 Antibody surface plasmon resonance experiment

A concrete comparison used a Biacore T100 with a CM5 chip bearing the target receptor; unused reactive surface groups were blocked. At $25{}^{\circ }\mathrm{C}$ in a pH 7.4 buffer solution, intact IgG and its Fab fragment were injected for $180\mathrm{s}$ at $5\mu \mathrm{L}/\min$; dissociation was monitored for $3600\mathrm{s}$. The optical response tracks changes in refractive index near the surface, rather than counting occupied paratopes directly. A reference surface and blank injections corrected background; association and dissociation responses were fitted with a 1:1 model. The reported intact-IgG detachment was slower than that of the Fab fragment. ^[ref]

This comparison supports format-dependent attachment, not an intrinsic single-site antibody affinity for intact IgG. The reference and blanks address background, not two-arm avidity, surface accessibility or delivery by diffusion. The paper's fitted 1:1 constants alone cannot distinguish those mechanisms. Its Fab fragment comparison therefore motivates specifying the binding format before interpreting a dissociation constant; a good fit does not establish a unique molecular model.