Microchip arrays

Microchip arrays for parallel binding and detection of DNA or proteins for drug discovery and different clinical microsystems are under development [114]. 

Current methods combine at least one of four different principles of allelic discrimination (hybridization, primer extension, ligation, or restriction) with one of four different detection techniques (chemiluminescence/ fluorescence, fluorescence polarization, resonance energy transfer, and mass spectrometry). Assay formats range from (slab)- gel electrophoresis, plates, particles, fibre arrays, and microchip arrays to semi- and homogenous assays that do not require any further sample separation or purification. 

In a subsequent report, a group of researchers at the University of Texas created a microchip array of differential... 

DNA microchip arrays contain from several hundred to several thousand immobilized DNA reagents. They provide a systematic way to survey DNA and RNA variation and may well provide a standard tool for molecular biology research and clinical diagnostics. The peripherals such as MS and fluorescence detectors sit off-chip and are typically benchtop instrument sized. 

Fernandez-Suarez, M., Wong, S. Y. F., Warrington, B. H., Synthesis of a three-member array of cycloadducts in a glass microchip under pressure driven flow. 

For many applications, diode array detection has become routine. A photodiode array was used for simultaneous detection of 100 capillaries in zone electrophoresis and micellar electrokinetic chromatography (MEKC).1516 Deflection of a laser beam by acoustic waves was reported as a means to scan six capillary channels on a microchip.17 The design of a low-noise amperometric detector for capillary electrophoresis has been reported.18... 

Electronically active chips (e.g.. Nanogen s NanoChip Electronic Microarray) are true microchips in which microelectrodes (pads) become elements of the array (Figure 2.13). The microelectrodes are covered with materials that allow immobilization of probes. Each electrode is individually addressable so that specific probes can be attached to different electrodes. Hybridization is accelerated by electromotive force (emf) on the target. Enhanced stringency is also achieved by modulation of the emf (Heller et al., 2000). 

Dill, K., Montgomery, D.D., Wang, W., and Tsai, J.D., Antigen detection using microelectrode array microchips, Clin. Chim. Acta, 444, 66-78, 2001. 

Significant advances have been provided by the Haupt group in this field, [126], Biomimetic microchips were produced by depositing MIP microdot arrays on... 

Different methods are described to construct ultramicro electrodes48-62 such as insulation in glass or epoxy resin, the construction of ultramicro electrode arrays (an array of individual ultramicro electrodes to increase the current signal without losing the benefits of ultramicro electrode behaviour) by template synthesis, metal depositions in pores of membranes and by using the connecting wires in microchips. The latter has the advantage that each ultramicro electrode is individually addressable. 

FIGURE 7.22 (Top) Schematic representation of the microchip layout used for the CE separation with EC detection. (Bottom) Schematic representation of a cross section at the end of the separation channel comprising the microhole array decoupler, the working electrode, and the silver/AgCl reference electrode [191]. Reprinted with permission from Elsevier Science. 

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