Cas12a Trans-Cleavage of Hairpins Triggers a CHA Cascade for an Ultrasensitive SERS Aptasensor

Ultrasensitive detection of non-nucleic acid biomarkers using CRISPR/Cas12a remains a major challenge due to the lack of intrinsic signal amplification. Moreover, linear DNA reporters fail to maintain efficient downstream signal amplification after trans-cleavage, while pre-amplification procedures often lead to nonspecific signals, thereby compromising assay accuracy, particularly in complex biological matrices. Here, a highly SERS aptasensor is developed by harnessing CRISPR/Cas12a-driven trans-cleavage of hairpin substrates to trigger catalytic hairpin assembly (Cas12a-CHA), achieving robust cascade signal amplification. Target recognition is converted into customizable DNA triggers that precisely activate Cas12a, while a thymine-rich DNA/RNA reporter with dT5 motifs facilitates high enhances trans-cleavage efficiency, sustaining continuous CHA cycles. The integration of AuNF@4-MBA@Ag@H2 SERS nanotags that generate abundant plasmonic hotspots, the system provides significantly enhanced Raman readout. Benefiting from synergistic molecular amplification and nanostructure engineering, the aptasensor achieves an ultralow detection limit of 1.97 × 10^-17 g/mL, nearly 20,000-fold higher sensitivity than traditional sandwich assays, along with a broad dynamic range and high specificity. Furthermore, it exhibits excellent uniformity, reproducibility, stability, and recovery in spiked serum samples, using FGF2 used as a representative biomarker to validate its performance, highlighting great potential for clinical diagnostics and real-world applications.