High Sensitivity Assays for IgG, IgM, IgA to the N/S-Proteins

An indirect Enzyme-Linked Immunosorbent Assay (ELISA) is a common biochemical technique that is most suitable for determining total antibody concentrations in a sample. This method is commonly utilized to diagnose infection and to quantify antibodies against the invading antigen. In this method, a sample containing the primary antibody is incubated with an antigen-coated plate. Next, a biotin-labeled anti-human detection antibody that recognizes the primary antibody is added. An HRP-conjugated secondary antibody is then added, and when combined with a substrate, produces a signal amplification.

How indirect ELISA works

Current testing for the SARS-CoV-2 virus is limited, and compared to RT-qPCR, ELISA is a less complex procedure that uses more affordable and available equipment. Similarly, antigens and antibodies are considerably more stable than RNA, which reduces the potential of false-negative results. The ability to collect samples from many places in the body (and not restricted to nasal swabs) improves testing accuracy as well. Current serology measurements rely entirely on a host’s antibody response to the virus rather than detecting the virus itself. Indirect ELISA has been used to 1) diagnose patients who are more than 1 week post symptom onset, 2) determine potential immunity and risk of infection, 3) advance contact tracing, and 4) understand the extent of COVID19 spread and immunity in communities through epidemiological studies that are particularly important for fighting COVID-19 while minimizing economic impact.

Should I use the IgG, IgM, or IgA kit?

  • IgG is the most abundant antibody isotype (~70 75%) in the blood. IgG is predominantly responsible for long term immunity after infection.
  • IgM accounts for ~10% of antibodies in the blood and is produced first in response to acute infection.
  • IgA accounts for another ~10% of blood antibodies and is primarily responsible for protecting mucosal surfaces, which is why it could be especially important in COVID19. It has also been linked to disease severity. Testing for all three antibodies has improved sensitivity over any single antibody testing.


RayBiotech provides over 100 different indirect ELISAs for the various different protein mutations associated with each variant of SARS-CoV-2.

Sandwich-based ELISA for Antigen Detection

Need antigen detection as well? Try our Sandwich-based ELISA. Sandwich-based ELISA measuring viral antigens could be an alternative to RT-qPCR to detect current infections.

Catalog # Antigen Detected Sample Types Sensitivity Quantitative / Semi-Quantitative
ELV-COVID19N N protein Serum, Plasma, Cell Culture Supernatants, Nasopharyngeal swab 0.07 ng/mL Quantitative
ELV-COVID19S1 S-Protein (S1RBD) Serum, Cell Culture Supernatants 4.5 pg/ml Quantitative
ELH-ACE2 ACE-2 Serum, Plasma, Cell Culture Supernatants, Lysates 0.025 ng/ml Quantitative
ELH-NRP1 Neuropilin-1     Quantitative


  • Have these kits been used with real patient samples?
  • Do you provide testing services?
  • What samples are suitable for these tests?