Fig. 2 |. SFX sample delivery methods.
a | Gas dynamic virtual nozzle (GDVN)64. A suspension of crystal-containing liquid is pumped through an inner capillary, surrounded by an outer capillary through which a gas flows (dashed arrows). At the end of the GDVN, the outer capillary constricts to narrow the gas stream, accelerating both gas- and liquid. The liquid stream is focused into a narrow jet that breaks up into droplets. b | High viscosity extrusion (HVE) injector. Crystals are dispersed in a highly viscous medium and slowly extruded into a stream. A gas sheath prevents the stream from curling back onto itself. c | Microfluidic Electrokinetic Sample Holder (MESH)224,225. A high voltage (several kV) stretches a thin, slow-flowing stream of crystal-containing liquid between two electrodes. d | Serial Femtosecond Rotation crystallography (SF-ROX). A goniometer-mounted large crystal is translated and rotated between XFEL exposures. e | Drop-on-demand (DoD)83. Droplets of a crystal suspension are generated with, for example, a piezoelectric device. The droplet can be synchronized with and intersected by the XFEL pulse in free fall83, immersed in an oil stream85, or as shown in panel d, be deposited onto a tape and moved through the XFEL beam, Drop-on-Tape35 (DoT). f | Solid support methods. Crystals are deposited onto an X-ray transparent substrate, often referred to as a fixed target or chip, and scanned through the beam. Both unpatterned chips, on which crystals will assume random positions, and patterned chips (inset), which have wells for crystal location, are used.