Serial femtosecond crystallography (SFX) with X-ray free electron lasers (XFELs) has enabled crystal structure determination of reaction intermediates at ambient temperatures. Unlike traditional crystallography, where a single crystal is irradiated as it rotates, SFX usually involves the injection of a continuous stream of randomly oriented protein crystals in the path of the XFEL beam. Each crystal hit by the X-ray yields a diffraction snapshot, and thousands of these snapshots are merged to form a dataset. Although SFX has allowed the study of numerous protein structures not possible with standard crystallography at synchrotrons, the myriad of crystal suspensions for the many proteins of interest presents a technical challenge. At the European XFEL (EuXFEL), X-ray pulses are produced in 10-Hz bursts with MHz repetition rate within each burst, necessitating high-velocity jets to refresh crystal samples between pulses. Current sample delivery methods for protein crystals in viscous media extrude slowly and are therefore incompatible with the MHz pulses.
Researchers at Arizona State University have developed a sample delivery method that produces stable injection of a rather viscous crystal suspension at velocities compatible with the EuXFEL pulse structure. This is achieved by co-flowing an immiscible liquid using a 3D-printed device with a T-junction in close proximity to a gas dynamic virtual nozzle (GDVN). Pressures up to 1000 psi can be used which is required to drive a sample through more than a meter of small inner diameter capillaries to the co-flow device.
• Serial femtosecond crystallography (SFX) with X-ray free electron lasers (XFEL)
• Protein structure analysis
Benefits and Advantages
• Controlled injection results in reduced sample volume consumption
• Co-flow operation delivers a stable sample jet instead of dripping
• Tested at EuXFEL using photosystem II crystals