Figure 4.

Overview of the CRISPR-based assays. (A) Amplification-free detection of the SARS-CoV-2 RNA using the Cas13a- crRNA complex and a mobile phone camera. In both the SHERLOCK (B) and DETECTR (C) assays, the viral RNA is converted to dsDNA using RT-recombinase polymerase amplification. Subsequently, in SHERLOCK, complementary RNA generated from this DNA template by T7 transcription is subsequently detected by Cas13: RNA complexes binding to the target sequence, which leads to the cleavage of fluorescent RNA molecules. In the DETECTR method, T7 transcription does not occur and target sequences on RT-RPA reaction products are detected directly by Cas12: RNA complexes.