SHERLOCK (Specific High Sensitivity Enzymatic Reporter UnLOCKing) is a nucleic acid detection system based on CRISPR-Cas13a that can detect viruses, distinguish pathogenic bacteria, genotype human DNA and cell-free tumor DNA mutations.
SHERLOCK makes use of RNA guided RNase activity of Cas13a and collatoral RNase activity, which degrades non target RNA nearby. It uses the Leptotrichia wadei Cas13a ortholog, LwCas13a, along with the crRNA that targets the desired nucleic acid sequence. Either RNA or DNA viruses can be detected. Viral RNA from body fluids is first converted to DNA with reverse transcriptase. Sample DNA is amplified with recombinase polymerase amplification (RPA) followed by conversion to RNA with T7 RNA polymerase which is detected by the Cas13a-crRNA complex. Detection results in non-target RNA nearby, including a reporter RNA included in the SHERLOCK system. In the first version of CRISPRCRISPR, the reporter RNA fluoresces when cleaved, indicating Cas13a-crRNA has found a matching target nucleic acid sequence. A second version of SHERLOCK uses paper strips where the readout can be viewed with the naked eye similar to pregnancy tests.The second version also uses three Cas13 enzymes and one Cas12a enzyme to sense multiple targets like dengue and Zika virus in a single reaction.