Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Daniel K. Schwartz

Second Advisor

Theodore W. Randolph

Third Advisor

Robert H. Davis

Fourth Advisor

Andrew P. Goodwin

Fifth Advisor

Joseph J. Falke

Abstract

The overall objective of the work was to develop and apply novel analytical techniques for the characterization of heterogeneous dynamics in confined environments. In this thesis, several different scenarios were explored involving heterogeneous dynamics of molecules or particles that are relevant to specific applications. In particular, total internal reflection fluorescence microscopy (TIRFM) was employed, enabling single-molecule imaging and tracking, to examine the adsorption and retention of protein molecules on a variety of model surfaces during site-blocking processes. By constructing super-resolution maps of the model surfaces, surface heterogeneity (induced by anomalous strong adsorption sites) was quantified as a function of protein surface coverage. Intermolecular Förster resonance energy transfer (FRET) was applied for the direct detection of potential protein-protein associations on the model surfaces. Again using TIRFM, the dynamics of cadherin ectodomains were investigated on supported lipid bilayers. Cadherins are a type of transmembrane proteins whose structures are highly determined by Ca2+ concentration. Single-molecule tracking technique allowed the observation of heterogeneous dynamics of individual cadherin ectodomains at different Ca2+ levels while they were associating with lipids. By performing careful statistical analyses on cadherin diffusive behaviors, the presence of multiple modes was resolved within individual trajectories, providing detailed information about the interplay between the diffusion and conformation of cadherin at the molecular level. The other two projects described in this thesis provided insights into heterogeneous transport of nanoparticles in filtration processes. Specifically, an innovative nanoparticle tracking technique was developed, which enabled real-time imaging of nanoparticles while they were flowing through polymer filtration membranes and the characterization of membrane functional properties experienced by nanoparticles under different operating conditions. The functional tortuosity and particle retention in membrane, reflecting spatial heterogeneity and temporal heterogeneity in particle transport, were highly dependent on flow rate and tracer particle size and were correlated with each other. Additionally, systematic studies were performed to characterize membrane fouling mechanisms. Specifically, the evolution of effective flux, particle velocity and pathway tortuosity during fouling processes were measured in two different microfiltration membranes under “sticking” and “reduced-sticking” conditions, respectively. The single-particle tracking approach provided direct evidence for distinct fouling mechanisms, and the obtained comprehensive information can advance our understanding in complex mass transport and assist the design and optimization of separation processes.

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