EXAGO: An Argonaute-Based Primer-Free Exponential Amplification Strategy for Ultrasensitive Zero-Background Detection of Point Mutation

Ultrasensitive gene detection is crucial for precise molecular diagnostics. Conventional nucleic acid amplification methods frequently encounter nonspecific amplification triggered by exogenous primers, which limits their utility in ultrasensitive detection. Programmable gene editing tools, such as CRISPR/Cas and Argonaute (Ago), provide new avenues for developing next-generation detection technologies. Here, we develop an Ago-mediated exponential amplification strategy, EXAGO, for ultrasensitive detection of the epidermal growth factor receptor (EGFR) L858R mutation─a critical biomarker in nonsmall cell lung cancer. Leveraging the flexible programmability and single-base-resolution cleavage activity of Ago, EXAGO can specifically initiate DNA polymerase reactions at the target mutation site. The mechanism of dual-circuit operation allows the system to achieve an efficient exponential amplification under thermal cycling. By circumventing exogenous primers, it also prevents nonspecific amplification caused by primer misidentification at the source. Moreover, wild-type genes are entirely unable to trigger signal amplification, thereby underscoring their superior specificity and the potential for practical application. Experimental results demonstrated that EXAGO achieves femtomolar-level sensitivity and exhibits favorable recovery rates for detecting plasma-diluted samples. Moreover, the use of a thermostable enzyme allows direct compatibility with cell thermal lysis, enabling detection in cell lysates. In summary, EXAGO offers a robust and practical solution for accurate genetic mutation analysis in complex samples and promotes the application of Ago-based tools in molecular diagnostics.