Rapid testing is key to measuring and stopping the spread of COVID-19, but polymerase chain reaction (PCR) assays and other tests are time consuming and require expensive laboratory equipment, creating a bottleneck in obtaining results. A fast-track alternative has been developed as a clusters of regularly interspaced short palindromic repeats (CRISPR)-based diagnostic that uses a smartphone camera to provide accurate results in under 30 minutes.

Unlike other available protocols, the new 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 diagnostic takes advantage of the CRISPR Cas13 protein, which directly binds and cleaves RNA segments. This eliminates the DNA conversion and amplification steps required in PCR assays and greatly reduces the time needed to complete the analysis.

These proteins are is combined with a reporter molecule that becomes fluorescent when cut, and then mixed The test uses a smartphone camera to provide accurate results in under 30 minutes. Source: Parinaz Fozouni et al.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, the viral agent responsible for COVID-19, Cas13 will be activated and will cut the reporter molecule, causing the emission of a fluorescent signal. A smartphone camera essentially converted into a microscope then detects the fluorescence and reports that a swab tested positive for the virus.

Tests confirmed that the method could provide a very fast turnaround time of results for samples with clinically relevant viral loads. 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.

The assay could be adapted to a variety of mobile phones, making the technology easily accessible for point-of-care or even at-home use. The technology could also be expanded to diagnose other respiratory viruses beyond SARS-CoV-2.

A paper detailing the method devised by researchers from University of California Berkeley, University of California San Francisco, Gladstone Institutes, Chan Zuckerberg Biohub and San Jose State University is published in Cell.

Jennifer Doudna, Ph.D., a senior investigator at Gladstone and a professor at University of California Berkeley, recently won the 2020 Nobel Prize in Chemistry for co-discovering CRISPR-Cas genome editing, the technology that underlies this work.