Recently, the US Foods and Drug Administration’s (FDA) approved emergency-use of the coronavirus test using CRISPR technology developed by Sherlock Bioscience. The test can be done only in the certified laboratories.
Currently, COVID-19 test relies on PCR (polymerase chain reaction) which takes a few days to produce results. The CRISPR-based diagnosis can bring down the time required to return results from days to an hour and will undoubtedly speed up the test processed per day.
The SHERLOCK COVID-19 diagnostic kit works in a simple three steps and can give the results in an hour. The test makes use of the S gene and Orf1ab gene chosen from SARS-CoV-2 genome for the detection of its RNA in specimens. The kit relies on a device similar to a pregnancy test.
Now that we have an overall idea of how the test works. Let us understand, in more details, how CRISPR-based diagnosis work and what does exactly CRISPR mean.
What is CRISPR?CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats, a family of DNA sequences used in gene-editing technology that allows to ‘cut’ and ‘paste’ genes into DNA more accurately. To make it more simple, it is an invisible scissor (molecular scalpel). The technology relies on a guided mechanism that targets to destroy foreign DNA or RNA. Prokaryotes that occurred earlier infected with a virus has this defence mechanism. It occurs as a part of the microbial immune system, including archaea and bacteria. Bacterial like S. pyogenes uses CRISPR to memorize the sequences of an invader and Cas9 (CRISPR associated protein 9, an enzyme) to destroy them. Interestingly, these molecules can be extracted and used as a scissor to cut DNA from other species, including eukaryotes, for example, humans.
How the CRISPR test kit for coronavirus works?The basic molecules used in the CRISPR technology, are CRISPR-Cas complex, reporter molecules (short stretches of DNA/RNA to which a fluorophore is attached to an end and a quencher to the other). These molecules do not emit any light until the quencher is attached to the other end. Once the quencher is cleaved apart, it generates a signal in the form of detectable colour change. Since CRISPR can complex with other Cas-family protein, therefore, researchers used Cas13 in the diagnostic kit for COVID-19 (Cas12, Cas9 for DNA and Cas13 for RNA)
The first step involves 25min of incubation to amplify (making larger quantities) the extracted nucleic acid and usually done using a commercially available kit called RPA kit (Recombinase polymerase Amplification kit). The second step is the incubation for 30 min, and in that period of incubation, Cas13 is used to detect pre-amplified viral RNA sequence. The final step is followed by incubation for 2 min, and the result can be detected visually. A presence of two lines shows the test to be positive, and a single line in the bottom indicates it to be negative.
Hope this was helpful to make the things more clear to you and the people from the non-scientific background.
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