Fig 1: Binder pair screening in human serum and patient samples (PS 1–18).a Molecular modeling of the distances between N-terminus of ACE2 to the N-terminus of RBD is ~60 Å and to the C-terminus is ~53 Å (PDB ID: 6M0J). As such, luciferase fragments can be fused at either terminus of RBD and N-terminus of ACE2. b (S)RBD-ß9 and ß10-ACE2 binder pair was screened with increasing concentrations of neutralizing Ab (NAb, Sino Biological 40592-MM57) in human serum. c Using (S)RBD-ß9 and ß10-ACE2 binder pair, the signal between 0 µg/mL of NAb (darker color) vs. 100 µg/mL of NAb (lighter color adjacent bar) shows a 10-fold decrease upon neutralization. d Testing 18 patient plasma samples: (S)RBD-ß9 and ß10-ACE2 were mixed directly with plasma samples, followed by the addition of the detection solution (?11S and substrate). Samples 16, 17, and 18 (indicated by ‡ above bar) are known to be convalescent whereas other samples are from ICU patients with unknown antibody presence/levels. Source data are provided as a Source data file.