①Measured by its binding ability in a functional ELISA. Immobilized SARS-CoV-2-S1-RBD at 2 μg/ml can bind human ACE2 , the EC50 is 6.597-8.187 ng/ml. ②Measured by its binding ability in a functional ELISA. Immobilized SARS-CoV-2-S1-RBD at 2 μg/ml can bind Biotin-S Antibody , the EC50 is 21.54-26.77 ng/ml.