Effective Surface Diffusion of a Polyelectrolyte within Nanoscale Confinement

Intermittent (“hopping”) surface diffusion of poly-L-lysine in a nanoslit was studied using single-molecule tracking microscopy. Three surface chemistries were employed to understand the interplay of long-range electrostatic attraction and short-range interactions: an amine-functionalized silica surface, an oligo(ethylene oxide) (OEG) modified surface, and an equally mixed surface. Diffusion increased rapidly with slit height until saturating for values <30 nm. While diffusion at a semi-infinite interface was significantly faster for OEG surfaces, the diffusion increased most rapidly with slit height for amine-functionalized surfaces, resulting in surface diffusion that was virtually independent of surface chemistry in gaps <15nm. Kinetic Monte Carlo simulations, using parameters obtained empirically from diffusion at a single interface, suggested that these trends were primarily due to strong H-bonding interactions between PLL and amine surface ligands, which led to increased rates of re-adsorption after hops and longer waiting periods between flights, and that long-range electrostatic attraction had a minor influence.