Fig. 2.

Schematic depict of the principles of the neutralizing antibody detection by microfluidic diffusional sizing. A When the labeled ACE2 is mixed with the spike trimer, the two binding partners form a complex that diffuses relative slower than the ACE2 alone. That results in an increase of the R_h. B When the labeled ACE2 is mixed with spike trimer pre-incubated with the neutralizing antibody, the spike trimer can no longer bind to the labeled ACE2 as it is blocked by the antibody. Therefore, the measured R_h will be equivalent to the R_h of the labeled ACE2 alone.