Figure 1.

The two non-overlapping epitopes used for the ELISA. In yellow space fill is a nanobody that recognizes the ACE2 RBD epitope [13,14] known as cluster 2 [15] (group 1 [18]) epitope and in blue a second nanobody [14] which recognizes a different RBD epitope, first described in the CR3022 structure [16,17], known as cluster 1 [15] (group 4 [18]) epitope.