Gas Dynamic Virtual Nozzles
Gas Dynamic Virtual Nozzles (GDVN), injectors producing steady liquid microjet, are the standard device for Serial Femtosecond Crystallography (SFX) experiments.
Steady jetting is obtained by utilizing a flow-focusing configuration, consisting of a sample feeding capillary positioned in front of a gas aperture ice. The outer sheath gas, typically helium, accelerates the sample meniscus into a smaller liquid jet diameter than that of a Rayleigh jet from the sample capillary. The flow-focusing and accelerating effect in the liquid jet is achieved due to the presence of the pressure gradient induced by the surrounding gas stream. The gas focusing or “lens” effect is created by the properly shaped converging gas aperture.
Fig 1. GDVN schematic. Sierra et al.
GDVNs generate a liquid jet of micron-scale 1microns diameter, with a jet 10-100 m/s, and typic a typical flow rate of 10-100 A small and steady jet can exist over a short distance, typically 100-500 microns, and eventually breaks up into droplets due to Rayleigh-Plateau instability.
GDVN jets can be used at atmospheric pressure as well as in a vacuum environment. Typically, GDVNs are used in Serial Femtosecond Crystallography (SFX) experiments and in Wide/Small Angle Scattering (WAXS/SAXS) experiments. Flow rates and jet speeds can be optimized in a wide range in accordance with the experiment parameters such as beam diameter and X-ray pulse repetition rate.
GDVNs are also widely used in time-resolved structural biology experiments. To improve and extend the capability of classic GDVN for time-resolved crystallography application, different types of mixing devices and Double Flow Focusing Nozzles (DFFN) were developed and successfully used in 2021.
|Sample Flow Rate||20-100 µL/min||1-50 µL/min|
|Substrate Flow Rate||-||10-100 µL/min|
|Jet Speed||10-100 m/s||10-100 m/s|
|Jet Structure/Diameter||Cylindrical jet||Coaxial cylindrical jet|
Currently, LCLS uses 3D printed GDVNs, DFFNs, and mixers. Glass nozzles and Chips are available for specific experimental conditions as well.
Pros and Cons of Gas Dynamic Virtual Nozzles
|Nozzle Type||Jet Features||Sample Properties||Pros||Cons|
|GDVN||Cylindrical jet, 20-100 µL/min flow rate||Low viscosity liquid||
|Mixer plus GDVN||Cylindrical jet||Two low miscible liquids||
|DFFN||Coaxial cylindrical jet||Two immiscible (DFFN) or miscible (Mix-and-inject) liquids||
|Chip nozzles, DFFN||Cylindrical or sheet jet||Not available for crystallography||