<p>The present invention provides a useful system for assays that comprises a solid support, a plurality of capture oligonucleotides immobilized onto the solid support, and complementary oligonucleotides attached to capture ligands. A detectable label can be directly attached to the capture oligonucleotides or the complementary oligonucleotides. The labeled oligonucleotides can be detected, and used to determine the quality of the assay. A labeled detector ligand corresponding to a target ligand can also be independently detected apart from the labeled oligonucleotide.</p>
