Although CRISPR-Cas12a [clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR-associated protein 12a] combining pre-amplification technology has the advantage of high sensitivity in biosensing, its generality and specificity are insufficient, which greatly restrains its application range. Here, we discovered a new targeting substrate for LbaCas12a (Lachnospiraceae bacterium Cas12a), namely double-stranded DNA (dsDNA) with a sticky-end region (PAM⁻SE⁺ dsDNA). We discovered that CRISPR-Cas12a had special enzymatic properties for this substrate DNA, including the ability to recognize and cleave it without needing a protospacer adjacent motif (PAM) sequence and a high sensitivity to single-base mismatches in that substrate. Further mechanism studies revealed that guide RNA (gRNA) formed a triple-stranded flap structure with the substrate dsDNA. We also discovered the property of low-temperature activation of CRISPR-Cas12a and, by coupling with the unique DNA hybridization kinetics at low temperature, we constructed a complete workflow for low-abundance point mutation detection in real samples, which was fast, convenient and free of single-stranded DNA (ssDNA) transformation. The detection limits were 0.005–0.01% for synthesized strands and 0.01–0.05% for plasmid genomic DNA, and the mutation abundances provided by our system for 28 clinical samples were in accordance with next-generation sequencing results. We believe that our work not only reveals novel information about the target recognition mechanism of the CRISPR-Cas12a system, but also greatly broadens its application scenarios.

Detecting small molecules is pivotal across fields like clinical diagnostics, environmental monitoring, and food safety. The CRISPR-Cas12a system, known for its simplicity and sensitivity, offers a promising basis for small molecule detection. However, current CRISPR-based detection methods face challenges, including complex design requirements, high background noise, and limited adaptability to different targets. In our study, we introduce the SBS-Cas system, leveraging a split crRNA mode to induce spatial hindrance on the scaffold strand through molecular binding. This approach prevents the assembly with Cas12a, effectively masking its trans-cleavage activity. By introducing small molecules that competitively bind to the macromolecule, we eliminate this spatial hindrance, activating Cas12a. Our results demonstrate high sensitivity, versatility, and adaptability in small molecule detection across multiple reactions, with successful intracellular imaging and responsive fluctuations in complex environments underscoring the system’s robustness. This innovative CRISPR-Cas12a-based approach establishes a low-background, highly sensitive platform for small molecule detection. SBS-Cas promises not only to enhance tools for clinical, environmental, and food safety applications but also to advance CRISPR research, providing insights and expanding possibilities in molecular detection science.

Sensitive and specific DNA hybridization is essential for nucleic acid chemistry. Competitive composition of probe and blocker has been the most adopted probe design for its relatively high sensitivity and specificity. However, the sensitivity and specificity were inversely correlated over the length and concentration of the blocker strand, making the optimization process cumbersome. Herein, we construct a theoretical model for competitive DNA hybridization, which disclose that both the thermodynamics and kinetics contribute to the inverse correlation. Guided by this, we invent the 4-way Strand Exchange LEd Competitive DNA Testing (SELECT) system, which breaks up the inverse correlation. Using SELECT, we identified 16 hot-pot mutations in human genome under uniform conditions, without optimization at all. The specificities were all above 140. As a demonstration of the clinical practicability, we develop probe systems that detect mutations in human genomic DNA extracted from ovarian cancer patients with a detection limit of 0.1%.