Cat # 4355S, RRID:AB_2797606 Anti-His-HRP Genscript Cat # A00612, RRID:AB_915573 Avidin-HRP) Sino Biologicals Cat # 40589-V08B1 SARS-CoV-2 spike protein (ECD, His & Flag Tag) GenScript Cat extracellular domain purchased from Sino Biological and Genscript.