Analysis of multi-hit crystals in serial synchrotron crystallography experiments using high-viscosity injectors

© 2021 by the authors. Licensee MDPI, Basel, Switzerland. Serial Synchrotron Crystallography (SSX) is rapidly emerging as a promising technique for collecting data for time-resolved structural studies or for performing room temperature microcrystallography measurements using micro-focused beamlines. SSX is often performed using high frame rate detectors in combination with continuous sample scanning or high-viscosity or liquid jet injectors. When performed using ultra-bright X-ray Free Electron Laser (XFEL) sources serial crystallography typically involves a process known as ’diffract-and-destroy’ where each crystal is measured just once before it is destroyed by the intense XFEL pulse. In SSX, however, particularly when using high-viscosity injectors (HVIs) such as Lipidico, the crystal can be intercepted multiple times by the X-ray beam prior to exiting the interaction region. This has a number of important consequences for SSX including whether these multiple-hits can be incorporated into the data analysis or whether they need to be excluded due to the potential impact of radiation damage. Here, we investigate the occurrence and characteristics of multiple hits on single crystals using SSX with lipidico. SSX data are collected from crystals as they tumble within a high viscous stream of silicone grease flowing through a micro-focused X-ray beam. We confirmed that, using the Eiger 16M, we are able to collect up to 42 frames of data from the same single crystal prior to it leaving the X-ray interaction region. The frequency and occurrence of multiple hits may be controlled by varying the sample flow rate and X-ray beam size. Calculations of the absorbed dose confirm that these crystals are likely to undergo radiation damage but that nonetheless incorporating multiple hits into damage-free data should lead to a significant reduction in the number of crystals required for structural analysis when compared to just looking at a single diffraction pattern from each crystal.