This study introduces C-Jump, a method for measuring how fast biomolecules bind and release each other — the association (k_on) and dissociation (k_off) rates — while they stay free in solution, without attaching them to a sensor surface as SPR or BLI require. C-Jump is built on Flow Induced Dispersion Analysis (FIDA): a sample is pulse-injected into a capillary containing its binding partner, and a controlled flow induces a rapid concentration change whose effect on the complex's size is read out. Using a Fida Neo instrument, the authors measured kinetics for protein–protein and protein–small-molecule pairs, including an interaction in 90% human serum, using only nanoliter–nanogram sample amounts.