There are two basic approaches to detect a conformational change:
The first approach is to include a sizing measurement into a kinetic. This way, the association and dissociation kinetics of the test compound to the ligand molecule will be recorded and at equilibrium (in between association and dissociation) a sizing or stopped flow experiment will be performed. This approach is particularly suitable, if you are also interested in the kinetic rate constants and the affinity constant of the interaction between test compound and ligand.
The second approach utilizes the sizing tool for His6-tagged proteins in switchBUILD. In this case, the His6-tagged ligand molecule is pre-incubated with the compounds to be tested, immobilized on the switchSENSE chip and a sizing experiment is performed. Especially when testing very weakly binding compounds (e.g. fragments), this strategy is advisable as very long pre-incubation times can be chosen.