Biophysical Resource had a BEACON Fluorescence Polarization System, which provides a rapid and reliable way to measure molecular interactions of wide range of biological molecules including proteins, nucleic acids, carbohydrates, lipids and drugs.

In general, the fluorescence polarization experiment employs a small molecule that is fluorescently labeled (for example, drug compound or nucleic acids).  Fluorescence polarization measures the extent of molecular rotation during the period between excitation and emission. Since small molecules rotate quickly during the excited state, upon emission the light is de-polarized (low polarization value).  Binding to large molecules (like, for example, antibodies or DNA-binding proteins) slows the rotation of labeled molecules and the emitted light remains polarized (high polarization values).  The general scheme for such experiment is as follows:

unbound ligand   +  protein   ======   bound ligand:protein
low polarization                                                      high polarization
 

Thus, by following the value of fluorescence polarization one can construct a binding curve.