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The X-ray Speckle Visibility Spectroscopy and the Approach to Protein Dynamics

NST Nanoscience Seminar
Luxi Li, Brookhaven National Laboratory
August 19, 2013 11:00AM to 12:00PM
Building 440, Room A105-106
The dynamics of the meso-scale soft matter material becomes popular in the pastdecay. The collective motions of colloids and polymers have been studied by the X-ray Photon Correlation Spectroscopy (XPCS). However, the instrumental limit, such as the readout rate of the area detectors, and the high risk of the sample radiation damage are the main obstacles for XPCS method. In this work, I’m going to introduce a novel variation of XPCS, namely the X-ray Speckle Visibility Spectroscopy (XSVS). XSVS method is capable of studying the sample motions one order of magnitude faster than XPCS does under the same experimental condition. In addition XSVS is considered as a single-shot experiment.

The coherent X-ray scattering patterns taken with different acquisition times were analyzed by the pixel photon count statistics. The acquisition time dependent speckle contrast was fit to extract the characteristic time of the sample motion. The PMMA suspension in decalin was studied by XSVS as an example ofthis new method. Protein function is related to the stochastic motions of the protein molecules, especially the collective motion in the meso-scale. In macromolecular diffraction, the diffuse scattering around the bragg peaks results from the protein collective motions, such as domain fluctuations. We performed XSVS experiment on Concanavalin A (ConA) crystals. The diffuse component from the ConA diffraction pattern was analyzed. The preliminary results will be presented in this talk.