Mechanistic insights of CRISPR/Cas nucleases for programmable targeting and early-stage diagnosis: A review

Conventional and routine diagnostics such as polymerase chain reaction (PCR) and serological tests are less sensitive, costly, and require sample pretreatment procedures. CRISPR/Cas systems that inherently assist bacteria and archaea in destroying invading phage genetic materials via an RNA-mediated interference strategy have been reconstituted in vitro and harnessed for nucleic and non-nucleic acid diagnostics. CRISPR/Cas-based diagnostics (CRISPR-Dx) are cost-effective, possess excellent sensitivity (attomolar) and specificity (single base distinction), exhibit fast turnaround response, and support nucleic acid extraction-free workflow. However, CRISPR-Dx still needs to address various challenges to translate the laboratory work into end-user tailored solutions. In this perspective, we review the relevant progress of CRISPR/Cas systems-based diagnostics, focusing on the comprehensive customization and applications of leading and trending CRISPR/Cas systems as platform technologies for fluorescence, colorimetric, and electrical signal detection. The impact of the CRISPR game-changing technology on the COVID-19 pandemic is highlighted. We also demonstrate the role of CRISPR/Cas systems for carryover contamination prevention. The advancements in signal amplification strategies using engineered crRNAs, novel reporters, nanoparticles, artificial genetic circuits, microfluidics, and smartphones are also covered. Furthermore, we critically discuss the translation of CRISPR-Dx's basic research into end-user diagnostics for commercialization success in the near future. Finally, we discuss the complex challenges and alternative solutions to harness the CRISPR/Cas potential in detail.