Polyelectrolyte Surface Diffusion in a Nanoslit Geometry

The surface diffusion of poly-l-lysine (PLL) in a planar
nanoslit was studied using convex lens-induced confinement (CLiC)
single-molecule tracking microscopy. Three surface chemistries were
employed to understand the interplay of electrostatic and short-range
interactions: an amine-functionalized silica surface, an oligo­(ethylene
oxide) (OEG)-modified surface, and a 1:1 mixture of the two ligands.
Effective surface diffusion coefficients increased rapidly with slit
height until saturating for slit heights <30 nm. While diffusion
at a semi-infinite interface was significantly faster for OEG surfaces,
the diffusion coefficient increased most rapidly with slit height
for amine-functionalized surfaces, resulting in surface diffusion
within very thin slits being nearly independent of surface chemistry.
Intermittent random walks were simulated within a planar slit geometry,
using experimentally measured parameters obtained from diffusion at
a single interface to account for the characteristic short-range interactions
between PLL and each surface chemistry, and were in good agreement
with experimental measurements.