A high-fidelity DNAzyme-assisted CRISPR/Cas13a system with single-nucleotide resolved specificity

A CRISPR/Cas system represents an innovative tool for developing a new-generation biosensing and diagnostic strategy. However, the off-target issue (i.e., mistaken cleavage of nucleic acid targets and reporters) remains a great challenge for its practical applications. We hypothesize that this issue can be overcome by taking advantage of the site-specific cleavage ability of RNA-cleaving DNAzymes. To test this idea, we propose a DNAzyme Operation Enhances the Specificity of CRISPR/Cas13a strategy (termed DOES-CRISPR) to overcome the problem of relatively poor specificity that is typical of the traditional CRISPR/Cas13a system. The key to the design is that the partial hybridization of the CRISPR RNA (crRNA) with the cleavage fragment of off-target RNA was not able to activate the collateral cleavage activity of Cas13a. We showed that DOES-CRISPR can significantly improve the specificity of traditional CRISPR/Cas13a-based molecular detection by up to ∼43-fold. The broad utility of the strategy is illustrated through engineering three different systems for the detection of microRNAs (miR-17 and let-7e), CYP2C19*17 gene, SARS-Cov-2 variants (Gamma, Delta, and Omicron) and Omicron subtypes (BQ.1 and XBB.1) with single-nucleotide resolved specificity. Finally, clinical evaluation of this assay using 10 patient blood samples demonstrated a clinical sensitivity of 100% and specificity of 100% for genotyping CYP2C19*17, and analyzing 20 throat swab samples provided a diagnostic sensitivity of 95% and specificity of 100% for Omicron detection, and a clinical sensitivity of 92% and specificity of 100% for XBB.1 detection.