<figcaption>http://www.the-scientist.com/article/flash/24106/1/ Click to view enlarged diagram Credit: ILLUSTRATION: ANDREW MEEHAN</figcaption>
http://www.the-scientist.com/article/flash/24106/1/ Click to view enlarged diagram Credit: ILLUSTRATION: ANDREW MEEHAN

There are a number of ways to multiplex, but one of the most common relies on solution-based arrays of microscopic beads measuring several microns in diameter.

Like planar microarrays, these arrays are addressable - that is, each location within the array is known. But in this case, the "array" (1) is really a set of coded microspheres, each of which has an identifying color and associated bioreceptor (e.g., antibody, oligonucleotide, receptor, or enzyme). One color class might be reserved for IL-2, say, while another is reserved for IFN-gamma. Or they may represent different SNPs.

The array is mixed and incubated with a biological sample (2), after which a detection reagent (a dye-conjugated secondary antibody, for instance) is applied (3). The beads then pass single-file through a flow cytometer, which reads the reaction using two lasers (4).

The first laser induces...

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