Fused Silica Slides Research Articles

DNA Curtains and Nanoscale Curtain Rods: High-Throughput Tools for Single Molecule Imaging

Single molecule visualization of protein-DNA complexes can reveal details of reaction mechanisms and macromolecular dynamics inaccessible to traditional biochemical assays. However, these techniques are often limited by the inherent difficulty of collecting statistically relevant information from experiments explicitly designed to look at single events. New approaches that increase throughput capacity of single molecule methods have the potential for making these techniques more readily applicable to a variety of biological questions involving different types of DNA transactions. Here we show that nanofabricated chromium barriers, which are located at strategic positions on a fused silica slide otherwise coated with a supported lipid bilayer, can be used to organize DNA molecules into molecular curtains. The DNA that makes up the curtains is visualized by total internal reflection fluorescence microscopy (TIRFM) allowing simultaneous imaging of hundreds or thousands of aligned molecules. These DNA curtains present a robust experimental platform portending massively parallel data acquisition of individual protein-DNA interactions in real time.

Effect of aluminium sulphate on interactions between silica surfaces studied by atomic force microscopy

Surface interaction forces between different types of silica surfaces (pure silica beads, borosilicate glass beads, polished silicon wafers and fused silica slides) were measured by atomic force microscopy (AFM) in solutions of aluminium sulphate (alum) in order to understand the role of hydrated aluminium species on the coagulation of negatively charged oxide colloids in drinking water treatment. The alum coagulant concentration used in this study was 150 μM aluminium. The alum solutions were prepared from analytical grade Al 2(SO 4) 3·16H 2O. It was found that the presence of aluminium sulphate at a concentration close to the values typically used in industrial scale water treatment applications generally induced strong, long-range repulsive forces between the various types of surfaces studied. At this alum concentration streaming potential measurements indicated reversal in the sign of the surface charge. It was also found that whenever borosilicate glass beads were used, the interaction force became strongly attractive when the AFM cell was flushed with deionised water. It was argued that this attraction occurred because of the charge nonuniformity of the aluminium hydrates adsorbed at the glass surface. A mechanism was proposed to explain the observed interaction phenomena based on the deduced microstructure of the adsorbed surface layers and to rationalise the new findings for applications in drinking water treatment.

Second‐harmonic spectroscopy of nano‐interfaces

Optical second-harmonic is shown to be a noninvasive, interface-sensitive probe of silicon nanocrystals. The TEM01 spatial mode of SHG radiation from a silicon nanocrystal composite indicates there is nonlocal dipolar (quadrupolar) polarization source which is proportional to the gradient of the incoming electric field. With two orthogonally polarized laser beams, we enhanced the SHG from nanocrystals by creating wavelength-scale, forward-radiating gradient in the second-harmonic polarization. The quantitative features of two-beam SHG were also studied with a fused silica slide. We demonstrate several techniques for isolating the nano-interface signal from the (bulk-quadrupolar) substrate signal in our samples. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrathin layered myoglobin-polyion films functional and stable at acidic pH values.

Cross-linking of myoglobin (Mb) promoted by 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide within films of polystyrene sulfonate after layer-by-layer self-assembly provided remarkable stabilization. Cross-linking greatly improved adhesion of the films to fused silica slides and allowed extensive optical studies over a wide pH range. Circular dichroism and visible absorbance spectra showed that Mb retained its native conformation when films were placed in solutions of pH as low as 2 and up to pH 11. Linear dichroism revealed an average orientation of the Mb iron heme cofactors of 58 degrees to the film normal. High concentrations of urea did denature the protein in the films, however. At pH 1, Mb in solution is fully unfolded but retained considerable alpha-helical content in the cross-linked films. Both the polyion film environment and cross-linking seem to play roles in stabilizing protein secondary structure and function at low pH. Cross-linked myoglobin-polyion films on pyrolytic graphite electrodes were used in strongly acidic solutions for the electrochemical catalytic reduction of trichloracetic acid, hydrogen peroxide, and oxygen. The pH-dependent catalytic reduction of trichloracetic acid was faster in 0.1 M HCl than in the medium pH range.

Photophysical studies of aerosol-OT films loaded with biological macromolecules and made from reverse micelles

Thin surfactant films loaded with trypsin were made by dipcoating a fused-silica slide in reverse micelles of bis(2-ethylhexyl) sulfosuccinate sodium salt [AOT] in organic solvents. The fluorescence quenching analysis of charge transfer between Ru(bpy) 3 2+ and MV2+ in the absence of the enzyme has revealed that the original micellar structure is to a large extent transferred into the structure of the film. Nondried films contain a substantial amount of the organic solvent thus they consist of a hydrophilic and a hydrophobic subphase while the surfactant is placed at the interface. These films are transparent matrices and make excellent hosts for photophysical studies. When trypsin was introduced in the reverse micellar solution it was transferred into the film and solubilized in the hydrophilic subphase.

Photophysical Studies in AOT Films Deposited on Fused Silica Slides

Thin surfactant films were made by dip-coating a fused-silica slide in reverse micelles of bis(2-ethylhexyl) sulfosuccinate sodium salt [AOT] in cyclohexane. The fluorescence quenching analysis of charge transfer between Ru(bpy)[formula]and MV2+, of resonance energy transfer between pyrene and coumarin-153, and of pyrene excimer formation has revealed that the original micellar structure is to a large extent transferred into the structure of the film. The film consists of a hydrophilic and a hydrophobic subphase. Nondried films contain entrapped cyclohexane which allows diffusion of the hydrophobic probes in the film and a rather random distribution of them. Drying leads to solvent evaporation and hydrophobic probe aggregation. The kinetics of the hydrophilic probes reflect the structure of the hydrophilic domain which is not affected by drying procedure. The above films are transparent matrices and make excellent hosts for photophysical studies.

Compositional and Microstructural Characterization of RuO2 ‐ TiO2 Catalysts Synthesized by the Sol‐Gel Method

In this study mixtures were prepared from solution using and three different precursors for, , and and tris (2, 4‐pentanedionate) Ru(III). Multi‐layer coatings were deposited by spin coating onto fused silica slides with and without an intermediate, 200 nm thick, vacuum deposited Ti film. Samples heat treated at 200, 300, and 400°C were studied by several techniques (Rutherford backscattering spectrometry (RBS), elastic recoil detection, (ERD), nuclear reaction analysis (NRA), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and x‐ray diffraction (XRD) to characterize morphological and compositional changes and to test the reproducibility of the preparation method. In all cases a single crystalline phase, the solid solution of the two component oxides, was detected by XRD. The films appeared to have a low density, and hydrogen and carbon were still found in the coatings after each heat treatment; their content was reduced only at 400°C for samples B and C. The surface of the films displayed increasing percentages of .

Electrokinetics of the silica-solution interface: a flat plate streaming potential study

Details for the construction of a flat plate streaming potential apparatus are presented. Measurements using this apparatus on fused silica slides are reported and analyzed on the basis of a Gouy-ChapmanStern-Grahame (GCSG) model for the electrical double layer at the silica-aqueous solution interface. It is found that the GCSG model can only partly account for the experimental results. Possible reasons for the discrepancy between experiment and theory are discussed.

Surface damage evolution and optical performance of beadblasted fused silica

Optical measurements were made with improved quantitative estimation of the damage evolution of the fused silica surface. The mechanical damage was induced by a sandblasting system using spherical glass beads. Development of the surface damage was measured by the changes in the specular transmission and reflection, and by inspection using a surface profilometer and a scanning electron microscope. The changes in the transmittance versus the duration of beadblasting were measured for single fused silica slides and for a few consecutive slides. Theoretical expressions were developed to describe the stages in surface deterioration and conclusions were obtained for the fused silica surface removal mechanism.

Protection by diamond-like carbon films on fused silica slides from erosion by the impact of solid particles

Measurements were made with a new test for improved quantitative estimation of the mechanical protection of thin films on optical materials. The mechanical damage was induced by a sandblasting system using spherical glass beads. Development of the surface damage was measured by the changes in the specular transmission and reflection and by inspection using a surface profilometer (and a scanning electron microscope). The changes in the transmittance with the duration of sandblasting were measured for uncoated and coated fused silica slides. It was determined that the diamond-like carbon films double the useful optical lifetime of the fused silica. Conclusions were obtained for the fused silica surface removal mechanism and for the film removal mechanism.