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PubMed2006

Synthesis of silicon nitride nanowires by the pyrolysis of perhydropolysilazane.

Silicon nitride nanowires synthesized by the pyrolysis of perhydropolysilazane without using any catalysts are reported. After pyrolysis at 1073 K in N2/NH3 atmosphere, the synthetic nanowires are discrete and curly with diameters about tens of nanometers and lengths of hundreds of nanometers. While after post-treatment at 1873 K in N2 atmosphere, the nanowires are continuous and randomly distributed with diameters about tens of nanometers and several microns in length. There are no bulbs or droplets on the tips of the nanowires, and two gas-solid mechanisms are proposed to explain their growth.

Chemical Fractionation↗
PubMed2006

Fabrication of nanopores in a 100-nm thick Si3N4 membrane.

Textured alumina films have been used to fabricate nanoscale pores in Si3N4 membranes. A few nanometer-thick alumina layer was used as a masking material for nanopore fabrication, and the pattern was transferred into a 100-nm thick, 200 microm x 200 microm Si3N4 membrane by reactive ion etching (RIE). The nanopores were found to be concentrated in a approximately 150-microm diameter region at the center of the membrane.

Crystallization↗
PubMed2006

Triphenyl benzene-bridged fluorescent silsesquioxane: shape-controlled hybrid silicas by hydrolytic conditions.

A new silsesquioxane molecule was synthesized, in which triphenyl benzene was connected with three Si(OC2H5)3 groups using three urea groups as the bridge. The molecule could self-assemble through the intermolecular H-bonding among urea groups and pi-pi interaction of triphenyl benzene core in the solution and it could also be transferred into hybrid silicas by hydrolysis. When the non-preorganized silsesquioxane was hydrolyzed, isolated spherical hybrid silica was gained. However, when the silsesquioxane was preorganized before the hydrolyzation uniform interconnected spherical hybrid silica and intertwined nanofibrous one could be generated under acidic and basic conditions, respectively. The photoluminescence (PL) spectra of the obtained hybrid silicas showed that they still kept the emission properties of their precursor silsesquioxane, and the shift of the emission bands was due to the pi-pi interaction of triphenyl benzene in the course of polycondensation.

Benzene↗
PubMed2000

Effect in vitro acidification on plaque fluid composition with and without a NaF or a controlled-release fluoride rinse.

Plaque fluid ion concentration changes, especially fluoride, in response to the pH decrease associated with a cariogenic episode are important components of the caries process. A "controlled-release" (CR) fluoride rinse, based on the controlled release of fluoride in the presence of calcium, has been shown to form large fluoride reservoirs in resting plaque. In this study, the in vitro acid-induced release of fluoride, and other ions, was examined in 48-hour-fasted plaque fluid from subjects (n = 11) who received no rinse, or who used a 228-ppm CR or NaF fluoride rinse 1 hr before being sampled. After collection, the plaque was centrifuged to yield plaque fluid, acidified (0.1 microL of 0.5 mol/L HCl per milligram plaque), and then re-centrifuged before a second sample was obtained. Although previous studies indicated a higher plaque fluid fluoride after the new rinse relative to NaF, no statistically significant difference was observed here. Average fluoride release after acidification (average pH, 5.2) was statistically greater following the use of the CR rinse (153 micromol/L) compared with the NaF rinse (17 micromol/L). No fluoride release was seen in the no-rinse samples. The pH, free calcium, phosphate, acetate, propionate, and buffer capacity were not affected by the different amounts of fluoride deposited in the plaque. However, following acid addition, an increase in free calcium and phosphate was observed, which was also independent of the rinse. The large release of fluoride following acidification suggests that the new rinse may provide an improved cariostatic effect.

Acetates↗
PubMed2002

Focal cerebral ischemia in rats produced by intracarotid embolization with viscous silicone.

Many factors contribute to the severity of neuronal cell death and the functional outcome in stroke. We describe an embolic model of focal cerebral ischemia in the rat that does not require craniotomy and is compatible with continuous measurement of regional CBF using multichannel laser Doppler flow (LDF) technique. Either a 22 microliters (large lesion) or 11 microliters (small lesion) bolus of viscous silicone was injected cephalad into the internal carotid artery. Upon injection, LDF decreased abruptly, most severely in the parietal cortex (-74% +/- 5%) in the large lesion and in the occipital cortex (-69% +/- 10%) in the small lesion model. Over the first hour, post-embolization LDF improved in most areas (e.g. -48% +/- 9% parietal, large lesion) but declined in the small lesion group in the occipital region (-81% +/- 8%). CBF measured by [C]14-IAP autoradiography 1 h post-embolization in the large lesion model demonstrated near-hemispheric ischemia (70% of hemisphere) with sparing of cingulate cortex. Autoradiography demonstrated that ischemia in the small lesion was largely cortical. Light microscopy of brains embolized with 11 microliters of dyed silicone showed filling of pial vessels with no silicone in the Circle of Willis or parenchyma. No animals in the large lesion group survived 24 h. Thirteen of 15 animals in the small lesion group survived for two weeks with resolution of initial hemiplegia, ocular asymmetry and weight loss. Hematoxylin-eosin staining two weeks post-embolization showed signs of severe hypoxia and infarction. In conclusion, the intracarotid silicone embolization technique produces a titrable, reproducible permanent ischemic injury by blocking perfusion in the pial circulation, and is amenable to multisite monitoring with laser Doppler flowmetry. The smaller embolus produces cortical infarction with high rate of survival and neurological recovery.

Animals↗
PubMed2003

Micromachined, silicon filament light source for spectrophotometric microsystems.

A miniature broadband light source is a critical element in a spectrophotometric microsystem. The design, fabrication, and characterization of a highly stable, miniature broadband light source that comprises filaments of single-crystal silicon are presented. Electrical current versus voltage and radiant emittance spectra under constant voltage bias are measured and related to filament dimensions. A maximum stable operating temperature for these filaments is estimated to be 1200 K. Resistance drift is demonstrated to be less than 0.5% over a 10-h period of continuous operation with visible incandescence. Emittance spectra of a multifilament array, measured at three different electrical biases, are presented and shown to compare well with theoretical blackbody radiation spectra. A continuous, total radiated power of 10.7 mW was achieved with a 1 mm x 1 mm filament array with peak emittance at lambda=2.7 micrometers.

Hot Temperature↗
PubMed1990

Reactive airway dysfunction syndrome in three police officers following a roadside chemical spill.

The reactive airway dysfunction syndrome (RADS) is a recently described syndrome in which bronchial hyperreactivity and asthmatic symptoms develop in previously healthy individuals after a single large exposure to an irritating gas, fume, or vapor. We report a cluster of three Philadelphia police officers who developed RADS after a common exposure to toxic fumes from a roadside truck accident. Results of initial pulmonary function testing were normal in all three, and methacholine challenge was required for diagnosis in two out of the three. This syndrome needs to be recognized by physicians dealing with environmental or industrial medicine as a potential cause of loss of work or inability to perform on the job. Also, there is a potential for multiple individuals to develop this syndrome from a single incident.

Accidents, Traffic↗
PubMed2005

Nanoelectrodes integrated in atomic force microscopy cantilevers for imaging of in situ enzyme activity.

For investigation of laterally resolved information on biological activity, techniques for simultaneously obtaining complementary information correlated in time and space are required. In this context, recent developments in scanning probe microscopy are aimed at information on the sample topography and simultaneously on the physical and chemical properties at the nanometer scale. With the integration of submicro- and nanoelectrodes into atomic force microscopy (AFM) probes using microfabrication techniques, an elegant approach combining scanning electrochemical microscopy with AFM is demonstrated. This instrumentation enables simultaneous imaging of topography and obtainment of laterally resolved electrochemical information in AFM tapping mode. Hence, topographical and electrochemical information on soft surfaces (e.g., biological species) and polymers can be obtained. The functionality of tip-integrated electrodes is demonstrated by simultaneous electrochemical and topographical studies of an enzyme-modified micropattern.

Enzymes↗
PubMed1986

A new covalently modified support for gas-liquid phase sequencing.

A new method for activation of glass fiber supports for immobilisation of proteins and peptides in gas-liquid phase sequencing is described. The new support offers several advantages over the presently used carrier polybrene: no precycling is required, initial yields are improved and background contamination is lower. This leads to an overall increase in detection sensitivity. The derivatisation method includes acid activation and subsequent covalent coating of glass fibers with quaternary ammonium groups thereby giving the glass surface a high binding capacity for both proteins and peptides. The activated glass has been successfully used for sequencing proteins and peptides isolated by HPLC as well as by electroelution from polyacrylamide gels.

Chromatography, Gas↗
PubMed2005

Following the formation of supported lipid bilayers on mica: a study combining AFM, QCM-D, and ellipsometry.

Supported lipid bilayers (SLBs) are popular models of cell membranes with potential biotechnological applications and an understanding of the mechanisms of SLB formation is now emerging. Here we characterize, by combining atomic force microscopy, quartz crystal microbalance with dissipation monitoring, and ellipsometry, the formation of SLBs on mica from sonicated unilamellar vesicles using mixtures of zwitterionic, negatively and positively charged lipids. The results are compared with those we reported previously on silica. As on silica, electrostatic interactions were found to determine the pathway of lipid deposition. However, fundamental differences in the stability of surface-bound vesicles and the mobility of SLB patches were observed, and point out the determining role of the solid support in the SLB-formation process. The presence of calcium was found to have a much more pronounced influence on the lipid deposition process on mica than on silica. Our results indicate a specific calcium-mediated interaction between dioleoylphosphatidylserine molecules and mica. In addition, we show that the use of PLL-g-PEG modified tips considerably improves the AFM imaging of surface-bound vesicles and bilayer patches and evaluate the effects of the AFM tip on the apparent size and shape of these soft structures.

Aluminum Silicates↗
PubMed2005

Effect of ion-binding and chemical phospholipid structure on the nanomechanics of lipid bilayers studied by force spectroscopy.

The nanomechanical response of supported lipid bilayers has been studied by force spectroscopy with atomic force microscopy. We have experimentally proved that the amount of ions present in the measuring system has a strong effect on the force needed to puncture a 1,2-dimyristoyl-sn-glycero-3-phosphocholine bilayer with an atomic force microscope tip, thus highlighting the role that monovalent cations (so far underestimated, e.g., Na(+)) play upon membrane stability. The increase in the yield threshold force has been related to the increase in lateral interactions (higher phospholipid-phospholipid interaction, decrease in area per lipid) promoted by ions bound into the membrane. The same tendency has also been observed for other phosphatidylcholine bilayers, namely, 2-dilauroyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, and 1,2-dioleoyl-sn-3-phosphocholine, and also for phosphatidylethanolamine bilayers such as 1-palmitoyl-2-oleoyl-sn-3-phosphoethanolamine. Finally, this effect has been also tested on a natural lipid bilayer (Escherichia coli lipid extract), showing the same overall tendency. The kinetics of the process has also been studied, together with the role of water upon membrane stability and its effect on membrane nanomechanics. Finally, the effect of the chemical structure of the phospholipid molecule on the nanomechanical response of the membrane has also been discussed.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2005

The electromechanics of DNA in a synthetic nanopore.

We have explored the electromechanical properties of DNA on a nanometer-length scale using an electric field to force single molecules through synthetic nanopores in ultrathin silicon nitride membranes. At low electric fields, E < 200 mV/10 nm, we observed that single-stranded DNA can permeate pores with a diameter >/=1.0 nm, whereas double-stranded DNA only permeates pores with a diameter >/=3 nm. For pores <3.0 nm diameter, we find a threshold for permeation of double-stranded DNA that depends on the electric field and pH. For a 2 nm diameter pore, the electric field threshold is approximately 3.1 V/10 nm at pH = 8.5; the threshold decreases as pH becomes more acidic or the diameter increases. Molecular dynamics indicates that the field threshold originates from a stretching transition in DNA that occurs under the force gradient in a nanopore. Lowering pH destabilizes the double helix, facilitating DNA translocation at lower fields.

Biophysics↗
PubMed2003

Gene expression of surfactant protein-A and thyroid transcription factor-1 in lungs of rats exposed to silicon-carbide whisker in vivo.

Intratracheal instillation studies have shown that exposure to silicon carbide whisker (SiCW), an asbestos substitute, produces pulmonary fibrotic changes, suggesting that SICW might have a fibrogenic potential. It is thought that surfactant protein is a good biomarker of lung injury and pulmonary fibrotic activity. In order to explore whether or not surfactant protein is associated with lung disorder through exposure to SiCW, we examined the expression of SP-A, SP-C and thyroid transcription factor-1 (TTF-1), a common transcription factor of SP-A and SP-C mRNA in lungs exposed to SiCW. Male Wistar rats were administered 2 mg or 10 mg of SiCW suspended in saline by a single intratracheal instillation, and were sacrificed at 3 d, 1 wk, 1 month, 3 months and 6 months after the intratracheal instillation. RNA was subsequently extracted from the lungs, and expression of SP-A, SP-C and TTF-1 mRNA from the lungs was observed by reverse transcription-polymerase chain reaction (RT-PCR). Exposure to 2 mg of SiCW showed a decrease in mRNA of SP-A and TTF-1 at 6 months, but exposure to 10 mg of SiCW showed decreased levels of SP-A and TTF-1 mRNA at 3 d and 6 months. On the other hand, 2 mg of SiCW increased the level of SP-C mRNA from 3 d to 3 months, and 10 mg of SiCW decreased the levels of SP-C mRNA in the rat lungs at 3 d, 1 month and 6 months. No clear tendency to the expression of SP-C was observed, but the patterns of expression of TTF-1 and SP-A were similar. These data suggest that SP-A and TTF-1 are associated with not only the acute phase but also the chronic phase in lungs exposed to SiCW.

Animals↗
PubMed2005

Experimental approaches and analytical technique for determining heavy metals in fallen dust at ferrosilicon production factory in Edfu, Aswan, Egypt.

In this study aimed to evaluate the pollution extent of metals and nonmetals inside and outside the ferrosilicon production factory in Edfu, Aswan, Egypt, raw materials (quartz, cokes, iron oxides), ferrosilicon alloy, silica fume, dust and suspended dust (at different sites) samples were collected from the factory, and fallen dust samples were collected from outside the factory, horizontally (at different sites and different distance and directions) and vertically (at different floors in the selected buildings). Gravimetric methods, X-ray fluorescence (XRF), flame photometer, wide range carbon determinator and atomic absorption spectroscopy tools were used for elements determination. The results indicating that the fallen dust and its element contents on southern factory walls being higher than those on eastern factory walls may be due to the nature of the dusts and effects of wind force and wind direction. Fallen dust levels in different regions outside the factory were found to be affected by the distance, direction and floors. The nature of dust samples was affected by gravity and the suspended dust in different factory units depended on the work capacity and method of handling materials by personnel in different production units. Silica fume was a complicated problem, had dangerous effect against the workers' health, and was characterized by high concentrations of SiO(2) (90.6%approximately 93.6%) and heavy metals (Mn, 420.6 x 10(-6) approximately 520.3 x 10(-6); Fe, 2354 x 10(-6)approximately 2685 x 10(-6); Co, 80.7 x 10(-6) approximately 101.6 x 10(-6) and Ni, 5.3 x 10(-6) approximately 6.05 x 10(-6)). The TSP (Total Suspended Particulate) levels in all factory units were higher than the recommended air quality value (70 microg/m(3)) under Egyptian law. The effect of ferrosilicon factory fallen dust on the surrounding regions decreased with increasing distance between the factory and these regions. The suspended dust samples in the factory units and their components greatly exceeded national and international standards, so health and environmental criteria must be enforced on these units.

Dust↗
PubMed2003

An indirect spectrophotometric method for the determination of silicon in serum, whole blood and erythrocytes.

An indirect method for the determination of silicon in blood samples has been developed. The proposed method overcame interference from a large amount of salts and phosphate in blood samples, and enabled us to determine the silicon contents in serum and whole blood by the same operation. After blood samples were digested by microwave heating, silicon, present as silicate in the sample solution, was reacted with molybdate to form a silicomolybdate complex. The complex was then separated from unreacted molybdate by a cation-exchange resin column. The molybdate liberated from the complex was spectrophotometrically determined in place of silicon. Since the method is not affected the composition of matrices between serum and whole blood, it could achieve good precision and accuracy, and could also estimate the silicon contents in erythrocytes from those in serum and whole blood. The sensitivity of the method was almost equal to that of the conventional silicomolybdenum blue method, and the calibration curve was linear up to 50 micromol l(-1) of silicon with a detection limit of 1.1 micromol l(-1) in whole blood. The mean concentrations of silicon in five healthy subjects were 11 micromol l(-1) for serum, 28 micromol l(-1) for whole blood and 50 micromol l(-1) for erythrocytes. Thus, the obtained distribution ratio between serum and erythrocytes was in the range of 0.15-0.39, and was found to be included in a narrow range.

Calibration↗
PubMed2006

HPLC retention behaviors of pi-electron rich compounds on Ni2+- and Cu2+-phthalocyanine derivatives bound to silica gels in polar eluents.

The effect of the central metal of columns packed with silica gels binding Ni(2+)- and Cu(2+)-phthalocyanine derivatives (Ni-and Cu-PCS(D)s) on the retention behavior of poly-aromatic-hydrocarbons (PAHs) thereof in a polar eluent was examined. The retention factors of PAHs on the Ni- and Cu-PCS(D)s in 80% methanol showed a good linear correlation. The Cu-PCS(D) column exhibited the pi-pi interactions for PAHs, while the Ni-PCS(D) column exhibited the pi-d interactions for PAHs in addition to the pi-pi interaction for PAHs. Further, an investigation of the retention behavior of anthracene derivatives having different substituents revealed that the Ni- and Cu-PCS(D) columns could recognize the differences of substituents only in a polar eluent.

Chromatography, High Pressure Liquid↗
PubMed2003

Dose reduction in patients undergoing chest imaging: digital amorphous silicon flat-panel detector radiography versus conventional film-screen radiography and phosphor-based computed radiography.

OBJECTIVE: We sought to compare the radiation dose delivered to patients undergoing clinical chest imaging on a full-field digital amorphous silicon flat-panel detector radiography system with the doses delivered by a state-of-the-art conventional film-screen radiography system and a storage phosphor-based computed radiography system. Image quality was evaluated to ensure that the potential reduction in radiation dose did not result in decreased image acuity. SUBJECTS AND METHODS. Three groups of 100 patients each were examined using the amorphous silicon flat-panel detector, film-screen, or computed radiography systems. All patient groups were matched for body mass index, sex, and age. To measure the entrance skin dose, we attached 24 calibrated thermoluminescent dosimeters to every patient. The calculation of the effective dose, which represents the risk of late radiation-induced effects, was based on measurements on an anthropomorphic phantom. Image quality of all three systems was evaluated by five experienced radiologists, using the European Quality Criteria for Chest Radiology. In addition, a contrast-detail phantom study was set up to assess the low-contrast detection of all three systems. RESULTS: The amorphous silicon flat-panel detector radiography system allowed an important and significant reduction in both entrance skin dose and effective dose compared with the film-screen radiography (x 2.7 decrease) or computed radiography (x 1.7 decrease) system. In addition, image quality produced by the amorphous silicon flat-panel detector radiography system was significantly better than the image quality produced by the film-screen or computed radiography systems, confirming that the dose reduction was not detrimental to image quality. CONCLUSION: The introduction of digital flat-panel radiography systems based on amorphous silicon and cesium iodide is an important step forward in chest imaging that offers improved image quality combined with a significant reduction in the patient radiation dose.

Adult↗