Engineers at MIT and Harvard University have designed a small tabletop device that can detect SARS-CoV-2 from a saliva sample in about an hour. In a new study, they showed that the diagnostic is just as accurate as the PCR tests now used.
The device can also be used to detect specific viral mutations linked to some of the SARS-CoV-2 variants that are now circulating. This result can also be obtained within an hour, potentially making it much easier to track different variants of the virus, especially in regions that don’t have access to genetic sequencing facilities.
“We demonstrated that our platform can be programmed to detect new variants that emerge, and that we could repurpose it quite quickly,” says James Collins, the Termeer Professor of Medical Engineering and Science in MIT’s Institute for Medical Engineering and Science (IMES) and Department of Biological Engineering. “In this study, we targeted the U.K., South African and Brazilian variants, but you could readily adapt the diagnostic platform to address the Delta variant and other ones that are emerging.”
The new diagnostic, which relies on CRISPR technology, can be assembled for about $15, but those costs could come down significantly if the devices were produced at large scale, the researchers say.
The new diagnostic is based on SHERLOCK, a CRISPR-based tool that Collins and others first reported in 2017. Components of the system include an RNA guide strand that allows detection of specific target RNA sequences, and Cas enzymes that cleave those sequences and produce a fluorescent signal. All of these molecular components can be freeze-dried for long-term storage and reactivated upon exposure to water.
Last year, Collins’ lab began working on adapting this technology to detect the SARS-CoV-2 virus, hoping that they could design a diagnostic device that could yield rapid results and be operated with little or no expertise. They also wanted it to work with saliva samples, making it even easier for users.
“Our goal was to create an entirely self-contained diagnostic that requires no other equipment,” Tan says. “Essentially the patient spits into this device, and then you push down a plunger and you get an answer an hour later.”
The Delta variant was not yet widespread when the researchers performed this study, but because the system is already built, they say it should be straightforward to design a new module to detect that variant. The system could also be easily programmed to monitor for new mutations that could make the virus more infectious.
The researchers first tested their device with human saliva spiked with synthetic SARS-CoV-2 RNA sequences, and then with about 50 samples from patients who had tested positive for the virus. They found that the device was just as accurate as the gold standard PCR tests now used, which require nasal swabs and take more time and significantly more hardware and sample handling to yield results.
The researchers believe their device could be produced at a cost as low as $2 to $3 per device. If approved by the FDA and manufactured at large scale, they envision that this kind of diagnostic could be useful either for people who want to be able to test at home, or in health care centers in areas without widespread access to PCR testing or genetic sequencing of SARS-CoV-2 variants.
