Illumina has received US Patent No. 7,033,754, "Decoding of array sensors with microspheres." The patent claims a substrate with discrete sites distributed on the surface of the substrate. The sites on the surface comprise a population of microspheres with at least a first and a second subpopulation, according to the patent's abstract. Each subpopulation includes a bioactive agent and an identifier-binding ligand that will bind a decoder-binding ligand to elucidate the identity of the bioactive agent, the abstract states.