Serial femtosecond crystallography based on X-ray free-electron laser sources (X-FELs) provides new opportunities for structural sciences, in particular in the view of time-resolved investigations of dynamic processes. Even though every ultrafast shot of the very intense, coherent laser employed destroys the sample due to Coulomb explosion, X-ray diffraction data can be collected in the so-called 'diffract-before-destroy' regime.
Our aim: To improve sample preparation methods for X-FEL-based protein nano-crystallography by the development of fixed-target supports optimized for protein crystal preparation, to adapt the required liquid handling system to minimize sample consumption, and to perform pump-probe experiments on the solid supports.
The diffraction yield from both 2D and 3D protein nanocrystals is too low to allow the use of synchrotron radiation. X-FELs provide an alternative.
High efficiency measurements at X-FELs require high density and very well ordered deposition of the biological material – usually 2D or 3D crystals of proteins – on a solid substrate, which is scanned through the beam. This approach results in much higher hit rates and much lower sample consumption than the commonly used liquid jets.
Well-established microfabrication technology based on materials like silicon and silicon nitride makes it possible to create an ultrathin, low-background sample packaging. These fixed-target solid supports protect the loaded crystals from dehydration, and allow measurements to be made at room temperature, i.e., the structure of macromolecules can be determined in a close-to-natural environment at high resolution.
Further development towards even more highly X-ray transparent, less fragile, easy to mass-fabricate devices is required to improve data quality and allow cost-efficient high-throughput measurements at FELs in the future.