Biacore analysis of m909 Fab. rFRβ was immobilized on a CM5 sensor chip at 210 resonance units (RU). m909 Fab at 1, 10, 100, 400, and 800 nM was tested. A 1:1 binding model gave the equilibrium dissociation constant (KD) of 56.72 nM. The colored lines are the binding curves, and the black lines are the fitted curves. Fab, antigen-binding fragment; rFRβ, recombinant folate receptor beta.