Wei S. Zhang,Jianbin Pan,Feng Li,Min Zhu,Mengting Xu,Hongyan Zhu,Yanyan Yu,Gaoxing Su
The outbreak of the pandemic caused by the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) calls for an urgent unmet need for developing a facial and cost-effective detection method. The requirement of well-trained personnel and sophisticated instrument of current primary mean (reverse transcription polymerase chain reaction, RT-PCR) may hinder the practical application worldwide. In this regard, a reverse transcription recombinase polymerase amplification (RT-RPA) coupled with CRISPR-Cas12a colorimetric assay is proposed for the SARS-CoV-2 detection. The methodology we have described herein utilizes DNA-modified gold nanoparticles (AuNPs) as a universal colorimetric readout and can specifically target ORF1ab and N regions of the SARS-CoV-2 genome. After the virus genome is amplified through RT-RPA, the resulting abundant dsDNA will bind and activate Cas12a. Under trans-cleavage degradation, the capped DNA substrate will be hydrolyzed gradually from AuNPs, demonstrating a change in the surface plasmon resonance (SPR), which can be facially monitored by UV–vis absorbance spectroscopy and naked eye observation. The high amplification efficiency from RT-RPA and Cas12a trans-cleavage process bring the sensitivity of our method to 1 copy of viral genome sequence per test. Notably, under the dual variations inspecting from the isothermal amplification and Cas12a activation process, the false positive events from other beta coronavirus members can be effectively avoided and thus significantly improve the specificity. Furthermore, the reliability of this colorimetric assay is validated by standard clinical samples from the hospital laboratory department. Through integration of the inherently high sensitivity and specificity from an RPA-coupled Cas12a system with the intrinsic simplicity of AuNP-based colorimetric assay, our method increases the practical testing availability of SARS-CoV-2.
The construction of a rapid, simple, and specific nucleic acid detection platform is of great significance to the control of the large-scale spread of infectious diseases. We have recently established a magnetic pull-down-assisted colorimetric method based on the CRISPR/Cas12a system (termed M−CDC), which effectively integrates the advantages of CRISPR/Cas12a, magnetic beads-based separation, and AuNP bioprobe to provide a simple and specific biosensing platform for nucleic acid assay. The M−CDC method is compatible with point-of-care testing and enables the detection of nucleic acid samples in less than an hour without relying on expensive and complex instruments. In this paper, step-by-step instructions for M−CDC assay, including recombinase polymerase amplification (RPA)/reverse transcription-polymerase chain reaction (RT-RPA) of DNA or RNA, Cas12a-mediated target recognition and cleavage, and subsequent magnetic beads-mediated colorimetric readouts are provided. In addition, the protocol for the expression and purification of Lachnospiraceae bacterium -Cas12a (LbCas12a) protein, the design and synthesis of high-efficient crRNA, and the preparation of AuNP bioprobe are also offered.
Lijuan Yin,Liangyuan Wang,Lu Yin,Lingzhi Yang,Baoxue Gao,Shuli Man,Fufeng Liu,Long Ma
Norovirus (NoV) represents a leading cause of foodborne illness worldwide and is the predominant agent of non-bacterial acute gastroenteritis. The development of rapid, highly sensitive, specific, and point-of-care detection methods is critical for the protection of public health and food safety. In this study, we developed a lyophilized paper-based microfluidic analytical device (μPAD) that integrates reverse transcription recombinase polymerase amplification (RT-RPA) with CRISPR/Cas12a technology. By incorporating a smartphone-assisted portable fluorescence detection device, the platform achieves a high level of integration, simplicity, and intelligence. It demonstrates a detection limit for NoV as low as 1 copy/μL within 45 min, with no cross-reactivity against other common microorganisms or the human genome. The fluorescence intensity on the chips exhibits a strong linear relationship with NoV RNA concentration, enabling accurate quantification. Moreover, the lyophilized RPA-CRISPR paper chips retain stability for up to 8 weeks at room temperature, underscoring their suitability for point-of-care applications. When applied to real food and environmental samples for NoV detection, the platform showed 100% concordance with RT-qPCR and maintained a detection sensitivity of 1 copy/μL. This work provides a robust approach for rapid, sensitive, and on-site detection of norovirus, and the platform architecture holds promise for broader application in detecting other microorganisms.
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