The reaction dissociation constant is widely used to describe the strength of interactions between biomolecules. In the biochemical convention, as opposed to in physical chemistry, Kd is presented with a unit (usually mole per litre with an appropriate prefix). Typical values of Kd of immunological complexes are usually in the nanomolar or micromolar range. Generally, the Kd is determined using surface plasmon resonance (SPR) . But there are also other kineticbased methods which are applied for Kd determination, like bio-layer interferometry , fluorescence correlation microscopy , thermal shift assay , nuclear magnetic resonance , gel chromatography , and electrochemical impedance spectroscopy .