Tribos: A Modular Hairpin-Enhanced CRISPR/Cas12a Biosensor for Ultrasensitive Detection of HER2 Protein.

Accurate detection of human epidermal growth factor receptor 2 (HER2) is critical for early breast cancer screening and personalized therapy. This study constructed a target-triggered, hairpin-enhanced CRISPR/Cas12a biosensor named "Tribos" for ultrasensitive HER2 detection. The system integrates an aptamer hairpin switch (HAS), HAS-allosterically triggered rolling circle amplification (RCA), and a hairpin-enhanced CRISPR/Cas12a fluorescence reporter module. Taking advantage of Cas12a's high affinity for stem-loop structures, we designed a double-stem-loop reporter probe (DS-FQ) and validated its trans-cleavage enhancement mechanism via molecular docking. Under optimal conditions, Tribos exhibited a linear range from 10 fg/mL to 10 ng/mL, with a limit of detection as low as 1.08 fg/mL. In clinical validation with 29 breast cancer patients and 13 healthy controls, the sensor achieved a sensitivity of 82.76% and a specificity of 100%, which were highly consistent with clinical diagnoses and ELISA results, and it effectively distinguished different HER2 expression levels. The modular design of Tribos offers a new strategy for high-performance CRISPR diagnostics and lays a foundation for next-generation molecular diagnostic technologies based on nucleic acid conformational regulation.