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As of September 3, 2020, SARS-CoV-2 — the coronavirus that causes COVID-19 — has infected more than 26 million people worldwide. Accurate testing is key to controlling the virus and reducing transmission.
Currently, the real-time reverse transcription-polymerase chain reaction (RT-PCR) test is the best way to test for SARS-CoV-2 infection.
In this test, the RNA — a single-strand molecule — goes through reverse transcription. In this process, an enzyme converts the RNA into double-stranded DNA.
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After reverse transcription, scientists copy specific regions of the genome, using the PCR process. Then, they introduce primers, which are small sections of DNA that bind to particular DNA sequences of the SARS-CoV-2 genome.
The scientists then insert a fluorescent dye (also called a probe), the swab sample, and the primer into a PCR machine. The scientists register the sample as positive for SARS-CoV-2 if fluorescent signal marks appear.
The United States, Europe, and Asia use the RT-PCR tests widely. While these standard tests are highly scalable, their greatest limitation is that they require a laboratory set-up.
The test needs to run through different temperatures in each cycle to amplify the viral genetic material so that scientists can analyze it. This increases waiting times for results in regions that do not have access to the infrastructure and expertise required for RT-PCR tests.
Considering these limitations, a group of researchers at the University of Illinois Urbana-Champaign set out to design a cheap, fast, and portable test.
In a study published in the Proceedings of the National Academy of Sciences, the Illinois team explained how they developed a prototype test. According to their paper, the test can detect the SARS-CoV-2 virus in less than 40 minutes by using a hand-held reader, 3D-manufactured cartridge, and a smartphone.
Instead of relying on amplification of the viral genetic material by running it through 35–40 different cycles with varying temperatures, the new prototype test uses a far simpler process.
Known as loop-mediated isothermal amplification (LAMP), scientists developed this testing method 20 years ago and have used it as a more cost-effective alternative for amplifying DNA.
Scientists have already used this technique to detect the DNA in tuberculosis and malaria.
More recently, scientists have developed RT-LAMP (reverse transcription-LAMP) to detect RNA in viruses, such as HIV.
The test works by heating a sample to 149°F (65°C), which inactivates any viruses that are present. Researchers then break open the virus and detect the genetic sequence that identifies the SARS-CoV-2.
The main limitation of the RT-LAMP method is that it requires complex development of four to six primers targeting six to eight different regions of the virus genetic material, compared to two primers for the RT-PCR test.
Reports indicate that RT-LAMP is less sensitive than a traditional PCR test and cannot detect a virus that is present at low levels.
Despite this limitation, the researchers used the RT-LAMP method because it does not require commercial thermocyclers. Thermocyclers amplify samples of RNA and DNA during the PCR technique.
Additionally, the RT-LAMP procedure does not require multiple steps for viral attraction and can rely on disposable cartridges.
The researchers constructed their prototype from commercially available components that included a 3D printed cartridge and a smartphone-based optical reader. They demonstrated the viability of this diagnostic system by testing 20 nose swabs, 10 of which were positive for SARs CoV-2.
They placed the swabs in a viral transport media solution, which stirred the viruses gently so that they moved from the swab into the solution. They then thermally lysed, or incubated, a portion of the sample at 95ºC for 1 minute.
Following this, they loaded the sample and RT-LAMP reagents in 1 milliliter (ml) and 5 ml syringes and injected the components into the 3D-printed microfluidic cartridge.
The operator then places the cartridge inside the portable smartphone cradle with a heating chamber. When the cartridge reaches 65ºC, the results appear on the smartphone cradle within 30–40 minutes.
If the smartphone emits a fluorescent light, it denotes a positive test. The test correctly detected SARS-CoV-2 in all 10 viral transport medium clinical samples.
In this video, the team demonstrates how the portable test works.
In their paper, the authors propose that the point-of-care test “is designed for accessibility and the potential for scale-up.” They continue:
“This approach could enable the scalable deployment of COVID-19 diagnostics without laboratory-grade infrastructure and resources, especially in settings where a diagnosis is required at the point of collection, such as schools, facilities that care for the elderly or disabled, or sporting events.”
The researchers are now working with Fast Radius Inc., a Chicago-based technology company, to manufacture the microfluidic cartridges.
One of the authors, William King, co-founded the company.
