Sample delivery for structural biology at the European XFEL.

Serial femtosecond crystallography (SFX) at X-ray free electron lasers (XFELs) is a valuable technique for time-resolved structural studies on enzymes. This method allows for the collection of high-resolution datasets of protein structures at various time points during a reaction initiated by light or mixing. Experiments are performed under non-cryogenic conditions and allow the collection of radiation damage free structures. At the European XFEL (EuXFEL), SFX experiments are mainly performed with liquid jets produced by gas dynamic virtual nozzles (GDVNs) and less frequent with a high viscous extruder (HVE). In this chapter we describe these delivery methods, with the focus on GDVNs. Instrumentation, sample requirements, and preparation steps for SFX beamtimes are discussed. Other sample delivery methods available at the EuXFEL are briefly introduced at the end of this chapter.