PCR tests, also known as molecular tests or nucleic acid tests, are widely used to detect the presence of SARS-CoV-2, the virus that causes COVID-19. They can, however, take a few days to process, resulting in unnecessary quarantine for negative individuals or delays for those who need proof of negative testing for travel or other obligations. Rapid antigen-detecting tests, on the other hand, are less reliable than PCR tests.
PCR test results are generated within an hour however there are other time consuming factors that need to be considered such as sending the sample to the lab and it's processing there. Principal investigator Weihua Guan, associate professor of electrical engineering and of biomedical engineering in Penn State’s College of Engineering said “We wanted to create a viable alternative to the PCR for people to use at home, without having to endure the invasive nasal test.”
To tackle this issue of time while also maintaining the accuracy of the test, researchers at Penn State University have come up with a new saliva based test which can give results within 45 minutes and has also shown sensitivity on par with PCR tests in the preliminary testing round.
The testing kit developed by Guan and his team is compact (palm sized) and requires an individual to spit into a cartridge which is then inserted into a processing platform. Within 45 minutes, the test results are generated and sent to a custom Android app developed by the researchers.
To detect the virus, the platform employs reverse transcription loop-mediated isothermal amplification, or RT-LAMP. The saliva is heated to 203 degrees Fahrenheit, which is the temperature at which viral particle shells break apart and release their genetic material. In a microfluidic cartridge, the genetic material is mixed with pre-packaged reagents. Finally, the sample is cooled to 149 degrees Fahrenheit, causing another chemical reaction that multiplies a few viral molecules into billions of copies, making the virus easier to identify. If the virus is found in the saliva sample, the user will see a positive result on their smartphone app.
Guan and his colleagues tested the setup by injecting inactivated SARS-CoV-2 virus particles into commercially purchased human saliva samples, they also used clinical specimens. The kit was accurate in it's determination of whether the sample was positive or negative.
“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 researchers plan on continuing the clinical testing and also improving the shelf life of the kit as the enzymes in the prototype degrade at room temperature..A provisional patent has also been filed with intentions of commercializing it pending the scaled-up clinical testing and review by the U.S. Food and Drug Administration.
Research paper:
Zifan Tang et al, SLIDE: Saliva-Based SARS-CoV-2 Self-Testing with RT-LAMP in a Mobile Device, ACS Sensors (2022). DOI: 10.1021/acssensors.2c01023
Journal information: ACS Sensors.
By Bishakha Choudhury
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