The team, led by Jennifer Doudna, a 2020 Nobel laureate in chemistry and a professor at the University of California, Berkeley, used CRISPR gene editing to come up with a way to detect the new coronavirus in just five minutes. The test method does not require expensive laboratory equipment to operate and can be used in doctors’ offices, schools, and office buildings. The results were published on the preprinted platform medRxiv.
Max Wilson, a molecular biologist at the University of California, Santa Barbara, says this looks like an absolutely reliable test.
In May, two research groups reported a new CRISPR-based coronavirus detection method that can detect viruses in about an hour, much faster than the 24 hours required for traditional testing.
The new test method is currently the fastest diagnostic method based on CRISPR.
CRISPR testing works by identifying an RNA sequence of about 20 bases, a base sequence unique to the new coronavirus.
They bind to the target RNA sequence in a solution by creating a “wizard” RNA that complements the target RNA sequence.
When the “wizard” RNA binds to the target RNA, the CAS13 “scissors” enzyme of the CRISPR tool activates and cuts off the nearby single-stranded RNA.
Moreover, the shear releases separate fluorescent particles into the test solution, and when the sample is lasered, the released fluorescent particles glow, indicating the presence of the virus.
The initial CRISPR testing method required researchers to first amplification of viral RNA before testing and diagnosis, which undoubtedly increased the complexity, cost and time of testing. This new CRISPR diagnostic method does not require the amplification of new coronavirus RNA.
The team also spent months testing hundreds of “wizard” RNAs to find multiple “wizard” RNAs that could work together to improve detection sensitivity.
Using a single “wizard” RNA, the researchers reported, 100,000 viruses could be detected per microlith solution. If they add a second “wizard” RNA, they can detect 100 viruses per microlith.
Melanie Ott, a virologist at the University of California, San Francisco, who co-led the study, said the method is still not as good as traditional new coronavirus diagnostic devices, which use expensive laboratory machines to track viruses and track one virus per microlith.
However, she said, the new diagnostic method can accurately identify a batch of five positive clinical samples, each test takes five minutes, while the standard test takes a day or more to get results.
Wilson says the new method also has another key advantage: it can quantify the number of viruses in the sample.
When traditional testing is achieved by amplification of genetic material, the amount of existing genetic material is changed to make it impossible to determine the number of viruses in the sample.
In contrast, the fluorescent signal strength detected by the new detection method is directly related to the number of viruses in the sample. This reveals not only whether the sample is positive, but also how many viruses the patient is carrying.
Wilson says this information can help doctors develop treatment plans based on each patient’s situation.