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
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.
Standard SARS-CoV-2 Proteins
A recombinant form of the target protein is often required for assay development. Sino Biological recommends the following reagents as the standard: