Researchers have developed a simple, glucose-meter test that can help people monitor their own antibody levels against the SARS-CoV-2 virus, that causes COVID-19. The team from Johns Hopkins University in the US noted that over-the-counter COVID-19 tests can quickly show whether a person is infected with SARS-CoV-2.
However, if a person has a positive result, there is no at-home test to assess how long they will remain protected against reinfection. In the Journal of the American Chemical Society, researchers described a simple, accurate glucose-meter-based test incorporating a novel fusion protein.
They said that consumers could someday use this assay to monitor their own SARS-CoV-2 antibody levels. Vaccines against SARS-CoV-2 and infection with the virus itself can guard against future infections for a while, but it's unclear exactly how long that protection lasts, the researchers said.
A good indication of immune protection is a person's level of SARS-CoV-2 antibodies, but the gold standard measurement — the enzyme-linked immunosorbent assay (ELISA) — requires expensive equipment and specialized technicians, they said. Glucose meters are readily available, easy to use and can be integrated with remote clinical services, according to the researchers.
Researchers have been adapting these devices to sense other target molecules, coupling detection with glucose production. For example, if a detection antibody in the test binds to an antibody in a patient's blood, then a reaction occurs that produces glucose — something the device detects very well.
Invertase is an attractive enzyme for this type of analysis because it converts sucrose into glucose, but it's difficult to attach the enzyme to detection antibodies with chemical approaches. The researchers wanted to see whether producing a fusion protein consisting of both invertase and a detection antibody would work in an assay that would allow SARS-CoV-2 antibody levels to be read with a glucose meter.
They designed and produced a novel fusion protein containing both invertase and a mouse antibody that binds to human immunoglobulin (IgG) antibodies. The team showed that the fusion protein bound to human IgGs and successfully produced glucose from sucrose.
The researchers then made test strips with the SARS-CoV-2 spike protein on them. When dipped in COVID-19 patient samples, the SARS-CoV-2 antibodies bound to the spike protein. Adding the invertase/IgG fusion protein, then sucrose, led to the production of glucose, which could be detected by a glucose meter.
The researchers validated the test by performing the analysis with glucose meters on a variety of patient samples, and found that the new assay worked as well as four different ELISAs. The method can also be adapted to test for SARS-CoV-2 variants and other infectious diseases, they added.
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