Overview of Sample Delivery Methods for Serial Crystallography / 生物化学与生物物理进展

ABSTRACT

The sample delivery method is one of the key steps in implementing serial femtosecond crystallography research using X-ray free-electron lasers. Serial femtosecond crystallography can effectively capture the ultrafast dynamic processes of biological molecules, such as protein conformational changes and intermediate states in chemical reactions. It is of great significance for scientists to better understand the structure and function of biological molecules, reveal the mechanisms of life activities, and provide important technical means for drug development and biotechnology. When conducting experiments at X-ray free-electron laser beamline station, it is crucial to transport the samples to the region where it interacts with the free-electron laser pulses. The choice of suitable sample delivery method plays a decisive role in the sample consumption and experimental efficiency, and it is also an important factor for the success or failure of the experiment. This article reviews the latest research progress and future development directions of sample delivery methods in serial crystallography. It also introduces commonly used sample delivery methods and their applicable ranges, aiming to provide reference and guidance for scientists engaged in serial crystallography research. The sample transport methods of free electron lasers mainly include liquid injection and fixed target sample transport. The liquid injection method is achieved through various liquid sample injectors. The aqueous solution is driven by a peristaltic pump on high performance liquid chromatography (HPLC) into a sample storage, and the aqueous solution pushes the piston in the sample storage to extrude the sample solution into the sample transport pipeline, and finally sprays it out through the nozzle to reach the XFEL interaction region. For micro-nano crystals,3 preparation methods are introduced, including free interface diffusion method, seeding method, and batch crystallization, and characterization methods are also introduced. For the requirements of high sample transmission efficiency and low sample consumption, a gas-based liquid flow transport method is introduced, which is based on the principle of focusing the sample jet by coaxial gas to form a jet with a small diameter and fast flow rate. At the same time, the extended double flow focusing nozzle and mixed injection nozzle are briefly described. For samples in viscous media, a high viscosity liquid injection device is introduced, and the advantages and disadvantages of different media are explained and exemplified. In addition, the principle and example of electrostatic spinning injector and piezoelectric driven droplet injection technology applied to low-velocity serial crystallography experiments are also introduced. For the above liquid injection methods, a characterization method using a coaxial microscope or side-view microscope to measure the diameter and stable length of the liquid flow is introduced. Compared with the liquid injection method, the fixed target method is to fix the crystal on a support chip with a periodic array structure, and collect data through scanning. The working principle, sample environment, support materials, etc. of the fixed target method are briefly introduced in the article. With the advancement and development of technologies such as free electron lasers and detectors, various sampling methods for serial crystallography are constantly being innovated and optimized. By selecting appropriate sample delivery methods, it will be possible to improve experimental efficiency, reduce sample consumption, and open up new possibilities for researchers in the field of structural biology of biomacromolecules.