Receptor-ligand interactions are crucial to many biological processes such as inflammatory cascade and tumor metastasis [1-2].To mediate cell adhesions, receptors and their ligands have to be anchored onto two apposed surfaces, which is so-called two-dimensional (2D) interaction.2D forward rate, kf, defines the rate of association per unit contact area (in m2/s), and 2D association kinetics governs the bond formations as well as cell adhesions.While the dissociation kinetics of receptor-ligand bond has been extensively investigated [3-6], the association kinetics, however, is poorly characterized, mainly because it is difficult to manipulate simultaneously the approach and separation of surface-to-surface, and to determine the moments when the bond starts to form or begins to dissociate.