Researchers adjust a cell phone camera for SARS-CoV-2 detection

Researchers have developed a test that can detect the presence of SARS-CoV-2 in a nasal swab using a device attached to a regular smartphone, they report Dec. 4 in the journal. Cell. While more research is needed before such a test can be rolled out, the results are promising and may ultimately apply to broader screening for other viruses.

“Our study shows that we can perform the detection portion of this test very quickly, doing the measurement with mass-produced consumer electronics,” said Daniel Fletcher, a bioengineer at the University of California at Berkeley and co-senior author of the paper. “We don’t need expensive laboratory equipment.”

Fletcher and other co-senior author Melanie Ott (@TheOttLab), a virologist at Gladstone Institutes and the University of California, San Francisco, began collaborating with Nobel laureate Jennifer Doudna about two years ago, also co-author of the study. a quick home test for HIV. They were looking for the need for frequent testing that has arisen because of current drug trials that require close monitoring of patients’ viral loads. When COVID-19 hit the market in January, they quickly turned their research around to develop a test that would detect the presence of another virus: SARS-CoV-2.

The test uses CRISPR-Cas technology. Specifically, RNA in the sample can be detected with the Cas13 enzyme, eliminating the need for reverse transcription of the RNA into DNA and then amplification by PCR technology used in current standard assays. When Cas13 binds to the virus’s RNA, it cleaves all surrounding RNA sequences; the researchers added an RNA-based probe to the reaction that cleaves and produces fluorescence that can be detected with the camera. The test provides results within 30 minutes of detection time.

In the current study, which was primarily intended to test the amplification-free CRISPR-Cas technology and detector, the nasal swabs were enriched with SARS-CoV-2 RNA. The researchers are currently working on a solution that would induce a one-step reaction in which the RNA is released from the virus without the need for purification. Since amplification is not required, the assay can quantify the amount of virus in the sample.

“It’s super exciting to have this quantitative aspect in the test,” said Ott. “PCR is the gold standard, but you have to go through so many steps. There are huge opportunities here for pathogens and for biology in general to make RNA quantification more accurate.”

The fluorescence detector consists of a laser to produce illumination and to generate the fluorescence and an additional lens to help capture light. The phone is placed on top. “One takeaway is that the phone’s camera is ten times better than the plate reader in the lab,” says Ott. “This can be directly translated into a better diagnostic reader.” Previous research in Fletcher’s lab has led to telephone devices that visually detect parasites in blood and other samples, and the current test shows how telephone cameras can also be useful for molecular detection.

Ultimately, Fletcher and Ott would like this type of test to be part of a broader system that could be used at home to screen not only for SARS-CoV-2, but other viruses as well, such as viruses that cause colds and flu. But more immediately, the researchers hope to use this technology to develop a testing device that can be rolled out to pharmacies and drop-in clinics. They want to cut the cost of cartridge testing to about $ 10. The latter device probably wouldn’t actually use a phone, but it has a phone camera built into it.

Ott notes that what they learned in developing this SARS-CoV-2 test can also be applied to their work with HIV testing. “We will have to change the extraction methods because we will be dealing with blood instead of nasal swabs, but it is really helpful that we developed the fluorescent detection part,” she says. “This is the beginning of an era where we can give the individual greater authority and autonomy” in terms of self-testing.

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The researchers were mainly supported by the National Institutes of Health.

Cell, Fozouni et al .: “Direct detection of SARS-CoV-2 with CRISPR-Cas13a and a cell phone”
https: //www.cell.with/cell/entire text/S0092-8674(20) 31623-8

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