(430e) Polymer-Tethered Ligand-Receptor Interactions between Surfaces

We study the interaction between two parallel surfaces having randomly distributed receptors on one and polymer-tethered ligands on the other. We examine the interplay between the specific ligand-receptor binding and the conformation degrees of freedom of the polymer tether, and address the difference due to the mobility of the species. The case where one or both species are mobile is solved exactly and the case where both species are immobile is treated both by Monte Carlo direct sampling and by an analytical density expansion. The combination of the entropic repulsion due to chain confinement at smaller surface separations, and the attraction due to ligand-receptor binding which can take place at significant chain stretching, results in a minimum in the interaction free energy. For the same set of parameters, stronger binding is obtained when one or both species are mobile. In the case where both ligands and receptors are immobile, binding is limited by the availability of receptors within the reach of the ligand; for a given binding energy, and receptor and ligand densities, there exists an optimal chain length that yields the lowest minimum in the interaction free energy. When one or both species are mobile, we also examine the difference between closed and open systems, the latter corresponding to interaction between small portions of two large surfaces. Finally we show examples of controlling the interaction potential between the surfaces using different types of ligand-receptor interactions and non-specific repelling polymers.