Fig. 4.

Collateral cleavage-based electrochemical RNA biosensor. (a) Without the presence of the target RNA, the Cas13-crRNA complex exhibits no cleavage activity towards the reporter RNA; hence, the glucose oxidase-labelled 6-FAM antibody remains immobilized on the electrode via affinity of the biotin antibody and reporter RNA labelled with 6-FAM and biotin. Hence, glucose oxidase can mediate amperometric detection of H₂O₂. (b) However, if the target RNA is present within the sample, Cas13a-crRNA cleaves the RNA reporter, and glucose oxidase is washed out and provides no (or lower) current response (modified from Ref. [87]).