*2.2. Crystal Growth*

Chicken egg white lysozyme microcrystals smaller than 20 μm were used as testing samples. We used the controlled variable method to explore the crystallization conditions to grow microcrystals. For plate A (sitting-drop vapor-diffusion crystallization), the side of the centerline of plate A needs to be sealed with a Kapton membrane before the crystallization experiment, and then 0.8 μL of crystallization drops were added to each protein well and 8 μL of reservoir solution was added to each reservoir well. The lysozyme crystallization drops are prepared by dissolving 10 mg/mL of lysozyme protein in a reservoir solution. The reservoir solution is a solution with a concentration of 0.2 M citric acid and 0.2 M sodium acetate at a 1:1 ratio, 12% (w/v) NaCl, and then a mix 0.4 μL of a protein sample and 0.4 μL of a reservoir solution. Finally, the other side of plate A was sealed, lysozyme microcrystals were grown with the sitting-drop vapor-diffusion method, and microcrystals appeared after 6 h of incubation at 291 K. For plate B (hanging-drop vapor-diffusion method), the crystallization drops and reservoir solution used were the same as plate A. The side of the centerline of plate B also needs to be sealed with a Kapton membrane before the crystallization experiment, and then 0.8 μL of crystallization drops comprised of 0.4 μL of a protein sample and 0.4 μL of a reservoir solution were added to each large protein well and 0.4 μL of crystallization drops comprised 0.2 μL of a protein sample and 0.2 μL of a reservoir solution were added to each small protein well. The bottom of the crystallization plate was sealed with a Kapton membrane and 40 μL of reservoir solution was added to each reservoir well. Finally, plate B was assembled with the incubation chambers (Figure 1c,d) by covering or inserting, and lysozyme microcrystals were grown with the hanging-drop vapor-diffusion method. Microcrystals appeared after 6 h of incubation at 291 K.
