Molecular interaction and transport limitation in macromolecular binding to surfaces.

Binding of macromolecules to surfaces, or to surface-attached binding partners, is usually described by the classical Langmuir model, which does not include interaction between incoming and adsorbed molecules or between adsorbed molecules. The present study introduces the Surfint model, including such interactions. Instead of the exponential binding behaviour of the Langmuir model, the Surfint model has tanh binding equations, as confirmed by a random sequential adsorption (RSA) computer simulation. For high binding affinity, sorption kinetics become diffusion-limited as described by the existing unstirred-layer model Unstir, for which we present the exact analytical solution of its binding equations expressed in Lambert W-functions. Low-affinity binding of thrombin on heparin, and high-affinity binding of prothrombin on phospholipid vesicles, were measured by ellipsometry and were best described by the Surfint and Unstir models, respectively.