2.10. Plaque assay

For HSV-1 and VSV, the viral titer was determined by the plaque assay as described previously ^[29]. Briefly, approximately 1.5 × 10⁵ Vero E6 or Huh7 cells were seeded into each well of 24-well plates and maintained in the complete growth medium. Before infection, the cell-culture mediums were removed. After adsorption for 1 h, the inoculums were removed, and the cells were overlaid with 1000 µl plaque medium (containing 2% carboxymethylcellulose, CMC, and 2% FBS). After 48 h of incubation, cells were fixed with the fixed buffer as described previously.

For SARS-CoV-2, approximately 1.0 × 10⁴ ffu viruses were treated in the illumination device for 30 min. And then each treated virus was added into each well. After adsorption for 1 h, the inoculums were removed, and the cells were overlaid with 1000 µl plaque medium. After 48 h of incubation, cells were fixed with the fixed buffer. After staining with1% Crystal Violet, the numbers of plaques were counted.