Introduction

DNA microarrays represent a novel technology that incorporates elements from the fields of microfluidics, microfabrication, molecular biology, chemistry, and bio-informatics. High-density arrays have changed the scope of genetic analysis by allowing researchers to examine thousands of genes in parallel, enabling whole-genome analysis in a single experiment. DNA microarrays, manufactured using photolithographic combinatorial synthesis techniques[1-4] or physical deposition,[5-7] have proven to be invaluable for gaining a genome-wide perspective for genotyping, haplotyping, and gene expression profiling experiments.

Test sites on high-density arrays are defined by the sequence of the DNA probe that is spotted or synthesized at a particular location. Target hybridization is mediated by controlling the temperature and salt concentrations of the hybridization and wash buffers. In contrast, active electronic microarrays are composed of individually controlled microelectrodes (test sites). These arrays use electric field control to drive the transport of charged molecules from the bulk solution to activated test sites, allowing addressing and hybridization reactions to occur within seconds.[8-10] Nucleic acids will concentrate only at the activated test sites; the remaining sites are unaffected and available for subsequent use. In addition to concentrating nucleic acids, electronic control can also be utilized to denature double-stranded DNA and to discriminate single base mismatches between target molecules and reporter probes. Electronic microarrays thus provide flexibility, enabling multiplexed analysis of different targets from multiple samples, and are particularly well suited to clinical diagnostics laboratories where flexibility, reproducibility, and accuracy are critical.

generated by applying a positive direct current (DC) bias to one or more microelectrodes and a negative bias to counter electrodes; negatively charged DNA molecules in the bulk solution are electronically transported, or addressed, to the activated test sites. By applying a negative DC bias to the microelectrodes, denaturation of double-stranded DNA and removal of mismatched or weakly hybridized reporter oligonucleotides can be achieved. Independent control of the test sites enables the user to electronically address samples in any configuration, allowing complete flexibility in assay design.

A gel permeation layer containing streptavidin is present over the array surface. This layer protects the DNA from electrochemical by-products during activation and enables retention of biotinylated target DNA sequences. Electronic activation not only concentrates the target over the test site, but also provides an electrochemical environment conducive to attachment of the biotinylated DNA to the activated test site. These features of the electronic microarray ensure that the biotinylated DNA will be present only at the designated sites, and allow sequential addressing of biotinylated DNA targets from multiple samples onto different test sites of an array without carry-over (Midwest Research Institute and Nanogen, internal results).

The NanoChip Molecular Biology Workstation is the instrument system in which NanoChip electronic micro-arrays are processed. Electronic addressing of samples is done in the ''loader'' component, which can process up to four NanoChip cartridges simultaneously. Fluorescent signal detection occurs in the ''reader'' component. Both the loader and reader are capable of performing fluidic and thermal processes. A computer interface controls the workstation and provides software for data analysis and management.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

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