Illumina’s BeadArray Technology is based on 3-micron silica beads that self assemble in microwells on either of two substrates: fiber optic bundles or planar silica slides. When randomly assembled on one of these two substrates, the beads have a uniform spacing of ~5.7 microns. Each bead is covered with hundreds of thousands of copies of a specific oligonucleotide that act as the capture sequences in one of Illumina’s assays. BeadArray technology is utilized in Illumina's iScan System for a broad range of DNA and RNA analysis applications. The original Infinium II Assay was great, but Infinium HD is remarkable. Most samples have an average call rate of 99.9% off the shelf, which makes downstream curation of data a whole lot easier. For those who aren’t curating their data, there's much less downstream work because there is less likelihood of false positives and negatives due to the higher sample call rates. In addition to data quality, the ability to run four samples per chip clearly gets to the answers a lot faster.
BeadArray technology is deployed on either of two multi-sample array formats for DNA or RNA-analysis applications. With multi-sample BeadChip formats, uniform pits are etched into the surface of each substrate to a depth of approximately 3 microns prior to assembly. Beads are then randomly assembled and held in these microwells by Van der Waals forces and hydrostatic interactions with the walls of the well.