Self-Sustaining miRNA Amplification Diagnostics via Catalytic Hairpin Assembly and Split Activator-Initiated CRISPR/Cas12a Hybrid Feedback Circuit with Target Regeneration and Recycling.

To meet the growing demand for ultrasensitive diagnostics, representative hybrid platforms integrating nonenzymatic isothermal nucleic acid amplification such as catalytic hairpin assembly (CHA) with CRISPR/Cas systems have been developed. However, two major challenges remain: background leakage from spontaneous hairpin hybridization and inherent fluorescence from conventional ssDNA reporters. Here, we present a self-sustaining isothermal biosensing platform that addresses these limitations by combining CHA with a split activator-initiated CRISPR/Cas12a feedback circuit for the ultrasensitive detection of miRNA-155, a key biomarker of breast cancer. In our design, miRNA-155 initiates CHA to form a DNA duplex, which, along with the miRNA, acts as split activators to trigger CRISPR/Cas12a. Cas12a cleaves a ds-loop DNA reporter, releasing fluorescence and regenerating the target. This dual-recognition mechanism ensures strict target dependence, reduces background noise, and, with the reporter design, minimizes leakage. The released miRNA reactivates CHA, enabling continuous signal amplification through a self-sustaining feedback loop involving successive CHA and Cas12a trans-cleavage cycles, enhancing detection sensitivity. Via these features, the platform achieves attomolar sensitivity and excellent specificity, even distinguishing single-base miRNA variants. Direct detection of endogenous miRNA-155 in serum samples from breast cancer patients demonstrated clear differentiation from healthy controls. This strategy provides a robust molecular detection platform for the accurate and ultrasensitive detection of low-abundance miRNAs in biomedical studies.