Porous Silica Layer Research Articles

SiO2 Entrapment of Animal Cells for Hybrid Bioartificial Organs

ABSTRACTSi-alkoxides in gas phase are reactive towards the surface of animal cells, depositing a homogeneous layer of porous silica. This encapsulation method preserves cell viability and does not alter the hindrance of the biological load.In the prospective use for the design of a hybrid bioartificial liver, hepatocytes in a collagen matrix can be entrapped by the siliceous deposit which provides definite mechanical stability to the collagen matrix and molecular cutoff vs. high molecular weight proteins, including immunoglobulins. The functionality of the encapsulated cell load is maintained for the expressions of typical liver and pancreas metabolic activities.

Sol-Gel Derived Silica Layers for Low-k Dielectrics Applications

AbstractPorous silica exhibits attractive dielectric properties, which make it a potential candidate for use as insulator into interconnect structures. A new way of preparation of highly porous silica layers by the sol-gel route was investigated and is presented. The synthesis strategy was based on the use of common and low toxicity reagents and on the development of a simple process without gaseous ammonia post-treatment or supercritical drying step. Defect free layers were deposited by spin coating on 200 mm silicon wafers and characterized. Thin layers with a total porosity larger than 70% and an average pore size of 5 nm were produced. The dielectric constant measured under nitrogen flow on these highly porous layers is equal to ∼ 2.5, which can be compared to the value calculated from the measured porosity, ∼ 1.9. This difference is explained by the presence of water adsorbed on the hydrophilic surface of the unmodified silica.

Consequences of TiO 2 doping on the optical properties of porous silica layers coated on silica optical fibers

The paper deals with the investigation of optical properties of porous silica and TiOTi chains – doped porous silica layers coated on silica optical fibers. The porous layers composed of dried gels have been prepared by the sol–gel method from alkoxides. The refractive indices and optical attenuation of the layers have been determined from the measured angular distributions of the output optical power. For this purpose, a model based on geometrical optics has been developed. The interaction of the porous layers with benzene, toluene, xylene and hexane has been investigated by measuring the changes of the output optical power induced by the effect of vapors of the hydrocarbons in air. On the basis of these measurements, the porosity of the layer, partition coefficients and equilibrium adsorption constants of the hydrocarbons have been estimated. The measured decrease of the optical power for the aromatic hydrocarbons and the increase of the output power for the aliphatic hydrocarbon have been explained on the basis of the developed model.

High Surface Area Substrates for DNA Arrays

ABSTRACTHigh-density, spatially addressable arrays of DNA probes offer a high-throughput approach to DNA sequence analysis that is likely to have a major impact on biological and genetic research. These arrays are comprised of short strands of immobilized DNA (“probe”) sequences prepared synthetically on a planar glass support. Samples of unknown, fluorescentlylabeled strands of “target' DNA can be analyzed by sequence-specific binding (“hybridization”) to the arrays in order to extract detailed sequence information. The detection sensitivity of these arrays is dependent on quantity and density of immobilized probe molecules on the surface, as well as the thermodynamics of nucleic acid hybridization. In this report, substrates with a porous, “3-dimensional” surface layer were investigated as a means of increasing the number of available probes, and therefore the amount of detectable bound target per unit area. Two methods for creating porous silica layers were investigated - a “subtractive” method and an “additive” method. For the systems investigated, the additive method, sol-gel processing, offered the most promising route for high density DNA arrays.

Optical fibre sensor coated with porous silica layers for gas and chemical vapour detection

Fibre optic sensors have been conceived in new technologies for detecting very small amounts of chemical, gaseous and biological species. Recently, new polymer-clad silica (PCS) fibres coated with thin porous silica layers have been developed. These porous layers have been prepared by the sol-gel method using the dip-coating technique. In this work, this new material has been investigated for detecting gases and vapours. By choosing a fixed incident angle, variation of light power transmitted through the fibre is detected as the vapour or gas to be detected is sorbed in the porous silica layer. Good sensitivity and reversibility have been obtained for this system. Moreover, both the response time and the desorption time have been found less than 2 min. Chlorinated hydrocarbons such as trichloroethylene, carbon tetrachloride, chloroform, dichloromethane and alkanes such as propane, butane and hexane can be detected with detection limits of 0.6, 1.5, 1.7, 4, 25, 10 and 5% respectively.

Quantitative study of the hydroxylation and of the chemical grafting of oxidized porous silicon

A porous silica layer was obtained by anodic dissolution of silicon and thermal oxidation. The initial porous structure of silicon is preserved after well defined oxidation treatments. The silica layer was hydrated and chemically modified by grafting bromohexyl silane. The adaptation of different analytical methods allows the determination of the silanol and the graft densities. The experimental conditions for obtaining the highest densities were defined. These results will be applied to the preparation of ion sensitive membranes for ISFET.

Performance of porous silica layers in open-tubular columns for liquid chromatography

Progress has been made in the preparation of porous silica layers in fused-silica capillaries for open-tubular liquid chromatography. The porous silica layer is prepared by (i) static coating of the silica precursor, polyethoxysiloxane (PES), followed by (ii) converting the PES film into a porous silica layer with ammonia solution. The porous silica layer can be easily modified by silane reagents commonly used in packed column high-performance liquid chromatography. The performance of the silica layer with the different phase systems was tested with polyaromatic hydrocarbons and derivatized amino acids as samples.

The application of porous silica layers in open tubular columns for liquid chromatography

Two methods to realize a porous retentive silica layer on the inner wall of 10–25 µm fused silica capillaries for OTLC, etching and precipitation of silica from solution, have been investigated. Etching of the fused silica capillaries with 1M KOH, creates an activated surface, but the capacity of the silica layer is too small to serve as retentive layer in OTLC. Better prospects are offered by the precipitation of silica from a solution of polyethoxysiloxane, dynamically coated on the inner wall of the fused silica capillary. It appears to be possible to deposite a porous silica layer up to 0.8 µm thick (in a 25 µm capillary) by this method, which seems to be suitable for liquid-solid an dynamically generated liquid-liquid chromatography in open tubular columns. The performance of these columns are demonstrated by means of efficient separations of test mixtures using on-column fluorescence detection.

Thin-layer chromatographic and high-performance thin-layer chromatographic ready-for-use preparations with concentrating zones

Thin-layer chromatography (TLC) and high-performance thin-layer chromatography (HPTLC) ready-for-use preparations with concentrating zones consist of a narrow inert layer of a synthetic porous silica of medium pore volume, extremely large pore diameter ( ca. 5000 nm) and extremely small internal surface area (less than 1 m 2/g), with a very sharp interface leading to the chromatographic layer. The concentrating effect is manifested both after the application of spots (without difficulty at any level) and after large-area application by immersion, whereby it is possible to dose into the dry or wet layer. The extremely narrow line of substance that is formed at the interface provides an optimal starting situation for chromatography. Quantitative determinations are improved, with simultaneous enhancement of the sensitivity of detection. In comparison with layers that are uniform throughout, significantly improved separation performances are attained, particularly when larger amounts are applied, and very dilute solutions and substances with lower R F values can be used. The selection of a suitable solvent can be used to prevent or select the adsorption of salts or of polar neutral substances in the concentrating zone as desired. With direct application of urine, serum, etc., the ingredients are initially extracted in a continuous process, the so-called “clean-up”, then they are concentrated, followed by chromatography. The technique is of general importance for liquid chromatography.