A cascaded CHA–CRISPR/Cas12a photoelectrochemical platform enabled by S-scheme Bi 2 WO 6 /BiOBr for piR-823 detection

fM), with an ultralow detection limit of 0.34 fM (S/N = 3). It also demonstrates high specificity, good reproducibility, and satisfactory recovery (96.87%-103.41%) in exosome lysate. This work not only presents an efficient PEC biosensing platform for piRNA analysis but also offers guidance for the rational construction of S-scheme heterojunctions in high-performance PEC biosensors, holding great promise for early colorectal cancer diagnosis and prognostic monitoring.