Triplex DNA clamp regulates Cas12a activation for ssDNA and RNA sensing

We present a molecular strategy that enables the programmable activation of the CRISPR–Cas12a system in response to triplex DNA formation triggered by single-stranded DNA (ssDNA) or RNA inputs. Our triplex-controlled Cas12a assay leverages the high specificity of clamp-like triplex structures to control a toehold-based strand displacement reaction within a rationally designed DNA hairpin (PAM-Switch). Upon displacement and protospacer adjacent motif (PAM) complementation, the Cas12a ribonucleoprotein (RNP) is activated, initiating trans-cleavage and producing a concentration-dependent fluorescent signal. By decoupling target recognition (via triplex formation) from direct hybridization with the Cas12a–crRNA complex, the assay eliminates the need for target-specific crRNAs. This design also allows multiple detection of distinct nucleic acid (NA) targets using a single Cas12a reaction mix. Through the use of triplex-based clamps, the proposed platform achieves enhanced specificity for single-nucleotide variants and supports the detection of both ssDNA and RNA targets across a broad range of lengths (10–20 nucleotides), addressing key limitations in current Cas12a-based diagnostics and opening new avenues for NA sensing.