Fig. 9

Behavior of the ACE2 binding activity of samples mRBD and dRBD during a stress stability at 37 °C. Biological activity measured as the binding of the monomeric and dimeric RBD protein to the ACE2 receptor by a sandwich ELISA. A Bar graph of the absorbance at 490 nm of the monomeric RBD (mRBD) samples keeping at 37 °C at different times. B Bar graph of the absorbance at 490 nm of the dimeric RBD (dRBD) samples keeping at 37 °C at different times