This study characterized the in-solution interaction between the therapeutic antibody adalimumab and the inflammatory cytokine TNF-α, and Flow Induced Dispersion Analysis (FIDA) was used to measure the apparent hydrodynamic radius (size) of fluorescently labeled TNF-α across an adalimumab titration series. Using a Fida 1 instrument, the researchers determined binding affinity (Kd), complex sizes, stoichiometry and kinetics without surface immobilization, in both phosphate buffer and human plasma. The size-based readout revealed higher-order, avidity-stabilized complexes whose formation depended on the absolute and relative concentrations of the two binding partners. Capillary-mixing and complex-dissociation modes showed smaller complexes form rapidly while larger avidity-stabilized species require longer reaction times and dissociate slowly. FIDA was central to the work, providing both affinity and structural information under biorelevant conditions in a single, immobilization-free assay.