Novel at-home saliva-based Covid-19 test as effective as PCR diagnosis

PTI, Aug 10, 2022, 10:02 AM IST

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Researchers have developed an at-home, saliva-based testing platform for Covid-19 that is as effective as a PCR test, and can provide results in just 45 minutes.

PCR tests are considered the gold standard in detecting the presence of SARS-CoV-2, the virus that causes Covid-19.

However, these tests can take a few days to process, resulting in unnecessary quarantine for negative individuals or delays for those who require proof of negative testing for travel or other commitments.

Rapid antigen-detecting tests, on the other hand, are convenient, but less reliable than PCR tests, according to the researchers.

To bridge the gap between accuracy and convenience, researchers at the Pennsylvania State University (Penn State) in the US developed the test which can detect the virus with the same level of sensitivity as PCR tests.

“PCR test results take about an hour to develop in a lab, but you have to factor in the time it takes to send the sample to a lab and for the lab to process it,” said Weihua Guan, an associate professor at Penn State.

“We wanted to create a viable alternative to the PCR for people to use at home, without having to endure the invasive nasal test,” said Guan, principal investigator of the study published in the journal ACS Sensors.

The researchers developed a palm-sized testing kit, where an individual spits into a cartridge and inserts it into processing platform. Within 45 minutes, test results are sent to a custom android app developed by the researchers.

The platform uses a technology called reverse transcription loop-mediated isothermal amplification, or RT-LAMP, to detect the virus.

In this technology, the testing device first heats the saliva to 95 degrees Celsius, the temperature at which viral particle shells break apart and release their genetic material.

The genetic material is then mixed with pre-packaged reagents in a microfluidic cartridge.

The sample is cooled to 65 degrees Celsius, triggering another chemical reaction in which a few viral molecules are multiplied into billions of copies, making the virus easier to identify.

If the virus is present in the saliva sample, the user will receive a positive result on their connected smartphone app.

The researchers tested the set up by infusing human saliva samples purchased commercially with inactivated SARS-CoV-2 virus particles and ran the samples through the prototype.

They also tested a few clinical specimens. The platform accurately determined whether every sample was positive or negative for the virus.

“We tested hundreds of mock samples and controlled the quantity of Covid particles in each one,” Guan said.

“Our platform proved to be highly sensitive to the presence of the virus in both the mock and clinical samples, with the standards set by the PCR test as our benchmark,” the scientist added.