A cascaded CHA-CRISPR/Cas12a photoelectrochemical platform enabled by S-scheme Bi₂WO₆/BiOBr for piR-823 detection

Exosomal piR-823 is a promising specific biomarker for colorectal cancer, yet its ultrasensitive detection remains challenging due to its extremely low abundance and high sequence complexity. Herein, we developed a cascaded CHA-CRISPR/Cas12a photoelectrochemical (PEC) sensing platform enabled by an S-scheme Bi₂WO₆/BiOBr heterojunction for the reliable detection of piR-823. The flower-like spherical Bi₂WO₆/BiOBr heterojunction exhibits enhanced visible-light absorption and efficient charge transfer arising from the S-scheme structure, which establishes a strong photoactive basis for the PEC platform. By integrating catalytic hairpin assembly with CRISPR/Cas12a trans-cleavage activity, a cascaded signal amplification strategy is established, which significantly improves the detection sensitivity. Under optimized conditions, the platform shows a distinct negative correlation between transient photocurrent and the logarithm of piR-823 concentration (1.0-1.0 × 10⁶ 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.