Glass, porous solid support

The subsequent explosion of array technologies has been sparked by two key inno-vations. The first is the use of non-porous solid support, such as glass, which has facilitated the miniaturization of the array and the development of fluorescence-hybridization detection (16, 17, 18). The second critical iimovation has been the development of methods for high-density spatial synthesis of oligonucleotides, which allows the analysis of thousands of genes at the same time. Because DNA cannot bind directly to the glass, the surface is first treated with silane to covalently attach reactive amine, aldehyde, or epoxies groups that allow stable attachment of DNA, proteins, and other molecules. 

Porous glass (PG) modified with covalently adsorbed poly(p-nitrophenyl acrylate), as described in Sect. 4.1, turned out to be a highly suitable carrier for immobilization of various biospecific ligands and enzymes. When the residual active ester groups of the carrier were blocked by ethanolamine, the immobilized ligands when bound to the solid support via hydrophilic and flexible poly(2-hydroxyethyl acrylamide). The effective biospecific binding provided by the ligands... 

Syntactic foam contains an orderly arrangement of hollow sphere fillers. They are usually glass microspheres approximately 100 microns (4 mils) in diameter, provide strong, impervious supports for otherwise weak, irregular voids. As a result, syntactic foam has attracted considerable attention both as a convenient and relatively lightweight buoyancy material and as a porous solid with excellent shock attenuating characteristics. The latter characteristic is achieved... 

Sensors based on the above reaction scheme have been developed for Al3+, Zn2+, Cu2+, Ca2+, Pb2+, Hg2"1", K+, Li+, etc. A polycation, protamine sensor has also been developed using 2/7/-dichlorofluorescein octadecyl ester (DCFOE) doped in polymer membranes. However, most of these sensors are pH dependent due to the pH dependence of the cation complexation reactions. The cation ion indicators can be immobilized on any solid support, such as silica, cellulose, ion-exchange resin, porous glass, sol-gel, or entrapped in polymer membranes. 

Both proteins and nucleic acids may be immobilized to a variety of solid supports. For high density microarrays, glass slides are the preferred substrates because of their flatness and optical properties. Better spot resolution is also possible on nonporous glass as opposed to porous membranes, primarily due to a reduction in diffusion at the surface-liquid interface. However, keep in mind that spot (droplet) diffusion can occur on most substrates by the actions of surfactants and other wetting agents including proteins. Control of spot size and morphology is required in order to achieve reproducible and reliable results with microarrays. 

New polymeric solid supports have been devised, which include macroporous styrene-divinylbenzene containing large fixed pores, porous glass beads, insoluble carbohydrate polymers, poly(ethylene oxide), cross-linked derivatives of polyacrylamide resins, and graft copolymers of polystyrene and poly(ethylene oxide). The last two have been the most effective and widely used and have competed well with the original copoly(styrene-divi-nylbenzene) beads. 

As with thermal conductivity, we see in this section that disorder can greatly affect the mechanism of diffusion and the magnitude of diffusivities, so that crystalline ceramics and oxide glasses will be treated separately. Finally, we will briefly describe an important topic relevant to all material classes, but especially appropriate for ceramics such as catalyst supports—namely, diffusion in porous solids. 

An alternative method for achieving the effect of a small diameter is to coat a thin layer of porous solid on a solid core (such as glass). Such materials were widely used in the early days of LC and are usually called pellicular supports. Typically the porous layer is 1-2 pm thick, and the solid core has a diameter of about 40 pm. Pellicular solids are easier to pack than microporous solids, but they are less stable, have smaller capacities, and are more expensive. Since good packing methods are now known for the microporous solids, the pellicular solids have become much less popular. They are commonly used in guard columns (discussed later in this chapter). 

Isolated enzymes usually attached through amino or carboxyl groups to a solid support Variety of supports such as porous glass, cellulose, ceramics, metallic oxides... 

These columns, less commonly used today, have diameters of 1/8 or 1/4 inch (3.18 and 6.35 mm) and a length of between 1-3 m (Figures 2.7 and 2.8). Manufactured from steel or glass, the internal wall of the tube is treated to avoid catalytic effects with the sample. They can withstand a carrier gas flow rate within the range 10M 0 mL/min. They contain an inert and stable porous support on which the stationary phase can be impregnated or bounded (between 3 and 20 per cent). This solid support, having a specific surface area of 2-8m /g, is made of spherical... 

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