Silver colloidal nanoparticle stability: influence on Candida biofilms formed on denture acrylic

Funda����o de Amparo �� Pesquisa do Estado de S��o Paulo (FAPESP)

S��ntese de nanopart��culas de prata suportadas sobre nanotubos de carbono de paredes m��ltiplas para eletrooxida����o de benzeno

Silver nanoparticles (Ag) were deposited on multi-walled carbon nanotube by eletroless. The hybrid Ag/MWCNT was used in the modification of glassy carbon electrode (GC) surface. The electrochemical characterization confirmed the presence of Ag in the nanocomposite has been showed that the synthesis was successful. The GC electrode modified with Ag/MWCNT film was evaluated for electro-oxidation of benzene. The electrochemical behavior presented an improvement on the catalytic surface in relation to non-modified GC electrode. The anodic peak current increased the magnitude in three times when compared with the CG electrode modified only with MWCNT

In vitro reduction of Streptococcus mutans biofilm on silver nanoparticle-modified resin composite

Introduction: Currently, new methods to reduce biofilm formation on biomaterials are very studied, for example the use of silver nanoparticles, which were bactericidal. However, there are few studies investigating the benefits of these particles in dental restorative materials. Objective: This study aimed to compare in vitro the Streptococcus mutans biofilm formation on conventional light-cured composite resin with that on experimental light-cured composite resin, modified with silver nanoparticles. Material and methods: Discs were produced with either conventional resin (control group) and resin modified with different concentrations of silver nanoparticles, 0.1%, 0.3% and 0.6 % wt. (groups 1, 2 and 3, respectively). The samples were incubated in bacterial suspension (S. mutans) enriched with 20% sucrose to promote biofilm growth on the surfaces. Incubation times were 1, 4 and 7 days. After each period, adherent biofilms were disaggregated by ultrasound. Then, the numbers of viable cells recovered from the biofilms were counted through the serial dilution method. A morphological analysis of biofilm was also performed by Scanning Electron Microscopy. The data were subjected to Anova and Tukey���s test (�� = 0.05). Results: The number of viable cells was statistically lower in groups 2 and 3 than in group 1 and control group, after the three incubation periods, without statistical difference between groups 2 and 3. The number of viable cells was statistically lower in group 1 than in control group, after 4 and 7 days of incubation. Conclusion: Resins modified with silver presented reduction of S. mutans biofilm on their surfaces, according to the conditions of this study.

Efficient plasmonic coupling between Er3+:(Ag/Au) in tellurite glasses

We report a systematic study of the localized surface plasmon resonance effects on the photoluminescence of Er3+-doped tellurite glasses containing Silver or Gold nanoparticles. The Silver and Gold nanoparticles are obtained by means of reduction of Ag ions (Ag+ -> Ag-0) or Au ions (Au3+ -> Au-0) during the melting process followed by the formation of nanoparticles by heat treatment of the glasses. Absorption and photoluminescence spectra reveal particular features of the interaction between the metallic nanoparticles and Er3+ ions. The photoluminescence enhancement observed is due to dipole coupling of Silver nanoparticles with the I-4(13/2) -> I-4(15/2) Er3+ transition and Gold nanoparticles with the H-2(11/2)-> I-4(13/2) (805 nm) and S-4(3/2) -> I-4(13/2) (840 nm) Er3+ transitions. Such process is achieved via an efficient coupling yielding an energy transfer from the nanoparticles to the Er3+ ions, which is confirmed from the theoretical spectra calculated through the decay rate. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Straightforward Synthesis of Carbon-Supported Ag Nanoparticles and Their Application for the Oxygen Reduction Reaction

In this paper we report a simple and environmentally friendly synthesis of silver nanoparticles (AgNps) and their activities towards the oxygen reduction reaction (ORR). Ultraviolet spectroscopy (UV-vis) and transmission electron microscopy confirmed the formation of poly(vinyl pyrrolidone)-protected colloidal AgNps through direct reduction of Ag+ by glycerol in alkaline medium at room temperature. For the ORR tests, the AgNps were directly produced onto carbon to yield the Ag/C catalyst. Levich plots revealed the process to occur via 2.7 electrons, suggesting that the carbon support contributes to the ORR. We discuss here possibilities of improving the catalytic properties of the Ag/C for ORR by optimizing the parameters of the synthesis.

Novel SrTi1-xFexO3 nanocubes synthesized by microwave-assisted hydrothermal method

We report herein for the first time a facile synthesis method to obtain SrTi1-xFexO3 nanocubes by means by a microwave-assisted hydrothermal (MAH) method at 140 degrees C. The effect of iron addition on the structural and morphological properties of SrTiO3 was investigated. X-ray diffraction measurements show that all STFO samples present a cubic perovskite structure. X-ray absorption spectroscopy at Fe absorption K-edge measurements revealed that iron ions are in a mixed Fe2+/Fe3+ oxidation state and preferentially occupy the Ti4+-site. UV-visible spectra reveal a reduction in the optical gap (E-gap) of STFO samples as the amount of iron is increased. An analysis of the data obtained by field emission scanning electron microscopy points out that the nanoparticles present a cubic morphology independently of iron content. According to high-resolution transmission electron microscopy results, these nanocubes are formed by a self-assembly process of small primary nanocrystals.

Plasmons as sensors

���Plasmon��� is a synonym for collective oscillations of the conduction electrons in a metal nanoparticle (excited by an incoming light wave), which cause strong optical responses like efficient light scattering. The scattering cross-section with respect to the light wavelength depends not only on material, size and shape of the nanoparticle, but also on the refractive index of the embedding medium. For this reason, plasmonic nanoparticles are interesting candidates for sensing applications. Here, two novel setups for rapid spectral investigations of single nanoparticles and different sensing experiments are presented.rnrnPrecisely, the novel setups are based on an optical microscope operated in darkfield modus. For the fast single particle spectroscopy (fastSPS) setup, the entrance pinhole of a coupled spectrometer is replaced by a liquid crystal device (LCD) acting as spatially addressable electronic shutter. This improvement allows the automatic and continuous investigation of several particles in parallel for the first time. The second novel setup (RotPOL) usesrna rotating wedge-shaped polarizer and encodes the full polarization information of each particle within one image, which reveals the symmetry of the particles and their plasmon modes. Both setups are used to observe nanoparticle growth in situ on a single-particle level to extract quantitative data on nanoparticle growth.rnrnUsing the fastSPS setup, I investigate the membrane coating of gold nanorods in aqueous solution and show unequivocally the subsequent detection of protein binding to the membrane. This binding process leads to a spectral shift of the particles resonance due to the higher refractive index of the protein compared to water. Hence, the nanosized addressable sensor platform allows for local analysis of protein interactions with biological membranes as a function of the lateral composition of phase separated membranes.rnrnThe sensitivity on changes in the environmental refractive index depends on the particles��� aspect ratio. On the basis of simulations and experiments, I could present the existence of an optimal aspect ratio range between 3 and 4 for gold nanorods for sensing applications. A further sensitivity increase can only be reached by chemical modifications of the gold nanorods. This can be achieved by synthesizing an additional porous gold cage around the nanorods, resulting in a plasmon sensitivity raise of up to 50 % for those ���nanorattles��� compared to gold nanorods with the same resonance wavelength. Another possibility isrnto coat the gold nanorods with a thin silver shell. This reduces the single particle���s resonance spectral linewidth about 30 %, which enlarges the resolution of the observable shift. rnrnThis silver coating evokes the interesting effect of reducing the ensemble plasmon linewidth by changing the relation connecting particle shape and plasmon resonance wavelength. This change, I term plasmonic focusing, leads to less variation of resonance wavelengths for the same particle size distribution, which I show experimentally and theoretically.rnrnIn a system of two coupled nanoparticles, the plasmon modes of the transversal and longitudinal axis depend on the refractive index of the environmental solution, but only the latter one is influenced by the interparticle distance. I show that monitoring both modes provides a self-calibrating system, where interparticle distance variations and changes of the environmental refractive index can be determined with high precision.

Occurrence and Origin of Placer Gold in Montana

From time immemorial man has used gold as a medium of exchange, a mea��sure of value, as jewelry and for ornamentation. Placer gold has led dir��ectly or indirectly to the settlement of lands, California and Alaska being the two best known examples. It has led the way to the discovery of other important mineral wealth, the discovery of the copper and silver deposits at Butte, Montana and the discovery of the silver deposits at Cripple Creek, Colorado being two good examples.

Testing and Concentration of a Low Grade Gold Ore from Marysville, Montana

The purpose of this thesis was to investigate and attempt to concentrate low grade cyanided tailings rejected from the old Montana Mining and milling Company's mill situated 4 miles below the town of Marysville, Montana.

Refining of Low Grade Zinc-Gold Precipitates

The purpose of this investigation was to ascertain if advantage could be taken of the copper in the precipitates as a collecting agent of the precious metals in the direct smelting furnace.The products produced to be low grade anode bullion and a slag low in precious metals, high in zinc and lead.

Selectively filled photonic liquid crystal fibers = Fibras de cristal fot��nico selectivamente llenas con cristal l��quido

El presente trabajo de Tesis se ha centrado en el dise��o, fabricaci��n y caracterizaci��n de dispositivos basados en fibras de cristal fot��nico infiltrado selectivamente con cristales l��quidos, pol��meros y una mezcla de ambos. Todos los dispositivos son sintonizables, y su ��rea de aplicaci��n se centra en comunicaciones ��pticas y sensores. La manipulaci��n y fusionado de fibras fot��nicas, el llenado selectivo de determinadas cavidades y la alineaci��n rec��proca de fibras mantenedoras de polarizaci��n son tareas muy espec��ficas y delicadas para las que se requieren protocolos muy estrictos. Previo a la fabricaci��n de dispositivos ha sido necesaria por tanto una tarea de sistematizaci��n y creaci��n de protocolos de fabricaci��n. Una vez establecidos se ha procedido a la fabricaci��n y caracterizaci��n de dispositivos. Los dispositivos fabricados se enumeran a continuaci��n para posteriormente detallar una a una las singularidades de cada uno. ��� Interfer��metros intermodales hechos a partir de una porci��n de fibra fot��nica soldada entre dos fibras est��ndar, bien monomodo o PANDA (mantenedora de polarizaci��n). Estos interfer��metros han sido sumergidos o bien llenados selectivamente con cristales l��quidos para as�� sintonizar la se��al interferom��trica guiada a trav��s de la fibra. ��� Infiltraci��n de fibras fot��nicas con cristales l��quidos colest��ricos con especial ��nfasis en la fase azul (blue phase) de estos materiales. Las mol��culas de cristal l��quido se autoalinean en volumen por lo que la infiltraci��n de fibras fot��nicas con estos cristales l��quidos es muy interesante, pues es conocida la dificultad de alinear apropiadamente cristales l��quidos dentro de cavidades microm��tricas de las fibras fot��nicas. ��� Grabaci��n de redes hologr��ficas de forma selectiva en las cavidades de una fibra fot��nica. Estas redes hologr��ficas, llamadas POLICRYPS (POlymer-LIquid CRYstal-Polymer Slices), son redes fabricadas a base de franjas de pol��mero y cristal l��quido alineado perpendicularmente a dichas franjas. Las franjas son a su vez perpendiculares al eje de la fibra como lo puede ser una red de Bragg convencional. El cristal l��quido, al estar alineado perpendicularmente a dichos franjas y paralelo al eje de la fibra, se puede conmutar aplicando un campo el��ctrico externo, modificando as�� el ��ndice efectivo de la red. Se puede fabricar por lo tanto una red de Bragg sintonizable en fibra, muy ��til en comunicaciones ��pticas. ��� Llenado selectivo de fibras fot��nicas con polidimetilsiloxano (PDMS), un pol��mero de tipo silicona. Si se realiza un llenado selectivo asim��trico se puede inducir birrefringencia en la fibra. El ��ndice de refracci��n del PDMS tiene una fuerte dependencia t��rmica, por lo que se puede sintonizar la birrefringencia de la fibra. ��� Estudio te��rico de llenado selectivo de fibras fot��nicas con PDMS dopado con nanopart��culas de plata de 5, 40 y 80 nm. Estas nanopart��culas poseen un pico de absorci��n en torno a los 450 nm debido a resonancias superficiales localizadas de plasmones (LSPR). La resonancia del plasmon tiene una fuerte dependencia con el ��ndice de refracci��n del material colindante, y al ser ��ste PDMS, la variaci��n de ��ndice de refracci��n se ve amplificada, obteniendo una absorci��n sintonizable. Se ha propuesto la fabricaci��n de polarizadores sintonizables usando esta t��cnica. Como ya se ha dicho, previamente a la fabricaci��n ha sido necesaria la protocolizaci��n de diversos procedimientos de fabricaci��n de alta complejidad, as�� como protocolizar el proceso de toma de medidas para optimizar los resultados. Los procedimientos que han requerido la formulaci��n de protocolos espec��ficos han sido los siguientes: ��� Llenado selectivo de cavidades en una fibra fot��nica. Dichas fibras tienen generalmente un di��metro externo de 125 ��m, y sus cavidades son de entre 5 y 10 ��m de di��metro. Se han desarrollado tres t��cnicas diferentes para el llenado/bloqueado selectivo, pudi��ndose combinar varios protocolos para la optimizaci��n del proceso. Las t��cnicas son las siguientes: o Llenado y bloqueado con un prepol��mero. Dicho prepol��mero, tambi��n llamado adhesivo ��ptico, est�� inicialmente en estado l��quido y posee una cierta viscosidad. Las cavidades de la fibra fot��nica que se desea llenar o bloquear poseen un di��metro diferente al resto, por lo que en el proceso de llenado aparecen dos frentes de llenado dependientes de su di��metro. A mayor di��metro, mayor velocidad de llenado. Polimerizando cuando existe dicha diferencia en los frentes se puede cortar por medio, obteniendo as�� una fibra parcialmente bloqueada. o Colapsamiento de las cavidades de menor di��metro mediante aplicaci��n de calor. El calor producido por un arco voltaico de una soldadora de fibra est��ndar fusiona el material exterior de la fibra produciendo el colapsamiento de las cavidades de menor di��metro. En esta t��cnica tambi��n es necesaria una diferencia de di��metros en las cavidades de la fibra. o Bloqueo una a una de las cavidades de la fibra fot��nica con adhesivo ��ptico. Este procedimiento es muy laborioso y requiere mucha precisi��n. Con este sistema se pueden bloquear las cavidades deseadas de una fibra sin importar su di��metro. ��� Alineaci��n de una fuente de luz linealmente polarizada con una fibra mantenedora de polarizaci��n ya sea PANDA o fot��nica. As�� mismo tambi��n se han alineado entre s�� fibras mantenedoras de polarizaci��n, para que sus ejes r��pidos se fusionen paralelos y as�� el estado de polarizaci��n de la luz guiada se mantenga. ��� Sistematizaci��n de toma de medidas para caracterizar los interfer��metros modales. ��stos son altamente sensibles a diversas variables por lo que el proceso de medida es complejo. Se deben aislar variables de forma estrictamente controlada. Aunque todos los dispositivos tienen en com��n el llenado selectivo de cavidades en una fibra fot��nica cada dispositivo tiene sus peculiaridades, que van a ser explicadas a continuaci��n. ABSTRACT The present Thesis has been centered in the design, fabrication and characterization of devices based on photonic crystal fibers selectively filled with liquid crystals, polymers and a mixture of both. All devices are tunable and their work field is optical communications and sensing The handling and splicing of photonic crystal fibers, the selective filling of their holes and the aligning of polarization maintaining fibers are very specific and delicate tasks for which very strict protocols are required. Before the fabrication of devices has therefore been necessary task systematization and creation of manufacturing protocols. Once established we have proceeded to the fabrication and characterization of devices. The fabricated devices are listed below and their peculiarities are detailed one by one: ��� Intermodal interferometers made with a portion of photonic crystal fiber spliced between two optical communication fiber pigtails, either single mode or PANDA (polarization-maintaining) fiber. These interferometers have been submerged or selectively filled with liquid crystals to tune the interferometric guided signal. ��� Infiltration of photonic fibers with cholesteric liquid crystals with special emphasis on their blue phase (blue phase). The liquid crystal molecules are self-aligning in volume so the infiltration of photonic fibers with these liquid crystals is very interesting. It is notoriously difficult to properly align liquid crystals within micron cavities such as photonic fibers. ��� Selectively recording of holographic gratings in the holes of photonic crystal fibers. These holographic gratings, called POLICRYPS (POlymer-LIquid CRYstal-Polymes Slices), are based on walls made of polymer and liquid crystal aligned perpendicular to them. These walls are perpendicular to the axis of the fiber as it can be a conventional Bragg grating. The liquid crystal is aligned perpendicular to the walls and parallel to the fiber axis, and can be switched by applying an external electric field and thus change the effective index of the grating. It is thus possible to manufacture a tunable Bragg grating fiber, useful in optical communications. ���������Asymmetrically selective filling of photonic crystal fibers with a silicone polymer like called polydimethylsiloxane (PDMS) to induce birefringence in the fiber. The refractive index of PDMS has temperature dependence, so that the birefringence of the fiber can be tuned. ��� Theoretical study of photonic crystal fibers selectively filled with PDMS doped with silver nanoparticles of 5, 40 and 80 nm. These nanoparticles have an absorption peak around 450 nm due to localized surface plasmon resonances (LSPR). Plasmon resonance has a strong dependence on the refractive index of the adjacent material, and as this is PDMS, the refractive index variation is amplified, obtaining a tunable absorption. Fabrication of tunable polarizers using this technique has been proposed. Before starting the fabrication, it has been necessary to optimize several very delicate procedures and different protocols have been designed. The most delicate procedures are as follows: ��� Selective filling of holes in a photonic crystal fiber. These fibers generally have an outer diameter of 125 ��m, and their holes have a diameter around between 5 and 10 ��m. It has been developed three different techniques for filling / selective blocking, and they can be combined for process optimization. The techniques are: o Filling and blocked with a prepolymer. This prepolymer also called optical adhesive is initially in liquid state and has a certain viscosity. The holes of the photonic crystal fiber that are desired to be filled or blocked should have a different diameter, so that in the filling process appear two different fronts depending on the hole diameter. The holes with larger diameter are filled faster. Then the adhesive is polymerized when there is such a difference on the front. A partially blocked fiber is obtained cutting between fronts. o Collapsing of holes of smaller diameter by application of heat. The heat produced by an arc of a standard fusion splicer fuses the outer fiber material producing the collapsing of the cavities of smaller diameter. In this technique also you need a difference of diameters in the fiber holes. o Blocking one by one the holes of photonic crystal fiber with optical adhesive. This procedure is very laborious and requires great precision. This system can block unwanted cavities regardless fiber diameter. ��� Aligning a linearly polarized light source with a polarization-maintaining fiber (either a PANDA fiber as a photonic crystal fiber). It is needed also an aligning between polarization-maintaining fibers, so that their fast axes parallel merge and that is state of polarization of light guided is maintained. ��� Systematization of taking measurements to characterize the modal interferometers. These are highly sensitive to several variables so the measurement process is very complicated. Variables must be fixed in a very controlled manner. Although all devices have the common characteristic of being selectively filled PCFs with some kind of material, each one has his own peculiarities, which are explained below.

Glucose-induced Autophagy of Peroxisomes in Pichia pastoris Requires a Unique E1-like Protein

Cytosolic and peroxisomal enzymes necessary for methanol assimilation are synthesized when Pichia pastoris is grown in methanol. Upon adaptation from methanol to a glucose environment, these enzymes are rapidly and selectively sequestered and degraded within the yeast vacuole. Sequestration begins when the vacuole changes shape and surrounds the peroxisomes. The opposing membranes then fuse, engulfing the peroxisome. In this study, we have characterized a mutant cell line (glucose-induced selective autophagy), gsa7, which is defective in glucose-induced selective autophagy of peroxisomes, and have identified the GSA7 gene. Upon glucose adaptation, gsa7 cells were unable to degrade peroxisomal alcohol oxidase. We observed that the peroxisomes were surrounded by the vacuole, but complete uptake into the vacuole did not occur. Therefore, we propose that GSA7 is not required for initiation of autophagy but is required for bringing the opposing vacuolar membranes together for homotypic fusion, thereby completing peroxisome sequestration. By sequencing the genomic DNA fragment that complemented the gsa7 phenotype, we have found that GSA7 encodes a protein of 71 kDa (Gsa7p) with limited sequence homology to a family of ubiquitin-activating enzymes, E1. The knockout mutant gsa7�� had an identical phenotype to gsa7, and both mutants were rescued by an epitope-tagged Gsa7p (Gsa7-hemagglutinin [HA]). In addition, a GSA7 homolog, APG7, a protein required for autophagy in Saccharomyces cerevisiae, was capable of rescuing gsa7. We have sequenced the human homolog of GSA7 and have shown many regions of identity between the yeast and human proteins. Two of these regions align to the putative ATP-binding domain and catalytic site of the family of ubiquitin activating enzymes, E1 (UBA1, UBA2, and UBA3). When either of these sites was mutated, the resulting mutants [Gsa7(��ATP)-HA and Gsa7(C518S)-HA] were unable to rescue gsa7 cells. We provide evidence to suggest that Gsa7-HA formed a thio-ester linkage with a 25���30 kDa protein. This conjugate was not observed in cells expressing Gsa7(��ATP)-HA or in cells expressing Gsa7(C518S)-HA. Our results suggest that this unique E1-like enzyme is required for homotypic membrane fusion, a late event in the sequestration of peroxisomes by the vacuole.

Synthesis of Silver Nanoparticle Based Conductive Inks for Additively Manufactured Electronics

Thesis (Master's)--University of Washington, 2016-06

Effect of the preparation technique on the catalytic properties of mesoporous V-HMS for the oxidation of toluene

Various mesoporous catalysts with vanadium loadings between 0.5 and 6 V wt.% and surface areas around 1300 m(2)/g were synthesized using the isomorphous substitution (IS) and molecular designed dispersion (MDD) techniques. Their catalytic properties were tested using toluene as a model VOC in a fixed bed reactor at temperatures between 300 and 550 degrees C. It was found that during the oxidation of toluene, over V-HMS synthesized via IS, conversion of toluene mainly results in carbon oxides, benzene, benzaldehyde and water. Total conversion is greatly improved when the vanadium content is increased from around 1.5 to 3.0 wt.%, but an increase in the textural porosity (V-TEX/V-MESO) from 0.3 to 0.6 had no discernable effect on the conversion. This can be explained by the fact that a V-TEX/V-MESO as low as 0.3 is sufficient to facilitate the access of toluene into the framework confined mesopores without any molecular transport limitations. However, when using V-HMS synthesized by MDD, conversion of toluene is greatly improved when the V-TEX/ V-MESO ratio is increased from 0.1 to 0.6. This is because the diffusion limitations are minimized by this increase. V-HMS synthesized via MDD does not exhibit selectivity to benzaldehyde, favoring total oxidation to CO and CO2. This different oxidation mechanism can be explained in terms of location, accessibility and number of active species on the surface of the HMS support. (c) 2005 Elsevier Inc. All rights reserved.

Reactivity of crotonaldehyde and propene over Au/Pd(111) surfaces

The surface chemistry of crotonaldehyde and propene, primary and secondary reaction products in the aerobic selective oxidation of crotyl alcohol, has been studied by temperature-programmed reaction over Au/Pd(111) surface alloys. Gold strongly promotes desorption versus reaction at mole fractions ���0.3 (crotonaldehyde) and ���0.8 (CH); only ���5% of the chemisorbed aldehyde or alkene react over Au-rich alloys. Surprisingly, co-adsorbed oxygen strongly suppresses crotonaldehyde decomposition over both clean Pd(111) and alloy surfaces, while CH combustion, an important undesired side-reaction over unpromoted Pd(111), is also moderated by Au. �� the Owner Societies.