SARS-CoV-2 Antigen Test

The ongoing COVID-19 pandemic has changed the way people live and work as no one would ever imagine. Millions around the globe caught the disease with no clear end in sight. Expanding diagnostic capacity has been a critical factor in the battle to control the spread of the virus. While traditional PCR-based test remains the golden standard, there is an increasing demand in other diagnostic methods that can allow quicker, easier, and more cost-effective tests. The antigen test is an alternative diagnostic method that relies on the immunodetection of the viral antigens in biological samples. The presence of the antigen will directly indicate that the tested individual carries the virus.

The two main antigens for coronavirus SARS-CoV-2 are the spike (S) protein and the nucleocapsid (N) protein. The nucleocapsid protein has emerged as a better target for diagnostic antigen tests because it's more conserved, and it's more abundant. The detection of the antigens can be done in many different ways, but all would require a pair of antibodies that can specifically recognize the target antigen with high sensitivity and specificity.

 

Antibody Pairs for SARS-CoV-2 N Protein and S Protein

Sino Biological has developed a large panel of antibodies against SARS-CoV-2 N protein and the S protein. Extensive testing was performed and we have identified three top pairs for each of the two targets. These pairs can be used to assemble detection assays for the corresponding antigen.

Antibodies Specific to SARS-CoV-2 Antigen

One of the main concerns for the antigen tests is whether the antibody pair also detects other circulating coronaviruses. To further validate the specificity, these antibodies were tested against a full panel of N proteins from the common coronaviruses. The result came back as all antibodies against the N proteins have no cross-reactivity in ELISA.

Cross-Reactivity Tests

It's essential to identify cross-reactivity issues early in assay development. The main concern for SARS-CoV-2 antigen detection is the cross-reactivity against other circulating common coronavirus types, including HCoV-HKU1, HCoV-OC43, HCoV-NL63, and HCoV-229E. Sino Biological developed a comprehensive panel of N and S proteins for these virus types:

Nucleocapsid Proteins

Type Cat# Description Expressed Host
HCoV-HKU1 40642-V07E Human Coronavirus HKU1 Nucleocapsid Protein (His Tag) E. coli
HCoV-OC43 40643-V07E Human Coronavirus OC43 Nucleocapsid Protein (His Tag) E. coli
HCoV-NL63 40641-V07E Human Coronavirus NL63 Nucleocapsid Protein (His Tag) E. coli
HCoV-229E 40640-V07E Human Coronavirus 229E Nucleocapsid Protein (His Tag) E. coli

Spike Proteins

Type Cat# Description Expressed Host
HCoV-HKU1 40021-V08H Human coronavirus HKU1 (isolate N1) Spike S1 Protein (His Tag) HEK293 Cells
HCoV-HKU1 40602-V08H Human coronavirus HKU1 (isolate N5) Spike S1 Protein (His Tag) HEK293 Cells
HCoV-HKU1 40606-V08B Human coronavirus HKU1 (isolate N5) Spike S1+S2 ECD Protein (His Tag) Insect Cells
HCoV-OC43 40607-V08B Human coronavirus OC43 Spike S1+S2 ECD Protein (His Tag) Insect Cells
HCoV-OC43 40607-V08H1 Human coronavirus OC43 Spike S1 Protein (His Tag) HEK293 Cells
HCoV-NL63 40600-V08H Human coronavirus NL63 Spike S1 Protein (His Tag) HEK293 Cells
HCoV-NL63 40604-V08B Human coronavirus NL63 Spike S1+S2 ECD Protein (His Tag) Insect Cells
HCoV-229E 40601-V08H Human coronavirus 229E Spike-S1 Protein (His Tag) HEK293 Cells
HCoV-229E 40605-V08B Human coronavirus 229E Spike S1+S2 ECD Protein (His Tag) Insect Cells
Novel Immunodiagnostics for COVID-19