Cas12aFDet: A CRISPR/Cas12a-based fluorescence platform for sensitive and specific detection of Listeria monocytogenes serotype 4c.

The CRISPR/Cas12a system has displayed remarkable potential in the development of new methods for nucleic acid detection owing to the trans-cleavage activity of Cas12a. Despite the tremendous development in recent years, existing CRISPR/Cas12a-based methods have several limitations such as the time-consuming process, which takes up to 2 h, and the risk of aerosol contamination during DNA amplicon transfer. Herein, we propose a CRISPR/Cas12a-based fluorescence detection platform named "Cas12aFDet" for rapid nucleic acid detection that overcomes these limitations. By integrating PCR or recombinase-aided amplification (RAA) methods with Cas12a-mediated cleavage in a sealed reaction tube, Cas12aFDet-based detection of amplified products could be accomplished within 15 min, while avoiding amplicon contamination. The detection limits of PCR-based Cas12aFDet and RAA-based Cas12aFDet were determined to be 3.37 × 101 cfu/mL and 1.35 × 102 cfu/mL of Listeria monocytogenes serotype 4c in pure culture, respectively. Most importantly, RAA-based Cas12aFDet exhibited 0.64 aM sensitivity for DNA detection, and showed high specificity for detection of other serotypes of Listeria and non-Listeria strains. Furthermore, the feasibility of the RAA-based Cas12aFDet method was evaluated in spiked and natural samples, enabling the quantitative detection of 1.35 × 108-1.35 × 103 cfu/g fresh grass carp of the target L. monocytogenes serotype 4c, and the results obtained for 22 natural aquatic samples were highly consistent with those of the culture-based serotyping method. The established Cas12aFDet platform is expected to provide a new paradigm for the sensitive and specific detection of pathogens in food safety and clinical diagnosis.