Recognition of DNA Target Formulations by CRISPR-Cas12a Using a dsDNA Reporter.

CRISPR-Cas12a is a powerful platform for DNA-based diagnostics. The detection scheme relies on unselective shredding of a fluorescent ssDNA reporter upon target DNA recognition. To extend the reporter library beyond ssDNAs, we discovered a fluorescent reporter type using a dsDNA template. In this design, the fluorescence of the dsDNA reporter is quenched via contact-quenching mechanism. Upon detection, the quenched fluorescence recovers with the activation Cas12a complex. Here, we compared the probing performance of two dsDNA reporters with two ssDNA reporters. The rate of the Cas12a trans-cleavage reaction was studied using one of the dsDNA reporters under different settings. The detection of different sizes of dsDNA or ssDNA targets was studied systematically under three different temperatures. Lower thresholds for ssDNA and dsDNA target size were identified. The mismatch tolerance and target specificity were examined for both ssDNA and dsDNA targets, separately. The probing performance of the dsDNA reporter was evaluated in a random DNA pool with and without target strands. We report that dsDNA can serve as a tunable fluorescence reporter template expanding the toolbox for Cas12a-based diagnostics.