < 25) clusters are completely oxidized to Au(I):SG complexes while Aun(SG)m (n ≥ 25) clusters are etched into Au25: SG by free GSH molecules. On the basis of this observation, a model is proposed to explain our recent finding that Au25 (SG)18 clusters are selectively formed during the reaction of triphenylphosphine-stabilized Au11 clusters and an excess amount of GSH.

Gum Arabic as a Phytochemical Construct for the Stabilization of Gold Nanoparticles: In Vivo Pharmacokinetics and X‐ray‐Contrast‐Imaging Studies

Abstract: Gold nanoparticles (AuNPs) have exceptional stability against oxidation and therefore will play a significant role in the advancement of clinically useful diagnostic and therapeutic nanomedicines. Despite the huge potential for a new generation of AuNP-based nanomedicinal products, nontoxic AuNP constructs and formulations that can be readily administered site-specifically through the intravenous mode, for diagnostic imaging by computed tomography (CT) or for therapy via various modalities, are still rare. Herein, we report results encompassing: 1) the synthesis and stabilization of AuNPs within the nontoxic phytochemical gum-arabic matrix (GA-AuNPs); 2) detailed in vitro analysis and in vivo pharmacokinetics studies of GA-AuNPs in pigs to gain insight into the organ-specific localization of this new generation of AuNP vector, and 3) X-ray CT contrast measurements of GA-AuNP vectors for potential utility in molecular imaging. Our results demonstrate that naturally occurring GA can be used as a nontoxic phytochemical construct in the production of readily administrable biocompatible AuNPs for diagnostic and therapeutic applications in nanomedicine.

High electron mobility InAs nanowire field-effect transistors

Abstract: Single-crystal InAs nanowires (NWs) are synthesized using metal-organic chemical vapor deposition (MOCVD) and fabricated into NW field-effect transistors (NWFETs) on a SiO(2)/n(+)-Si substrate with a global n(+)-Si back-gate and sputtered SiO(x)/Au underlap top-gate. For top-gate NWFETs, we have developed a model that allows accurate estimation of characteristic NW parameters, including carrier field-effect mobility and carrier concentration by taking into account series and leakage resistances, interface state capacitance, and top-gate geometry. Both the back-gate and the top-gate NWFETs exhibit room-temperature field-effect mobility as high as 6580 cm(2) V(-1) s(-1), which is the lower-bound value without interface-capacitance correction, and is the highest mobility reported to date in any semiconductor NW.

Metal nitride cluster fullerenes: their current state and future prospects.

Abstract: The world of endohedral fullerenes was significantly enlarged over the past seven years by the cluster fullerenes, which contain structures such as the M(2)C(2) carbides and the M(3)N nitrides. While the carbide clusters are generated under the standard arc-burning conditions according to stabilization conditions, the nitride cluster fullerenes (NCFs) are formed by varying the composition of the cooling gas atmosphere in the arc-burning process. The special conditions for NCF synthesis is described in detail and the optimum conditions for the production of NCFs as the main product in fullerene syntheses are given. A general review of all NCFs reported to date consists of the structures, properties, and stability of the NCFs as well as the abundance of the NCFs in the fullerene soot. It is shown that all cages with even carbon atoms from C(68) to C(98) are available as endohedral nitride cluster structures (with the exception of C(72), C(74), and C(76)). Specifically, the NCFs form the largest number of structures that violate the isolated pentagon rule (IPR). Finally some practical applications of these cluster fullerenes are illustrated and an outlook is given, taking the superior stability of these endohedral fullerenes into account.

Self-repairing coatings containing active nanoreservoirs.

Abstract: Nanocontainers with the ability to release encapsulated active materials in a controlled way can be employed to develop a new family of self-repairing multifunctional coatings, which possess not only passive functionality but also rapid feedback activity in response to changes in local environment. Several approaches to fabricate self-repairing coatings on plastic and metal substrates were surveyed. The release of the active materials occurs only when triggered, which prevents leakage of the active component out of the coating and increases coating durability. This Review also covers some principles and recent developments in the fabrication of nanocontainers with good compatibility with the coating components, the possibility to encapsulate and upkeep active material, and permeability properties of the shell controlled by external stimuli. Depending on the nature of the sensitive components introduced into the container shell, reversible and irreversible changes of the shell permeability can be induced by various stimuli. Different responses can be then observed varying from fine effects like tunable permeability to more drastic ones like total rupture of the container shell.

Dendrimer-entrapped gold nanoparticles as a platform for cancer-cell targeting and imaging.

Abstract: We present a general approach for the targeting and imaging of cancer cells using dendrimer-entrapped gold nanoparticles (Au DENPs). Au DENPs were found to be able to covalently link with targeting and imaging ligands for subsequent cancer-cell targeting and imaging. The Au DENPs linked with defined numbers of folic acid (FA) and fluorescein isothiocyanate (FI) molecules are water soluble, stable, and biocompatible. In vitro studies show that the FA- and FI-modified Au DENPs can specifically bind to KB cells (a human epithelial carcinoma cell line) that overexpress high-affinity folate receptors and they are internalized dominantly into lysosomes of target cells within 2 h. These findings demonstrate that Au DENPs may serve as a general platform for cancer imaging and therapeutics.

Environmentally Friendly Methodologies of Nanostructure Synthesis

Abstract: Environmentally friendly synthetic methodologies have gradually been implemented as viable techniques in the synthesis of a range of nanostructures. In this work, we focus on the application of green-chemistry principles to the synthesis of complex metal oxide and fluoride nanostructures. In particular, we describe advances in the use of the molten-salt synthetic methods, hydrothermal protocols, and template-directed techniques as environmentally sound, socially responsible, and cost-effective methodologies that allow us to generate nanomaterials without the need to sacrifice sample quality, purity, and crystallinity, while allowing control over size, shape, and morphology.

Identification of active biomolecules in the high-yield synthesis of single-crystalline gold nanoplates in algal solutions.

Abstract: In this work, single-crystalline gold nanoplates were produced by treating an aqueous solution of chloroauric acid with the extract of the unicellular green alga Chlorella vulgaris at room temperature. The results suggest proteins as the primary biomolecules involved in providing the dual function of Au(III) reduction and the size- and shape-controlled synthesis of the nanogold crystals. A protein with a molecular weight of approximately 28 kDa was isolated and purified by reversed-phase HPLC; this protein tested positive for the reduction of chloroauric acid in aqueous solution. The isolated protein (named gold shape-directing protein, or GSP for convenience) was then used to produce gold nanoplates with distinctive triangular and hexagonal shapes in high yields (approximately 90 %). The kinetics of the reduction reaction could be manipulated through changes in the GSP concentration to produce plates with lateral sizes ranging from nanometers to micrometers. The growth of gold nanoplates in the GSP solution with time was monitored by microscopic and spectroscopic techniques, thereby allowing the detection of several key intermediates in the growth process.

The synthesis and fabrication of one-dimensional nanoscale heterojunctions.

Abstract: There are a variety of methods for synthesizing or fabricating one-dimensional (1D) nanostructures containing heterojunctions between different materials. Here we review recent developments in the synthesis and fabrication of heterojunctions formed between different materials within the same 1D nanostructure or between different 1D nanostructures composed of different materials. Structures containing 1D nanoscale heterojunctions exhibit interesting chemistry as well as size, shape, and material-dependent properties that are unique when compared to single-component materials. This leads to new or enhanced properties or multifunctionality useful for a variety of applications in electronics, photonics, catalysis, and sensing, for example. This review separates the methods into vapor-phase synthesis, solution-phase synthesis, template-based synthesis, and other approaches, such as lithography, electrospinning, and assembly. These methods are used to form a variety of heterojunctions, including segmented, core/shell, branched, or crossed, from different combinations of semiconductor, metal, carbon, and polymeric materials.

Nanorod-coated PNIPAM microgels: thermoresponsive optical properties.

Abstract: Nanoparticles and in particular gold nanorods have interesting optical properties arising from two well-differentiated plasmon modes. The frequency of such modes can be altered by their chemical environment and coupling with neighboring rods. This study investigates new composite materials made of gold nanorods adsorbed on thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) microgels. It is shown that the thermally induced collapse of the polymer network inside the particles leads to a red shift of the longitudinal plasmon band of the gold rods, which is found to be fully reversible.

Antibacterial Properties of Silver‐Doped Titania

Abstract: Silver has been known to exhibit strong cytotoxicity towards a broad range of micro-organisms. Silver composites with a tailored slow silver-release rate are currently being investigated for various applications. Silver has an oligodynamic effect, that is, silver ions are capable of causing a bacteriostatic (growth inhibition) or even a bactericidal (antibacterial) impact. Nanometer-sized inorganic particles and composites display unique physical and chemical properties and represent a unique class of materials in the development of novel devices, which can be used in numerous physical, biological, biomedical, and pharmaceutical applications. Silver composites have applications in many industries, such as aerospace, surface coatings (e.g., in refrigerators, food processing, kitchen furniture), and for use in hospitals. Research indicates that silver is also effective in purification systems for disinfecting water or air. However, in order to make the use of silver economical, there is a need to find cheaper ways of using silver in potential applications without jeopardizing its functionalities. The bactericidal behavior of silver nanoparticles is attributed to the presence of electronic effects, which are a result of the changes in the local electronic structure of the surfaces of the smaller-sized particles. These effects are considered to be contributing towards an enhancement of the reactivity of silver-nanoparticle surfaces. It has been reported that ionic silver strongly interacts with thiol groups of vital enzymes and inactivates them. It has been suggested that DNA loses its replication ability once the bacteria have been treated with silver ions. Two-dimensional (2D) electrophoresis and protein-identification analyses of the antibacterial action of silver nanoparticles have revealed an accumulation of envelope-protein precursors. Silver nanoparticles target the bacterial membrane, which leads to the deACHTUNGTRENNUNGstabilization of the plasma-membrane potential and the depletion of the levels of intracellular adenosine triphosphate (ATP), resulting in bacterial cell death. Bacteria cells grow by a process called binary fission in which one cell doubles in size then splits in half to produce two identical daughter cells. If a bacterial population in an environment is without any growth restrictions by nutrient or metabolic products, the number of bacteria increases as an exponential function of time. Bacterial growth can be depicted generally by the growth curve shown in Figure 1.

Massively Parallel Dip‐Pen Nanolithography of Heterogeneous Supported Phospholipid Multilayer Patterns

Abstract: Phospholipids are an essential component of biological membranes, as their lyotropic liquid-crystalline nature enA them to self-assemble into two-dimensional bilayer sheets under physiological conditions. [1] Micro- and nanoscopic heterogeneities, such as lipid rafts [2, 3] and focal adhesions, [4, 5] are vital to the biological function of lipid bilayer membranes. Lithographically patterned phospholipid membranes can be used as cell-surface models [6] and have been used in several applications, including biochemical sensors, [7] drug screening and delivery, [8, 9] the analysis of cell–cell interactions, [3, 10] and to address fundamental biological questions in membrane trafficking. [11] However, in order to create model systems that are capable of mimicking the structural complexity of biological membranes, a method is necessary that allows both high-resolution patterning and parallel deA of different phospholipid materials over large areas. Here, we demonstrate that a new, noncovalent modality of dip-pen nanolithography (DPN) is a suitable approach for the rapid fabrication and integration of large-scale phospholipid nanostructure libraries on a variety of substrates. This method provides a lateral resolution down to 100 nm and an areal throughput of 5 cm 2 min 1 . Previously, micropatterned lipid bilayers on solid supports have been prepared using several approaches. A microarrayer that deposits nanoliter droplets of phospholipid solutions can be used to create arrays of supported lipid bi

Structural Color in Porous, Superhydrophilic, and Self‐Cleaning SiO2/TiO2 Bragg Stacks

Abstract: Thin-film Bragg stacks exhibiting structural color have been fabricated by a layer-by-layer (LbL) deposition process involving the sequential adsorption of nanoparticles and polymers. High- and low-refractive-index regions of quarter-wave stacks were generated by calcining LbL-assembled multilayers containing TiO(2) and SiO(2) nanoparticles, respectively. The physical attributes of each region were characterized by a recently developed ellipsometric method. The structural color characteristics of the resultant nanoporous Bragg stacks could be precisely tuned in the visible region by varying the number of stacks and the thickness of the high- and low-refractive-index stacks. These Bragg stacks also exhibited potentially useful superhydrophilicity and self-cleaning properties.

One-step production of polymeric microtubes by co-electrospinning

Abstract: Herein we demonstrate the ability to fabricate polymeric microtubes with an inner diameter of approximately 3 mm through co-electrospinning of core and shell polymeric solutions. The mechanism by which the core/ shell structure is transformed into hollow fibers (microtubes) is primarily based on the evaporation of the core solution through the shell and is described here in detail. Additionally, we present the filling of these microtubes, thus demonstrating their possible use in microfluidics. We also report the incorporation of a protein (green fluorescent protein) within such fibers, which is of interest for sensorics.

Multifunctionalized polymer microcapsules: novel tools for biological and pharmacological applications

Abstract: We describe recent developments with multifunctional nanoengineered polymer capsules. In addition to their obvious use as a delivery system, multifunctional nanocontainers find wide application in enzymatic catalysis, controlled release, and directed drug delivery in medicine. The multifunctionality is provided by the following components: 1) Luminescent semiconductor nanocrystals (quantum dots) that facilitate imaging and identification of different capsules, 2) superparamagnetic nanoparticles that allow manipulation of the capsules in a magnetic field, 3) surface coatings, which target the capsules to desired cells, 4) metallic nanoparticles in the capsule wall that act as an absorbing antenna for electromagnetic fields and provide heat for controlled release, and 5) enzymes and pharmaceutical agents that allow specific reactions. The unique advantage of multifunctional microcapsules in comparison to other systems is that they can be simultaneously loaded/functionalized with the above components, allowing for the combination of their properties in a single object.

Temperature‐, pH‐, and Magnetic‐Field‐Sensitive Hybrid Microgels

Abstract: We demonstrate a simple route for the preparation of novel hybrid particles with multiple sensitivities. Aqueous polymeric microgels are modified by magnetite nanoparticles in the preparation of temperature- and pH-sensitive hybrids with a high magnetic response. Up to 15 wt % of magnetite nanoparticles are loaded into microgels. The influence of the amount of magnetite in the microgel structure on the morphology and colloidal properties is discussed. The presence of the magnetite nanoparticles in the microgel decreases its degree of swelling and shifts the volume phase-transition temperature to higher values. Nanostructured composite films with controlled morphologies can be prepared by water evaporation and deposition of the hybrid microgels on a solid substrate.

Growth of gold bipyramids with improved yield and their curvature-directed oxidation.

Abstract: The surface-plasmon properties of Au bipyramids are investigated using the finite-difference time-domain method. It is found that both the extinction cross sections and local electric-field enhancements of Au bipyramids are larger than those of Au nanorods that have longitudinal surface plasmon (LSP) wavelengths close to those of Au bipyramids. Following this result the growth of Au bipyramids using cationic surfactants of variously sized headgroups as stabilizing agents is carried out. It is found that the growth using cetyltributylammonium bromide (CTBAB) produces Au bipyramids with tunable LSP wavelengths in high yields. The oxidation behaviour of Au bipyramids using hydrogen peroxide as the oxidizing agent is fully explored and the oxidation is found to occur preferentially at highly curved surface sites. It is further demonstrated that the oxidation rate can be controlled by varying the amounts of hydrogen peroxide and hydrochloric acid. This oxidation approach can be used in conjunction with the seed-mediated growth in CTBAB solutions to produce Au bipyramids, the LSP wavelengths of which are finely tunable from 650 to 1300 nm.