Current Nanoscience - Volume 5, Issue 3, 2009

Reducing the microbial load on environmental surfaces is an important means of preventing hospital cross-infection and there is great interest in developing self-disinfecting surface coatings for this purpose. The aims of this study were to produce a coating containing a light-activated antimicrobial agent (LAAA) that could exert an antimicrobial effect when illuminated with white light and to ascertain whether the antimicrobial activity could be enhanced by the presence of gold nanoparticles. Silicone polymers that contained either the LAAA methylene blue (MB) or MB together with 2 nm gold nanoparticles were produced. A suspension of Staphylococcus aureus was placed on the surface of the polymers which were exposed to white light for various periods of time and the number of viable organisms remaining were determined. Polymers containing MB or MB plus nanogold achieved a light dose-dependent killing of the test organism. In the case of the polymers exposed to the lowest light dose (a 4 hour exposure time) the kills attained by the MB-containing polymers were significantly greater when nanogold was present. These findings suggest that polymers containing MB and nanogold could provide a coating that would exert an antimicrobial effect at the low light intensities encountered in many hospital environments.

ZnO nanotubes array has been fabricated by a facile hydrothermal treatment of ZnO seeded silicon substrate in a sealed system. The as prepared ZnO nanotubes are single crystalline and have a [0001] preferential growth direction. Shape and size of the ZnO product is found to be sensitive to reaction conditions. Diffusion-limited crystal growth is proposed to explain the formation mechanism of ZnO nanotubes.

A simple route has been developed for the preparation of a series of one-dimensional rare earth (Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) precursors by solvothermal treatment of corresponding rare earth nitrate in mixed solvents of N,Ndimethylformamide (DMF) and water at 200 °C without using any surfactant or additive. By a simple thermal transformation process, a series of rare earth oxides (Y2O3, Pr2O3, Nd2O3, Sm2O3, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, and Yb2O3) with onedimensional structures have been obtained using corresponding one-dimensional rare earth precursor. The one-dimensional morphology of rare earth precursors can be well preserved and reproduced during the thermal transformation to corresponding rare earth oxides. This novel synthetic method also allows easy doping of rare earth ions into one-dimensional rare earth oxides examplified by Eu and Er doped yttrium oxide (Y2O3:Eu and Y2O3:Er). The photoluminescence properties of one-dimensional Y2O3:Eu and Y2O3:Er are investigated.

Nanocrystalline CuO with particle size of about 24 nm was directly synthesized by sol-gel auto combustion method using citric acid as a reducing agent/fuel and nitrate as oxidizing agent at low temperature of 200°C. Thermal decomposition of the nitrate-citrate xerogel was investigated by thermogravimetric/differential thermal analysis (TG/DTA) technique in the temperature range 30-500°C. The yielding product calcined at 400°C was characterized for CuO by X-ray diffraction, Field enhanced scanning electron microscope (FESEM) and UV-vis absorption spectroscopy. The morphological properties of the prepared oxide after the combustion synthesis reveal that the particles are bound together into agglomerates of different shapes and sizes. The band gap is estimated to be 2.05 eV according to the results of the optical measurements. A possible mechanism for the formation of CuO has also been discussed.

Water-soluble CdS nanospheres assembled from CdS quantum dots (QDs) have been prepared using CdCl2 and thioglycolic acid in mixed solvents of glycerine and ethanolamine at an elevated temperature. The size of CdS nanospheres could be controlled through adjusting the experimental parameters. The UV-Visible absorption and photoluminescence spectra of CdS nanospheres were investigated. The deep-trap luminescence at ∼600 nm quenched at elevated temperatures or longer reaction time and exclusive blue luminescence derived from the band-edge emission of aqueous colloid of CdS nanospheres was observed. The formation mechanism of CdS nanospheres assembled from CdS QDs was discussed.

ZnO nanoneedles were successfully deposited on flexible polymer substrates at room temperature by activated reactive evaporation. Neither a catalyst nor a template was employed in this synthesis. These synthesized needles measured 500 - 600 nm in length and its diameter varied from 30 - 15 nm from the base to the tip. The single-crystalline nature of the nanoneedle was observed by highresolution transmission electron microscopy studies. The Raman studies on these nanoneedles had shown that they are oxygen deficient in nature. A possible growth mechanism has been proposed here, in which the nanoneedles nucleate and grow in the gas phase by vaporsolid mechanism.

Probe-shaped GaN nanorods were successfully synthesized on Si(111) substrates through ammoniating Ga2O3/Mo films at 950 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the as-synthesized nanorods. The results show that the synthesized sample is well crystallized GaN with hexagonal wurzite structure. And the GaN nanorods own probe-shaped morphology and smooth surface. X-ray photoelectron spectroscopy (XPS) confirms the formation of bonding between Ga and N and the surface stoichiometry of Ga:N of 1:1. The representative photoluminescence spectrum at room temperature exhibits a strong UV light emission band centered at 371.5 nm. Finally, the growth process of probe-shaped GaN nanorods was briefly discussed.

The objective of this work is to develop a novel photodynamic drug nanocarrier consisting of magnetite and a drug with silica shell by sol-gel method. The nanocarriers were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). These nanocarriers were approximately spherical, sized in the range of 30-50 nm. It was confirmed that the drug was enwrapped in the nanocarriers by observing the ultraviolet-visible (UV-vis) absorption spectra. The generation of singlet oxygen (1O2) was measured by the use of N, N-Dimethyl-4-nitrosoaniline (RNO) as a selective scavenger. Using laser to irradiate the nanocarriers and RNO system, the decrease in the absorption peak of RNO at 440 nm was due to the 1O2 released from the nanocarriers, which proved that the photodynamic drug could work normally.

In this research, RF magnetron sputtering was employed to grow 3D nano-structured ITO thin films using the barrier-layer side of an anodic aluminum oxide (AAO) as the template. The template was prepared by immersing this side of an AAO film into a 30 wt% phosphoric acid solution to modify the surface of the barrier layer in such a manner that a contrasting surface was obtained. The resistivity and crystallinity of the deposited ITO thin film were characterized by I-V curves and X-ray diffraction (XRD). As illustrated in the I-V curve measurements, the resistivity of the ITO film after annealing was 8.25x10-3 Ω -cm. The XRD analysis results of the annealed ITO film clearly showed the characteristic (222) and (400) peaks which characterize the crystallinity. A nano-hemispheric TiO2/ITO array electrode for dye-sensitized solar cells (DSSC) was further fabricated through electrophoretic deposition of TiO2 nanoparticles on the nano-hemispheric ITO array.

Carbon nanotube (CNT) growth on catalyst as a function of time, temperature, diameter of the CNT, damping factor of the system, and the type of catalyst is investigated via a theoretical analysis on the phonon vibration of the system. Simulations demonstrate that CNTs with larger diameter grow lesser owing to higher damping factors and CNT inertia. In addition, an optimum temperature for the growth is obtained for a CNT with a specific diameter and catalyst. Finally effect of the type of the catalyst on the growth is also discussed. Simulations from the theory are in good agreement with reported experimental results.

Carbon fibers were uniformly coated with carbon nanotubes by catalytic decomposition of acetylene using thermal chemical vapor deposition technique at 700 °C. The nanotube coated fibers were employed for the fabrication of unidirectional multi-scale composites with epoxy matrix. As the carbon nanotubes were directly grown on carbon fibers they remain firmly attached with the fiber substrate therefore they are anticipated to modify the interfacial characteristics of the composites and in turn considerably alter the mechanical behavior. Moreover, the direct growth of carbon nanotubes on fiber facilitates uniform distribution of carbon nanotubes in the polymer matrix. The composite specimens made of carbon nanotubes coated fibers showed a significant enhancement of 48% and 85% in the tensile and flexure strength respectively as compared to composites made of carbon fibers undergone similar thermal cycle but without carbon nanotubes growth. The morphology of carbon nanotubes coating on carbon fibers was examined at nano-level using high resolution TEM which showed growth of carbon nanotubes with different morphology and diameter ranging from 5-50 nm. Specimens failed in tensile were further investigated for fractographic analysis using SEM which showed improved fiber/matrix interfacial bonding indicated by less fiber pull out.

Deoxyribonucleic acid (DNA) biosensor based on a carbon nanotube (CNT) modified electrode was developed as an anticancer drug screening device for rapid electrochemical detection of cyclophosphamide. Screen-printing technology was employed to fabricate electrodes for biosensor construction. The interaction of cyclophosphamide with double stranded (ds) calf thymus DNA was detected with the developed CNT-based biosensor and compared with the carbon paste based biosensor by using differential pulse voltammetry. The preliminary results indicate that the developed CNT-based DNA biosensor exhibited a faster response and a higher detection reproducibility compared to the carbon paste based biosensor.

In this paper a novel and effective method of manufacturing aligned fibers with nano-scale diameters based on electrospinning is described. The conventional procedure of electrospinning has been modified to generate nanofibers as uniaxially aligned array for specific applications. In comparison with typical method, the electrospinning is performed into the hollow metallic cylinder as a collector so that the needle is located in center of the cylinder. The jet coming out of the needle rotates and spun nanofibers assemble in the inner surface of the cylinder. Fibers produced by this method are well-aligned and can be spread over a large area. The influences of the applied voltage and collector diameter on alignment of nanofibers were investigated using image analysis techniques. In addition, Optimum conditions to maximize fibers alignment were obtained.

Mask-image-like block copolymer nanotemplates with densely packed polystyrene (PS) nano-dots were prepared by a simple top-down/bottom-up hybrid method using one-step excimer laser irradiation on perpendicular cylinder-containing block copolymer masks. Together with preferential etching of more ultraviolet (UV)-sensitive block component, non-selective removal of all block components, which reduced the overall sample thickness and finally provided block copolymer nanotemplates with freestanding PS nanocylinders, simultaneously occurred during the excimer laser irradiation at an appropriate laser intensity. The numerical analysis on the photothermal ablation of periodically nanopatterned block copolymer masks revealed that, by using sufficiently low laser intensity, we could suppress the microscopic level surface melt flows of block components, as long as the intensity was high enough to induce a matrix- assisted photothermal ablation in the less UV-sensitive block component. Such surface melt flows would, otherwise, severely undermine the initial orders of nanopatterns in the block copolymer masks.

The interfaces of dissimilar materials suffer high stress gradients due to the presence of thermal and stiffness mismatches of bonded materials. Interfaces of dissimilar materials are prone to crack initiations, leading to delaminations. The atomistic effects have to be taken into account correctly when the system becomes extremely small such as in nano-scale. The experimental test for this scale situation is an impossible expectation because the helpless experimental technologies in present time. So the simulation under atomic model is a cogent means to investigate the behavior of nanocracks on micro/nano-interfacial structure. In this paper, an atomic model is proposed to investigate the effect of nanocracks on interfacial behavior under thermal flux conditions. The simulations results show the propagation mechanisms of cracks and the corresponding change of temperature distribution in the heat transfer process. The comparison on the thermal flux for cases of cracks added and cracks free is also presented.

In this paper, we report the synthesis of barium zirconate, BaZrO3, (BZ) nanotubes fabricated by the modified sol-gel method within the nanochannels of anodic aluminum oxide (AAO) templates. The morphology, structure, and composition of as prepared nanotubes were characterized by means of X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), selected-area electron diffraction (SAED), high resolution TEM (HRTEM) and energy-dispersive X-ray spectroscopy (EDX). The results of XRD and SAED indicated that postannealed (at 650°C for 1 h) BZ nanotubes (BZNTs) exhibited a polycrystalline cubic perovskite crystal structure. SEM and TEM analysis revealed that BZNTs possessed a uniform length and diameter (∼200 nm) and the thickness of the wall of the BZNTs was about 20 nm. Y-junctions, multiple branching and typical T-junctions were also observed in some BZNTs. EDX analysis demonstrated that stoichiometric BaZrO3 was formed. HRTEM image confirmed that the obtained BZNTs were composed of nanoparticles in the range of 5-10 nm. The possible formation mechanism of BZNTs was discussed.

The activity of herbal medicines depends on overall function of a variety of active components, as all the constituents provide synergistic action and thus enhance the therapeutic value. The nature serves us with the exact proportion of all the constituents for various ailments in a single species. Each active constituent plays an important role and they are all related to each other. However most of the herbal origin drugs possess insoluble character leading to lower bioavailability and increased systemic clearance requiring repeated administration or higher dose, which makes the drug as a poor candidate for therapeutic use. To conquer these obstacles, related research in the field of herbal medicines has not yet been profoundly investigated. In phyto-formulation research, developing nano dosage forms (Polymeric Nanoparticles (Nanospheres & Nanocapsules), Liposomes, Proliposomes, Solid Lipid Nanoparticles, and Nanoemulsion etc.) has large number of advantages for herbal drugs, including enhancement of solubility and bioavailability, protection from toxicity, enhancement of pharmacological activity, enhancement of stability, improving tissue macrophages distribution, sustained delivery, protection from physical and chemical degradation etc. Thus the nano sized drug delivery systems of herbal drugs have a potential future for enhancing the activity and overcoming problems associated with plant medicines.

In the microchannel-emulsification approach for producing nano-/subnano-liter droplets, the external energy input into the droplet accounts for the variation of the droplet surface free energy during its growth on the terrace. Avoiding the demand for an infinite energy input is the mechanism responsible for the experimental observation that there is always some remaining dispersed liquid on the terrace after generation of one droplet. A better empirical relation exists for correlating the experimental data of the droplet size in the literature. Based on a balance of the surface tension and the drag force, we have also developed a simple scaling model for predicting the size of droplets fabricated in microfluidic T-junctions.

Lipid matrix nanoparticles, such as solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC), have been sought as a useful alternative for formulating poorly soluble drugs intended for several administration routes, e.g. oral, parenteral and topical. These systems are surfaced by a film of surfactant in an aqueous phase, being therefore physicochemically and thermodynamically stable having a mean particle size below 1 μm. The matrix of SLN is solely composed of a pure solid lipid (melting point above 40°C) whereas NLC is composed of a blend of solid and liquid lipids, which must also be solid at both body and room temperatures. The achievements of SLN and NLC as drug carrier systems are due to several advantages, e.g. incorporation of hydrophobic and hydrophilic drug molecules (including peptides and proteins), controlled release, protection of chemically labile drugs, fulfil several prerequisites for an optimum colloidal drug carrier. The present review aims to emphasize the special features of lipid matrix nanoparticles, in particular for controlled release purposes. An overview on pharmacokinetic and biopharmaceutic results achieved by different research groups is given and their parameters are analyzed.

The current rise in the interest in physical phenomena at nano spatial scale is described hereby as a natural consequence of the scientific progress in manipulation with matter with an ever higher sensitivity. The reason behind arising of the entirely new field of nanoscience is that the properties of nanostructured materials may significantly differ from their bulk counterparts and cannot be predicted by extrapolations of the size-dependent properties displayed by materials composed of microsized particles. It is also argued that although a material can comprise critical boundaries at the nano scale, this does not mean that it will inevitably exhibit properties that endow a nanomaterial. This implies that the attribute of “nanomaterial” can be used only in relation with a given property of interest. The major challenges faced with the expansion of resolution of the materials design, in terms of hardly reproducible experiments, are further discussed. It is claimed that owing to an unavoidable interference between the experimental system and its environment to which the controlling system belongs, an increased fineness of the experimental settings will lead to ever more difficulties in rendering them reproducible and controllable. Self-assembly methods in which a part of the preprogrammed scientific design is substituted with letting physical systems spontaneously evolve into attractive and functional structures is mentioned as one of the ways to overcome the problems inherent in synthetic approaches at the ultrafine scale. The fact that physical systems partly owe their properties to the interaction with their environment implies that each self-assembly process can be considered a co-assembly event.