Identifying and isolating individuals who may be contagious with the coronavirus is key to limiting the spread of the disease. But even months into the pandemic, many patients are still waiting days to receive COVID-19 test results.
Scientists have developed a CRISPR-based COVID-19 diagnostic test that, with the help of a smartphone camera, can provide a positive or negative result in 15 to 30 minutes. Unlike many other tests that are available, this test also gives an estimate of viral load or the number of virus particles in a sample, which can help doctors monitor the progression of a COVID-19 infection and estimate how contagious a patient might be. The technique was designed in collaboration with the Gladstone Institute of Virology.
Most COVID-19 diagnostic tests rely on a method called polymerase chain reaction (PCR), which searches for pieces of the SARS-CoV-2 viral RNA in a sample. These PCR tests work by first isolating the viral RNA, then converting the RNA into DNA, and then amplifying the DNA segments — making many identical copies — so that the segments can be more easily detected. The new diagnostic test takes advantage of the CRISPR Cas13 protein, which directly binds and cleaves RNA segments. This eliminates the DNA conversion and amplification steps and greatly reduces the time needed to complete the analysis.
In the test, CRISPR Cas13 proteins are “programmed” to recognize segments of SARS-CoV-2 viral RNA and then combined with a probe that becomes fluorescent when cleaved. When the Cas13 proteins are activated by the viral RNA, they start to cleave the fluorescent probe. With the help of a handheld device, the resulting fluorescence can be measured by the smartphone camera. The rate at which the fluorescence becomes brighter is related to the number of virus particles in the sample.
Recent models of SARS-CoV-2 suggest that frequent testing with a fast turnaround time is what we need to overcome the current pandemic. Now that the CRISPR-based assay has been developed for SARS-CoV-2, it could be modified to detect RNA segments of other viral diseases like the common cold, influenza, or even human immunodeficiency virus. The team is currently working to package the test into a device that could be made available at clinics and other point-of-care settings and that one day could even be used in the home.
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