 |
Aug. 24, 2006 — What is a microarray?
 |
Response by
Jennifer Love
Technician, Whitehead Institute Center for Microarray Technology |
|
Formal definition: A tool used to
sift through and analyze the information contained within
a genome or proteome. A microarray consists of different
nucleic acid or protein probes that are chemically attached
to a substrate, which can be a microchip, a glass slide
or a microsphere-sized bead.
What does that mean? In its simplest
form, a microarray is any array (a large number of ordered
objects) of biological material, printed on a solid
substrate in a “micro” format, which allows
many objects to share a relatively small area. An example
might be a glass microscope slide (approximately 1x3
inches) with 30,000 objects printed on it.
 |
| A closeup of a microarray printer
head, showing the detail of a microarray printing
pin. |
The objects are placed on the substrate by a robot
that can deposit very small volumes of material into
discrete spots on the array. The material being deposited
is in liquid form, and small pins dip down into wells
of a microplate, pick up a small volume via capillary
action, and then touch down on the substrate, leaving
a tiny dot of liquid behind. This process is repeated
by several pins operating in parallel, over many plates
of material. The material being spotted can fall under
several categories, and is typically DNA, RNA or proteins.
 |
| A snapshot of a microarray with
a fluorescent probe. The image is generated by a
microarray scanner. |
Scientists can use a microarray to answer thousands
of questions at once. In the commonly used “genome
array,” for example, the entire genome for an
organism can be represented on one slide, with each
spot containing multiple copies of a short DNA sequence
(oligonucleotide) that uniquely identifies one gene.
Then, a sample of RNA, which represents all of the genes
being converted into protein at that moment in the cell’s
lifecycle, can be fluorescently labeled and applied
to the microarray
A gene present in the RNA sample
finds its DNA counterpart on the microarray, and binds
to it, and then the spot becomes fluorescent. A microarray
scanner is then used to “read” the microarray.
It zooms in on the array and measures the fluorescence
in each spot. The more fluorescent a spot is, the more
copies of that gene were present in the RNA sample.
 |
| A microplate, containing nucleic
acids or protein in solution, to be used with a
microarray printer. |
Usually, a microarray is used as a means to compare
the profiles of two different samples to one another.
For instance, with the genome array, one could determine
which genes are being turned on or off incorrectly to
cause skin cancer by comparing the RNA profile of a
cancerous skin cell to that of a healthy skin cell.
Then, drugs or other treatments could potentially be
developed.
There are many new an exciting uses for microarrays.
For a detailed introductory paper examining microarray
technology, dowload Introduction
to Microarray Technology (2.6 MB PDF).
|
