2'--Methyl modified guide RNA promotes the single nucleotide polymorphism (SNP) discrimination ability of CRISPR-Cas12a systems.

The CRISPR-Cas12a system has been widely applied to genome editing and molecular diagnostics. However, off-target cleavages and false-positive results remain as major concerns in Cas12a practical applications. Herein, we propose a strategy by utilizing the 2'--methyl (2'-OMe) modified guide RNA (gRNA) to promote the Cas12a's specificity. Gibbs free energy analysis demonstrates that the 2'-OMe modifications at the 3'-end of gRNA effectively suppress the Cas12a's overall non-specific affinity while maintaining high on-target affinity. For general application illustrations, HBV genotyping and SARS-CoV-2 D614G mutant biosensing platforms are developed to validate the enhanced Cas12a's specificity. Our results indicate that the 2'-OMe modified gRNAs could discriminate single-base mutations with at least two-fold enhanced specificity compared to unmodified gRNAs. Furthermore, we investigate the enhancing mechanisms of the 2'-OMe modified Cas12a systems by molecular docking simulations and the results suggest that the 2'-OMe modifications at the 3'-end of gRNA reduce the Cas12a's binding activity to off-target DNA. This work offers a versatile and universal gRNA design strategy for highly specific Cas12a system development.