## 4 Recent Progress in Beamlines
### Noble Sample Delivery System Developed for Time-Resolved SFX  
The sample delivery instrument is one of the major components to perform serial femtosecond crystallography (SFX) at XFEL facilities. The instrument supports the experimental scheme of \"diffract-before-destruct\" by continuously supplying fresh microcrystals to the X-ray interaction point. In particular, since protein crystals are quite sensitive to the sample environment (humidity, temperature, etc. ), the sample delivery technique should  
Figure 8: XAS static spectrum (up) and transient absorption spectrum (down) at 10 ps and experimental (black) and fitted (red) kinetic spectrum (middle) of [Ru(bpy)\({}_{3}\)]\({}^{2+}\) complex at 2.844 keV. provide a proper sample environment to keep the protein crystals in a stable condition during the delivery process. So far, many attempts have been made to develop sample delivery instruments, such as the gas dynamic virtual nozzle (GDVN) [48; 49], electrospinning [50], lipidic cubic phase injector [51], acoustic injector [52], viscous medium extruder [21; 53; 54; 55], goniometer-based scanning [56], and micro tubing [26]. Here, we developed a microliter volume (MLV) syringe injector driven by a high-performance liquid chromatography (HPLC) pump. Many crystallization processes of membrane proteins with LCP typically use MLV syringes. In addition, to reduce sample consumption through sample injection, soluble microcrystals are uniformly mixed with a highly viscous medium using MLV syringes. This novel instrument makes it possible to directly use the syringe itself as a sample injector, which helps to increase experiment efficiency through a simpler preparation procedure for sample injection. Figure 9 shows a photo of the injector equipment assembly. It has a plunger fine control unit (PFCU), MLV syringe, and needle. The PFCU is composed of an SUS cylinder with a single channel at the center, a water plunger made of Teflon, and a PEEK cap that closes one side of the SUS cylinder with a 10-32 tap. The internal dimension of the cylinder for water flow is 5 mm in diameter and 102 mm in length when the water plunger is inserted in the channel. This length can cover the whole plunger travel length of most MLV syringes. To manipulate the plunger position, the syringe plunger should be inserted into the PFCU until it reaches one end of the Teflon water plunger. The syringe plunger plate was modified to an SUS cylinder with 4.8 mm in diameter and 9.0 mm in height. To perform crystallography experiments, the viscous medium mixed with microcrystals is filled inside of a gastight Hamilton syringe (1700 series, volume: 100 \(\upmu\)L). The loaded sample can be extruded through a syringe needle via fine control of the plunger. To control the sample flow rate exactly, the PFCU is driven by the HPLC pump. The operational scheme is shown in Figure 9. The upper PEEK cap serves as a connection point with an HPLC pump through a PEEK tubing (OD: 1/16 inch). The HPLC pump (LC-20 AD, Shimadzu) provides water to transmit proper pressure to the syringe flange for extrusion of the sample. The pump provides the maximal pressure of 40 MPa, with flow rates between 0.0001 and 10.00 mL/min. In addition, it is quite advantageous to deliver samples in an isocratic condition. The viscous sample is extruded to the X-ray interaction point through a 22s-gauge Hamilton SUS needle (ID: \(\sim\)150 \(\upmu\)m). The MLV syringe injector is designed to be operated inside of the MICOSS, which is an SFX dedicated sample chamber established at the PAL-XFEL [21]. Figure 10a shows the installation photo of the injector. The unique feature is the simultaneous application of multiple optical laser pumps, which is feasible for the time-resolved study of macro  
Figure 9: Photo of MLV syringe injector assembly and schematic drawing of the injector operation. molecules. Owing to the transparent glass barrel of the Hamilton syringe, an optical laser beam can penetrate into the syringe and illuminate the samples directly.