TITLE: Fluorescence Correlation Spectroscopy Studies Characterizing Diffusion and Photophysical Properties of Proteins

The primary focus of the research presented here is the characterization of diffusion using Fluorescence Correlation Spectroscopy (FCS). To understand the nature of the anomalous diffusion observed in living systems, we characterized diffusion in complex in vitro systems including the diffusion of proteins. random-coil polymers. or dyes in crowded random-coil polymer solutions and the diffusion of polymer beads in agarose gels. Anomalous diffusion is defined where the mean-square-displacement follows a power law in time, <r\t » OC la, with a;r 1. We observed that diffusion of proteins in dextran solutions is subdiffusive (a < 1) where a decreases with increasing dextran concentration and molecular weight until it reaches a limit value of a ~ 3/4. Because subdiffusion implies a length-scale dependent diffusion coefficient, observations were performed at multiple length-scales (0.2- 1.5 /-lm) which allow two complementary methods of determining a from the power law relationship between the length-scale and the diffusion time and from the width of the decay of correlation data at each length-scale. We report the first direct observations of subdiffusion using these two methods