Diffusion of fluorescent molecules in micro- and nanostructured environments

Abstract

The thesis deals with phenomena of molecular diffusion in liquid environments. The examination of diffusing molecules provides information about the molecules themselves, and also about the structure of the surrounding media. This work deals with diffusion phenomena on length scales below 100 μm. The liquid phase consists of water or water/surfactant emulsions. The microstructures are fluidic channels etched in wafers of crystalline silicon. In these channels, diffusion-limited mixing at a liquid boundary is examined. These experiments took place in a stationary liquid flow. Environments on the nanoscale are made of binary liquids forming supramolecular orders by self-assembly. From these structures, the micellar and the lamellar structure are examined in particular. The focus is on the influence of cholesterol on the mobility of probe molecules in the lamellar phase. The main experimental method is Fluorescence Correlation Spectroscopy (FCS). Additionally, fundamentals for the tracking of single molecules are established by analyzing video recordings of fluorescing particles. The thesis provides advanced insight into the nature of molecular motion in nearly ideal systems. Further conclusions for investigations in natural environments, as they exist in eukaryotic cells, can be drawn from the experiments.