PddCas: A Polydisperse Droplet Digital CRISPR/Cas-Based Assay for the Rapid and Ultrasensitive Amplification-Free Detection of Viral DNA/RNA

SATORI: Amplification-free digital RNA detection method for the diagnosis of viral infections

With the recent global outbreak of COVID-19, there is an urgent need to establish a versatile diagnostic method for viral infections. Gene amplification test or antigen test are widely used to diagnose viral infections; however, these methods generally have technical drawbacks either in terms of sensitivity, accuracy, or throughput. To address this issue, we recently developed an amplification-free digital RNA detection method (SATORI), which can identify and detect viral genes at the single-molecule level in approximately 9 min, satisfying almost all detection performance requirements for the diagnosis of viral infections. In addition, we also developed practical platforms for SATORI, such as an automated platform (opn-SATORI) and a low-cost compact fluorescence imaging system (COWFISH), with the aim of application in clinical settings. Our latest technologies can be inherently applied to diagnose a variety of RNA viral infections, such as COVID-19 and Influenza A/B, and therefore, we expect that SATORI will be established as a versatile platform for point-of-care testing of a wide range of infectious diseases, thus contributing to the prevention of future epidemics. This article is an extended version of the Japanese article published in the SEIBUTSU BUTSURI Vol. 63, p. 115-118 (2023).

Rapid and Sensitive Diagnosis of COVID-19 Using an Electricity-Free Self-Testing System

Rapid and sensitive detection of coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is essential for early diagnosis and effective treatment. Nucleic acid testing has been considered the gold standard method for the diagnosis of COVID-19 for its high sensitivity and specificity. However, the polymerase chain reaction (PCR)-based method in the central lab requires expensive equipment and well-trained personnel, which makes it difficult to be used in resource-limited settings. It highlights the need for a sensitive and simple assay that allows potential patients to detect SARS-CoV-2 by themselves. Here, we developed an electricity-free self-testing system based on reverse transcription loop-mediated isothermal amplification (RT-LAMP) that allows for rapid and accurate detection of SARS-CoV-2. Our system employs a heating bag as the heat source, and a 3D-printed box filled with phase change material (PCM) that successfully regulates the temperature for the RT-LAMP. The colorimetric method could be completed in 40 min and the results could be read out by the naked eye. A ratiometric measurement for exact readout was also incorporated to improve the detection accuracy of the system. This self-testing system is a promising tool for point-of-care testing (POCT) that enables rapid and sensitive diagnosis of SARS-CoV-2 in the real world and will improve the current COVID-19 screening efforts for control and mitigation of the pandemic.

CDetection.v2: One-pot assay for the detection of SARS-CoV-2

Introduction

The ongoing 2019 coronavirus disease pandemic (COVID-19), caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and its variants, is a global public health threat. Early diagnosis and identification of SARS-CoV-2 and its variants plays a critical role in COVID-19 prevention and control. Currently, the most widely used technique to detect SARS-CoV-2 is quantitative reverse transcription real-time quantitative PCR (RT-qPCR), which takes nearly 1 hour and should be performed by experienced personnel to ensure the accuracy of results. Therefore, the development of a nucleic acid detection kit with higher sensitivity, faster detection and greater accuracy is important.

Methods

Here, we optimized the system components and reaction conditions of our previous detection approach by using RT-RAA and Cas12b.

Results

We developed a Cas12b-assisted one-pot detection platform (CDetection.v2) that allows rapid detection of SARS-CoV-2 in 30 minutes. This platform was able to detect up to 5,000 copies/ml of SARS-CoV-2 without cross-reactivity with other viruses. Moreover, the sensitivity of this CRISPR system was comparable to that of RT-qPCR when tested on 120 clinical samples.

Discussion

The CDetection.v2 provides a novel one-pot detection approach based on the integration of RT-RAA and CRISPR/Cas12b for detecting SARS-CoV-2 and screening of large-scale clinical samples, offering a more efficient strategy for detecting various types of viruses.