Flow-induced dispersion analysis (FIDA) is an immobilization-free technology used for characterization and quantification of biomolecular interaction and protein concentration under native conditions. In the FIDA assay, the size of a ligand (indicator) with affinity to the target analyte is measured. When the indicator interacts with the analyte the apparent size increases and this change in size can be used to determine the analyte concentration and interaction. Additionally, the hydrodynamic radius of the analyte-indicator complex is obtained. A FIDA assay is typically completed in minutes and only requires a modest sample consumption of a few µl.