Li normally studies blood cell development and how blood cells become cancerous, not infectious diseases or diagnostics. So to develop this test, he sought advice from MIT faculty members Hadley Sikes and Sangeeta Bhatia, SM ’93, PhD ’97, who have expertise in the technology. With their help, his lab developed a device that can measure the amount of antibodies that block the SARS-CoV-2 receptor binding domain (RBD) from binding to ACE2, the human receptor the virus uses to infect cells.
The first step in the test is to add the blood sample to viral RBD protein that has been labeled with tiny gold particles. A few drops of the sample are then placed on a paper strip with two test lines embedded in it.
One of these lines attracts free viral RBD proteins, while the other attracts any RBD that has been captured by neutralizing antibodies. A strong signal from the second line indicates a high level of neutralizing antibodies in the sample, meaning you’re well protected. The results can be read in about 10 minutes. For a more precise measurement of antibody levels, a smartphone app can measure the intensity of each line and calculate the ratio of neutralized to infectious RBD protein.
When the researchers tested their device in about 60 people who had been infected with SARS-CoV-2 and 30 who had not, results were similar in accuracy to lab tests. The team also tested a series of samples from two people before they received a vaccine and at several points afterwards. Their level of neutralizing antibodies peaked around seven weeks after the first of two doses and then slowly declined to about 10% of the peak.
The test could be easily adapted to different variants of SARS-CoV-2 by swapping in new proteins, Li says. The researchers now hope to partner with a diagnostics company that can license and manufacture large quantities of the tests and obtain FDA approval for their use.
