Oligonucleotide encoded chemical libraries

A system for screening chemical compounds for their ability to modulate the biological activity of a cell or a component of a cell, comprising:

• a) an array comprising a plurality of confined volumes wherein each confined volume is separated from other confined volumes,
• b) a plurality of beads where each bead is suitable for disposal in each confined volume, wherein each bead comprises a plurality of substantially identical bead-bound compounds, wherein said bead-bound compounds are covalently linked to the bead by a cleavable linker such that said compounds are releasable from said bead in a measurable dose dependent manner as part of an assay,
• c) said beads further comprising a plurality of substantially identical bead-bound DNA barcodes linked to the bead (i) by a cleavable linker or (ii) by a non-cleavable linker, wherein if the DNA barcodes are linked to the bead by a cleavable linker, the cleavable linker is orthogonal to the cleavable linker used to link the bead-bound compounds to the bead, and wherein the DNA barcode identifies the compound.