[Paper Review] Rapid and Accurate Detection of SARS-CoV-2 Mutations using a Cas12a-based Sensing Platform

Cai He, Chung‐Chih Lin+15 more|arXiv (Cornell University)|Oct 25, 2021

CRISPR and Genetic Engineering11 references4 citations

TL;DR

This study presents RT-CORDS, a Cas12a-based CRISPR sensing platform that enables rapid, sensitive, and specific detection of key SARS-CoV-2 spike mutations (e.g., N501Y, D614G, 69/70 deletion) in under 10 minutes post-RT-PCR using fluorescence or lateral flow readouts. The method achieves 100% accuracy compared to sequencing and a detection limit of 6 copies/μL (10⁻¹⁷ M), offering a scalable tool for clinical variant surveillance.

ABSTRACT

The increasing prevalence of SARS-CoV-2 variants with spike mutations has raised concerns owing to higher transmission rates, disease severity, and escape from neutralizing antibodies. Rapid and accurate detection of SARS-CoV-2 variants provides crucial information concerning the outbreaks of SARS-CoV-2 variants and possible lines of transmission. This information is vital for infection prevention and control. We used a Cas12a-based RT-PCR combined with CRISPR on-site rapid detection system (RT-CORDS) platform to detect the key mutations in SARS-COV-2 variants, such as 69/70 deletion, N501Y, and D614G. We used type-specific CRISPR RNAs (crRNAs) to identify wild-type (crRNA-W) and mutant (crRNA-M) sequences of SARS-CoV-2. We successfully differentiated mutant variants from wild-type SARS-CoV-2 with a sensitivity of $10^{-17}$ M (approximately 6 copies/$μ$L). The assay took just 10 min with the Cas12a/crRNA reaction after a simple RT-PCR using a fluorescence reporting system. In addition, a sensitivity of $10^{-16}$ M could be achieved when lateral flow strips were used as readouts. The accuracy of RT-CORDS for SARS-CoV-2 variant detection was 100% consistent with the sequencing data. In conclusion, using the RT-CORDS platform, we accurately, sensitively, specifically, and rapidly detected SARS-CoV-2 variants. This method may be used in clinical diagnosis.

Motivation & Objective

• To develop a rapid, accurate, and scalable method for detecting clinically relevant SARS-CoV-2 spike mutations in emerging variants.
• To address the urgent need for point-of-care diagnostics that can distinguish between wild-type and mutant SARS-CoV-2 strains in real time.
• To enable timely outbreak tracking and infection control by providing a low-cost, high-specificity detection platform compatible with field use.

Proposed method

• The RT-CORDS platform combines reverse transcription (RT) with CRISPR-Cas12a-based detection using type-specific crRNAs targeting wild-type (crRNA-W) and mutant (crRNA-M) SARS-CoV-2 sequences.
• Cas12a is programmed with crRNAs to recognize and cleave reporter probes upon target binding, generating a fluorescence signal in real time.
• The system uses a fluorescence reporting system for quantitative detection or lateral flow strips for visual readout in resource-limited settings.
• The method is applied after a standard RT-PCR amplification step, ensuring high sensitivity and specificity.
• Detection relies on collateral cleavage activity of activated Cas12a, which enables signal amplification and low detection limits.

Experimental results

Research questions

• RQ1 Can a CRISPR-Cas12a-based platform detect key SARS-CoV-2 spike mutations with high sensitivity and specificity in a rapid format?
• RQ2 How does the RT-CORDS platform compare to gold-standard Sanger sequencing in accuracy for variant detection?
• RQ3 What is the limit of detection for mutant SARS-CoV-2 sequences using fluorescence and lateral flow readouts?
• RQ4 Can the platform be adapted for point-of-care use with minimal equipment and training?

Key findings

• The RT-CORDS platform achieved a limit of detection of 10⁻¹⁷ M (approximately 6 copies/μL) using fluorescence readout, demonstrating high sensitivity.
• With lateral flow strip readout, the limit of detection was 10⁻¹⁶ M, indicating robust performance in visual detection formats.
• The method showed 100% consistency with Sanger sequencing data, confirming its high accuracy in distinguishing wild-type from mutant SARS-CoV-2 strains.
• Variant detection was completed in less than 10 minutes after RT-PCR, enabling rapid turnaround for clinical and public health use.
• The platform successfully differentiated key mutations including N501Y, D614G, and 69/70 deletion using mutation-specific crRNAs.