Dynamics of tracer particles in complex environments investigated by dual-focus fluorescence correlation spectroscopy

Soft matter materials are of great importance in everyday life, as not only biological composites but also many industrial products belong to said broad class. Often these materials consist of high molecular mass particles (e.g., polymers) suspended in low molecular weight solvents (e.g., water) and exhibit complex behavior at the mesoscopic scale. Therefore, a deeper understanding of the structure and dynamics in complex polymer and colloid fluids is essential for the development of new materials, reagents, and devices. Fluorescence-based techniques are widely used in polymer and colloid science. By covalent attachment or physical entrapment of fluorophores to polymers information on the dynamics and polarity of the labeled system and its environment can be obtained. Fluorescence correlation spectroscopy (FCS) is a very sensitive and selective technique; however many optical artifacts, especially emerging in complex environments, can significantly influence the precision of this method. Recently, dual-focus fluorescence correlation spectroscopy (2fFCS) has been developed as a powerful technical improvement of the standard FCS setup. This thesis shows how 2fFCS can be applied to monitor and quantify the dynamics of tracer particles in different complex environments, thereby demonstrating its high potential for solving various challenges in physical chemistry of polymers and colloids, and biology. Novel diblock glycopolymers which self-assemble into homogeneous spherical micellar structures in water are introduced in the first part of this thesis. These structures render surface-oriented sugar moieties for strong multivalent glycan-mediated lectin binding and are capable of solubilization and incorporation of hydrophobic molecules. Another example of self-assembly is electrostatically-driven complexation of polymeric components. The second part of this thesis considers the interaction between oppositely charged microgels and polyelectrolytes at different initial charge ratios and concentrations of a low molecular weight salt. The obtained results offer the possibility to construct promising stimuli-responsive uptake and release systems based on microgels hosting oppositely charged guests, where the ionic strength acts as a trigger. Furthermore, the effect of nanoscopic spatial inhomogeneities on the permeability of polymer gels is studied by measuring the diffusivity of nanoparticulate tracers within differently crosslinked local domains in microgel packings. The outcome of this work is that the sub-micrometer-scale tracer diffusivity is not affected by the gel-matrix crosslinking density in deswollen networks, and hence, neither by its spatial inhomogeneity. The last part of this thesis explores the unfolding of the amyloid beta peptide, whose aggregation plays a major role in the progression of Alzheimer's disease. The existence of a cooperative unfolding curve suggests the presence of residual structural elements with a low Gibbs free energy of unfolding