Showing papers in "Journal of Nanoscience and Nanotechnology in 2004"

Toxicological hazards of inhaled nanoparticles--potential implications for drug delivery.

Abstract: Nanoparticles (NP), here defined as particles with a diameter smaller then 100 nm, are increasingly used in different applications, including drug carrier systems and to pass organ barriers such as the blood-brain barrier. On the other hand, a large body of know-how is available regarding toxicological effects of nanoparticle (NP) after inhalation. More specifically, a number of effects of inhaled NP are attributed to their (i) direct effects on the central nervous system, (ii) their translocation from the lung into the bloodstream, and (iii) their capacity to invoke inflammatory responses in the lung with subsequent systemic effects. This paper gives a brief review on the toxicology of inhaled NP, including general principles and current paradigms to explain the special case of NP in pulmonary toxicology. Since the evidence for health risks of NP after inhalation has been increasing over the last decade, this paper tries to extrapolate these findings and principles observed in inhalation toxicology into recommendations and methods for testing NP for nanocarrier purposes. A large gap is present between research on NP in inhalation toxicology and in nanoscaled drug carrying. This review recommends a closer interaction between both disciplines to gain insight in the role of NP size and properties and their mechanisms of acute and chronic interaction with biological systems.

Biodistribution of carbon single-wall carbon nanotubes in mice

Abstract: Carbon nanotubes are promising for use in biomedical and pharmaceutical sciences. Therefore, it becomes imperative to know the basic biological properties of carbon nanotubes in vivo. We labeled the water-soluble hydroxylated carbon single-wall nanotubes with radioactive 125I atoms, and then the tracer was used to study the distribution of hydroxylated carbon single-wall nanotubes in mice. They moved easily among the compartments and tissues of the body, behaving as small active molecules though their apparent mean molecular weight is tremendously large. This study, for the first time, affords a quantitative analysis of carbon nanotubes accumulated in animal tissues.

Influence of the surface properties on nanoparticle-mediated transport of drugs to the brain.

Abstract: Poly(alkyl cyanoacrylate) nanoparticles enable the delivery of a number of drugs, including doxorubicin, loperamide, tubocurarine, the NMDA receptor antagonist MRZ 2/576, and the peptides dalargin and kytorphin across the blood-brain barrier (BBB) after coating with surfactants. However, only the surfactants polysorbate (Tween) 20, 40, 60 and 80, and some poloxamers (Pluronic F 68) can induce this uptake. The mechanism for the delivery across the BBB most likely is endocytosis via the LDL receptor by the endothelial cells lining the brain blood capillaries after injection of the nanoparticles into the blood stream. This endocytotic uptake seems to be mediated by the adsorption of apolipoprotein B and/or E adsorption from the blood. Thus, the nanoparticles could mimic lipoprotein particles and act as "Trojan Horses." The drug, then, may be released either within these cells followed by passive diffusion into the brain or be transported into the brain by transcytosis.

Recent advances in polymer nanofibers.

Abstract: Polymer nanofibers, with diameters in the nanometer range, possess larger surface areas per unit mass and permit easier addition of surface functionalities compared with polymer microfibers Hence, polymer nanofiber mats are being considered for use as filters, scaffolds for tissue engineering, protective clothing, reinforcement in composite materials and sensors Although some of these applications are in the development stage, a few have been commercially exploited Research on polymer nanofibers, nanofiber mats, and their applications has seen a remarkable growth over the last few years However, a review of the various issues related to these nanofibers has not been published This article presents a review of the recent trends in the processing methods and characterization techniques for polymer nanofibers Research challenges and future trends in the processing and characterization of polymer nanofibers are discussed in the article Five processing methods have been examined in this review, namely drawing, template synthesis, phase separation, self-assembly, and electrospinning Among these methods, electrospinning has been used to convert a large variety of polymers into nanofibers and may be the only process that has the potential for mass production The structure, morphology, and geometry of nanofibers and the porosity and tensile properties of nanofiber mats can be investigated through conventional techniques and instruments But new techniques are needed for the mechanical testing of single nanofibers Although measurement of mechanical properties such as tensile modulus, strength, and elongation is difficult because of the small diameters of the fibers, these properties are crucial for the proper use of nanofiber mats

Cationic silica nanoparticles as gene carriers: synthesis, characterization and transfection efficiency in vitro and in vivo.

Abstract: The potential of cationic SiO2 nanoparticles was investigated for in vivo gene transfer in this study. Cationic SiO2 nanoparticles with surface modification were generated using amino-hexyl-amino-propyltri-methoxysilane (AHAPS). The zeta potential of the nanoparticles at pH = 7.4 varied from -31.4 mV (unmodified particles; 10 nm) to +9.6 mV (modified by AHAPS). Complete immobilization of DNA at the nanoparticle surface was achieved at a particle ratio of 80 (w/w nanoparticle/DNA ratio). The surface modified nanoparticle had a size of 42 nm with a distribution from 10-100 nm. The ability of these particles to transfect pCMVbeta reporter gene was tested in Cos-1 cells, and optimum results were obtained in the presence of FCS and chloroquine at a particle ratio of 80. These nanoparticles were tested for their ability to transfer genes in vivo in the mouse lung, and a two-times increase in the expression levels was found with silica particles in comparison to EGFP alone. Very low or no cell toxicity was observed, suggesting silica nanoparticles as potential alternatives for gene transfection.

Ferroelectric random access memories.

Abstract: Ferroelectric random access memory (FeRAM) is a nonvolatile memory, in which data are stored using hysteretic P-E (polarization vs. electric field) characteristics in a ferroelectric film. In this review, history and characteristics of FeRAMs are first introduced. It is described that there are two types of FeRAMs, capacitor-type and FET-type, and that only the capacitor-type FeRAM is now commercially available. In chapter 2, properties of ferroelectric films are discussed from a viewpoint of FeRAM application, in which particular attention is paid to those of Pb(Zr,Ti)O3, SrBi2Ta2O9, and BiFeO3. Then, cell structures and operation principle of the capacitor-type FeRAMs are discussed in chapter 3. It is described that the stacked technology of ferroelectric capacitors and development of new materials with large remanent polarization are important for fabricating high-density memories. Finally, in chapter 4, the optimized gate structure in ferroelectric-gate field-effect transistors is discussed and experimental results showing excellent data retention characteristics are presented.

Synthesis of high purity silicon nanoparticles in a low pressure microwave reactor.

Abstract: The formation of pure single crystalline silicon nanoparticles by microwave induced decomposition of silane in a low pressure flow reactor is reported. The morphology and crystal structure of the particles are characterized in situ by particle mass spectrometry (PMS) and ex situ by means of X-ray diffraction, high resolution transmission electron microscopy, electron energy loss spectroscopy, and infrared spectroscopy. The preparation method allows for the adjustment of the mean

A titania nanotube-array room-temperature sensor for selective detection of hydrogen at low concentrations.

Abstract: A tremendous variation in electrical resistance, from the semiconductor to metallic range, has been observed in titania nanotube arrays at room temperature, approximately 25 degrees C, in the presence of < or = 1000 ppm hydrogen gas. The nanotube arrays are fabricated by anodizing titanium foil in an aqueous electrolyte solution containing hydrofluoric acid and acetic acid. Subsequently, the arrays are coated with a 10 nm layer of palladium by evaporation. Electrical contacts are made by sputtering a 2 mm diameter platinum disk atop the Pd-coated nanotube array. These sensors exhibit a resistance variation of the order of 10(4) in the presence of 100 ppm hydrogen at 25 degrees C. The sensors demonstrate complete reversibility, repeatability, high selectivity, negligible drift and wide dynamic range. The nanoscale geometry of the nanotubes, in particular the points of tube-to-tube contact, is believed to be responsible for the outstanding hydrogen gas sensitivities.

Optical properties and potential applications of doped semiconductor nanoparticles.

Abstract: Recent studies on the optical properties, in particular, luminescence, of a variety of doped semiconductor nanoparticles are reviewed. The effects of quantum confinement, temperature and pressure on luminescent properties are discussed. In addition, electroluminescence, cathodoluminescence, magnetoluminescence and related applications involving doped semiconductor nanoparticles are presented. A new phenomenon, upconversion luminescence of doped nanoparticles, is reviewed and its potential applications are discussed. While more research efforts are necessary in order to fully understand the fundamentals and explore the great technological potential behind doped nanoparticles, recent results already show that this is a new and exciting field with applications in many areas. In particular, the emerging field of "spintronics", where spin states are exploited in analogy to conventional electronic states, is discussed and the advantages of using doped semiconductor nanoparticles are elucidated.

Supported membrane nanodevices.

Abstract: Supported membrane nanodevices are based on natural or artificial ion channels embedded in a lipid membrane deposited on a chip wafer. Membrane conductance is modulated by biorecognitive events, with the use of intrinsic binding sites of the ion channel or via artificial sites fused to the channel protein. Artificial ion gates are constructed by coupling a specific ligand for the analyte near the channel entrance or a site important to triggering channel conformation. The binding event leads to the closure of the ion channel or induces a conformational change of the channel, reducing the ion flux. The signal transduced from the device is the decrease in the ion flux-induced electron current at a silver-silver chloride electrode at ultimate single-molecule sensitivity. Among the natural ion channels, gramicidin A, a transport antibiotic, was found to be most suitable, and thus was used by AMBRI, Australia, to set up prototypes of membrane biochips, using self-association of the dimer. Covalent dimerization-based devices, developed by the Vienna group, make use of the down-regulation of the permanently open membrane-spanning bisgramicidine ion channel. The reactive group at the C-terminus, a hydroxy group, allows precise coupling of the analyte-binding moiety in gramicidin as well as bisgramicidin. The device is set up with bilayer membranes deposited on apertures of a hydrophobic frame structure produced via microlithography, facing an aqueous or hydro-gel micro-environment on both sides, constructing black lipid membranes or patch-clamp devices "on chip." The setup of the device needs gel membrane supports that allow membrane formation and contribute to the stability of the bilayer by exposure of functional groups that promote electrostatic interaction and formation of hydrogen bridges and enable the introduction of covalent spacers and anchors. Photo-cross-linked polyvinylpyrrolidone and polyacrylamide, electropolymerized polydiaminobenzene and coated agarose, as well as various chemical modifications of these polymers, were employed as membrane supports. With optimized assemblies, the membrane support did allow the formation of stable bilayer membranes, proved by "gigaseal" (electrical sealing with giga-ohm resistance) to be free of any point defects in the lipid assembly. Supports with and without hydrophilic and hydrophobic anchors were studied with reference to promoting the formation of a self-assembled membrane, to their electric resistance, and to the capability to insert functional ionophores. All components, including novel chemically engineered ion channels, novel amphiphilic lipids, a microlithographically designed chip, isolating polymer frames, and a hydrogel membrane support, are combined in the new bionanodevice. Sensitivity and specificity were proved, for example, with the use of an antibody-antigen couple down-regulating the ion flux through the membrane channel. Single ion channels incorporated in the supported lipid bilayer gave stable signals at an operational stability of several hours, which is already sufficient to test and screen for membrane receptors but still insufficient to use this device as a sensor for off-site application. Further optimization to increase operational and storage stability is done by a number of groups to allow a broad application of these devices.

Employing Raman spectroscopy to qualitatively evaluate the purity of carbon single-wall nanotube materials.

Abstract: Carbon single-wall nanotubes (SWNTs) have highly unique electronic, mechanical and adsorption properties, making them interesting for a variety of applications. Raman spectroscopy has been demonstrated to be one of the most important methods for characterizing SWNTs. For example, Raman spectroscopy may be employed to differentiate between metallic and semi-conducting nanotubes, and may also be employed to determine SWNT diameters and even the nanotube chirality. Single-wall carbon nanotubes are generated in a variety of ways, including arc-discharge, laser vaporization and various chemical vapor deposition (CVD) techniques. In all of these methods, a metal catalyst must be employed to observe SWNT formation. Also, all of the current synthesis techniques generate various non-nanotube carbon impurities, including amorphous carbon, fullerenes, multi-wall nanotubes (MWNTs) and nano-crystalline graphite, as well as larger micro-sized particles of graphite. For any of the potential nanotube applications to be realized, it is, therefore, necessary that purification techniques resulting in the recovery of predominantly SWNTs at high-yields be developed. It is, of course, equally important that a method for determining nanotube wt.% purity levels be developed and standardized. Moreover, a rapid method for qualitatively measuring nanotube purity could facilitate many laboratory research efforts. This review article discusses the application of Raman spectroscopy to rapidly determine if large quantities of carbon impurities are present in nanotube materials. Raman spectra of crude SWNT materials reveal tangential bands between 1500-1600 cm(-1), as well as a broad band at approximately 1350 cm(-1), attributed to a convolution of the disorder-induced band (D-band) of carbon impurities and the D-band of the SWNTs themselves. Since the full-width-at-half-maximum (FWHM) intensity of the various carbon impurity D-bands is generally much broader than that of the nanotube D-band, an indication of the SWNT purity level may be obtained by simply examining the line-width of the D-band. We also briefly discuss the effect of nanotube bundling on SWNT Raman spectra. Finally, sections on employing Raman spectroscopy, and Raman spectroscopy coupled with additional techniques, to identify the separation and possible isolation of a specific nanotube within purified SWNT materials is provided. Every SWNT can be considered to be a unique molecule, with different physical properties, depending on its (n, m) indices. The production of phase-pure (n, m) SWNTs may be essential for some nanotube applications.

Laser ablation process for single-walled carbon nanotube production.

Abstract: Different types of lasers are now routinely used to prepare single-walled carbon nanotubes. The original method developed by researchers at Rice University used a "double-pulse laser oven" process. Several researchers have used variations of the lasers to include one-laser pulse (green or infrared), different pulse widths (ns to micros as well as continuous wave), and different laser wavelengths (e.g., CO2, or free electron lasers in the near to far infrared). Some of these variations are tried with different combinations and concentrations of metal catalysts, buffer gases (e.g., helium), oven temperatures, flow conditions, and even different porosities of the graphite targets. This article is an attempt to cover all these variations and their relative merits. Possible growth mechanisms under these different conditions will also be discussed.

Drug delivery to the brain--realization by novel drug carriers.

Abstract: Delivery of drugs to the brain is still a major challenge. Successful delivery across the bloodbrain barrier has only been achieved in some cases, e.g., using pro-drugs. The review describes the delivery to the brain using nanoparticulate drug carriers in combination with the novel targeting principle of "differential protein adsorption" (PathFinder technology). The PathFinder technology exploits proteins in the blood which adsorb onto the surface of intravenously injected carriers for targeting. Apolipoprotein E is the targeting moiety for the delivery of particles to the endothelials of the blood-brain barrier. To reach therapeutic drug level in the brain, nanoparticulate drug carriers with sufficiently high loading capacity are reviewed, including drug nanocrystals (nanosuspensions), lipid drug conjugate (LDC) nanoparticles and lipid nanoparticles (solid lipid nanoparticles-SLN, nanostructured lipid carriers-NLC). The features are described, including regulatory aspects and large scale production.

Cationic poly(lactide-co-glycolide) nanoparticles as efficient in vivo gene transfection agents.

Abstract: Poly(lactide-co-glycolide) (PLGA), a biocompatible and biodegradable polyester co-polymer of PLA and PGA, has been recognized for its ability to deliver genes. However, gene delivery by PLGA nanoparticles is limited by their negative charge and their poor transport through mucosal barriers. In this study, PLGA nanoparticles were surface modified with cationic chitosan in an effort to improve their gene delivery capability. PLGA nanoparticles were synthesized by emulsion-diffusion-evaporation technique using PVA-chitosan (PLGA1) or PVA-chitosan-PEG (PLGA2) blend as stabilizers. This method is reproducible and produces nanoparticles with hydrodynamic diameter <200 nm. The nanoparticles were characterized by zetasizer, photon correlation spectroscopy and atomic force microscopy. A549 epithelial cells were transfected in vitro with PLGA particles complexed with a reporter plasmid encoding green fluorescent protein. PLGA particles transferred EGFP gene, but were less efficient than the lipofectamine control. The nanoparticles were also tested for their ability to transport across the nasal mucosa in vivo in mice. The results show that both PLGA1 and PLGA2 facilitate gene delivery and expression in vivo with increased efficiency and without causing inflammation, as measured by IL-6. Together, these results indicate that chitosan-modified PLGA nanoparticles have greater potential as gene carriers.

Luminescent nanoparticle probes for bioimaging.

Abstract: Bioimaging with luminescent nanoparticle probes have recently attracted widespread interest in biology and medicine. In comparison with commonly used organic dyes, luminescent nanoparticles are better in terms of photostability and sensitivity. These optical features of nanoparticle probes are critical for real time tracking and monitoring of biological events in the cellular level, which may not be accomplished using regular fluorescent dyes. Nanoparticle probes are also shown highly suitable for immunoassay and other diagnostic and therapeutic applications. In this article, we describe a variety of optical nanoparticle probes such as quantum dots, metal nanoparticles, dye-doped nanoparticles etc. for bioimaging applications.

Controlled surface functionalization of silica nanospheres by covalent conjugation reactions and preparation of high density streptavidin nanoparticles.

Abstract: Silica nanoparticles with a diameter of 100 nm were covalently modified at their surface by adjustable amounts of amine and carboxyl functional groups. Bioconjugation studies of two proteins, streptavidin and streptactin, with the functional nanoparticles resulted in optimum binding of the proteins to a long-chain carboxyl-terminated linker. The surface functionalization of the nanoparticles was monitored by a variety of independent methods, including zeta-potential measurements, dynamic light scattering (DLS), scanning electron microscopy (SEM), particle charge detection titrations (PCD) and elemental analysis. At the surface of the nanoparticles, a functional surface group density of 1.8 amino groups per nm2 was realized. The amine functions were quantitatively transferred to carboxyl groups coupled with a linker elongation. Streptavidin was immobilized by covalent binding to the carboxyl linkers and resulted in a protein density at the surface of the nanoparticles that was three times higher than the highest binding densities at nanoparticles published to date. The binding capacity of the streptavidin-covered nanoparticles for ligand biotin was quantified by titration with biotin-4-fluorescein to 2.5 biotin binding sites per 100 nm2.

A novel fluorescent label based on organic dye-doped silica nanoparticles for HepG liver cancer cell recognition.

Abstract: In this paper, we report a method for the recognition of HepG liver cancer cells with the use of a novel fluorescent label based on organic dye-doped fluorescent silica nanoparticles. The novel organic dye-doped silica nanoparticles are prepared with a water-in-oil microemulsion technique. The silica network is produced by the controlled synchronous hydrolysis of tetraethoxysilane and 3-amino-propyltriethoxysilane (APTES). The organic dye fluorescein isothiocyanate is doped inside as a luminescent signaling element, through covalent bonding to the amino group of APTES. The organic dye-doped core-shell nanoparticles are highly luminescent and exhibit minimal dye leaching and excellent photostability. A novel fluorescent label method based on biological fluorescent nanoparticles has been developed. The dye-doped fluorescent silica nanoparticles are covalently immobilized with anti-human liver cancer monoclonal antibody HAb18. We have used antibody-labeled fluorescent nanoparticles to recognize HepG liver cancer cells. It has been observed that the bioassay based on the organic dye-doped nanoparticles can identify the target cells selectively and efficiently. The fluorescent nanoparticle label also exhibits high photostability.

Gas-phase production of single-walled carbon nanotubes from carbon monoxide: a review of the hipco process.

Abstract: The latest process for producing large quantities of single-walled carbon nanotubes (SWNTs) to emerge from the Rice University, dubbed HiPco, is living up to its promise. The current production rates approach 450 mg/h (or 10 g/day), and nanotubes typically have no more than 7 mol % of iron impurities. Second-generation HiPco apparatus can run continuously for 7-10 days at a time. In the HiPco process nanotubes grow in high-pressure, high-temperature flowing CO on catalytic clusters of iron. Catalyst is formed in situ by thermal decomposition of iron pentacarbonyl, which is delivered intact within a cold CO flow and then rapidly mixed with hot CO in the reaction zone. Upon heating, the Fe(CO)5 decomposes into atoms that condense into larger clusters. SWNTs nucleate and grow on these particles in the gas phase via CO disproportionation: CO + CO --> CO2 + C (SWNT), catalyzed by the Fe surface. The concentration of CO2 produced in this reaction is equal to that of carbon and can therefore serve as a useful real-time feedback parameter. It was used to study and optimize SWNT production as a function of temperature, pressure, and Fe(CO)5 concentration. The results of the parametric study are in agreement with current understanding of the nanotube formation mechanism.

Factors affecting kinesin-based transport of synthetic nanoparticle cargo.

Abstract: Recently, kinesin biomolecular motors and microtubules filaments (MTs) were used to transport metal and semiconductor nanoparticles with the long-term goal of exploiting this active transport system to dynamically assemble nanostructured materials. In some cases, however, the presence of nanoparticle cargo on MTs was shown to inhibit transport by interfering with kinesin-MT interactions. The primary objectives of this work were (1) to determine what factors affect the ability of kinesin and MTs to transport nanoparticle cargo, and (2) to establish a functional parameter space in which kinesin and MTs can support unimpeded transport of nanoparticles and materials. Of the factors evaluated, nanoparticle density on a given MT was the most significant factor affecting kinesin-based transport of nanoparticles. The density of particles was controlled by limiting the number of available linkage sites (i.e., biotinylated tubulin), and/or the relative concentration of nanoparticles in solution. Nanoparticle size was also a significant factor affecting transport, and attributed to the ability of particles < 40 nm in diameter to bind to the "underside" of the MT, and block kinesin transport. Overall, a generalized method of assembling and transporting a range of nanoparticle cargo using kinesin and MTs was established.

Nucleation and growth of single-walled nanotubes: the role of metallic catalysts.

Abstract: We present a review of experimental and theoretical results on the nucleation and growth of single-walled nanotubes, with particular emphasis on the growth of nanotube bundles emerging from catalyst particles obtained from evaporation-based elaboration techniques. General results are first discussed. Experiments strongly suggest a root-growth process in which carbon, dissolved at high temperatures in catalytic particles, segregates at the surface at lower temperatures to form tube embryos and finally nanotubes through a nucleation and growth process. A theoretical analysis of the reasons carbon does not always form graphene sheets to wrap the particles suggests analogies with other surface or interface instabilities, in particular, with those found in epitaxial growth. In the second part, detailed experimental results for nickel-rare earth metal catalysts are presented. By using various electron microscopy techniques, it is shown that carbon and the rare earth metal co-segregate at the surface of the particle and form carbide platelets, providing nucleation sites for nanotubes growing in directions perpendicular to the surface. A simple theoretical model is then presented in which the role of the rare earth metal is just to transfer electrons from metal to carbon. The graphene sheet is shown to become unstable; pentagons and heptagons are favored, which can explain the occurrence of local curvatures and of tube embryos. Finally, a brief discussion of some recent atomistic models is given.

Morphology effects on the optical properties of silver nanoparticles.

Abstract: Employing methods developed for the control of shape and size in silver nanoparticles, we have compared the optical properties of nanorods, nanoprisms, nanodisks, and nanospheres. Solutions of these particles show distinct surface plasmon resonant absorption signatures that are directly correlated with the symmetries of their morphology. Nonlinear optical behavior for suspensions of these nanostructures, for nanosecond pulses at 532 and 1064 nm, have been correlated to plasmon resonances determined by shape and size.

Formation of nanoparticle arrays on S-layer protein lattices.

Abstract: Crystalline bacterial cell surface layers (S-layers) composed of identical protein units have been used as binding templates for well-organized arrangements of nanoparticles. Isolated S-layer proteins were recrystallized into monomolecular arrays on solid substrates (such as silicon wafers and SiO2-coated grids) and in suspension forming so-called self-assembly products. These S-layer assemblies were studied by atomic force microscopy and transmission electron microscopy (TEM). The orientation of the S-layer lattice, exhibiting anisotropic surface properties, on the solid surface and on the self-assembly products, was compared with the orientation on the bacterial cell. On both bacterial cells and SiO2 surfaces the outer face of the S-layer protein was exposed. On the self-assembly products occasionally the inner face was also visible. Metal- and semiconductor nanoparticles 2 to 10 nm in mean diameter were covalently or electrostatically bound to the solid-supported S-layers and self-assembly products. TEM studies reveal that upon activation of carboxyl groups in the S-layer lattice with 1-ethyl-3,3'(dimethylaminopropyl)carbodiimide (EDC), a close-packed monolayer of 4-nm amino-functionalized CdSe nanoparticles could be covalently established on the S-layer lattice. Because of electrostatic interactions, anionic citrate-stabilized Au nanoparticles (5 nm in diameter) formed a superlattice at those sites where the inner face of the S-layer lattice was exposed. In contrast, cationic semiconductor nanoparticles (such as amino-functionalized CdSe particles) formed arrays on the outer face of the solid-supported S-layer lattices.

Synthesis of palladium nanoparticles using a continuous flow polymeric micro reactor.

Abstract: A continuous flow polymeric micro reactor, fabricated using a negative photo resist SU-8 on a 10 x 10 cm PEEK (polyetheretherketone) substrate by standard UV lithography, was utilized to synthesize palladium nanoparticles The nanoparticles were characterized by Transmission Electron Microscopy, Selected Area Electron Diffraction and X-ray Diffraction The Pd nanoparticles synthesized in the micro reactor were found to have a narrower size distribution when compared with those obtained by the conventional batch process

Nanofabrication with atomic force microscopy.

Abstract: Atomic force microscopy (AFM) was developed in 1986. It is an important and versatile surface technique, and is used in many research fields. In this review, we have summarized the methods and applications of AFM, with emphasis on nanofabrication. AFM is capable of visualizing surface properties at high spatial resolution and determining biomolecular interaction as well as fabricating nanostructures. Recently, AFM-based nanotechnologies such as nanomanipulation, force lithography, nanografting, nanooxidation and dip-pen nanolithography were developed rapidly. AFM tip (typical radius ranged from several nanometers to tens of nanometers) is used to modify the sample surface, either physically or chemically, at nanometer scale. Nanopatterns composed of semiconductors, metal, biomolecules, polymers, etc., were constructed with various AFM-based nanotechnologies, thus making AFM a promising technique for nanofabrication. AFM-based nanotechnologies have potential applications in nanoelectronics, bioanalysis, biosensors, actuators and high-density data storage devices.

Towards pick-and-place assembly of nanostructures.

Abstract: We examine an approach to three-dimensional pick-and-place assembly of wire-like nanoscale components, such as carbon nanotubes and silicon nanowires, on microstructures inside a scanning electron microscope. In this article we demonstrate that microfabricated electrostatically acutuated tweezers can pick up silicon nanowires and show how electron beam deposition of carbon residues can be used to assemble carbon nanotubes on microelectrodes.

Template-assisted nano-patterning: from the submicron scale to the submolecular level.

Abstract: Regular pattern formation based on template synthesis is overviewed from the submicron scale to the submolecular level. Size of patterns of course depends on size of template. Specificity and precision of interaction between the templates and between patterned materials are apparently correlated with the size and precision of patterns.

A simple route towards CuO nanowires and nanorods.

Abstract: CuO nanowires and nanorods were synthesized through a novel controllable solution-phase hydrothermal method using a nonionic surfactant polyethylene glycol (PEG) as the structure-directing template. The lengths of obtained 1D CuO nanostructures could be successfully controlled through choosing different molecular weights of PEG. The phase structures and morphologies were investigated by XRD, TEM, HRTEM and SAED. The formation mechanisms of the nanorods and nanowires were investigated and discussed on the basis of the experimental results.

On the growth mechanism of single-walled carbon nanotubes by catalytic carbon vapor deposition on supported metal catalysts.

Abstract: A comprehensive kinetic study was performed to throw light on the formation mechanism of single walled carbon nanotubes (SWNTs) in chemical vapor deposition processes. SWNTs were synthesized by catalytic decomposition of methane or ethylene on supported transition metal catalysts. Kinetic curves (the amount of SWNT as a function of time) were obtained as a function of the nature and the preparation of the supported catalysts, temperature, the fluxes of the gases (the reagent hydrocarbon and the carrying gas), and the partial pressure of the hydrocarbon. The final products were characterized by transmission electron microscopy, Raman spectroscopy, chemical analysis, and thermogravimetric measurements. The fundamental factors determining the SWNT formation are discussed in detail, taking into consideration several observations from the literature as well.

Template synthesis of gold nanotubes in an anodic alumina membrane.

Abstract: Nanotube-containing membranes prepared by the template method show promise for use as highly selective filters for membrane-based chemical and biological separations. Most of the work to date has been done on gold nanotubes prepared by electroless deposition of Au within the pores of polymeric filtration membranes. These polymeric filters have very low porosities (< 1%), and, as a result, the flux through Au nanotube membranes based on these templates is very low. In contrast, the other popular template membranes-anodic aluminas-have high porosities-30% to 50%. In spite of this potential advantage of anodic alumina templates, there have been no reports of electrolessly plated Au nanotubes within the pores of these templates. This is because the electroless plating method used to deposit Au nanotubes in polymeric templates does not work in aluminas. We have developed a modified electroless plating strategy that can be used to deposit high-quality Au nanotubes within the pores of the alumina templates. We describe this new plating method here.

Carbon nanotubes and other fullerene nanocrystals in domestic propane and natural gas combustion streams.

Abstract: Carbon nanotubes and other aggregated fullerene-related multi-layer shell structures have been collected in propane and natural gas flame emissions from domestic cooking stoves and observed by transmission electron microscopy. Some aggregated nanoparticles collected on 3 mm electron microscope grids by thermal precipitation were mostly multi-walled nanotubes; many tangled and distorted, and aggregated with other closed-concentric, multi-shell forms. Such clean-burning regimes may be major contributors to complex particulate matter in indoor and outdoor air.