Development and application of sensitive, specific, and rapid CRISPR-Cas13-based diagnosis

Nucleic acid detection is a necessary part of medical treatment and fieldwork. However, the current detection technologies are far from ideal. A lack of timely and accessible testing for identifying cases and close contacts has allowed severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the causative virus of the ongoing coronavirus disease-2019 (COVID-19) pandemic, to spread uncontrollably. The slow and expensive detection of mutations-predictors for chronic diseases such as cancer-form a barrier to personalized treatment. A recently developed diagnostic assay is ideal and field-ready-it relies on CRISPR-Cas13. CRISPR-Cas13 works similarly to other CRISPR systems: Cas13 is guided by a crRNA to cleave next to a specific RNA target sequence. Additionally, Cas13 boasts a unique collateral cleavage activity; collateral cleavage of a fluorescent reporter detects the presence of the target sequence in sample RNA. This system forms the basis of CRISPR-Cas13 diagnostic assays. CRISPR-Cas13 assays have >95% sensitivity and >99% specificity. Detection is rapid (<2 h), inexpensive ($0.05 per test), and portable-a test using lateral flow strips is akin to a pregnancy test. The recent adaptation of micro-well chips facilitates high-level multiplexing and is high-throughput. In this review, we cover the development of CRISPR-Cas13 assays for medical diagnosis, discuss the advantages of CRISPR-Cas13-based diagnosis over the traditional reverse transcription polymerase chain reaction (RT-PCR), and present examples of detection from real patient samples.