Polyelectrolyte Surface Diffusion in a Nanoslit Geometry

Abstract

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 aminefunctionalized 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.

Non-Brownian Interfacial Diffusion: Flying, Hopping, and Crawling

“…For example, in analyzing trajectories of negatively charged HSA on charged surfaces, we found that the waiting-time distributions were well-described by power-law functions that broadened as the charge of the surface was made more positive (by deposition of charged organo-silane modifiers), corresponding to a systematic increase in the (negative) power-law exponent. 37,47 This trend reflected increasingly attractive electrostatic interactions. Related phenomena were associated with other types of intermolecular interactions, such as those between dextran and a temperatureresponsive poly(N-isopropylacrylamide) (PNIPAAM) polymer film (Figure 5a), where the dextran exhibited a broad distribution of waiting times at low temperature (where the PNIPAAM film comprised a hydrophilic brush) and a less broad distribution at slightly higher temperatures (where the PNIPAAM collapsed into a dense hydrophobic film), (Figure 5b).…”

Diffusion of Short Semiflexible DNA Polymer Chains in Strong and Moderate Confinement

“…Lenses and surfaces were prepared via solvent-assisted vapor deposition using a neutral oligoethylene glycol silane, methoxy­(triethyleneoxy)­propyl­trimethoxysilane (Gelest), as previously described to reduce nonspecific adsorption of the DNA samples. In addition, all DNA solutions contained 0.1 mg/mL concentration of BSA (Sigma-Aldrich), which had been previously filtered (Corning), to act as a site-blocking agent.…”

“…Single molecule tracking, height profile measurements, and object heights were determined as described previously . The coefficient of variation for confinement heights during a particular trajectory was <10%.…”

“…Single molecule tracking, height profile measurements, and object heights were determined as described previously. 33 The coefficient of variation for confinement heights during a particular trajectory was <10%. Before tracking analysis, movies were adjusted by using the histogram-matching photobleach correction in Fiji, after which an average image was taken and subtracted from each movie frame.…”

How stickiness can speed up diffusion in confined systems

“…This type of model was first proposed in the 90's when it was realized that the effective lateral dispersion of molecules adsorbed at a fluid-solid interface is significantly mod-ified by temporary excursions into the fluid [29]. The stochastic motion resulting from interplay of bulk and surface diffusion has recently been directly observed experimentally [30][31][32][33][34]. It is also known that surface mediated transport gives rise to non-trivial effects in the context of target search kinetics [35][36][37][38] and that in certain cases the search efficiency can be tuned via the parameters of the surface mediated diffusion model.…”