Illumina BeadArray™ technology uses beads containing 50-mer gene-specific probes, which hold several hundred thousand copies of the probe across the beads surface. Associated with the probe is a short addressable sequence, which is used during the array manufacturing process to identify the bead. Illumina uses the TotalPrep RNA Amplification kit from Ambion to perform one round of amplification from 50-500 ng of total RNA. The cDNA synthesis and in vitro transcription amplification are followed by hybridization. The BeadChips are imaged using iScan readers.
The Illumina HumanHT-12 Expression BeadChips™ contain more than 47,000 probes derived from the National Center for Biotechnology Information Reference Sequence (NCBI) RefSeq Release 38 (November 7, 2009) and other sources . There is one slide format which can process 12 samples simultaneously.
The Illumina MouseWG-6 Expression BeadChips™ contain more than 46,000 probes derived from the National Center for Biotechnology Information Reference Sequence (NCBI RefSeq) database (Build 36, Release 22), supplemented with probes derived from the Mouse Exonic Evidence Based Oligonucliotide (MEEBO) set as well as exemplar protein-coding sequences described in the RIKEN FANTOM2 database. The MouseWG-6 can process 6 samples at once. The minimum number of samples per study is 12.
Detailed information about the chips is available from the Illumina web site