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At least 811 records · Page 45Linked to original sources
PubMed2005

Nanoscale-controlled spacing provides DNA microarrays with the SNP discrimination efficiency in solution phase.

We have prepared solid substrates modified with a cone-shaped dendron that generates mesospacing (3.2 nm on average) on the surface. This nanoscale-controlled surface provided an ideal DNA microarray in which each probe DNA strand was given ample space for the incoming target DNA, resulting in selectivity as high as that in solution (100: < 1). In addition, high hybridization yield confirms that DNA probes on the mesospaced surface are sterically unhindered for the hybridization.

Base Sequence↗
PubMed2005

Probing the effects of conjugation path on the electronic transmission through single molecules using scanning tunneling microscopy.

A systematic study of the relationship between the molecular structure of a series of thiol end-capped oligo-phenylenevinylenes (OPVs) and the coherent electronic transmission at the single molecule level was measured by scanning tunneling microscopy (STM). This reveals a significant change in the electronic transparency of various OPV derivatives due to the insertion of a methylene spacer group or due to nitro group substitution. Apparently, changes in the conjugation path through the central benzene ring from para to meta substitution does not have a profound effect on the electronic transparency of the molecules.

Journal Article↗
PubMed2006

Using perylene-doped polymer nanotubes as fluorescence sensors.

Al(2)O(3) filters (200 nm) are used as templates to form polymer nanotubes containing an energy donor (perylene). The perylene is isolated from chemical interactions but can undergo electronic energy transfer to acceptor molecules in aqueous solutions passing through the membrane. This energy transfer is analyzed quantitatively in terms of both radiative and nonradiative (Forster transfer) mechanisms and provides a way for the chemically inert filter to sense the presence of analyte molecules in the filtrate.

Energy Transfer↗
PubMed1993

The surface analysis of implant materials. 1. The surface composition of a titanium dental implant material.

The surfaces of titanium (Ti) plates, as models for Ti implants, have been characterized by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS). Plates were prepared with rough and smooth surface topographies--the rough being similar to that of an implant. The XPS data has been used to construct a model of the plates' surface chemical structure, from the gas-solid interface through to pure Ti metal. At the surface of as-received plates, which underwent the same preparative procedure as an implant, considerable surface contamination was detected. In particular, high levels of carbon (C) contaminants were detected; the nature of this C was elucidated by fitting the C 1s core line and from the secondary ion mass spectra. The oxygen (O) 1s core line could not be fitted using a minimum of 2 gaussian peaks, demonstrating the multiplicity of O environments. The detection of other elements in the XPS analysis further demonstrated that, in nominally pure Ti plates, the surface chemical composition deviates considerably from that of the bulk. The data obtained from the plates were confirmed by examination of a Ti abutment. The handling of Ti plates with stainless steel tweezers was investigated. No obvious change in surface chemistry was detected. All the above results bring into serious questions the validity of rigorous protocols demanded, in some techniques, in the handling and use of Ti implants.

Dental Implants↗
PubMed2003

Optical encoding with shaped DAM-1 molecular sieve particles.

This work introduces a new high-throughput screening particle - a Dallas Amphorous Material No. 1 (DAM-1) molecular sieve particle. In contrast to porous silica microspheres, the 2-8-microm sized DAM-1 molecular sieve particles are available in a variety of shapes and morphologies including spheres, hexagons, rods, gyroids, and discoids. The advantage of using DAM-1 molecular sieve particles is the ability to encode an array by particle shape, which in turn permits the repeated use of luminescent reporter dyes. In this technical note, we demonstrate optical decoding of fluorescein- and Texas Red-modified shaped molecular sieve particles using reflectance and fluorescence microscopies.

Biosensing Techniques↗
PubMed2002

Activated neutrophils oxidize extracellular proteins of endothelial cells in culture: effect of nitric oxide donors.

Protein oxidation of human umbilical-vein endothelial cells (HUVEC) in culture was examined under various conditions of oxidative stress. Extracellular protein (ECP) oxidation was assessed by determining dityrosine bond formation, which is indicated by the covalent coupling of the membrane-impermeable tyramine-fluorescein conjugate (TyrFluo) to HUVEC proteins. The acetylated membrane-permeable form of TyrFluo (acetylTyrFluo) was used for the determination of intracellular protein (ICP) oxidation. Oxidative stress was induced by exposing the HUVEC to PMA-activated human neutrophils, to a horseradish peroxidase/hydrogen peroxide (HRP/H(2)O(2)) system or to H(2)O(2) alone. Coupling of the probes was determined by confocal laser scanning microscopy and by Western blotting using anti-fluorescein antibody. Diethylamine nitric oxide (DEANO) was used to determine the effect of NO on the tyrosyl radical formation in proteins. The oxidative burst generated by activated neutrophils for 15 min, resulted in inducing dityrosine formation in ECP of HUVEC. Similar results were obtained with HRP/H(2)O(2), but H(2)O(2) alone did not have any effect on ECP. In the presence of DEANO (0.1 mM or higher), ECP oxidation was almost completely inhibited. This indicates that NO may protect endothelial cells against protein oxidation by activated neutrophils under pro-inflammatory conditions. Activated neutrophils did not oxidize ICP of HUVEC, which strongly suggests that the effect of the oxidative burst was restricted to the proteins exposed to the medium.

Cells, Cultured↗
PubMed2002

Modulation of the GABA(A)-gated chloride channel by reactive oxygen species.

The accumulation of reactive oxygen species during cellular injury leads to oxidative stress. This can have profound effects on ionic homeostasis and neuronal transmission. Gamma-aminobutyric acid (GABA) neurotransmission is sensitive to reactive oxygen species, but most studies have indicated that this is due to alterations in GABA release. Here, we determined whether reactive oxygen species can alter GABA(A) receptor-gated Cl- channels in the adult hippocampus. First, we measured the effects of hydrogen peroxide on intracellular Cl- using UV laser scanning confocal microscopy and the Cl(-)-sensitive probe, 6-methoxy-N-ethylquinolium iodide (MEQ). Superfusion of adult rat hippocampal slices with hydrogen peroxide for 10 min decreased MEQ fluorescence (elevation in [Cl-]i) significantly in area CA1 pyramidal cell soma. Alterations in [Cl-]i were prevented by the vitamin E analog Trolox, an antioxidant that scavenges free radicals. After exposure of slices to hydrogen peroxide, the ability of the GABA agonist muscimol to increase [Cl-]i was attenuated. To determine if GABA(A) receptors were sensitive to oxidative insults, the effect of hydrogen peroxide on the binding of [35S]t-butylbicyclophosphorothionate (TBPS) to GABA-gated Cl- channels was measured using receptor autoradiography and homogenate binding assays. Hydrogen peroxide inhibited [35S]TBPS binding in a regionally selective manner, with the greatest inhibition in cerebral cortex, hippocampus and striatum, areas vulnerable to oxidative stress. Similarly, xanthine and xanthine oxidase, which generate superoxide radicals, reduced [35S]TBPS binding in these regions. The effect of hydrogen peroxide on [35S]TBPS binding was non-competitive and was prevented by Trolox and the iron chelator, deferoxamine. We conclude that reactive oxygen species may compromise GABA(A)-mediated neuronal inhibition via interaction with pre and postsynaptic sites. A reduction in GABA(A)-gated Cl- channel function during periods of oxidative stress may contribute to the development of neuronal damage.

Animals↗
PubMed1998

The efficiency of X-ray production at low energies.

The absolute efficiency of X-ray production has been determined for the K-lines of Al, Si and Cu; for the L-lines of Fe, Co, Cu, Ge and As; and for the M-lines of Hf, Ir, Pt, Au and Bi, using overvoltage ratios in the range 1-10. These emissions, with the exception of the Cu K, have critical excitation energies below 2.6 keV and are therefore typical of the lines used for X-ray microanalysis at low beam energies. For K-lines it is found that the experimental results are in good agreement with a Bethe, or a Casnati, crosssection model. For the L- and M-lines a Monte Carlo technique has been used to find an effective X-ray generation cross-section for each of the elements. The functional forms of these cross-sections are found to be in general agreement with proposed theoretical models.

Electron Probe Microanalysis↗
PubMed2001

Bacterial community associated with Pfiesteria-like dinoflagellate cultures.

Dinoflagellates (Eukaryota; Alveolata; Dinophyceae) are single-cell eukaryotic microorganisms implicated in many toxic outbreaks in the marine and estuarine environment. Co-existing with dinoflagellate communities are bacterial assemblages that undergo changes in species composition, compete for nutrients and produce bioactive compounds, including toxins. As part of an investigation to understand the role of the bacteria in dinoflagellate physiology and toxigenesis, we have characterized the bacterial community associated with laboratory cultures of four 'Pfiesteria-like' dinoflagellates isolated from 1997 fish killing events in Chesapeake Bay. A polymerase chain reaction with oligonucleotide primers specific to prokaryotic 16S rDNA gene sequences was used to characterize the total bacterial population, including culturable and non-culturable species, as well as possible endosymbiotic bacteria. The results indicate a diverse group of over 30 bacteria species co-existing in the dinoflagellate cultures. The broad phylogenetic types of dinoflagellate-associated bacteria were generally similar, although not identical, to those bacterial types found in association with other harmful algal species. Dinoflagellates were made axenic, and the culturable bacteria were added back to determine the contribution of the bacteria to dinoflagellate growth. Confocal scanning laser fluorescence microscopy with 16S rDNA probes was used to demonstrate a physical association of a subset of the bacteria and the dinoflagellate cells. These data point to a key component in the bacterial community being species in the marine alpha-proteobacteria group, most closely associated with the alpha-3 or SAR83 cluster.

Animals↗
PubMed2002

Nickel content of as-received, retrieved, and recycled stainless steel brackets.

The purpose of this study was to investigate the composition of as-received, retrieved, and recycled stainless steel brackets. New, used, and recycled brand-matched, slot size-matched, and prescription-matched appliances were subjected to scanning electron microscopy and energy dispersive electron probe microanalysis. Elemental analysis was performed on randomly selected surface bracket base and wing areas, and metal content was statistically analyzed with the 2-way ANOVA and the Tukey test, with treatment (as-received, retrieved, and recycled) and bracket regions (base and wing) serving as discriminating variables (alpha = 0.05). The results showed that there was no difference in the surface composition of the base; however, surface area-wing analysis indicated that nickel content was decreased in retrieved and recycled specimens, implying that an ionic release effect occurred in vivo. Differences were noted between bracket base and wing with respect to elemental composition for the same brackets, implying that the base and wings are manufactured from different alloys.

Analysis of Variance↗
PubMed2004

Highly divergent SSU rRNA genes found in the marine ciliates Myrionecta rubra and Mesodinium pulex.

Myrionecta rubra and Mesodinium pulex are among the most commonly encountered planktonic ciliates in coastal marine and estuarine regions throughout the world. Despite their widespread distribution, both ciliates have received little attention by taxonomists. In order to better understand the phylogenetic position of these ciliates, we determined the SSU rRNA gene sequence from cultures of M. rubra and M. pulex. Partial sequence data were also generated from isolated cells of M. rubra from Chesapeake Bay. The M. rubra and M. pulex sequences were very divergent from all other ciliates, but shared a branch with 100% bootstrap support. Both species had numerous deletions and substitutions in their SSU rRNA gene, resulting in a long branch for the clade. This made the sequences prone to spurious phylogenetic affiliations when using simple phylogenetic methods. Maximum likelihood analysis placed M. rubra and M. pulex on the basal ciliate branch, following removal of ambiguously aligned regions. Fluorescent in situ hybridization probes were used with confocal laser scanning microscopy to confirm that these divergent sequences were both expressed in the cytoplasm and nucleolus of M. ruisra and M. pulex. We found that our sequence data matched several recently discovered unidentified eukaryotes in Genbank from diverse marine habitats, all of which had apparently been misattributed to highly divergent amoeboid organisms.

Animals↗
PubMed1998

Focal damage to cochlear microcirculation measured using a non-contact laser blood flowmeter in guinea pigs.

The focal microcirculation damage induced by a photochemical reaction in the stria vascularis (SV) of the guinea pig cochlea was evaluated using a non-contact laser blood flowmeter (NCLBF) and the endocochlear potential (EP). Focal degeneration, including vascular thrombosis in the SV produced by the systemic infusion of rose bengal, and the illumination of green light in the second cochlear turn were observed with scanning and transmission electron microscopy. The NCLBF probe was placed at a position 10 mm from the cochlear surface, and the diameter of the laser light was focused to 1 mm in the green light illumination area. The change in NCLBF values induced by the loading of anoxia and administration of epinephrine agreed very well with those obtained with a conventional contact-type laser Doppler flowmeter. Significant decreases in the cochlear blood flow (CBF) (p < 0.01) and EP (p < 0.01) were observed at the site of the photochemical injury compared with the values at the non-illuminated area. CBF gradually decreased (82.0+/-7.3% at 10 min, 71.2+/-5.5% at 20 min, 64.3+/-11.2% at 30 min from the baseline, n=7), but blood pressure was stable. The EP values also decreased gradually during the first 13 min (79.9+/-3.7 mV at pre-illumination, 11.4+/-10.7 mV at 13 min, n=7). The gradual decline in the EP was comparable to the changes in the CBF. The NCLBF was useful for evaluating the haemodynamic properties of the cochlear microcirculation disorders, and this animal model is expected to be suitable for studying the pathology of focal cochlear vascular disease.

Animals↗
PubMed2001

The competence to acquire cellular desiccation tolerance is independent of seed morphological development.

Acquisition of desiccation tolerance and the related changes at the cellular level in wheat (Triticum aestivum cv. Priokskaya) kernels during normal development and premature drying on the ear were studied using a spin probe technique and low temperature scanning electron microscopy. During normal development, the ability of embryos to germinate after rapid drying and rehydration was acquired after completion of morphological development, which is a few days before mass maturity. The acquisition of desiccation tolerance, as assessed by germination, was associated with an upsurge in cytoplasmic viscosity, the onset of accumulation of protein and oil bodies, and the retention of membrane integrity upon dehydration/rehydration. These features were also used to assess cellular desiccation tolerance in the cases when germination could not occur. Slow premature drying was used to decouple the acquisition of cellular desiccation tolerance from morphogenesis. Upon premature drying of kernels on the ears of plants cut at 5 d after anthesis, desiccation-tolerant dwarf embryos were formed that were able to germinate. When plants were cut at earlier stages poorly developed embryos were formed that were unable to germinate, but cellular desiccation tolerance was nevertheless acquired. In such prematurely dried kernels, peripheral meristematic endosperm cells had already passed through similar physiological and ultrastructural changes associated with the acquisition of cellular desiccation tolerance. It is concluded that despite the apparent strong integration in seed development, desiccation tolerance can be acquired by the meristematic cells in the developing embryo and cambial layer of endosperm, independently of morphological development.

Adaptation, Physiological↗
PubMed1994

A retrospective analysis of unfertilized and presumed parthenogentically activated human oocytes demonstrates a high frequency of sperm penetration.

A total of 518 normal-appearing, meiotically mature human oocytes that were judged unfertilized after insemination in vitro were examined for sperm penetration by conventional fluorescence and laser scanning confocal microscopy with DNA-specific probes. A similar analysis was performed on 29 single pronuclear oocytes that were presumed to originate by spontaneous (parthenogenetic) activation. The results demonstrate that 22% of the unfertilized oocytes and 52% of the presumed parthenogenetic oocytes were actually penetrated. Sperm penetration occurred in both normozoospermic and male factor cases. The findings indicate the importance of penetration analysis in determining the causes of fertilization failure that may reside with the male or female gamete, especially when assessing the utility of and necessity for assisted fertilization in subsequent attempts. The results also suggest that the cytoplasmic capacity to decondense sperm DNA may decline more rapidly than the ability of the oocyte to be penetrated and to mount an effective block to polyspermy.

Cell Nucleus↗
PubMed1994

The neuroprotective kappa-opioid CI-977 alters glutamate-induced calcium signaling in vitro.

The effect of the neuroprotective kappa opioid agonist CI-977 on glutamate (GLU)-stimulated calcium signaling was studied in individual primary rat cortical neurons. Using laser scanning confocal microscopy and the fluorescent calcium probe fluo-3, both the sustained and biphasic intracellular calcium concentration [Ca2+]i changes induced by GLU (20-40 microM) were altered by CI-977 (25-100 nM), thereby shifting the neuronal population response from unbuffered to buffered patterns of [Ca2+]i flux. This effect was consistent with the previously demonstrated neuroprotective action of CI-977 against glutamate toxicity in vitro. The effect of CI-977 in altering GLU-induced [Ca2+]i signaling was attenuated by naloxone, consistent with a neuroprotective action of CI-977 at opioid receptors, presumably of the kappa subtype.

Animals↗
PubMed2001

Neuroprotection from glutamate toxicity with ultra-low dose glutamate.

The protective effects of ultra-low doses (ULD) of glutamate against glutamate toxicity was studied in primary rat spinal, cortical and cerebellar neurons. Neurons were exposed to four subtoxic, ultra-low concentrations of glutamate (10(-18) M, 10(-20)M, 10(-22) M and 10(-30) M) for 72 h and then subsequently challenged with toxic concentrations (25 microM) of glutamate. Neuron viability was consistently 10% higher in spinal and cortical neurons pre-exposed to glutamate concentrations of 10(-18) M and 10(-22) M, and in cerebellar neurons pre-exposed to 10(-20) M and 10(-30) M. Using laser scanning confocal microscopy and the fluorescent calcium probe fluo-3, we found no alterations in intracellular calcium dynamics in the protected cells. This protective effect is consistent with a growing body of evidence for tolerance induced by low-dose toxin exposure but is the first time that such tolerance has been demonstrated with ultra-low glutamate exposure. Our data show that pre-exposure of neuronal cells to ULD glutamate can protect against subsequent exposure to toxic levels of glutamate.

Animals↗
PubMed1983

The chloride corrosion behaviour of four orthodontic wires.

Potentiodynamic cyclic polarization of four orthodontic alloys (wires), namely Permachrome, Elgiloy, a beta-titanium alloy and Nitinol in a 1% NaCl solution within -500 mV and +300 mV (SCE) indicated the first three alloys to be passive whereas breakdown of passivity was observed on Nitinol. The SEM examination of the pre- and post-polarized alloy surfaces provided evidence which was consistent with the electrochemical measurements, in that the first three alloys exhibited no appreciable corrosion damage whereas pitting corrosion was observed on Nitinol. The results obtained from X-ray analysis of the pitted surface indicated that this pitting could be due to selective dissolution of nickel from Nitinol.

Chemical Phenomena↗