Antibody specificity and cross-reactivity test. Serial dilutions of recombinant SARS-CoV-2 Nprotein(A), 3 positive and 2 negative human nasopharyngeal swab specimens (20 uL)(B)and different concentrations of gamma-irradiated SARS-CoV-2 (nCoV, B&C), SARS-COV (SARS) (C)and MERS (C) were lysed in Viral Lysis Buffer and blotted with rabbit monoclonal anti-Nprimary antibody (1:2,000). HRP-conjugated highly cross-adsorbed goat anti-rabbitsecondary antibody (Cat:# 202, 1:2,000) was applied. The blots were incubated using the PiQ™ ECL Substrate Kit and imaged using a chemiluminescence digital imager. Note that 1) the NP POSNo.3 swab had a very low viral load: and 2) There was no cross-reactivity of the antibody with SARS or MERS

Chemiluminescent ELISA using SARS-CoV-2. Different concentrations of gamma-irradiatedSARS-CoV-2 viruses were lysed in the Viral Lysis Buffer and coated (150 uL) onmicroplate wells. Rabbit monoclonal anti-N antibody ( 1:10,000) and HRP.conjugated highly cross-adsorbed goat anti-rabbit secondary antibody (Cat# 202. 1:20.000) were used todetect the SARS-CoV-2 N protein. PiOT ECL substrates were used to producechemiluminescent signals. RLU, relative light unit. ARLU= RLU of the well with the primary antibodyRLU of the corresponding well without the primary antibody, everything else being equal.

Chemiluminescent ELISA using recombinant SARS-CoV-2 spike receptor bindingdomain (S-RBD). Different concentrations of recombinant S-RBD (referred to as S1) were lysed in the Viral Lysis Buffer and coated on microplate wells.Rabbit monoclonal anti-S antibody (1:10,000) and HRP-conjugated highly crossadsorbed goat anti-rabbit secondary antibody (Cat# 202, 1:20,000) were used to detect SARS-CoV-2 S-RBD. RLU, relative light unit. ARLU = RLU of the well with the primary antibody .RLU of the corresponding well without the primary antibody, everything else being equal.