Health Canada has approved four rapid-testing devices that could return results within 15 minutes in the midst of a increase in positive COVID-19 cases and a recorded backlog of book tests and results in Ontario. Researchers from the University of Toronto, meanwhile, are working on an approach that could yield five outcomes.
The project is a collaboration of researchers from the Faculty of Applied Science & Engineering, the Faculty of Pharmacy of Leslie Dan, and the Chemistry Department of the Faculty of Arts & Science. University Professors Ted Sargent and Shana Kelley are supervising it.
The normal research method in Canada is currently based on a process called polymerase chain reaction (PCR), which detects the SARS-CoV-2 RNA. The PCR test, conducted via a nasopharyngeal swab, is considered to be highly reliable and almost 100 per cent of the time detects positive ones.
However, the use of specialized devices such as thermal cyclers, which are only available in certain laboratory facilities, is required for PCR. This, combined with the logistics of transporting the samples to the laboratories, causes a bottleneck, which means that results can take up to four days to be obtained.
“We are trying to get away from the cotton swab,” says explains Surath Gomis, a PhD candidate in the Edward S. Rogers Sr. department of electrical and computer engineering. “Although the nasopharyngeal swab test is efficient, in addition to being slow it’s also invasive. And there is currently a need for rapid testing for a large subset of the population that is cost-effective and sensitive.”
Rapid point-of-care tests such as an antigen test that detects viral proteins instead of RNA through a liquid sample are considered less accurate than PCR. For example, an antigen test developed by Abbott Rapid Diagnostics in Germany – the first antigen test approved by Health Canada – has a reported sensitivity rate of 93.3 percent.
The equipment of the U of T team is also based on antigen tests. It detects specific viral proteins and intact viral particles from a saliva sample from a positive patient taken with a thermometer-like probe inserted into the mouth. The U of T team says its sensor is a more sensitive antigen testing approach than what is currently available.
Once saliva is collected, the probe’s antibodies, which are specific for SARS-CoV-2, recognize the virus and bind to it. This simple electrochemical binding event generates a unique signal that can then be detected by a measuring device attached to the sensor probe.
“We can measure an electric current that would look different if a virus were bound to it than if no virus was bound to it,” says Gomis.
In addition, its mechanism does not require sample pre-processing, making the platform easy to manage and user-friendly.
“Our saliva test is simple and fast,” says Jagotamoy Das, a senior researcher at the Faculty of Pharmacy. “After removing the sensor and a five-minute incubation, we can determine whether or not you have the virus”.
The team says that the degree of accuracy in antigen testing depends on the quality of the antibodies.
“We were fortunate to have access to high quality antibodies for our device, and we have found a very high accuracy rate that allows sensitive and specific detection of the SARS CoV-2 virus,” said Hanie Yousefi, a PhD student at the Leslie Dan Faculty of Pharmacy.
The team started working on the sensor two years ago with the goal of detecting biomarkers for diseases such as heart failure and cancer, but moved on to COVID-19 diagnostics after the outbreak of the pandemic.
The team has tested patient samples and hopes to find an industry partner for further development of the technology.
“PCR tests with nasopharyngeal swabs were the gold standard, but studies have appeared showing that saliva samples contain a comparable amount of virus particles,” says Yousefi. “Now is the time to use saliva samples as a reliable source”.