How do I determine the binding affinity?

Binding affinity can be determined using several experimental techniques including but not limited to: 

• Using a radiolabeled or tagged ligand in homologous competitive binding experiments and examining the relative binding competition between a tagged and untagged ligand
• The use of label-free methods that are based on real time such as dual-polarization interferometry, surface plasmon resonance, and multi-parametric surface plasmon resonance 
• Using an immobilization-free method called microscale thermophoresis (MST), which allows researchers to determine binding affinity without any limitation to the molecular weight of the ligand