Engineered CRISPR/Cas12a Enables Rapid SARS-CoV-2 Detection

Nguyen, L. T.; Rananaware, S. R.; Pizzano, B. L. M.; Stone, B. T.; Jain, P. K.

The coronavirus disease (COVID-19) caused by SARS-CoV-2 has swept through the globe at an unprecedented rate. CRISPR-based detection technologies such as DETECTR, SHERLOCK, and STOPCovid have emerged as a rapid and affordable platform that can shape the future of diagnostics. Recently, we reported engineered crRNAs for Cas12a, called ENHANCE, that enables enhanced detection of nucleic acids. Here we report development, clinical validation, and advancement of ENHANCE platform for detecting SARS-CoV-2. With an RT-LAMP pre-amplification step, ENHANCE detects samples down to a single copy with 95% accuracy and shows high specificity towards various isolates of SARS-CoV-2 against 31 highly similar and common respiratory pathogens. Utilizing LbCas12a-mediated trans-cleavage activity, ENHANCE works robustly in a wide range of magnesium concentration (3 mM-13 mM), allowing for further assay optimization. Additionally, ENHANCEv2 is developed to further improve the previously reported ENHANCE. ENHANCEv2 employs mutated LbCas12aD156R, engineered chimeric DNA-extended crRNA, and a dual reporter for both fluorescence-based reporter assay and lateral flow assay. Both ENHANCE and ENHANCEv2 are validated in 62 clinical nasopharyngeal swabs, showing 60/62 (96.7%) agreement with RT-qPCR results, and using only 5 L of sample and 20 minutes of CRISPR reaction. Lateral flow assay on paper strips displays 100% agreement with fluorescence-based reporter assay in the clinical validation. Following a 30-minute pre-amplification RT-LAMP step, the lyophilized ENHANCEv2 is shown to achieve high sensitivity and specificity while reducing CRISPR reaction time to as low as 3 minutes and maintaining its detection capability upon storage at room temperature for several weeks.