Three-Dimensional Tracking of Interfacial Hopping Diffusion

Theoretical predictions have suggested that molecular motion at interfaces—which influences processes including heterogeneous catalysis, (bio)chemical sensing, lubrication and adhesion, and nanomaterial self-assembly—may be dominated by hypothetical "hops" through the adjacent liquid phase, where a diffusing molecule readsorbs after a given hop according to a probabilistic "sticking coefficient." Here, we use three-dimensional (3D) single-molecule tracking to explicitly visualize this process for human serum albumin at solid-liquid interfaces that exert varying electrostatic interactions on the biomacromolecule. Following desorption from the interface, a molecule experiences multiple unproductive surface encounters before readsorption. An average of approximately seven surface collisions is required for the repulsive surfaces, decreasing to approximately two and a half for surfaces that are more attractive. The hops themselves are also influenced by long-range interactions, with increased electrostatic repulsion causing hops of longer duration and distance. These findings explicitly demonstrate that interfacial diffusion is dominated by biased 3D Brownian motion involving bulk-surface coupling and that it can be controlled by influencing short- and long-range adsorbate-surface interactions.Received 13 September 2017DOI:https://doi.org/10.1103/PhysRevLett.119.268001© 2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAdsorptionBrownian motionDesorptionRandom walksSurface & interfacial phenomenaSurface diffusionTransport phenomenaPhysical SystemsCharged polymersLiquid-solid interfacesSingle polymer chainsTechniquesFluorescence spectroscopyLangevin equationNon-Markovian processesSingle molecule techniquesPolymers & Soft Matter