Using low dose X-ray Speckle Visibility Spectroscopy to study dynamics of soft matter samples

TL;DR

This paper demonstrates that X-ray Speckle Visibility Spectroscopy (XSVS) can effectively study the dynamics of radiation-sensitive biological samples at ultra-low doses, revealing detailed microscopic behaviors with minimal radiation damage.

Contribution

The study introduces the application of XSVS at unprecedentedly low X-ray doses to analyze soft matter dynamics, enabling insights into radiation-sensitive samples with reduced damage.

Findings

Successfully tracked casein micelle dynamics in various conditions.

Observed deviations from Brownian motion in concentrated solutions.

Detected static speckle patterns in gelled acidic milk.

Abstract

We demonstrate the successful application of X-ray Speckle Visibility Spectroscopy (XSVS) experiments to study the dynamics of radiation sensitive, biological samples with unprecedentedly small X-ray doses of 45 Gy and below. Using XSVS, we track the dynamics of casein micelles in native, concentrated, and acidified solution conditions, while substantially reducing the deposited dose as compared to alternative techniques like sequential X-ray photon correlation spectroscopy (XPCS). The Brownian motion in a skim milk sample yields the hydrodynamic radius of the casein micelles while deviations from Brownian motion with a characteristic $q$-dependent diffusion coefficient $D(q)$ can be observed in more concentrated solution conditions. The low dose applied in our experiments allows the observation of static, frozen speckle patterns from gelled acidic milk. We show that the XSVS technique is especially suitable for tracking dynamics of radiation sensitive samples in combination with the improved coherent properties of new generation X-ray sources, emphasizing the great potential for further investigations of protein dynamics using fourth generation synchrotrons and free electron lasers.