Photon correlation spectroscopy can monitor quaternary structure by detecting changes in hydrodynamic radii(19). The most common uses for PCS are investigating dimer formation, such as that of bovine serum albumin(20).
PCS can also be used to monitor protein/receptor binding, like that shown below for the protein bovine panceatic trypsin inhibitor and trypsin(21).
Protein Dimer(22)
(22)