This technology measures the interaction of two molecules bioconjugated to donor and acceptor beads. Laser excitation leads to light emission which is directly proportional to the amount of binding, provided molecules are in proximity to cause a chemical reaction (interact). Users have modified this and coupled it to chemiluminescence emission. This technology has been adapted to study protein-protein, protein-DNA and receptor-ligand, immunoassay, phosphorylation and protease reactions.