A glass slide or bead on which are deposited biomolecules or other material in a regular micro-scale pattern to enable automated simultaneous multiple assays of target substances or activities. Microarrays are powerful analytical tools with wide-ranging applications. They can be designed to carry small DNA molecules (see DNA microarray), proteins (e.g. antibodies or antigens), carbohydrates or other organic molecules, or even individual living cells. These reagents are applied to the glass substrate in a regular microscopic grid pattern, each being identified by its unique coordinate, or address, on the grid. Interaction of a target substance (e.g. an antibody or a complementary nucleic acid) with a particular address on the microarray activates or attaches a label (e.g. a fluorescent dye). The microarray can then be ‘read’ by a scanner, which automatically assesses the amount of label at each address, and hence the amount of target substance. Even smaller-scale nanoarrays are already being developed, to increase further the scope and speed of this technology.
A living cell makes and uses thousands of different RNAs and proteins toperform all its vital functions. Real insight into cellular metabolism requiresknowledge of which components are being expressed by different cell types, forexample during development or under different physiological conditions, andhow their concentrations change over time.
Microarrays were developed in the 1990s for the automated analysis of thousands of different biomolecules simultaneously. They have enabled researchers to study the function of genes and their products (RNAs and proteins) on a genome-wide basis - the field of functional genomics. These techniques generate massive amounts of data, and computerized handling, analysis, and presentation of the data are crucial for valid interpretation.
Types of microarrays
DNA microarraysContain short oligonucleotides or larger DNA fragments that hybridize with complementary DNA or RNA sequences. Uses include:
Used to determine protein-protein interactions at a cellular scale.
Tissue microarrays Contain small thin sections of tissue taken from different tissue locations or pathology specimens.
Used to identify distribution of specific proteins throughout a tissue sample.
Chemical microarrays Contain chemical compounds.
Used, for example, to select potential drugs with particular chemical binding properties.
Preparation of DNA microarrays
There are two main types of DNA microarrays.
Oligonucleotide arrays (DNA chips)
DNA oligonucleotides (20-25 nucleotides) are assembled in situ on a quartz wafer or glass slide, using a photolithography process similar to that used to make microprocessor chips.
A single chip may contain up to a million specified oligonucleotides at regularly spaced sites called addresses, or ‘features’.
Poor or incorrect hybridization leads to signal ‘noise’.
Spotted microarrays Based on the principle of the dot-blot technique with complementary DNA obtained from clones of the genes of interest.
Subjects: Biological Sciences.