FIGURE 3.

Comparison of a priori predictions of the maximum expected bridging force (lines) and measurements with the SFA for biotin/streptavidin ligand/receptors (W = 35 k_BT) mounted on two tether lengths: (A) PEG₆₂₆₀ and (B) PEG₂₀₀₀ (T. L. Kuhl, S. Zalipsky, and J. Y. Wong, unpublished data). Forces were measured between unperturbed surfaces as they approached (•) and during withdrawal after surfaces had been pressed into adhesive contact (○). Discontinuities in the measured data exist from instabilities in the cantilever spring that support one of the functionalized surfaces. The a priori model correctly identifies the capture distances (D_B) and equilibrium resting positions (D_eq) to within experimental error (±0.1 D/L), and forces to within less than a factor of three.