MicroRNAs (miRNAs) are well-established biomarkers for tumor diagnosis and monitoring. Herein, we report a novel biosensing platform by engineering a structure-initiated variant of catalytic hairpin assembly (VCHA) that coordinates with strand displacement amplification (SDA) to drive cascade amplification for CRISPR/Cas12a-based detection. This system employs three hairpin probes which, upon recognizing the target miRNA, self-assemble into a key 5'-end dangling three-way conjugate (5'-DTC) structure. This structure serves as the exclusive trigger, simultaneously propagating the VCHA cycle and priming the SDA process through the coordinated action of polymerase and nicking enzyme. Consequently, VCHA and SDA operate synergistically within a unified circuit, generating abundant single-stranded activator DNA (acDNA) products. These acDNA molecules then activate the trans-cleavage activity of CRISPR/Cas12a, yielding a significantly amplified fluorescence readout. The VCHA-SDA/Cas12a platform demonstrated excellent performance for miRNA-155 detection, achieving a broad dynamic range from 1 pmol/L to 10 nmol/L with an ultra-low detection limit of 0.166 pmol/L. Furthermore, the platform successfully quantified miRNA levels in clinical plasma specimens and various cell lines, confirming its considerable potential as a robust tool for molecular diagnostics and clinical translation.
