High-viscosity sample-injection device for serial femtosecond crystallography at atmospheric pressure

A sample-injection device has been developed at SPring-8 Angstrom Compact Free-Electron Laser (SACLA) for serial femtosecond crystallography (SFX) at atmospheric pressure. Microcrystals embedded in a highly viscous carrier are stably delivered from a capillary nozzle with the aid of a coaxial gas flow and a suction device. The cartridge-type sample reservoir is easily replaceable and facilitates sample reloading or exchange. The reservoir is positioned in a cooling jacket with a temperature-regulated water flow, which is useful to prevent drastic changes in the sample temperature during data collection. This work demonstrates that the injector successfully worked in SFX of the human A_2A adenosine receptor complexed with an antagonist, ZM241385, in lipidic cubic phase and for hen egg-white lysozyme microcrystals in a grease carrier. The injection device has also been applied to many kinds of proteins, not only for static structural analyses but also for dynamics studies using pump-probe techniques.