Can you fit an entire genomic/proteomic analysis laboratory on a computer chip and do studies, which normally would take months, in a single day?
Yes. Microarray technology was developed in the 90s with the evolution of micro technology and development of integrated micro system technologies.
What is a Microarray?
A microarray is basically a multiplex assay of bio-molecules(DNA,RNA, Protein etc) using high throughput screening miniaturised, multiplexed and parallel processing and detection methods. This assay is usually done in microliters or even lesser quantities of the molecule. The concept and methodology of microarrays was first demonstrated by Tse Wen Chang in1983 in antibody microarrays in his publication and a series of patents. Hence the term ‘gene chip’ came into existence after 1995 paper by Ron Davis and Pat Brown labs at Stanford University. With the establishment of companies such as Affymertrix, Aglient, Applied Microarrays, Arrayit, Illumina, and others, the technology of DNA microarrays has become accessible and hence widely used.
Types of Microarrays
There are several different types of microarrays depending upon the sample they analyse.
- DNA Microarray, such as cDNA (complementary DNA, DNA with a single strand), oligonucleotide microarrays, BAC microarrays and SNP microarrays.
- MMChips, for surveillance of microRNA populations.
- Protein Microarrays.
- Peptide Microarrays, for analyses or optimization of protein-protein interactions, protein docking etc.
- Tissue Microarrays.
- Cellular Microarrays.
- Antibody Microarrays.
- Chemical Compound Microarrays.
- Phenotype Microarrays.
- Carbohydrate Microarrays. (Glycoarrays)
DNA microarrays are microarrays which analyse single stranded fragments of DNA molecule. DNA microarray is a chip with thousands of microscopic DNA spots or wells in which there are single stranded DNA fragments attached to the base, the glass or with polystyrene beads. DNA microarrays can be used to measure the expression levels of large numbers of genes simultaneously or to the genotype. Human genome contains about 21000 genes. To analyse such a large quantity of gene expressions, DNA microarrays are used in various fields ranging from cancer cell detection to bacterial genome studies. Each DNA spot contain picomoles of a specific DNA sequence, known as probes (or reporters or oligos). These can be a short section of a gene or other DNA element that are used to hybridize a cDNA or a cRNA(also called as antisense RNA) sample (called target) under high stringency conditions. Probe –target hybridization is usually detected and quantified by detection of fluorophore-, silver-, or chemiluminescence labelled tagerts to determine relative abundance of nucleic acid sequences in the target.
An Affymetrix Gene Titan
Procedure and Working
To understand the working of Microarrays, let us look at these videos to get in-depth visually aided presentation of the process.
Microarrays by Genome BC
How does the DNA microarray work?
MIT opencourseware on ChIP-seq Analysis.
A Virtual Lab by University of Utah, Health Sciences Dept.
-Author, Aditya Karmarkar