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At least 793 records · Page 44Linked to original sources
PubMed2006

Construction of a pH-driven supramolecular nanovalve.

[Structure: see text] The versatility of supramolecular chemistry has been exploited in constructing nanovalves based on mesoporous silica MCM-41 and the mutual recognition between secondary dialkylammonium ions and dibenzo[24]crown-8 (DB24C8). Naphthalene-containing dialkylammonium threads were tethered to the MCM-41, followed by loading with coumarin 460 and capping with DB24C8. Controlled release of coumarin 460 from the pores of MCM-41 was demonstrated using different bases. The rate of release of coumarin 460 from the nanovalves depends on the size of the base.

Coumarins↗
PubMed2004

Comparative investigation of the biocompatibility of various silicon nitride ceramic qualities in vitro.

There is a controversy about the biocompatibility of silicon nitride ceramics contained in the literature, which appears to be related to a factor of the individual chemical composition of different qualities of silicon nitride ceramics and of the different surface properties. This study attempts to investigate the cytotoxicity of different qualities of industrial silicon nitride ceramics applying an L929-cell culture model in a direct contact assay combined with a cell viability assessment. Five different qualities of industrial standard silicon nitride ceramics were chosen for in vitro testing. The chemical composition was determined by EDS analysis. Different biomedically approved aluminium oxide qualities, a titanium alloy, glass and polyvinylchloride (PVC) served as control materials. L929 mice fibroblasts were incubated directly on the materials for 24 h, stained with bisbenzimide and propidium iodine for double fluorochromasia viability testing, and evaluated by inversion-fluorescence microscopy to control cell morphology, viability and cell counts compared to empty well values. Scanning electron microscopy was applied to additionally investigate cell morphology. There was no observation of cytotoxic effects on the silicon nitride ceramic samples; moreover cell morphology remained the same as on aluminium oxide and titanium. Viability testing revealed the presence of avital cells exclusively on PVC, which served as a negative control. Cell counts on all polished surfaces showed significantly higher numbers, whereas some rough surface samples showed significantly lower numbers. We conclude that silicon nitride ceramics show no cytotoxic effects and should be considered for biomedical application owing to its favourable physiochemical properties, especially its superior resistance to mechanical stress, which would be useful for compression loaded conditions. Polished surfaces would appear to promote advanced biocompatibility.

Aluminum Oxide↗
PubMed1998

Coexisting conical bipolar and equatorial outflows from a high-mass protostar.

The BN/KL region in the Orion molecular cloud is an archetype for the study of the formation of stars much more massive than the Sun. This region contains luminous young stars and protostars but, like most star-forming regions, is difficult to study in detail because of the obscuring effects of dust and gas. Our basic expectations are shaped to some extent by the present theoretical picture of star formation, the cornerstone of which is that protostars accrete gas from rotating equatorial disks and shed angular momentum by ejecting gas in bipolar outflows. The main source of the outflow in the BN/KL region may be an object known as radio source I, which is commonly believed to be surrounded by a rotating disk of molecular material. Here we report high-resolution observations of silicon monoxide (SiO) and water maser emission from the gas surrounding source I. We show that within 60 AU of the source (about the size of the Solar System), the region is dominated by a conical bipolar outflow, rather than the expected disk. A slower outflow, close to the equatorial plane of the protostellar system, extends to radii of 1,000 AU.

Astronomical Phenomena↗
PubMed2001

Ion-beam sculpting at nanometre length scales.

Manipulating matter at the nanometre scale is important for many electronic, chemical and biological advances, but present solid-state fabrication methods do not reproducibly achieve dimensional control at the nanometre scale. Here we report a means of fashioning matter at these dimensions that uses low-energy ion beams and reveals surprising atomic transport phenomena that occur in a variety of materials and geometries. The method is implemented in a feedback-controlled sputtering system that provides fine control over ion beam exposure and sample temperature. We call the method "ion-beam sculpting", and apply it to the problem of fabricating a molecular-scale hole, or nanopore, in a thin insulating solid-state membrane. Such pores can serve to localize molecular-scale electrical junctions and switches and function as masks to create other small-scale structures. Nanopores also function as membrane channels in all living systems, where they serve as extremely sensitive electro-mechanical devices that regulate electric potential, ionic flow, and molecular transport across cellular membranes. We show that ion-beam sculpting can be used to fashion an analogous solid-state device: a robust electronic detector consisting of a single nanopore in a Si3N4 membrane, capable of registering single DNA molecules in aqueous solution.

Biosensing Techniques↗
PubMed2001

Interference-based detection of nucleic acid targets on optically coated silicon.

Sequence-specific detection of polynucleotides typically requires modified reporter probes that are labeled with radioactive, fluorescent, or luminescent moieties. Although these detection methods are capable of high sensitivity, they require instrumentation for signal detection. In certain settings, such as clinical point of care, instrumentation might be impractical or unavailable. Here we describe a detection approach in which formation of a nucleic acid hybrid is enzymatically transduced into a molecular thin film that can be visually detected in white light. The system exploits a flat, optically coated silicon-based surface to which capture oligonucleotides are covalently attached. The optimized system is capable of detection of nucleic acid targets present at sub-attomole levels. To supplement visual detection, signals can be quantitated by a charge-coupled device. The design and composition of the optical surface, optimization of immobilization chemistry for attachment of capture probes, and characterization of the efficiency of the hybridization process are presented. We describe the application of this system to detection of a clinically relevant target, the mecA gene present in methicillin-resistant Staphylococcus aureus.

Base Sequence↗
PubMed1978

Intrarenal hemodynamics in the transplanted rat kidney.

Regional and single glomerular blood flow conditions in the transplanted rat kidney after various periods of cold ischemia were investigated with use of the microsphere method. Intravascular injection of a silicon rubber compound (Microfil) allowed identification and sampling of single glomeruli. The periods of ischemia were two hours (minor damage), 12 hr (intermediate damage), and 16 hr (severe damage). After two hours of cold ischemia, the regional and total renal blood flows were fairly normal. After 12 hr and 16 hr of cold ischemia, the total and regional blood flows were reduced five minutes after recirculation, the reduction being pronounced in the deep cortex and juxtamedullary glomeruli. In the 12-hr group, the blood flow showed complete restitution after 65 min, whereas in the 16-hr group, the blood flow in the inner cortex and juxtamedullary glomeruli remained decreased. An impairment of medullary circulation would seem to be an important component in the pathophysiology of acute renal failure in this model.

Animals↗
PubMed2002

Biomolecular screening with encoded porous-silicon photonic crystals.

Strategies to encode or label small particles or beads for use in high-throughput screening and bioassay applications focus on either spatially differentiated, on-chip arrays or random distributions of encoded beads. Attempts to encode large numbers of polymeric, metallic or glass beads in random arrays or in fluid suspension have used a variety of entities to provide coded elements (bits)--fluorescent molecules, molecules with specific vibrational signatures, quantum dots, or discrete metallic layers. Here we report a method for optically encoding micrometre-sized nanostructured particles of porous silicon. We generate multilayered porous films in crystalline silicon using a periodic electrochemical etch. This results in photonic crystals with well-resolved and narrow optical reflectivity features, whose wavelengths are determined by the etching parameters. Millions of possible codes can be prepared this way. Micrometre-sized particles are then produced by ultrasonic fracture, mechanical grinding or by lithographic means. A simple antibody-based bioassay using fluorescently tagged proteins demonstrates the encoding strategy in biologically relevant media.

Animals↗
PubMed2003

Complex dewetting scenarios captured by thin-film models.

In the course of miniaturization of electronic and microfluidic devices, reliable predictions of the stability of ultrathin films have a strategic role for design purposes. Consequently, efficient computational techniques that allow for a direct comparison with experiment become increasingly important. Here we demonstrate, for the first time, that the full complex spatial and temporal evolution of the rupture of ultrathin films can be modelled in quantitative agreement with experiment. We accomplish this by combining highly controlled experiments on different film-rupture patterns with computer simulations using novel numerical schemes for thin-film equations. For the quantitative comparison of the pattern evolution in both experiment and simulation we introduce a novel pattern analysis method based on Minkowski measures. Our results are fundamental for the development of efficient tools capable of describing essential aspects of thin-film flow in technical systems.

Biomedical Engineering↗
PubMed2003

DNA molecules and configurations in a solid-state nanopore microscope.

A nanometre-scale pore in a solid-state membrane provides a new way of electronically probing the structure of single linear polymers, including those of biological interest in their native environments. Previous work with biological protein pores wide enough to let through and sense single-stranded DNA molecules demonstrates the power of using nanopores, but many future tasks and applications call for a robust solid-state pore whose nanometre-scale dimensions and properties may be selected, as one selects the lenses of a microscope. Here we demonstrate a solid-state nanopore microscope capable of observing individual molecules of double-stranded DNA and their folding behaviour. We discuss extensions of the nanopore microscope concept to alternative probing mechanisms and applications, including the study of molecular structure and sequencing.

DNA↗
PubMed2004

Heterogeneous enantioselective catalysts: strategies for the immobilisation of homogeneous catalysts.

Enantioselective formation of C-H, C-C, C-O and C-N bonds has been extensively studied using homogeneous asymmetric catalysts for many years. However, these catalysts have yet to make a significant impact in the industrial synthesis of fine chemicals. A central reason is that homogeneous asymmetric catalyst design requires relatively bulky ligands and catalyst re-use through recovery and recycle often causes problems. One mechanism to overcome this problem is to immobilise the asymmetric catalyst onto a support and the resulting heterogeneous asymmetric catalyst can, in principle, be readily re-used. This tutorial review covers the different methodologies for immobilisation, including: adsorption, encapsulation, tethering using a covalent bond and electrostatic interaction and is aimed at both researchers new to the field and those with a wider interest in the immobilisation of homogeneous catalysts. Most importantly, recent studies will be highlighted that demonstrate that immobilised catalysts can give higher enantioselection when compared with their non-immobilised counterparts and the question of how high enantioselection can be achieved is addressed.

Adsorption↗
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↗
PubMed2003

Influence of master fabrication techniques on the characteristics of embossed microfluidic channels.

We describe protocols for the fabrication of microfluidic devices in plastics using a number of different embossing masters. Masters were fabricated by deep reactive ion etching (DRIE) of silicon (100), wet etching of silicon (100) and (110), and SU-8 processing. Structures embossed into a cyclo-olefin polymer were characterized in terms of the quality of pattern transfer as well as of the surface roughness. High quality pattern transfer was achieved with masters containing structures with angled sidewalls. Pattern distortions occurring during de-embossing were minimized by using masters consisting of SU-8 (which has a thermal expansion coefficient close to that of the substrates). Structures embossed with SU-8 masters also exhibited the lowest surface roughness. However, due to structural deformation, the reusability of the masters prepared for this study extended to only five embossing experiments. Masters fabricated on silicon, on the other hand, were more robust, but were subject to breakage during the de-embossing phase of the experiment. The results of this study will guide researchers in choosing master fabrication methods that will provide profile and surface characteristics of embossed microfluidic channels that are advantageous to their specific application.

Coated Materials, Biocompatible↗
PubMed2003

Moment analysis of retention equilibrium, mass transfer kinetics, and thermodynamic properties in reversed-phase liquid chromatography using phenyl bonded silica gel.

Information about retention equilibrium, mass transfer kinetics, and related thermodynamic properties of chromatography using phenyldimethylsilyl (Ph)-silica gel was derived by moment analysis of pulse response peak profiles. The results for the Ph-silica gel were compared with those for octadecyldimethylsilyl (C18)-silica gel. Some parameters characterizing the chromatographic behavior of the two stationary phases were correlated with the hydrophobic surface area of sample molecules. Surface diffusion had a predominant role for intraparticle diffusion. An enthalpy-entropy compensation was established for both the retention equilibrium and surface diffusion. A linear correlation was observed between the logarithm of surface diffusion coefficient (Ds) and that of retention equilibrium constant (Ka), suggesting the establishment of a linear free energy relationship. The ratio of Ds to molecular diffusivity (Dm) decreased with increasing Ka and was correlated by a single curved line. The value of Ds was of the same order of magnitude with Dm when Ka became negligible. These results suggest the presence of a sort of correlation between surface diffusion and molecular diffusion and the restriction of the molecular mobility by surface diffusion due to the retention strength.

Air Pollutants↗
PubMed2004

Bulk-micromachined submicroliter-volume PCR chip with very rapid thermal response and low power consumption.

The current paper describes the design, fabrication, and testing of a micromachined submicroliter-volume polymerase chain reaction (PCR) chip with a fast thermal response and very low power consumption. The chip consists of a bulk-micromachined Si component and hot-embossed poly(methyl methacrylate)(PMMA) component. The Si component contains an integral microheater and temperature sensor on a thermally well-isolated membrane, while the PMMA component contains a submicroliter-volume PCR chamber, valves, and channels. The micro hot membrane under the submicroliter-volume chamber is a silicon oxide/silicon nitride/silicon oxide (O/N/O) diaphragm with a thickness of 1.9 microm, resulting in a very low thermal mass. In experiments, the proposed chip only required 45 mW to heat the reaction chamber to 92 degrees C, the denaturation temperature of DNA, plus the heating and cooling rates are about 80 degrees C s(-1) and 60 degrees C s(-1), respectively. We validated, from the fluorescence results from DNA stained with SYBR Green I, that the proposed chip amplified the DNA from vector clone, containing tumor suppressor gene BRCA 1 (127 base pairs at 11th exon), after 30 thermal cycles of 3 s, 5 s, and 5 s at 92 degrees C, 55 degrees C, and 72 degrees C, respectively, in a 200 nL-volume chamber. As for specificity of DNA products, owing to difficulty in analyzing the very small volume PCR results from the micro chip, we vicariously employed the larger volume PCR products after cycling with the same sustaining temperatures as with the micro chip but with much slower ramping rates (3.3 degrees C s(-1) when rising, 2.5 degrees C s(-1) when cooling) within circa 20 minutes on a commercial PCR machine and confirmed the specificity to BRCA 1 (127 base pairs) with agarose gel electrophoresis. Accordingly, the fabricated micro chip demonstrated a very low power consumption and rapid thermal response, both of which are crucial to the development of a fully integrated and battery-powered instrument for a lab-on-a-chip DNA analysis.

Calibration↗