CRISPR/Cas12a2 enables ultra-sensitive amplification-free RNA detection

Advances in clustered regularly interspaced short palindromic repeat (CRISPR) technologies have led to the use of diverse CRISPR-associated (Cas) proteins in diagnostic applications. Herein, we present a CRISPR/Cas12a2-based amplification-free RNA detection method that exhibits sub-attomolar sensitivity and substrate versatility. Cas12a2, a recently characterized RNA-guided nuclease, uniquely integrates bimolecular recognition through CRISPR RNA (crRNA)-target complementarity and protospacer flanking sequence identification, enabling highly specific trans-cleavage of single-stranded DNA, double-stranded DNA, and RNA. We have optimized key biochemical parameters, including pH, ionic strength, and temperature, to enhance the catalytic efficiency of Cas12a2. Based on the optimal activity conditions of Cas12a2, we have achieved ultra-sensitive viral RNA detection with a limit of detection of 46.7 aM through the strategic design and cooperative activation of crRNAs targeting conserved regions of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) genome. The diagnostic accuracy of the Cas12a2-based assay has been demonstrated for 26 SARS-CoV-2 variants, and it has further resulted in the definitive diagnosis of 317 clinical samples. This work establishes Cas12a2 as a promising molecular diagnostic tool that provides an amplification-free, rapid, and versatile solution for RNA detection. The adaptability and simplicity of the platform render it particularly well suited for point-of-care applications, paving the way for next-generation CRISPR diagnostics.