A Scalable, Easy-to-Deploy, Protocol for Cas13-Based Detection of SARS-CoV-2 Genetic Material

Jennifer N Rauch; Eric Valois; Sabrina C Solley; Friederike Braig; Ryan S Lach; Naomi J Baxter; Kenneth S Kosik; Carolina Arias; Diego Acosta-Alvear; Maxwell Z Wilson

These limitations underscore the need for alternative methods, such as CRISPR-based detection, to relieve some of the strain on the global supply chain for testing reagents. These state-ofthe-art methods are scalable, do not entail specialized instrumentation, and require very little specialized training. We designed CREST to capitalize on the strengths of both RT-qPCR and CRISPR-based detection, while addressing their shortcomings. CREST exploits the robustness and reliability of PCR, while harnessing the combined sensitivity and convenience of a coupled transcription-detection reaction. CREST can be run, from RNA sample to result, with no need for AC power or a dedicated facility, with minimal handling in ~2 hours. Because the signal saturates even at low input levels (Fig. 2B ) CREST offers the added advantage of binary result interpretation, similar to lateral flow test strips, but at a fraction of the price, as it does not require the costly antibodies or antibody-conjugates needed for lateral flow immunochromatography. Finally, while purified Cas13 is not yet commercially available, we were able to purify enough protein from a 1-liter bacterial culture for more than 500,000 reactions, and we can provide aliquots of protein upon request. Increasing the potential for field deployment of Cas13 for massive POC testing will require additional optimizations, such as lyophilization.