https://www.creative-biolabs.com/immuno-oncology/pathfinder-bevacizumab-bioassay-kit-2-plate-433.htm

The dimerization of PathFinder™ Bevacizumab Bioassay can identify when two subunits of a receptor-dimer pair dimerize in response to a ligand. One receptor subunit fused to an enzyme fragment acting as a donor and a second dimer partner fused to an enzyme fragment acting as an acceptor have been designed into the cells. It's possible that one or both receptors no longer include the cytoplasmic tail. When an agonist binds to one receptor subunit, it interacts with its dimer companion, which forces the two enzyme pieces to complement each other. As a result, a functioning enzyme is created, which hydrolyzes a substrate and produces a chemiluminescent signal.