Nucleic acid amplification technologies are pivotal in diagnostics but face challenges from nonspecific amplification and inefficient proofreading. CRISPR-based methods are hindered by persistent protein occupation postcleavage, limiting scalability. Here, we present an OMEGA IsrB Nickase Cyclic Exponential (ONCE) amplification, a novel isothermal strategy leveraging the RNA-guided nickase IsrB for site-specific proofreading. ONCE uniquely integrates DNA polymerase to cyclically displace IsrB from target sites, enabling high-fidelity, one-pot exponential amplification. Systematic validation de...