Silicon wafer array

Figure 11.24 A silicon wafer array, with micromachined pyramidal wells (detail shown right) for holding receptor derivatised beads. Fluid containing the experimental solution is added to the top of the array and flows through the bead matrix, and out of the bottom of the pyramidal wells holding the beads. Analyte binding by the differential receptors anchored to the beads gives a recognition pattern unique to each analyte mixture (reproduced with permission from [34] 2001 American Chemical Society).

There are other, nonhydrogel, new materials for chromatographic and electrophoretic separations [7,8,103,164,199,214,377,407], Eor example, Volkmuth and Austin [407] proposed electrophoretic studies in microlithographic arrays of posts and channels etched into sihcon wafers. This material may be useful for studying fundamental transport characteristics of macromolecules in defined media, and many recent studies have been conducted to develop chromatography and electrophoresis on silicon wafers with micron-scale channels... 

Electrochemical experiments have been carried out on materials deposited by PVD on silicon microfabricated arrays of Au pad electrodes [Guerin et al., 2006a]. The substrate is made up of a square silicon wafer capped with silicon nitride (31.8 mm x 31.8 mm), which has an array of 100 individually addressable Au pad electrodes. These electrodes make up a square matrix on the wafer, which can be masked when placed in a PVD chamber, allowing deposition of thin films on the Au electrodes. Figure 16.3 is a schematic drawing of the configuration. Small electrical contact pads in Au for the individual addressing of electrodes (0.8 mm x 0.8 mm) are placed on the boundaries. 

Figure 16.2 Thickness determination of An deposition onto a bare silicon wafer using a 10 x 10 contact mask in two geometries (see insets), using (a) AFM along the diagonal of an array of 100 electrodes and (b) AFM and ellipsometry for a deposition geometry that allowed an average of 10 fields of identical thickness across the wedge. The source temperatures and deposition times were (a) 1548K, 7200 s and (b) 1623K and 4500 s.

Figure 16.3 Silicon nitride pacified silicon wafer with an array of 100 individually addressable square Au electrodes.

In a DNA array, gene-specific probes are created and immobilized on a chip (silicon wafer, nylon or glass array substrate). Biological samples are labeled with fluorescent dyes or radioactivity. These labeled samples are then incubated with the probes to allow hybridizations to take place in a high fidelity manner. After incubation, non-hybridized samples are washed away and spot fluorescent or radioactivity signals resulting from hybridization can be detected. 

FIGURE 11.28 Silicon wafer-based electronic biochip (10 X10 arrays) (see Plate 11 for color version). 

The sample throughput of nanoESI is limited by the comparatively time-consuming procedure of manual capillary loading. A chip-based nanoESI sprayer on an etched silicon wafer allows for the automated loading of the sprayer array by a pipetting robot (Fig. 11.7). The chip provides a 10 x 10 array of nanoESI... 

Silicon wafers can act as substrates in the fabrication of DNA arrays. Chemical functionalization of silicon surfaces is compUcated by the fact that silicon spontaneously oxidizes in air to produce an amorphous sihca layer. 

A patterned array of goethite can be deposited from an Fe(N03)3 solution at 70 °C on an organic substrate mounted on a silicon wafer (Rieke et al., 1994). The organic surface contains a mixture of sulphonate groups (which bind the iron oxide) and nonbinding methyl groups (which permit development of a pattern). 

A chip-based nanospray interface between an HPLC and the MS has been introduced by Advion Biosystems (Ithaca, NY). This instrument aligns a specialized pipette tip with a microfabricated nozzle, set in an arrayed pattern on a silicon wafer. The advantage of this interface is that each sample is sprayed through a new nozzle, thus virtually eliminating cross contamination. 

Ping et al. have fabricated an integrated microsensor array on a silicon wafer for pH imaging [89]. Six different pH-sensitive colorimetric dyes (methyl violet 6B, phenolic red, alizarin complexone, 5-carboxy-fluorescein, alizarin red and methylthymol blue) were used to cover the whole pH range. The dyes were adsorbed on microbeads and placed in etched microwells on the silicon wafer. The indicator array was also used as a cation sensor chip (see Sect. 2.4). 

Hybride micro-FIA systems produced in silicon technology using oxygen microelectrodes and microcavities have been developed for measuring phosphate concentrations [96]. Multiple analyte biosensor arrays can also be realized using thin film and silicon technology. The so-called containment technology has been applied to immobilize enzymes in three dimensional cavities formed in silicon wafers to get fully process compatible biosensor devices [97] (Fig. 5). 

To reduce expense, efforts are made to exploit integrated thin film technologies. For example, arrays have been produced via thin film deposition of the pyroelectric onto a sacrificial layer, e.g. a suitable metal or polysilicon, which is then selectively etched away. Thermal isolation of the pyroelectric element is achieved through engineering a gap between it and the ROIC silicon wafer. Yias in the supporting layer permit electrical connections to be made between the detector and the wafer via solder bonds. Imaging arrays have been produced in this way incorporating sputtered PST and sol-gel formed PZT films. 

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