FIG 1.

Schematic representation of the capture ELISAs developed and used in this work for Stx2 detection. (A) VHH-based capture ELISAs developed in this work for Stx2 detection using specific nanobodies. Purified VHHs fused to a histidine tag (VHH-6×His) were used as capture antibodies. As detection antibodies, three types of VHHs were used: VHHs fused to the HA tag and obtained from the periplasmic extracts (PE) enriched in the corresponding HA-VHH, a VHH fused to the 6×His and HA tags and purified by metal-chelate affinity chromatography (HA-VHH-6×His), and an in vitro biotinylated VHH (biotin-VHH-6×His). In the last case, detection was performed by either spectrophotometry or chemiluminescence. (B) Commercial capture ELISA. This ELISA is based on a pair of monoclonal antibodies directed to the A subunit of Stx1 and Stx2. TMB, 3,3′,5,5′-tetramethylbenzidine.