Next-generation CRISPR/Cas-based ultrasensitive diagnostic tools: current progress and prospects

CRISPR/Cas has been explored as a powerful molecular scissor that uses a double-strand break mediated non-homologous end joining (NHEJ) or homology-directed repair (HDR) to achieve precise gene editing. Cas effectors come in several different forms, each with its own set of features and applications. SpCas9 was the first and most extensively studied CRISPR/Cas version, and it has been hailed as a biotechnology breakthrough that could potentially correct mutations to treat genetic diseases. Recently, the Cas12 and Cas13 effector variants of Class II, Type V and Type VI, have been explored for their specific collateral cleavage (trans-cleavage) activity on target recognition. This trans-cleavage activity helps in the recognition of target nucleic acids. CRISPR diagnostics technology utilized the binding of crRNA with Cas12/13 protein to form the Ribonucleoproteins (RNPs) complex, which further cleaves the target sequence in cis-cleavage, followed by the activation of trans-cleavage of a nonspecific fluorescent DNA/RNA probe, resulting in the production of a fluorescent signal that could be quantitatively recorded. Later, nanotechnology and mobile-based detection applications were incorporated into the system to develop advanced lateral flow-based strips and are also associated with the technology to make it more feasible. Overall, this review compiles the experimental evidence consolidating the application of CRISPR/Cas as next-generation biosensors for diagnostic applications.