Use of continuous sample translation to reduce radiation damage for XPCS studies of protein diffusion.

Laurence B Lurio,Suresh Narayanan,Qingteng Zhang,Eric M Dufresne,George M Thurston

doi:10.1107/s1600577521000035

Abstract

An experimental setup to measure X-ray photon correlation spectroscopy during continuous sample translation is presented and its effectiveness as a means to avoid sample damage in dynamics studies of protein diffusion is evaluated. X-ray damage from focused coherent synchrotron radiation remains below tolerable levels as long as the sample is translated through the beam sufficiently quickly. Here it is shown that it is possible to separate sample dynamics from the effects associated with the transit of the sample through the beam. By varying the sample translation rate, the damage threshold level, Dthresh= 1.8 kGy, for when beam damage begins to modify the dynamics under the conditions used, is also determined. Signal-to-noise ratios, Rsn ≥ 20, are obtained down to the shortest delay times of 20 µs. The applicability of this method of data collection to the next generation of multi-bend achromat synchrotron sources is discussed and it is shown that sub-microsecond dynamics should be obtainable on protein samples.

Highlights

X-ray photon correlation spectroscopy (XPCS) provides a unique window on molecular scale dynamics in materials, currently with a sensitivity to timescales from milliseconds to seconds (Sutton, 2008; Grubel et al, 2008; Leheny, 2012; Sinha et al, 2014; Sandy et al, 2018)
XPCS requires a high-intensity beam and measurements of dynamics are sensitive to both radiation-induced structural changes as well as other factors such as cross linking or ionization which might modify dynamics without obvious signatures in the static structure
The effect of sample transit through the focus of a Gaussian beam has been derived in the context of dynamic light scattering (Chowdhury et al, 1984; Taylor & Sorensen, 1986)

Summary

Introduction

X-ray photon correlation spectroscopy (XPCS) provides a unique window on molecular scale dynamics in materials, currently with a sensitivity to timescales from milliseconds to seconds (Sutton, 2008; Grubel et al, 2008; Leheny, 2012; Sinha et al, 2014; Sandy et al, 2018). A new generation of multi-bend achromat (MBA) synchrotron sources are becoming available, such as ESRF-EBS, MAX IV, PETRA IV and the APS-U. These will provide high brightness and nearly diffractionlimited X-ray beams which should enable XPCS measurements of molecular scale diffusion with sub-microsecond time resolution. Such machines could enable studies of biomaterials at physiologically relevant timescales, but X-ray induced damage remains a concern.

Results

Discussion

Conclusion