The short answer
When Cas12 or Cas13 finds its target, it does not stop — it starts cutting up loose genetic material nearby. Inside a cell that is a problem. In a test tube it is a gift: add a molecule that glows when cut, and the enzyme announces that it found what you were looking for. That is the basis of tests that can detect a virus in under an hour without laboratory equipment.
SHERLOCK (Cas13) and DETECTR (Cas12a) exploit collateral cleavage of reporter substrates after target recognition, typically preceded by isothermal amplification. These platforms achieve attomolar sensitivity with single-base discrimination and were deployed for SARS-CoV-2 detection, including under emergency use authorisation.
Sources
- Science (Gootenberg et al.) · 2017
Nucleic acid detection with CRISPR-Cas13a/C2c2 ↗