Photolithographic spatially

The resolution of the photolithographic process determines the maximum achievable density of the array (i. e. the amount of sequence information encoded on the chip). Table 2 shows the relationship between the resolution, in terms of smallest feature size, and the maximum density at which an array can be printed . Application of the photolithographic process using photolabile protecting groups currently provides a spatial resolution that allows arrays to be fabricated with densities on the order of 106 sequences/cm2, which corresponds to an individual feature size of 10 X 10 m. This feature size is near the limit of resolution that can be achieved by this method using standard photolithography equipment. 

By photolithographic techniques, we most specifically mean multi-color photolithography where spatially controlled index of refraction variations are created by photo-initiation of physical and chemical changes in the material. Again, this topic has been reviewed in considerable depth elsewhere so we will only briefly review the central concept here [2,3,5,63,64]. 

A special case of parallel synthesis is the spatially addressable synthesis pioneered by Fodor et al. [17,18] in 1991. Here, each member of the library is synthesized at a specific location on a functionalized silica wafer rather than on resin beads in separate reaction vessels. This approach, based initially upon solid-phase peptide synthesis and semiconductor photolithographic techniques by using photolabile amino protecting groups, allows the synthesis of combinatorial libraries containing about 50000 compounds localized to a 50 pm square site on a silica wafer ( library on a chip ). 

With the same number of chemical steps, the diversity and number of peptides synthesized using light-directed, spatially addressable chemical synthesis depends, among other factors, on the patterns of photolithographic masks used for each photodeprotection. Different masking strategies can be used. 

Microfabrication by SPMs is in part motivated by their potential to beat the diffraction limitations of optical methods for electronics applications. The spatial resolution of SPM is limited only by the tip size and STM has been used to manipulate individual atoms. However, the typical tip size in SFCM is ca. 1 pm and therefore a significant improvement over photolithographic resolution is not routinely obtained. Further, SPMs are rather slow since they are limited by the speed of the tip and this is especially so for SECM. Instead, SECM microfabrication is often more useful as a technique for patterning surfaces with chemical or biochemical functionality and fabricating microscopic structures with particular chemical properties. 

Stacked planar optics consists of planar optical components in a stack, as shown in Fig. 28. All components must have the same two-dimensional spatial relahonship, which can be achieved from planar technology with the help of photolithographic fabrication, as used in electronics. Once we align the optical axis and adhere all of the stacked components, two-dimensionally arrayed components are realized the mass production of axially aligned discrete components is also possible if we separate individual components. This is the fundamental concept of stacked planar optics, which may be a new type of integrated optics. 

Bhatia and colleagues [2] used microscale techniques to exert spatial control over cell adhesion at the 1-100 p,m scale to study diverse phenomena in hepatocytes such as the effect of cell spreading on cell behavior and surface topology on cell migration. They developed a photolithographic cell patterning technique to study the relative... 

The formation of electrical contacts between metal structures and devices is an integral aspect of circuit construction at all scales of commercial importance. Currently photolithographic, screen printing and microsoldering techniques are the methods of choice to establish connections. However, these approaches require masks, templates or intimate physical contact with the components. Spatially Coupled Bipolar Electrochemistry (SCBE) is a novel technique which makes use of electric fields to create electrical connections between components, which not only avoids physical contact but is also applicable in principle to the formation of three dimensional circuitry. The SCBE technique has been developed to a point where the construction of functional robust circuits has been achieved. Preliminary data demonstrating the application of this approach to the formation of polypyrrole bridges between isolated gold structures is also presented. 

The above results demonstrate the use of electrochemical and photolithographic methods for the spatially controlled deposition of enzymatic and anti-interference layers in a controlled way upon the surface of miniature electrodes. Although the results concentrate upon ucose measurement, the example of urease indicates that the electrochemical method should be extendible to other enzymes and we are currently investigating this. We beUeve the measurements made using the electrodes with the thin anti-interference layer are particularly interesting and show that the modified electrodes can be used in complex matrixes such as complex yeast extract medium. 

Photolithography is the most diffused technique for the fabrication of regular arrays of microelectrodes. Photolithography is a microfabrication technique which is based on the selective removal of parts of thin films (photoresist) exposed to UV light. This procedure allows one to obtain regular arrays of micro electrodes with high spatial resolution, nonetheless this technique requires special and expensive equipments besides, the photolithographic process requires access to a clean room. 

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