Adhesion energy of receptor-mediated interaction measured by elastic deformation

We investigated the role of receptor binding affinity in surface adhesion. A sensitive technique was developed to measure the surface energy of recept or-mediated adhesion. The experimental system involved a functionalized ela stic agarose bead resting on a functionalized glass coverslip. Attractive i ntersurface forces pulled the two surfaces together, deforming the bead to produce an enlarged contact area. The Johnson-Kendall-Roberts (JKR) model w as used to relate the surface energy of the interaction to the elasticity o f the bead and the area of contact. The surface energies for different comb inations of modified surfaces in solution were obtained from reflection int erference contrast microscopy (RICM) measurements of the contact area forme d by the bead and the coverslip. Studies with surfaces functionalized with ligand-receptor pairs showed that the relationship between surface energy a nd the association constant of the ligand binding has two regimes. At low b inding affinity, surface energy increased linearly with the association con stant, while surface energy increased logarithmically with the association constant in the high affinity regime.