CPM Seminar

Diffusion of Eye-lens Proteins Measured Using Coherent X-ray Scattering

Larry Lurio

Northern Illinois University

Over the past decade, x-ray photon correlation spectroscopy (XPCS) has emerged as an important tool to characterize dynamics in soft matter. In this technique a sample is illuminated with a coherent x-ray beam and the resulting scattering pattern is modulated by a random speckle pattern. The speckle intensities vary in time as the sample undergoes thermal fluctuations yielding information about molecular scale dynamics. While this technique holds out promise for revealing molecular motion in biomaterials, it has been extremely difficulty to apply to these systems since they have relatively modest scattering cross sections and damage easily. I report here on the first measurements of protein diffusion using XPCS. Measurements were made on concentrated alpha-crystallin suspensions; a protein which plays a key role in maintaining lens transparency. These measurements are able to probe protein diffusion over length scales comparable to the protein diameter, which are particularly important in understanding the connection between protein interactions and diffusive properties. I will also discuss the extension of XPCS to even faster times via the new technique of speckle visibility spectroscopy.