Remarkable feats of scientific effort and collaboration have been achieved since the onset of the COVID-19 pandemic, starting from the sequencing of the virus in January 2020 to authorizing the first vaccine by December 2020, which is arguably the fastest vaccine ever created.
Testing for COVID-19 has been an area of special focus for many researchers, including an interdisciplinary team at the University of Toronto. The team’s recent paper outlines a novel method for diagnosing COVID-19 that can provide results in five minutes and requires no specialist lab equipment.
Private companies have already developed similar at-home testing kits, but this method tests for COVID-19 in a new way — one that the researchers hope will be adapted for detecting other viruses.
The current landscape of COVID-19 testing
In addition to adhering to the health safety protocols in place, testing for COVID-19 is extremely important. Testing can not only help with quick identification of positive cases for contact tracing, but it can also help to prevent further spread of the virus, especially within highly affected populations.
There are currently two rapid test methods for detecting COVID-19: the polymerase chain reaction (PCR) tests and the antigen tests. In Ontario, free public testing uses PCR tests while commercial testing kits produced by private companies can be either type of test.
This is mostly because of how the tests work. Antigen tests are cheaper to produce because they require fewer chemical reagents. PCR tests require special chemical reagents and are conducted in laboratories.
The tests are also priced accordingly. In the US, the commercially-available BinaxNOW — an at-home test from Abbott Laboratories — costs around $31 per test and are sold in packages of six. In Canada, personal testing kits are available from Sinai Health at a cost of $160. Switch Health’s tests are also being given to travellers returning to Canada through select airports, including the Toronto Pearson Airport.
The lower price point has motivated a number of companies to produce their own versions. Even employers are beginning to see their potential; a group of 12 of the nation’s largest companies, including Scotiabank and Air Canada, have partnered with the Creative Destruction Lab at the Rotman School of Management to study how antigen tests can be widely used to screen employees working in person.
There are still general concerns about the use of antigen tests. They are known to be less reliable and deliver more false positives than PCR tests, which prompted experts to caution against their use earlier on. But the federal government has recently revised its position on antigen testing, saying that they can still supplement PCR tests if used narrowly and cautiously.
“A rapid antigen test is clearly better than no test at all, as long as it is not used as a free pass,” said Irfan Dhalla, an associate professor at the Dalla Lana School of Public Health, in an interview with The New York Times.
A new method for antigen testing
Enter a new method of antigen testing from researchers at the University of Toronto. A group of researchers spanning six different departments within U of T and two external research institutes have developed a device to detect SARS-CoV-2 particles from a person’s saliva within five minutes. The best part? It can be used by anyone in the comfort of their own home — no chemical reagents are required, and the test does not have to be sent to a laboratory.
Published in the Journal of the American Chemical Society, the researchers describe their device as a type of ‘assay,’ a general tool in the biologist’s toolkit for measuring the concentration of a specific substance — in this case, viral particles of SARS-CoV-2.
The assay is made of a sensor that can detect the so-called ‘spike protein’ of a SARS-CoV-2 viral particle, attached to a negatively-charged piece of DNA. A compound called ‘ferrocene’ is also attached to the DNA. The whole device is then placed on an electrode, standing upright like a pillar.
When the sensor detects the spike protein of a viral particle, the two become stuck together. Then, a positive electric charge is applied to the electrode, which pulls the negatively charged DNA chunk down to it. Once the DNA topples and touches the electrode, electrons are transferred to the ferrocene, which then undergoes an oxidation reaction.
The time taken for this final reaction reveals the presence of SARS-CoV-2. The heavy particles stick to the DNA chunk and slow the rate of its toppling. If the oxidation reaction is sufficiently slowed down, it can be attributed to a viral particle.
The shape of the pillar-like structure has inspired its name: the molecular pendulum. The technique has been used to detect proteins before, but never something as large as a virus.
“Our sensor is based on the concept of a molecular pendulum,” wrote Shana Kelley, a professor of biochemistry and an author of the study, in an email to The Varsity. “The sensor travels to the surface of an electrode with a characteristic time constant that slows down when the virus binds because of its size… [and] the kinetic properties of [the] electrochemical signal… allows us to visualize this change in travel time.”
Future directions
The researchers emphasized the accuracy of their test and the usefulness of using saliva to test for COVID-19.
They tested their device’s ability to detect SARS-CoV-2 directly from saliva samples from infected patients previously tested positive with PCR methods, with no human subjects as control in a blinded study. The results showed an observable oxidation reaction to infected samples within two minutes with an accuracy the researchers describe as comparable to PCR.
“Saliva is a pretty straightforward sample type but we were very pleased to see statistically significant signals within 2 minutes,” wrote Kelley.
A lead author of the study and doctoral candidate Hanie Yousefi also wrote in an email that “the sensitivity of the system is clinically relevant. Which means infected persons’ saliva carries a large enough load of the virus to be detected with the system.”
“All you need to do is add your saliva sample, wait for [a] few minutes, and read the result of your test. The measurements can even be made in the mouth,” she added.
Going forward, the researchers hope their molecular pendulum will be used for COVID-19 testing. Yousefi is confident that it can still be used if the virus mutates, writing that “the spike protein of the SARS-CoV-2 virus is resistant to mutations and is a good marker for sensing.”
“We are currently working on designing hand-held devices that can be used outside of [the] laboratory,” Kelley wrote.
She added, “In addition to answering the needs of the current pandemic, having this device commercialized and ready to use is a great asset for facing future pandemics… and for other diagnostics needs.”
