Skip to main content
Premium Trial:

Request an Annual Quote

UK Researchers Develop Low-Cost Molecular COVID-19 Testing in a Backpack

Premium

BALTIMORE – Researchers at Queen Mary University of London have developed a low-cost, lab-in-a-backpack testing platform that has the potential to enable molecular testing for SARS-CoV-2 and other infectious diseases in low-resource settings.

While the prototype still has a long path ahead for clinical implementation, its inexpensive design could also make it appealing for citizen science projects, according to the developers.

Published as part of an early preclinical study in PLOS One last week, the compact design features creatively sourced hardware — such as a centrifuge made from recycled computer hard drives and 3-D printed parts — and is estimated by the researchers to cost $51 to build.

"We were really glad to find out that everything is very low cost," said Stoyan Smoukov, professor of chemical engineering at Queen Mary University of London and the senior author of the study.

A key component of the setup is CentriDrive, a lab-built electronic centrifuge revamped from a used computer hard drive, a 3D-printed rotor made of polylactic acid plastic filament, and some other commercially available electronic components. The researchers estimated the total cost for the centrifuge to be approximately $28.

In addition to its low cost, the centrifuge is "almost matching all the commercial centrifuges by the specs," Smoukov said. According to the study, the device, made from a standard 7,200 revolutions-per-minute hard drive, can achieve a maximum speed of 11,650 rpm, or 7,600 rpm when loaded with the microfuge tubes. "I think the possibility here is also not only to do COVID tests but also to do blood tests and urine tests, other things where centrifuges are used," he added.

Smoukov said the prototype for the centrifuge was conceived prior to the pandemic, but when COVID hit, he and his graduate student Emily Lin, the study’s first author, started to ponder how they could harness it for low-cost COVID testing.

The design evolved over the course of the pandemic, Smoukov said, noting improvements the team made for the device to be more accessible. For one, they made the battery for the centrifuge rechargeable. "If you wanted to do [the assay] in a remote testing place, it was actually really good to have something that could be recharged," Smoukov said.

For the COVID-19 test, the team adopted a reverse transcription loop-mediated isothermal amplification, or RT-LAMP, protocol previously published by scientists at Harvard University Medical School. The workflow requires a few commercially available reagents for sample preparation — including lysis buffers, NaI and silica for nucleic acid binding, and ethanol — and a reaction mix for the RT-LAMP amplification.

The kit also comes with two micropipettes that cost $20 in total, a thermometer, and a thermos bottle for incubation. However, multiple pipetting and incubation steps will likely diminish the test's application for at-home use by untrained individuals.

To perform the test, users need to collect approximately 500 μl of saliva, inactivate it with a buffer, and incubate it in a thermos bottle with boiling water for five minutes. The sample then needs to be spun down using the CentriDrive for one minute at maximum speed. After collecting the supernatant, users need to add NaI followed by silica slurry. The mixture is then incubated at room temperature for 10 minutes before a 30-second centrifugation to harvest the precipitate.

After washing the silica precipitate with ethanol, LAMP primers and master mix are added and the reaction mix is incubated in the thermos bottle at 65°C for 30 minutes. In the end, positive reactions will turn yellow while negative controls remain pink. It is unclear, though, how easy it will be to maintain a constant water temperature in the thermos.

So far, the developers have only tested the system’s sensitivity using SARS-CoV-2 control RNA mixed with saliva at varying concentrations. The results indicated the test could detect as few as four viral genome copies per microliter. Using tap water instead of saliva reduced the assay’s sensitivity to eight copies per microliter.

According to the paper, the test takes about 80 minutes for one sample or 90 minutes for six, and the costs in reagents and consumables are approximately $3.50 per sample.

Manu Prakash, an associate professor of bioengineering at Stanford University, said that compared with widely used PCR-based COVID tests and antigen tests, LAMP assays are "somewhere in the middle." The method is more accurate than antigen tests, he said, but the RT-LAMP reaction is isothermal, meaning it does not require multiple heating steps for amplification like PCR, making it "far simpler" to work with. As a result, Prakash said, "there was an explosion in terms of the amount of work that has been done to demonstrate the value of RT-LAMP" since the pandemic hit.

Prakash’s own lab was one of them. His team has also been working on a low-cost, point-of-care molecular COVID-19 saliva test, called SnapDx, that aims to serve low-resource settings and is RT-LAMP-based.

One of the main challenges to building a simple-to-use amplification-based test is preventing cross contamination, he said. Amplification assays generate "billions of copies of that exact same sequence that you're looking for," he explained, and all those copies have to be kept inside the device to prevent contamination. "The issue is that when those sets of copies get released, they contaminate the table, they contaminate the other devices," he said. "Over time, one positive test can contaminate many other tests," leading to false positive results.

In the laboratory setting, contamination can be curbed by wearing gloves or other good laboratory practices, Prakash said, but molecular tests in the field need to reduce manual liquid handling to achieve that goal. That, he said, remains one of the "hardest problems" for engineers: "How do you do automation without any bells and whistles?"

Nonetheless, Prakash said his philosophy when it comes to low-cost testing and diagnostics is "all flowers bloom."

"It's the combination of many ideas everywhere that leads to fusions," he pointed out. "It's incredibly important for many people to … add onto each other's work because the challenge that we are facing is significant."

To that end, Smoukov said, his team decided to make the design not only open access but also open hardware, meaning everyone can get access to the blueprint and try to replicate the device. "Basically, what we've done is made this thing as if you're baking a cake," he said.

His team is currently not planning to pursue commercialization on its own. "We haven't even done tests with real viruses yet," he said, noting that the published study is only proof-of-design, and more validation in many areas is needed before the design could hit the market. "We're actually trying to give it away to anybody who wants to commercialize it," he said.

While commercialization may not be imminent, Smoukov thinks his design, with detailed instructions and inexpensive materials, could be useful for citizen science. Specifically, he said, by following the protocol described in the paper and replicating the study in classrooms, students could learn about the inner workings of LAMP-based COVID tests firsthand.

"For education, I think is great," he said, "because the cost of the whole thing is very low."

The Scan

Alzheimer's Risk Gene Among Women

CNN reports that researchers have found that variants in MGMT contribute to Alzheimer's disease risk among women but not men.

Still Hanging Around

The Guardian writes that persistent pockets of SARS-CoV-2 in the body could contribute to long COVID.

Through a Little Spit

Enteric viruses like norovirus may also be transmitted through saliva, not just the fecal-oral route, according to New Scientist.

Nature Papers Present Method to Detect Full Transcriptome, Viruses Infecting Asgard Archaea, More

In Nature this week: VASA-seq approach to detect full transcriptome, analysis of viruses infecting Asgard archaea, and more.