Crystallography on a chip - without the chip: sheet-on-sheet sandwich.

R Bruce Doak,Mario Hilpert,Ilme Schlichting,Thomas R M Barends,Miriam Stricker,Daehyun You,Christopher M Roome,Marco Kloos,Lutz Foucar,Robin L Owen,Marie Luise Grünbein,Kensuke Tono,Darren A Sherrell,Gabriela Nass Kovacs,Robert L Shoeman,Kiyoshi Ueda,Alexander Gorel

doi:10.1107/s2059798318011634

Abstract

Crystallography chips are fixed-target supports consisting of a film (for example Kapton) or wafer (for example silicon) that is processed using semiconductor-microfabrication techniques to yield an array of wells or through-holes in which single microcrystals can be lodged for raster-scan probing. Although relatively expensive to fabricate, chips offer an efficient means of high-throughput sample presentation for serial diffraction data collection at synchrotron or X-ray free-electron laser (XFEL) sources. Truly efficient loading of a chip (one microcrystal per well and no wastage during loading) is nonetheless challenging. The wells or holes must match the microcrystal size of interest, requiring that a large stock of chips be maintained. Raster scanning requires special mechanical drives to step the chip rapidly and with micrometre precision from well to well. Here, a `chip-less' adaptation is described that essentially eliminates the challenges of loading and precision scanning, albeit with increased, yet still relatively frugal, sample usage. The device consists simply of two sheets of Mylar with the crystal solution sandwiched between them. This sheet-on-sheet (SOS) sandwich structure has been employed for serial femtosecond crystallography data collection with micrometre-sized crystals at an XFEL. The approach is also well suited to time-resolved pump-probe experiments, in particular for long time delays. The SOS sandwich enables measurements under XFEL beam conditions that would damage conventional chips, as documented here. The SOS sheets hermetically seal the sample, avoiding desiccation of the sample provided that the X-ray beam does not puncture the sheets. This is the case with a synchrotron beam but not with an XFEL beam. In the latter case, desiccation, setting radially outwards from each punched hole, sets lower limits on the speed and line spacing of the raster scan. It is shown that these constraints are easily accommodated.

Highlights

Relatively expensive to fabricate, chips offer an efficient means of high-throughput sample presentation for serial diffraction data collection at synchrotron or X-ray freeelectron laser (XFEL) sources
The device consists of two sheets of Mylar with the crystal solution sandwiched between them. This sheet-on-sheet (SOS) sandwich structure has been employed for serial femtosecond crystallography data collection with micrometre-sized crystals at an XFEL
Serial femtosecond crystallography (SFX) at X-ray freeelectron lasers (XFELs) is a new and unique way to collect diffraction data such that the limitations of radiation damage imposed by conventional X-ray sources are largely alleviated

Summary

Introduction

Serial femtosecond crystallography (SFX) at X-ray freeelectron lasers (XFELs) is a new and unique way to collect diffraction data such that the limitations of radiation damage imposed by conventional X-ray sources are largely alleviated. For still longer time delays, microcrystal delivery by GDVN liquid-microjet injection becomes impractical owing to the limited length of the contiguous liquid jet (prior to Rayleigh breakup) and the minimum jet speed required for stable jetting: the crystals are carried out of the XFEL interaction zone before the arrival of the XFEL pulse One solution to this problem is to slow the jet speed by using viscous additives or media (Botha et al, 2015; Conrad et al, 2015; Sugahara et al, 2015, 2017; Kovacsovaet al., 2017). Provided that the crystals in the cells display sufficiently random orientations, the resulting SFX data collection can be highly efficient (Cohen et al, 2014; Hunter et al, 2014; Sherrell et al, 2015; Mueller et al, 2015) Chips introduce their own set of unique challenges. We characterized the performance of the SOS sandwich using SFX data collected at the SPring-8 Angstrom Compact free-electron LAser (SACLA) in Hyogo, Japan using 7.3 keV X-rays for SFX data collection and compared and contrasted its performance with that of the well established silicon chip (Mueller et al, 2015; Owen et al, 2017)

The silicon chip and the SOS sandwich

Sample loading of the chip and sandwich

Data collection and analysis

Results and discussion