Abstract
CRISPR-Cas diagnostics are revolutionizing point-of-care molecular testing due to the programmability, simplicity, and sensitivity of Cas systems with trans-cleavage activity. CRISPR-Cas12 assays are promising for detecting single nucleotide polymorphisms (SNPs). However, reports vary widely describing Cas12 SNP sensitivity, and an underlying mechanism is lacking. We systematically varied crRNA length and valency to investigate the role of crRNA architectures on Cas12 biosensing in the context of speed-of-detection, sensitivity, and selectivity. Our results demonstrate that crRNAs complementary to 20 base pairs of the target DNA is optimal for rapid and sensitive detection, while a complementary length of 15 base pairs is ideal for robust SNP detection. Additionally, we uncovered a unique periodicity in SNP sensitivity based on nucleotide position and developed a structural model explaining what drives Cas12 SNP sensitivity. Lastly, we showed that bivalent CRISPR-Cas sensors have synergistic and enhanced activity that is distance dependent.