DNA Flap-Controlled CRISPR/Cas12a Trans-Cleavage Enables Mix-and-Read FEN1 Activity Detection

CRISPR/Cas12a has emerged as a powerful biosensing tool, owing to its exceptional specificity and trans-cleavage-mediated signal amplification capability, for detecting flap endonuclease 1 (FEN1) activity. However, its reliance on additional preligation or replication steps increases operational complexity and raises the risk of false signals. Herein, we report a DNA flap-controlled CRISPR/Cas12a trans-cleavage (FCT-CRISPR) strategy that enables sensitive, accurate, and mix-and-read detection for FEN1 activity. In FCT-CRISPR, a flap-structured dumbbell DNA probe was ingeniously designed, in which the flap domain serves as a split activator, and the dumbbell scaffold acts as a steric hindrance unit. Upon FEN1 recognition and cleavage, the split activator is liberated from its constrained configuration in the dumbbell scaffold, thereby activating CRISPR/Cas12a trans-cleavage activity. FCT-CRISPR strategy avoids the reliance on exogenous DNA ligation or replication processes, allowing mix-and-read detection of FEN1 activity with a detection limit as low as 0.2 mU and excellent specificity against nontarget enzymes. In addition, the successful detection application in lysates of cancer cells demonstrates the potential of FCT-CRISPR for clinical use. This work establishes a sensitive, accurate, and mix-and-read platform for monitoring FEN1 activity and offers a promising tool for the early diagnosis of FEN1-related diseases.