fluorescence polarization Fluorescence polarization (FP) measurements are based on the assessment of the rotational motions of species. It is used to measure binding interactions. When linear polarized light is used to excite fluorophores, only those aligned with the plane of polarization will be excited. For fluorophores attached to small, rapidly rotating molecules, the initially photoselected orientational distribution becomes randomized prior to emission, resulting in low fluorescence polarization. But binding of the low molecular weight tracer to a large, slowly rotating molecule results in high fluorescence polarization. FP fluorescence method