New CRISPR-Based COVID-19 Test Uses Smartphone Camera to Provide Accurate Results in 30 Minutes

The novel approach developed by scientists at Gladstone Institutes (San Francisco, CA, USA), University of California, Berkeley (Berkeley, CA, USA), and University of California, San Francisco (UCSF; San Francisco, CA, USA) skips all the conversion and amplification steps, using CRISPR to directly detect the viral RNA. Not only can their new diagnostic test generate a positive or negative result, it also measures the viral load (or the concentration of SARS-CoV-2, the virus that causes COVID-19) in a given sample.

In the new test, the Cas13 protein is combined with a reporter molecule that becomes fluorescent when cut, and then mixed with a patient sample from a nasal swab. The sample is placed in a device that attaches to a smartphone. If the sample contains RNA from SARS-CoV-2, Cas13 will be activated and will cut the reporter molecule, causing the emission of a fluorescent signal. Then, the smartphone camera, essentially converted into a microscope, can detect the fluorescence and report that a swab tested positive for the virus. The researchers also say that their assay could be adapted to a variety of mobile phones, making the technology easily accessible.

When the scientists tested their device using patient samples, they confirmed that it could provide a very fast turnaround time of results for samples with clinically relevant viral loads. In fact, the device accurately detected a set of positive samples in under 5 minutes. For samples with a low viral load, the device required up to 30 minutes to distinguish it from a negative test. Not only does the new CRISPR-based test offer a promising option for rapid testing, but by using a smartphone and avoiding the need for bulky lab equipment, it has the potential to become portable and eventually be made available for point-of-care or even at-home use. And, it could also be expanded to diagnose other respiratory viruses beyond SARS-CoV-2. In addition, the high sensitivity of smartphone cameras, together with their connectivity, GPS, and data-processing capabilities, have made them attractive tools for diagnosing disease in low-resource regions.

"What really makes this test unique is that it uses a one-step reaction to directly test the viral RNA, as opposed to the two-step process in traditional PCR tests," said Melanie Ott, MD, PhD, director of the Gladstone Institute of Virology and one of the leaders of the study. "The simpler chemistry, paired with the smartphone camera, cuts down detection time and doesn't require complex lab equipment. It also allows the test to yield quantitative measurements rather than simply a positive or negative result."

"We chose to use mobile phones as the basis for our detection device since they have intuitive user interfaces and highly sensitive cameras that we can use to detect fluorescence," added UC Berkeley bioengineer Daniel Fletcher, PhD. "Mobile phones are also mass-produced and cost-effective, demonstrating that specialized lab instruments aren't necessary for this assay."

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Gladstone Institutes
University of California, Berkeley
University of California, San Francisco