Affinity Measurements Using Quartz Crystal Microbalance (QCM)

To determine the affinity, the KD,-value, between interaction molecules a number of techniques using labels are available, such as chromatography, isothermal titration calorimetry, radioimmuno- assay and the widely used enzyme-linked immunosorbent assay (ELISA). However, need and developments have enabled studies of molecules interacting in real time using biosensors, without labeling or chemical modifications. In addition to KD, biosensors provide kinetic information about the interaction revealing the kinetic rate constants, kon and koff. Biosensors have been used to study a vast variety of molecular events, such as characterization of antibody–antigen, nucleic acid, and protein interactions. The Quartz Crystal Microbalance (QCM) technology is label-free and a direct way to determine affinity and kinetic rate constants. Here, we present describe the basic experimental design of typical kinetic strategies as well as data processing and interpretation with the aim of calculating affinity and rate constants of molecular interactions.