Objective To establish a one-step detection method based on recombinase polymerase amplification (RPA) and CRISPR/Cas12a protein for the rapid and sensitive detection of human influenza B virus.

Methods RPA amplification primers were designed according to the conserved gene (NS1 gene) of human influenza B virus (Victoria lineage). The reaction system was established using the standard plasmid as the template. First of all, the reaction system was incubated at 37 ℃ for 15 minutes for RPA amplification. Then, the CRISPR/Cas12a system on the tube cap was thoroughly mixed with the RPA amplification product at the bottom of the tube through fast centrifugation, and real-time fluorescence detection was carried out at 37 ℃. The reaction conditions were optimized to establish a one-step RPA-CRISPR/Cas12a detection method for human influenza B virus. The sensitivity of the testing method was evaluated using standard plasmids and pseudoviruses, and the specificity was evaluated using other viruses that may cause febrile respiratory syndrome. The consistency between the results of the one-step detection method and those of RT-qPCR detection was evaluated by testing real samples.

Results A one-step detection method based on RPA-CRISPR/Cas12a was successfully established. The optimal reaction conditions included a reaction temperature of 37 ℃, a Cas12a/crRNA concentation ratio of 1∶1, a Cas12a concentration of 120 nmol/L, a single-stranded DNA (ssDNA) probe concentration of 300 nmol/L, and a primer concentration of 480 nmol/L. The method could detect standard plasmid DNA as low as 2.8 copies/μL within 25 minutes and pseudoviruses as low as 2.77 copies/μL within 30 minutes. The testing method showed high specificity, and no cross-reaction was observed with the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), influenza A (H1N1) virus, or respiratory syncytial virus subgroup A. When testing clinical samples, the sensitivity and the specificity for examining clinical samples were 93.33% and 100%, respectively, and consistency with RT-qPCR results was 97.14%.

Conclusion With the one-step detection method based on RPA-CRISPR/Cas12a established in this study, the whole sample detection process, including nucleic acid release, reverse transcription, isothermal amplification, CRISPR/Cas12a system cleavage, and fluorescence signal output, can be completed within 30 minutes. Its high sensitivity, specificity, and successful application in clinical samples highlight its potential for rapid point-of-care testing in clinical settings.