PEO-sheathed liquid jets increase sample delivery stability for serial femtosecond X-ray crystallography

Viscoelastic jets can be generated by the polyethylene oxide (PEO) sheathing of an aqueous solution using double-flow focusing nozzles (DFFNs) and represent an efficient method to deliver samples that are dispersed in low and medium-viscosity liquids for X-ray diffractive imaging experiments. Due to their micrometre diameter and millimetre length, such jets can be used for pump-probe serial femtosecond crystallography (SFX) in order to access a timescale of a few tens of microseconds. This range is in between the previously achievable ranges accessible at XFELs (picoseconds-to-microsecond time delays) and synchrotrons (a few hundred µs to millisecond delays), respectively. Here, we demonstrate their effectiveness to deliver protein microcrystals (lysozyme and photosystem II) in buffer compositions of various viscosities for SFX and explore capabilities of triple-flow focusing nozzles (TFFNs) that incorporate PEO-sheathing to control challenging-to-jet viscous buffers for time-resolved diffusive mixing experiments.