On correlated x-ray scattering : analysis of solution diffraction images using angular intensity correlations in both the hard matter and soft matter regimes
- Correlated X-ray scattering (CXS) is a novel X-ray technique that utilizes angular intensity correlations in solution scattering patterns in order to extract a three-dimensional correlation function, which depends solely on the molecular structure factor. We report here on two of the first CXS experiments involving three-dimensional solutions of many molecules, at wide scattering angles. The first was done at a synchrotron facility, where we measured CXS arising from silver nanoparticles (NPs) embedded in a glycerol and agarose buffer. Crucially, a nitrogen jet was used to promote NP immobilization during each exposure. By averaging angular intensity correlations from on the order of 10 000 exposures, we were able to recover a CXS function that agreed well with atomic models. The second experiment was done at an X-ray free electron laser (XFEL) facility, where we measured CXS arising from gold NPs. There, we acquired on the order to 100 000 snapshots of gold NPs in solution, and were able to recover a CXS function indicating that the average NP was twinned, information that was previously unknown to us. Further, we are able to distinguish two populations of NPs present: small, twinned NPs and large, non-twinned NPs. Because CXS signal-to-noise is very low on a per-shot basis, great care must taken in order to minimize artifactual correlations that might arise during the image analysis. Artifactual correlations are a potential consequence of many experimental aspects, including sample-inhomogeneity, detector shadows, detector gain anisotropies, and beam polarization. In order to suppress these artifacts, we paired exposures that were similar in their anisotropy, and correlated their difference. By working with the difference intensities, we were able to significantly improve our signal-to-noise, and ultimately show that CXS is a viable way to extract atomic-level information from solution scattering measurements. As the technique continues to be explored, and data analysis methods are refined, CXS could reveal new pathways for studying ensemble statistics of small bio-molecules in solution, complimenting current state-of-the-art structural techniques, e.g. single particle imaging, cryo-electron microscopy, and serial femtosecond X-ray crystallography.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Mendez, Derek Anthony, Jr
|Stanford University, Department of Applied Physics.
|Brünger, Axel T
|Brünger, Axel T
|Statement of responsibility
|Derek Anthony Mendez Jr.
|Submitted to the Department of Applied Physics.
|Thesis (Ph.D.)--Stanford University, 2017.
- © 2017 by Derek Anthony Mendez
- This work is licensed under a Creative Commons Attribution 3.0 Unported license (CC BY).
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