Single-molecule study of the synergistic effects of positive charges and Dopa for wet adhesion

Using AFM based single-molecule force spectroscopy, we studied the synergy between Dopa and lysine for wet adhesion on titania (TiO₂) and mica surfaces. We found that the binding forces for lysine-Dopa dipeptides are significantly higher when the positive charge of lysine is unprotected on both surfaces. However, such a synergistic effect is absent when the sequence is reversed. We attribute such differential synergistic effects to their distinct structure for load distribution within the molecules, which may represent a general principle for synergistic strong adhesion.