Amplification-free one-pot RNA detection by pairing CRISPR–Cas13a with cascade amplification circuit-driven DNAzyme (RAPID)

Abstract

RNA has become a versatile target for diagnosing a wide range of pathogens. The demand for rapid and accurate diagnostics in point-of-care (POC) or resource-limited settings is growing. However, most RNA-based assays depend on reverse transcription and complex instruments (e.g., RT-qPCR), restricting their use in these settings. Isothermal amplification methods provide a simpler alternative with reduced instrumentation requirements, but their high amplification efficiency raises concerns about nucleic acid carry-over contamination. To address these challenges, we developed RAPID (CRISPR–Cas13a with a cascade amplification circuit-driven DNAzyme), an isothermal, one-pot RNA detection biosensing platform that eliminates the need for sample pre-amplification. RAPID integrates the precise target recognition by CRISPR–Cas13a with robust signal amplification by a toehold-mediated strand-displacement DNA circuit, eliminating the need for reverse transcription and thermal cycling. This platform enables quantitative RNA detection within 30 min at 37 °C. By reprogramming RAPID crRNAs, we successfully detected both bacterial (e.g., Treponema pallidum and Neisseria gonorrhoeae) and viral (e.g., herpes simplex virus) targets. The RAPID platform is designed for versatile detection, being compatible with both fluorescence-based (RAPID-Flu) and lateral flow assay (RAPID-LFA) readouts. The RAPID-Flu and RAPID-LFA both demonstrated a sensitivity of 5 fM per reaction, exhibiting comparable detection limits. Both methods showed excellent specificity and high concordance with clinical diagnoses of Neisseria gonorrhoeae. In summary, the RAPID platform provides rapid, programmable, and visually interpretable solutions with strong potential for POC diagnostics. Its flexibility and portability make it particularly suitable for early diagnosis and on-site monitoring of diverse infectious pathogens.