TARGET LABELING
Labeling of targets for microarrays comes in two flavors: Single-color and Two-color
One-Color Labeling
Single-color labeling is used for platforms such as Affymetrix's Gene Chips (image above), in which one RNA target is hybridized to each chip. The hybridized, biotinylated targets are labeled post-hybridization with streptavidin-phycoerythrin. Signals from the hybridized features can then be detected using the Affymetrix Scanner. In this approach, differentially expressed genes are detected by comparing the intensity of hybridization signals between different chips.
Two-Color Labeling
Labeling is done via a T7-promoter mediated linear amplification procedure (Van Gelder et al., (1990) PNAS 87:1663-1667). This allows a ten- or more fold increase in the amount of starting material, allowing researchers to supply us with as little as 5 micrograms of total RNA per array.