DNA Microarray Technology

DNA microarray technology was developed by Patrick O. Brown, Joseph DeRisi, David Botstein and his colleagues in the mid 1990s. Microarray is basically a collection of microscopic features (most commonly DNA) which can be probed with target molecules to produce either quantitative (gene expression) or qualitative (diagnostic) data.

The successful implementation of microarray technologies has required the development of many methods and techniques for fabricating the microarrays and spotting the probes, for carrying out and detecting the hybridization reactions and informatics for analysing the data. A variety of DNA microarray and DNA chip devices and systems have now been developed and commercialized.

Steps:

Following are the steps of DNA microarray.

  1. Sample collection:

Two types of samples are taken; the test sample and the reference sample.

  1. Isolation of mRNA:

Using column or a solvent (phenol-choloroform), extraxt the RNA from both samples. Now extract mRNA from tRNA and rRNA. Since, mRNA has a a poly-A tail, to which the beads from the column will attach. Wash this mRNA with a buffer to remove the beads from mRNA tail. The buffer action disrupts the hybrid bonds by disrupting the pH.

  1. Labelled cDNA creation:

To the RNA, add labelling mix, containing poly-T primer, RT (reverse transcriptase) and nucleotides which are fluorescently dyed. The RT and primer first binds to the mRNA. Now, add the fluorescently dyed nucleotide which will creat the cDNA.

  1. Hybridization:

Add this cDNA to a microarray plate (can also be done by robotics). Both the samples should be added on the same plate. The ssDNA will bind to the cDNa which is already present on the plate.

  1. Data analysis:

Using a microarray scanner the data is analysed. This microarray scanner consists of a laser, camera and a computer. The laser scans the plates, the camera is used for for taking images and the computer gives the results.

Applications:

Following are the applications of DNA microarray technology.

It is used in molecular diagnostics, like; in gene expression, disease diagnostics, drug discovery, personalized medicines.

It is used for observing genomic loss and gains.

It is also used to observe mutations.

Microbes present in the environment can be identified with DNA microarray technology.

Advantages:

In case of Affymetrix genechip, it is speedy.

It is results are specific, reproducible and there is design flexibility.

It is affordable (in case of glass DNA microarray).

Limitations:

It is time consuming (in case of glass DNA microarray).

Affymetrix genechip is expensive. And Affymetrix genechip also limits the research flexibility.

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