How reliable is your RAT?

A fluorescently tagged nucleocapsid protein used to develop a benchmark for RATs.

Supplied by JCU Media.

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Written By

Tianna Killoran


College of Public Health, Medical and Veterinary Sciences

Publish Date

5 April 2023

From protein to pandemic

PhD Candidate Casey Toft, along with a team of JCU researchers, has developed a new scientific tool to accurately compare the effectiveness of our rapid antigen tests (RATs). While we have come to rely on RATs throughout the pandemic, Casey says that benchmarking these tests to guarantee their performance is crucial to public health and hopes his research will improve the rollout of virus detection devices in the future.

PhD Candidate Casey Toft is an investigator on a research project that is developing a benchmarking tool to ensure rapid antigen tests (RATs) are accurate and sensitive in COVID-19 detection and measure up to their claims.

After completing a Bachelor of Advanced Science majoring in Molecular and Cell Biology, Casey found himself continuing with a Master of Philosophy at JCU. He was conducting research under the supervision of Associate Professor Patrick Schaeffer on how bacteria replicate and the processes of bacterial replication termination. But mid-way through his studies, the COVID-19 pandemic struck.

“In my Master of Philosophy, I was studying unique bacterial proteins that interact with specific DNA sequences. This interaction can be so strong that the bacterial protein can stop the processes of fast-moving protein complexes — more than twenty times their size — in its tracks," Casey says. "We wanted to try to exploit this interaction to create new biotechnologies. A lot of this research gave me insight into the tools we can use to study things at this microscopic level of detail."

“But it was while I was doing this research that the COVID-19 pandemic began. So, our lab team got together and began thinking about how we can use the tools available to us at JCU and make a difference during the pandemic.

“Pretty early on we managed to produce a fluorescently tagged nucleocapsid protein that the virus heavily relies on to replicate itself,” he says. With this protein tagged, Casey and other researchers were able to learn more about its role in virus replication and how it could be used in virus detection. After completing his Master of Philosophy, Casey pursued a PhD at JCU and says they were able to obtain a Sandpit to Seed (S2S) fund to continue the research.

JCU PhD Candidate Casey Toft.

Supplied by JCU Media.

Testing the tests

If you go to your local supermarket or pharmacy, you are presented with a range of options for Rapid Antigen Tests (RATs). But which one should you choose? How do you know if the test will reliably detect COVID-19? What is the better choice among the many brand options?

Casey says that the team has managed to fluorescently tag a nucleocapsid protein that will enable researchers to benchmark RATs. “When a virus infects you, it gets your body to produce its proteins. The virus essentially hijacks your body’s cell machinery to help the virus continue replicating so that it can infect other people,” he says.

“Essentially, the most abundant protein produced during COVID-19 infection is the nucleocapsid protein. It is one of the most important proteins to understand, and it is what RATs detect the presence of to determine if you are infected with the virus or not.”

But Casey says that RATs often use a flawed system to evaluate their detection capabilities that can lead us to believe they are more sensitive than they really are. “Existing RATs detect the nucleocapsid protein, but researchers evaluate the RATs’ sensitivity using viral cultures, which are an indirect measure of the presence of the nucleocapsid protein. This can also produce highly conflicting data between laboratories,” he says. “So, our research developed a new and more robust tool that can accurately compare the sensitivity of RATs produced by different manufacturers.”

“We really need a tool that allows us to confidently say which RAT is better. This is critical in settings such as aged care and health care where many immunocompromised people are relying on the detection capabilities of these tests,” Casey says.

“If you’re visiting your grandmother in an aged care facility, you want to be sure that you don’t have COVID or the flu. While polymerase chain reaction (PCR) tests remain the gold standard, they are less readily available and can be so sensitive that they can return a positive result from an infection that occurred months ago,” he says. “Obviously that’s why we use RATs more often; they are easy to obtain and help gauge how contagious an individual is likely to be, but we need to be able to trust their results.”

Associate Professor Patrick Schaeffer on left and PhD Candidate Casey Toft on right, each wearing lab coats and holding up small vials.
Two hands holding a rapid antigen test with the testing kit on a desk in the background.
Left: Associate Professor Patrick Schaeffer and PhD Candidate Casey Toft. Supplied by JCU Media.

Fighting the flu in the future

Casey says that having a reference material that can benchmark RATs is important for the development of better RATs in the future. This can also help us to adapt and rapidly identify the sensitivity of RATs as new COVID variants emerge. “Whenever we have new mutations in the nucleocapsid protein, we can quickly adapt our reference material to enable us to continually test our tests and ensure they have sufficient sensitivity,” Casey says.

There is commercial potential for RATs to be adapted for detecting many other viruses and Casey says the tool he is working on will be important to ensure their reliability. “They’re now starting to bring out the triple RATs which detect Influenza A, B and SARS-COV-2 from the same sample. There’s potential here for us to build on our tool and test those as well,” he says.

“Ultimately, we want to make sure that we set suitable benchmarks to ensure the quality of the products that we have on the shelf. We don’t want consumers using tests that are performing poorly,” Casey says.

Using this new tool as a reference standard, Casey is now pursuing research into the development of a universal RAT that will simultaneously test for COVID-19, the flu and other respiratory viruses. “Hopefully these RATs will be cheaper to produce and with a bit of luck, more sensitive,” he says.

“It’s really nice for me to be able to do a research project that can be related to and help other people. It’s important research and while the process often involves a lot of troubleshooting, it’s a really good feeling once things begin to run smoothly,” Casey says.

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