Purification of Nb3 conjugating with biotin and detection of Nb1 coupling with HRP. (A) The Nb3 conjugated with biotin was purified on a streptavidin-containing column. (B) Analysis of the Nb1 coupled with HRP by ELISA. H3N2 antigen was coated onto the plate directly. Nb1, coupled with HRP, was used as a detector. After stopping the reaction, the readings were measured at 450 nm.