Lambda exonuclease assisted helicase-dependent amplification CRISPR/Cas12a detection of Listeria monocytogenes

We describe the construction of a protospacer adjacent motif-free CRISPR/Cas12a fluorescent biosensor based on lambda exonuclease (λ-exo) and helicase-dependent amplification (HDA) to detect Listeria monocytogenes(L. monocytogenes). The hlyA gene of L. monocytogenes was amplified by HDA. After λ-exo catalyzed cleavage of 5' phosphorylated single-stranded DNA of amplification product double-stranded DNA, the double-stranded DNA formed single-stranded DNA (ssDNA). The ssDNA as a substrate activated the trans-cleavage capability of CRISPR/Cas12a to cleave the reporter gene to produce fluorescence signals. Under optimized experimental conditions, the lower limit of L. monocytogenes detection by the fluorescent biosensor was 11.5 CFU/mL, with a linear range of detection from 10¹ to 10⁷ CFU/mL. The fluorescent biosensor permits simple and sensitive detection of L. monocytogenes and provides a promising analysis platform for clinical diagnosis and biomedical research without protospacer adjacent motif sequence ssDNA.