iSCAN: An RT-LAMP-coupled CRISPR-Cas12 module for rapid, sensitive detection of SARS-CoV-2

Efficient, specific and direct detection of double-stranded DNA targets using Cas12f1 nucleases and engineered guide RNAs

To address the limitations of the CRISPR/Cas12f1 system in clinical diagnostics, which require the complex preparation of single-stranded DNA (ssDNA) or in vitro transcripts (RNA), we developed a fluorescent biosensor named PDTCTR (PAM-dependent dsDNA Target-activated Cas12f1 Trans Reporter). This innovative biosensor integrates Recombinase Polymerase Amplification (RPA) with the Cas12f_ge4.1 system, facilitating the direct detection of double-stranded DNA (dsDNA). PDTCTR represents a significant leap forward, exhibiting a detection sensitivity that is a hundredfold greater than the original Cas12f1 system. It demonstrates the capability to detect Mycoplasma pneumoniae (M. pneumoniae) and Hepatitis B virus (HBV) with excellent sensitivity of 10 copies per microliter (16.8 aM) and distinguishes single nucleotide variations (SNVs) with high precision, including the EGFR (L858R) mutations prevalent in non-small cell lung cancer (NSCLC). Clinical evaluations of PDTCTR have demonstrated its high sensitivity and specificity, with rates ranging from 93%-100% and 100%, respectively, highlighting its potential to revolutionize diagnostic approaches for infectious diseases and cancer-related SNVs.This research underscores the substantial advancements in CRISPR technology for clinical diagnostics and its promising future in early disease detection and personalized medicine.

CRISPR/Cas12b assisted loop-mediated isothermal amplification for easy, rapid and sensitive quantification of chronic HBV DNA in one-pot

BACKGROUND

Currently, millions of people suffer from undiagnosed chronic hepatitis B (CHB) infection each year, which leads to high mortality rates attributed to cirrhosis and hepatocellular carcinoma. Previously reported assays, such as PCR-based assays, have limitations in terms of convenient for CHB screening in high-burden regions and resource-limited settings. Recently, diagnosis based on CRISPR/Cas, which has been considered as a potential method of point-of-care test (POCT) in resource-limited settings, offers a significant advantage in terms of high sensitivity and specificity. Therefore, there is an urgent need for the hepatitis B virus (HBV) detection utilizing CRISPR/Cas system.

RESULTS

We have proposed a one-pot of one-step method for CRISPR/Cas12b assisted loop-mediated isothermal amplification (LAMP) to facilitate the quick, sensitive, and precise quantification of HBV DNA. This method is designed for point-of-care testing following genomic extraction or sample heat treatment. We have optimized several critical factors, such as the reaction buffer, AapCas12b-gRNA concentration, reporter and its concentration, reaction temperature, and chemical additives, to significantly enhance the performance of the one-pot assay for HBV. Importantly, it exhibited no cross-reactivity between HBV and blood-borne pathogens. Moreover, the assay is capable of quantifying HBV DNA within 1 h with a limit of detection (LOD) of 25 copies per milliliter. Additionally, when tested on 236 clinical samples, the assay demonstrated a sensitivity of 99.00 % (198/200) and a specificity of 100.00 % (36/36) at the 99 % confidence level compared to real-time quantitative PCR.

SIGNIFICANCE

The utilization of convenient and reliable point-of-care diagnostic methods is crucial for reducing the burden of CHB globally. The assay we developed was helpful to improve the ability of HBV diagnosis for practical clinical translation, especially in high-burden regions and resource-limited settings. It has great advantages for rapid screening of CHB as well as evaluation of therapeutic efficacy as a companion diagnostic method.

Ratiometric nonfluorescent CRISPR assay utilizing Cas12a-induced plasmid supercoil relaxation

Most CRISPR-based biosensors rely on labeled reporter molecules and expensive equipment for signal readout. A recent approach quantifies analyte concentration by sizing λ DNA reporters via gel electrophoresis, providing a simple solution for label-free detection. Here, we report an alternative strategy for label-free CRISPR-Cas12a, which relies on Cas12a trans-nicking induced supercoil relaxation of dsDNA plasmid reporters to generate a robust and ratiometric readout. The ratiometric CRISPR (rCRISPR) measures the relative percentage of supercoiled plasmid DNA to the relaxed circular DNA by gel electrophoresis for more accurate target concentration quantification. This simple method is two orders of magnitude more sensitive than the typical fluorescent reporter. This self-referenced strategy solves the potential application limitations of previously demonstrated DNA sizing-based CRISPR-Dx without compromising the sensitivity. Finally, we demonstrated the applicability of rCRISPR for detecting various model DNA targets such as HPV 16 and real AAV samples, highlighting its feasibility for point-of-care CRISPR-Dx applications.

CRISPR-Cas based diagnostic tools: Bringing diagnosis out of labs

Timely detection is important for the effective management of infectious diseases. Reverse Transcription Polymerase Chain Reaction (RT-PCR) stands as the prime nucleic acid based test that is employed for the detection of infectious diseases. The method ensures sensitivity and specificity. However, RT-PCR is a relatively expensive technique due to the requirement of costly equipment and reagents. Further, it requires skilled personnel and established laboratories that are usually inaccessible in underdeveloped areas. On the other hand, rapid antigen based techniques are cost effective and easily accessible, but are less effective in terms of sensitivity and specificity. CRISPR-Cas systems are advanced diagnostic tools that combine the advantages of both PCR and antigen based detection techniques, and allows the rapid detection with high sensitivity/specificity. The present review aims to discuss the applicability of CRISPR-Cas based diagnostic tools for the infectious disease detection. The review further attempts to highlight the current limitations and future research directions to improve the CRISPR based diagnostic tools for rapid and effective disease detection.

Adeno-associated virus genome quantification with amplification-free CRISPR-Cas12a

Efficient manufacturing of recombinant Adeno-Associated Viral (rAAV) vectors to meet rising clinical demand remains a major hurdle. One of the most significant challenges is the generation of large amounts of empty capsids without the therapeutic genome. There is no standardized analytical method to accurately quantify the viral genes, and subsequently the empty-to-full ratio, making the manufacturing challenges even more complex. We propose the use of CRISPR diagnostics (CRISPR-Dx) as a robust and rapid approach to determine AAV genome titers. We designed and developed the CRISPR-AAV Evaluation (CRAAVE) assay to maximize sensitivity, minimize time-to-result, and provide a potentially universal design for quantifying multiple transgene constructs encapsidated within different AAV serotypes. We also demonstrate an on-chip CRAAVE assay with lyophilized reagents to minimize end user assay input. The CRAAVE assay was able to detect AAV titers as low as 7e7 vg/mL with high precision (<3% error) in quantifying unknown AAV titers when compared with conventional quantitative PCR (qPCR) method. The assay only requires 30 min of assay time, shortening the analytical workflow drastically. Our results suggest CRISPR-Dx could be a promising tool for efficient rAAV genome titer quantification and has the potential to revolutionize biomanufacturing process analytical technology (PAT).

Paper-based loop-mediated isothermal amplification and CRISPR integrated platform for on-site nucleic acid testing of pathogens

We report the development and initial validation of a paper-based nucleic acid testing platform that integrates Loop-mediated isothermal amplification (LAMP) with clustered regularly interspaced short palindromic repeats (CRISPR) technology, referred to as PLACID (Paper-based LAMP-CRISPR Integrated Diagnostics). LAMP eliminates the need for thermal cycling, resulting in simplified instrumentation, and the CRISPR-associated protein (Cas 12a) system eliminates false positive signals from LAMP products, resulting in highly selective and sensitive assays. We optimized the assay to perform both amplification and detection entirely on paper, eliminating the need for complex fluid handling steps and lateral flow assay transfers. Additionally, we engineered a smartphone-operated system that includes a low-powered, non-contact IR heating chamber to actuate paper-based LAMP and CRISPR reactions and enable the detection of fluorescent signals from the paper. The platform demonstrates high specificity and sensitivity in detecting nucleic acid targets with a limit of detection of 50 copies/μL. We integrate an equipment-free sample preparation separation technology designed to streamline the preparation of crude samples prior to nucleic acid testing. The practical utility of our platform is demonstrated by the successful detection of spiked SARS-CoV-2 RNA fragments in saliva, E. Coli in soil, and pathogenic E. Coli in clinically fecal samples of infected patients. Furthermore, we demonstrate that the paper-based LAMP CRISPR chips employed in our assays possess a shelf life of several weeks, establishing them as viable candidates for on-site diagnostics.

Simple, sensitive, and visual detection of 12 respiratory pathogens with one-pot-RPA-CRISPR/Cas12a assay

Respiratory infections pose a serious threat to global public health, underscoring the urgent need for rapid, accurate, and large-scale diagnostic tools. In recent years, the CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated) system, combined with isothermal amplification methods, has seen widespread application in nucleic acid testing (NAT). However, achieving a single-tube reaction system containing all necessary components is challenging due to the competitive effects between recombinase polymerase amplification (RPA) and CRISPR/Cas reagents. Furthermore, to enable precision medicine, distinguishing between bacterial and viral infections is essential. Here, we have developed a novel NAT method, termed one-pot-RPA-CRISPR/Cas12a, which combines RPA with CRISPR molecular diagnostic technology, enabling simultaneous detection of 12 common respiratory pathogens, including six bacteria and six viruses. RPA and CRISPR/Cas12a reactions are separated by paraffin, providing an independent platform for RPA reactions to generate sufficient target products before being mixed with the CRISPR/Cas12a system. Results can be visually observed under LED blue light. The sensitivity of the one-pot-RPA-CRISPR/Cas12a method is 2.5 × 100 copies/μL plasmids, with no cross-reaction with other bacteria or viruses. Additionally, the clinical utility was evaluated by testing clinical isolates of bacteria and virus throat swab samples, demonstrating favorable performance. Thus, our one-pot-RPA-CRISPR/Cas12a method shows immense potential for accurate and large-scale detection of 12 common respiratory pathogens in point-of-care testing.

Efficient magnetic enrichment cascade single-step RPA-CRISPR/Cas12a assay for rapid and ultrasensitive detection of Staphylococcus aureus in food samples

Staphylococcus aureus (S. aureus) is a prevalent foodborne pathogen that could cause severe food poisoning. Thus, rapid, efficient, and ultrasensitive detection of S. aureus in food samples is urgently needed. Here, we report an efficient magnetic enrichment cascade single-step recombinase polymerase amplification (RPA)-CRISPR/Cas12a assay for the ultrasensitive detection of S. aureus. Magnetic beads (MBs) functionalized with S. aureus-specific antibodies were initially used for S. aureus enrichment from the complex matrix, with 98% capture efficiency in 5 min and 100-fold sensitivity improvement compared with unenriched S. aureus. Next, a single-step RPA-CRISPR/Cas12a-based diagnostic system with optimized extraction-free bacteria lysis was constructed. This assay could detect as low as 1 copy/μL (five copies/reaction) of extracted DNA template and 10 CFU/mL of S. aureus within 40 min. Furthermore, the assay could effectively detect S. aureus in real food samples such as lake water, orange juice, pork, and lettuce, with concordant results to qPCR assays. The proposed cascade signal-amplification assay eliminates the need for lengthy bacterial culture and complex sample preparation steps. Hence, the proposed assay shows great application potential for rapid, efficient, and ultrasensitive detection of pathogens in real food samples.

A photocontrolled one-pot isothermal amplification and CRISPR-Cas12a assay for rapid detection of SARS-CoV-2 Omicron variants

CRISPR-Cas technology has widely been applied to detect single-nucleotide mutation and is considered as the next generation of molecular diagnostics. We previously reported the combination of nucleic acid amplification (NAA) and CRISPR-Cas12a system to distinguish major severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants. However, the mixture of NAA and CRISPR-Cas12a reagents in one tube could interfere with the efficiency of NAA and CRISPR-Cas12a cleavage, which in turn affects the detection sensitivity. In the current study, we employed a novel photoactivated CRISPR-Cas12a strategy integrated with recombinase polymerase amplification (RPA) to develop one-pot RPA/CRISPR-Cas12a genotyping assay for detecting SARS-CoV-2 Omicron sub-lineages. The new system overcomes the potential inhibition of RPA due to early CRISPR-Cas12a activation and cleavage of the target template in traditional one-pot assay using photocleavable p-RNA, a complementary single-stranded RNA to specifically bind crRNA and precisely block Cas12a activation. The detection can be finished in one tube at 39℃ within 1 h and exhibits a low limit of detection of 30 copies per reaction. Our results demonstrated that the photocontrolled one-pot RPA/CRISPR-Cas12a assay could effectively identify three signature mutations in the spike gene of SARS-CoV-2 Omicron variant, namely, R346T, F486V, and 49X, and distinguish Omicron BA.1, BA.5.2, and BF.7 sub-lineages. Furthermore, the assay achieved a sensitivity of 97.3% and a specificity of 100.0% and showed a concordance of 98.3% with Sanger sequencing results.IMPORTANCEWe successfully developed one-pot recombinase polymerase amplification/CRISPR-Cas12a genotyping assay by adapting photocontrolled CRISPR-Cas technology to optimize the conditions of nucleic acid amplification and CRISPR-Cas12a-mediated detection. This innovative approach was able to quickly distinguish severe acute respiratory syndrome coronavirus 2 Omicron variants and can be readily modified for detecting any nucleic acid mutations. The assay system demonstrates excellent clinical performance, including rapid detection, user-friendly operations, and minimized risk of contamination, which highlights its promising potential as a point-of-care testing for wide applications in resource-limiting settings.

Harnessing noncanonical crRNAs to improve functionality of Cas12a orthologs

There is a broad diversity among Cas12a endonucleases that possess nucleic acid detection and gene-editing capabilities, but few are studied extensively. Here, we present an exhaustive investigation of 23 Cas12a orthologs, with a focus on their cis- and trans-cleavage activities in combination with noncanonical crRNAs. Through biochemical assays, we observe that some noncanonical crRNA:Cas12a effector complexes outperform their corresponding wild-type crRNA:Cas12a. Cas12a can recruit crRNA with modifications such as loop extensions and split scaffolds. Moreover, the tolerance of Cas12a to noncanonical crRNA is also observed in mammalian cells through the formation of indels. We apply the adaptability of Cas12a:crRNA complexes to detect SARS-CoV-2 in clinical nasopharyngeal swabs, saliva samples, and tracheal aspirates. Our findings further expand the toolbox for next-generation CRISPR-based diagnostics and gene editing.

Portable, single nucleotide polymorphism-specific duplex assay for virus surveillance in wastewater

The Argonaute protein from the archaeon Pyrococcus furiosus (PfAgo) is a DNA-guided nuclease that targets DNA with any sequence. We designed a virus detection assay in which the PfAgo enzyme cleaves the reporter probe, thus generating fluorescent signals when amplicons from a reverse transcriptase loop-mediated isothermal amplification (RT-LAMP) assay contain target sequences. We confirmed that the RT-LAMP-PfAgo assay for the SARS-CoV-2 Delta variant produced significantly higher fluorescent signals (p < 0.001) when a single nucleotide polymorphism (SNP), exclusive to the Delta variant, was present, compared to the samples without the SNP. Additionally, the duplex assay for Pepper mild mottle virus (PMMOV) and SARS-CoV-2 detection produced specific fluorescent signals (FAM or ROX) only when the corresponding sequences were present. Furthermore, the RT-LAMP-PfAgo assay does not require dilution to reduce the impact of environmental inhibitors. The limit of detection of the PMMOV assay, determined with 30 wastewater samples, was 28 gc/μL, with a 95 % confidence interval of [11,103]. Finally, using a point-of-use device, the RT-LAMP-PfAgo assay successfully detected PMMOV in wastewater samples. Based on our findings, we conclude that the RT-LAMP-PfAgo assay can be used as a portable, SNP-specific duplex assay, which will significantly improve virus surveillance in wastewater.

Integrated approach for detection of SARS-CoV-2 and its variant by utilizing LAMP and ARMS-PCR

Global impact of COVID-19 pandemic has heightened the urgency for efficient virus detection and identification of variants such as the Q57H mutation. Early and efficient detection of SARS-CoV-2 among densely populated developing countries is paramount objective. Although RT-PCR assays offer accuracy, however, dependence on expansive kits and availability of allied health resources pose an immense challenge for developing countries. In the current study, RT-LAMP based detection of SARS-Cov-2 with subsequent confirmation of Q57H variant through ARMS-PCR was performed. Among the 212 collected samples, 134 yielded positive results, while 78 tested negative using RT-LAMP. Oropharyngeal swabs of suspected individuals were collected and processed for viral RNA isolation. Isolated viral RNA was processed further by using either commercially available WarmStart Master Mix or our in house developed LAMP master mix separately. Subsequently, the end results of each specimen were evaluated by colorimetry. For LAMP assays, primers targeting three genes (ORF1ab, N and S) were designed using PrimerExplorer software. Interestingly, pooling of these three genes in single reaction tube increased sensitivity (95.5%) and specificity (93.5%) of LAMP assay. SARS-CoV-2 positive specimens were screened further for Q57H mutation using ARMS-PCR. Based on amplicon size variation, later confirmed by sequencing, our data showed 18.5% samples positive for Q57H mutation. Hence, these findings strongly advocate use of RT-LAMP-based assay for SARS-CoV-2 screening within suspected general population. Furthermore, ARMS-PCR also provides an efficient mean to detect prevalent mutations against SARS-Cov-2.

Sensitive and Visual Detection of Brassica Yellows Virus Using Reverse Transcription Loop-Mediated Isothermal Amplification-Coupled CRISPR-Cas12 Assay

Brassica yellows virus (BrYV) is an economically important virus on cruciferous species. In this study, a one-pot reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay coupled with the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas12a system was developed for the detection of BrYV. The limit of detection of this method reached 32.8 copies of the BrYV ORF5, which is 100-fold more sensitive than the RT-LAMP method. Moreover, there was no cross-reactivity with other rapeseed-infecting RNA viruses or poleroviruses. We dried the CRISPR/Cas12a reagent in a trehalose and pullulan mixture to retain its efficacy at the RT-LAMP temperature of 63°C in order to allow portable BrYV detection in a water bath. The entire process can be performed in about 1 h, and a positive result can be rapidly and conveniently detected using a handheld UV lamp. In the field, the RT-LAMP-CRISPR/Cas12a assay was accurate and had higher sensitivity than RT-LAMP and reverse transcription-polymerase chain reaction assays. The novel RT-LAMP-CRISPR/Cas12a assay allows convenient, portable, rapid, low-cost, highly sensitive, and specific detection of BrYV and has great potential for on-site monitoring of BrYV.

New design strategies for ultra-specific CRISPR-Cas13a-based RNA detection with single-nucleotide mismatch sensitivity

An increasingly pressing need for clinical diagnostics has required the development of novel nucleic acid-based detection technologies that are sensitive, fast, and inexpensive, and that can be deployed at point-of-care. Recently, the RNA-guided ribonuclease CRISPR-Cas13 has been successfully harnessed for such purposes. However, developing assays for detection of genetic variability, for example single-nucleotide polymorphisms, is still challenging and previously described design strategies are not always generalizable. Here, we expanded our characterization of LbuCas13a RNA-detection specificity by performing a combination of experimental RNA mismatch tolerance profiling, molecular dynamics simulations, protein, and crRNA engineering. We found certain positions in the crRNA-target-RNA duplex that are particularly sensitive to mismatches and establish the effect of RNA concentration in mismatch tolerance. Additionally, we determined that shortening the crRNA spacer or modifying the direct repeat of the crRNA leads to stricter specificities. Furthermore, we harnessed our understanding of LbuCas13a allosteric activation pathways through molecular dynamics and structure-guided engineering to develop novel Cas13a variants that display increased sensitivities to single-nucleotide mismatches. We deployed these Cas13a variants and crRNA design strategies to achieve superior discrimination of SARS-CoV-2 strains compared to wild-type LbuCas13a. Together, our work provides new design criteria and Cas13a variants to use in future easier-to-implement Cas13-based RNA detection applications.

Discovery, classification and application of the CPISPR-Cas13 system

BACKGROUND

The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system is an acquired immune system of bacteria and archaea. Continued research has resulted in the identification of other Cas13 proteins.

OBJECTIVE

This review briefly describes the discovery, classification, and application of the CRISPR-Cas13 system, including recent technological advances in addition to factors affecting system performance.

METHODS

Cas13-based molecular therapy of human, animal, and plant transcriptomes was discussed, including regulation of gene expression to combat pathogenic RNA viruses. In addition, the latest progress, potential shortcomings, and challenges of the CRISPR-Cas system for treatment of animal and plant diseases are reviewed.

RESULTS

The CRISPR-Cas system VI is characterized by two RNA-guided higher eukaryotes and prokaryotes nucleotide-binding domains. CRISPR RNA can cleave specific RNA through the interaction between the stem-loop rich chain of uracil residues and the Cas13a protein. The CRISPR-Cas13 system has been applied for gene editing in animal and plant cells, in addition to biological detection via accurate targeting of single-stranded RNA.

CONCLUSION

The CRISPR-Cas13 system offers a high-throughput and convenient technology for detection of viruses and potentially the development of anti-cancer drugs in the near future.

Precision Genome Editing Techniques in Gene Therapy: Current State and Future Prospects

Precision genome editing is a rapidly evolving field in gene therapy, allowing for the precise modification of genetic material. The CRISPR and Cas systems, particularly the CRISPRCas9 system, have revolutionized genetic research and therapeutic development by enabling precise changes like single-nucleotide substitutions, insertions, and deletions. This technology has the potential to correct disease-causing mutations at their source, allowing for the treatment of various genetic diseases. Programmable nucleases like CRISPR-Cas9, transcription activator-like effector nucleases (TALENs), and zinc finger nucleases (ZFNs) can be used to restore normal gene function, paving the way for novel therapeutic interventions. However, challenges, such as off-target effects, unintended modifications, and ethical concerns surrounding germline editing, require careful consideration and mitigation strategies. Researchers are exploring innovative solutions, such as enhanced nucleases, refined delivery methods, and improved bioinformatics tools for predicting and minimizing off-target effects. The prospects of precision genome editing in gene therapy are promising, with continued research and innovation expected to refine existing techniques and uncover new therapeutic applications.

Loop-Mediated Isothermal Amplification-Integrated CRISPR Methods for Infectious Disease Diagnosis at Point of Care

Infectious diseases continue to pose an imminent threat to global public health, leading to high numbers of deaths every year and disproportionately impacting developing countries where access to healthcare is limited. Biological, environmental, and social phenomena, including climate change, globalization, increased population density, and social inequity, contribute to the emergence of novel communicable diseases. Rapid and accurate diagnoses of infectious diseases are essential to preventing the transmission of infectious diseases. Although some commonly used diagnostic technologies provide highly sensitive and specific measurements, limitations including the requirement for complex equipment/infrastructure and refrigeration, the need for trained personnel, long sample processing times, and high cost remain unresolved. To ensure global access to affordable diagnostic methods, loop-mediated isothermal amplification (LAMP) integrated clustered regularly interspaced short palindromic repeat (CRISPR) based pathogen detection has emerged as a promising technology. Here, LAMP-integrated CRISPR-based nucleic acid detection methods are discussed in point-of-care (PoC) pathogen detection platforms, and current limitations and future directions are also identified.

A universal all-in-one RPA-Cas12a strategy with de novo autodesigner and its application in on-site ultrasensitive detection of DNA and RNA viruses

Revolutionary all-in-one RPA-CRISPR assays are rapidly becoming the most sought-after tools for point-of-care testing (POCT) due to their high sensitivity and ease of use. Despite the availability of one-pot methods for specific targets, the development of more efficient methods for new targets remains a significant challenge. In this study, we present a rapid and universal approach to establishing an all-in-one RPA-Cas12a method CORDSv2 based on rational balancing amplification and Cas12a cleavage, which achieves ultrasensitive detection of several targets, including SARS-CoV-2, ASFV, HPV16, and HPV18. CORDSv2 demonstrates a limit of detection (LOD) of 0.6 cp/μL and 100% sensitivity for SARS-CoV-2, comparable to qPCR. Combining with our portable device(hippo-CORDS), it has a visual detection LOD of 6 cp/μL and a sensitivity up to 100% for SARS-CoV-2 and 97% for Ct<35 ASFV samples, surpassing most one-pot visual methods. To simplify and accelerate the process for new targets, we also develop a de novo autodesigner by which the optimal couples of primers and crRNA can be selected rapidly. As a universal all-in-one RPA-CRISPR method for on-site testing, CORDSv2 becomes an attractive choice for rapid and accurate diagnosis in resource-limited settings.

Rapid and sensitive one-tube detection of mpox virus using RPA-coupled CRISPR-Cas12 assay

Mpox is caused by a zoonotic virus belonging to the Orthopoxvirus genus and the Poxviridae family. In this study, we develop a recombinase polymerase amplification (RPA)-coupled CRISPR-Cas12a detection assay for the mpox virus. We design and test a series of CRISPR-derived RNAs(crRNAs) targeting the conserved D6R and E9L genes for orthopoxvirus and the unique N3R and N4R genes for mpox viruses. D6R crRNA-1 exhibits the most robust activity in detecting orthopoxviruses, and N4R crRNA-2 is able to distinguish the mpox virus from other orthopoxviruses. The Cas12a/crRNA assay alone presents a detection limit of 108 copies of viral DNA, whereas coupling RPA increases the detection limit to 1-10 copies. The one-tube RPA-Cas12a assay can, therefore, detect viral DNA as low as 1 copy within 30 min and holds the promise of providing point-of-care detection for mpox viral infection.

Unidirectional trans-cleaving behavior of CRISPR-Cas12a unlocks for an ultrasensitive assay using hybrid DNA reporters containing a 3' toehold

CRISPR-Cas12a can induce nonspecific trans-cleavage of dsDNA substrate, including long and stable λ DNA. However, the mechanism behind this is still largely undetermined. In this study, we observed that while trans-activated Cas12a didn't cleave blunt-end dsDNA within a short reaction time, it could degrade dsDNA reporters with a short overhang. More interestingly, we discovered that the location of the overhang also affected the susceptibility of dsDNA substrate to trans-activated Cas12a. Cas12a trans-cleaved 3' overhang dsDNA substrates at least 3 times faster than 5' overhang substrates. We attributed this unique preference of overhang location to the directional trans-cleavage behavior of Cas12a, which may be governed by RuvC and Nuc domains. Utilizing this new finding, we designed a new hybrid DNA reporter as nonoptical substrate for the CRISPR-Cas12a detection platform, which sensitively detected ssDNA targets at sub picomolar level. This study not only unfolded new insight into the trans-cleavage behavior of Cas12a but also demonstrated a sensitive CRISPR-Cas12a assay by using a hybrid dsDNA reporter molecule.

CRISPR/Cas12a-Assisted isothermal amplification for rapid and specific diagnosis of respiratory virus on an microfluidic platform

Respiratory viruses have long been a major cause of a global pandemic, emphasizing the urgent need for high-sensitivity diagnostic tools. Typical PCR technology can only determine the type of virus in the sample, which is unable to detect different variants of the same virus without costly and time-consuming gene sequencing. Here, we introduce a simple, fully enclosed, and highly integrated microfluidic system based on CRISPR/Cas12a and isothermal amplification techniques (LOC-CRISPR) that can specifically identify multiple common respiratory viruses and their variants. The LOC-CRISPR chip integrates viral nucleic acid extraction, recombinant polymerase amplification, and CRISPR/Cas12a cleavage reaction-based detection, contamination-free detection. In addition, the LOC-CRISPR chip was designed for multiplexed detection (two-sample input and ten-result outputs), which can not only detect the presence of SARS-CoV-2, H1N1, H3N2, IVB and HRSV but also differentiate the BA.1, BA.2, and BA.5 variants of SARS-COV-2. For clinical validation, the LOC-CRISPR chip was used to analyze 50 nasopharyngeal swab samples (44 positive and 6 negative) and achieved excellent sensitivity (97.8%) and specificity (100%). This innovative LOC-CRISPR system has the ability to quickly, sensitively, and accurately detect multiple target nucleic acid sequences with single-base mutations, which will further improve the rapid identification and traceability of respiratory viruses infectious diseases.

PNA-Pdx: Versatile Peptide Nucleic Acid-Based Detection of Nucleic Acids and SNPs

Monitoring diseases caused by pathogens or by mutations in DNA sequences requires accurate, rapid, and sensitive tools to detect specific nucleic acid sequences. Here, we describe a new peptide nucleic acid (PNA)-based nucleic acid detection toolkit, termed PNA-powered diagnostics (PNA-Pdx). PNA-Pdx employs PNA probes that bind specifically to a target and are then detected in lateral flow assays. This can precisely detect a specific pathogen or genotype genomic sequence. PNA probes can also be designed to invade double-stranded DNAs (dsDNAs) to produce single-stranded DNAs for precise CRISPR-Cas12b-based detection of genomic SNPs without requiring the protospacer-adjacent motif (PAM), as Cas12b requires PAM sequences only for dsDNA targets. PNA-Pdx identified target nucleic acid sequences at concentrations as low as 2 copies/μL and precisely detected the SARS-CoV-2 genome in clinical samples in 40 min. Furthermore, the specific dsDNA invasion by the PNA coupled with CRISPR-Cas12b precisely detected genomic SNPs without PAM restriction. Overall, PNA-Pdx provides a novel toolkit for nucleic acid and SNP detection as well as highlights the benefits of engineering PNA probes for detecting nucleic acids.

Micro- and nanosystems for the detection of hemorrhagic fever viruses

Hemorrhagic fever viruses (HFVs) are virulent pathogens that can cause severe and often fatal illnesses in humans. Timely and accurate detection of HFVs is critical for effective disease management and prevention. In recent years, micro- and nano-technologies have emerged as promising approaches for the detection of HFVs. This paper provides an overview of the current state-of-the-art systems for micro- and nano-scale approaches to detect HFVs. It covers various aspects of these technologies, including the principles behind their sensing assays, as well as the different types of diagnostic strategies that have been developed. This paper also explores future possibilities of employing micro- and nano-systems for the development of HFV diagnostic tools that meet the practical demands of clinical settings.

Development of a loop-mediated isothermal amplification (LAMP)-based electrochemical test for rapid detection of SARS-CoV-2

Rapid, reliable, sensitive, portable, and accurate diagnostics are required to control disease outbreaks such as COVID-19 that pose an immense burden on human health and the global economy. Here we developed a loop-mediated isothermal amplification (LAMP)-based electrochemical test for the detection of SARS-CoV-2 that causes COVID-19. The test is based on the oxidation-reduction reaction between pyrophosphates (generated from positive LAMP reaction) and molybdate that is detected by cyclic voltammetry using inexpensive and disposable carbon screen printed electrodes. Our test showed higher sensitivity (detecting as low as 5.29 RNA copies/μL) compared to the conventional fluorescent reverse transcriptase (RT)-LAMP. We validated our tests using human serum and saliva spiked with SARS-CoV-2 RNA and clinical (saliva and nasal-pharyngeal) swab samples demonstrating 100% specificity and 93.33% sensitivity. Our assay provides a rapid, specific, and sensitive test with an electrochemical readout in less than 45 min that could be adapted for point-of-care settings.

A 3D printed microfluidic device for scalable multiplexed CRISPR-cas12a biosensing

Accurate, rapid, and multiplexed nucleic acid detection is critical for environmental and biomedical monitoring. In recent years, CRISPR-Cas12a has shown great potential in improving the performance of DNA biosensing. However, the nonspecific trans-cleavage activity of Cas12a complicates the multiplexing capability of Cas12a biosensing. We report a 3D-printed composable microfluidic plate (cPlate) device that utilizes miniaturized wells and microfluidic loading for a multiplexed CRISPR-Cas12a assay. The device easily combines loop-mediated isothermal amplification (LAMP) and CRISPR-Cas12a readout in a simple and high-throughput workflow with low reagent consumption. To ensure the maximum performance of the device, the concentration of Cas12a and detection probe was optimized, which yielded a four-fold sensitivity improvement. Our device demonstrates sensitive detection to the fg mL- 1 level for four waterborne pathogens including shigella, campylobacter, cholera, and legionella within 1 h, making it suitable for low-resource settings.

Utility of CRISPR/Cas mediated electrochemical biosensors

Electrochemical biosensors represent a class of sensors that employ biological materials as sensitive elements, electrodes as conversion elements, and potential or current as detection signals. The integration of CRISPR/Cas systems into electrochemical biosensors holds immense potential, offering enhanced versatility, heightened sensitivity and specificity, reduced recovery time, and the ability to capture and identify analytes at low concentrations. In this review, we provided a succinct summary of the fundamental principles underlying electrochemical biosensors and CRISPR/Cas systems, and new progress of electrochemical biosensors based on CRISPR/Cas systems in virus, bacteria, and cancer detections. Besides, we discussed its pros and cons, present gaps, potential problem-solvers, and future prospects. To sum up, CRISPR/Cas mediated electrochemical biosensors will surely benefit us a lot in the detection of cells and microorganisms, and of course in other promising fields.

CRISPR/Cas-Based Diagnostics in Agricultural Applications

Pests and disease-causing pathogens frequently impede agricultural production. An early and efficient diagnostic tool is crucial for effective disease management. Clustered regularly interspaced short palindromic repeats (CRISPR) and the CRISPR-associated protein (Cas) have recently been harnessed to develop diagnostic tools. The CRISPR/Cas system, composed of the Cas endonuclease and guide RNA, enables precise identification and cleavage of the target nucleic acids. The inherent sensitivity, high specificity, and rapid assay time of the CRISPR/Cas system make it an effective alternative for diagnosing plant pathogens and identifying genetically modified crops. Furthermore, its potential for multiplexing and suitability for point-of-care testing at the field level provide advantages over traditional diagnostic systems such as RT-PCR, LAMP, and NGS. In this review, we discuss the recent developments in CRISPR/Cas based diagnostics and their implications in various agricultural applications. We have also emphasized the major challenges with possible solutions and provided insights into future perspectives and potential applications of the CRISPR/Cas system in agriculture.

New design strategies for ultra-specific CRISPR-Cas13a-based RNA-diagnostic tools with single-nucleotide mismatch sensitivity

The pressing need for clinical diagnostics has required the development of novel nucleic acid-based detection technologies that are sensitive, fast, and inexpensive, and that can be deployed at point-of-care. Recently, the RNA-guided ribonuclease CRISPR-Cas13 has been successfully harnessed for such purposes. However, developing assays for detection of genetic variability, for example single-nucleotide polymorphisms, is still challenging and previously described design strategies are not always generalizable. Here, we expanded our characterization of LbuCas13a RNA-detection specificity by performing a combination of experimental RNA mismatch tolerance profiling, molecular dynamics simulations, protein, and crRNA engineering. We found certain positions in the crRNA-target-RNA duplex that are particularly sensitive to mismatches and establish the effect of RNA concentration in mismatch tolerance. Additionally, we determined that shortening the crRNA spacer or modifying the direct repeat of the crRNA leads to stricter specificities. Furthermore, we harnessed our understanding of LbuCas13a allosteric activation pathways through molecular dynamics and structure-guided engineering to develop novel Cas13a variants that display increased sensitivities to single-nucleotide mismatches. We deployed these Cas13a variants and crRNA design strategies to achieve superior discrimination of SARS-CoV-2 strains compared to wild-type LbuCas13a. Together, our work provides new design criteria and new Cas13a variants for easier-to-implement Cas13-based diagnostics.

KEY POINTS

Certain positions in the Cas13a crRNA-target-RNA duplex are particularly sensitive to mismatches.Understanding Cas13a's allosteric activation pathway allowed us to develop novel high-fidelity Cas13a variants.These Cas13a variants and crRNA design strategies achieve superior discrimination of SARS-CoV-2 strains.

GRAPHICAL ABSTRACT

A CRISPR-based approach using dead Cas9-sgRNA to detect SARS-CoV-2

Rapid, highly specific, and robust diagnostic kits to detect viruses and pathogens are needed to control disease spread and transmission globally. Of the many different methods proposed to diagnose COVID-19 infection, CRISPR-based detection of nucleic acids tests are among the most prominent. Here, we describe a new way of using CRISPR/Cas systems as a rapid and highly specific tool to detect the SARS-CoV-2 virus using the in vitro dCas9-sgRNA-based technique. As a proof of concept, we used a synthetic DNA of the M gene, one of the SARS-CoV-2 virus genes, and demonstrated that we can specifically inactivate unique restriction enzyme sites on this gene using CRISPR/Cas multiplexing of dCas9-sgRNA-BbsI and dCas9-sgRNA-XbaI. These complexes recognize and bind to the target sequence spanning the BbsI and XbaI restriction enzyme sites, respectively, and protect the M gene from digestion by BbsI and/or XbaI. We further demonstrated that this approach can be used to detect the M gene when expressed in human cells and from individuals infected with SARS-CoV-2. We refer to this approach as dead Cas9 Protects Restriction Enzyme Sites, and believe that it has the potential to be applied as a diagnostic tool for many DNA/RNA pathogens.

Diagnostics and analysis of SARS-CoV-2: current status, recent advances, challenges and perspectives

The disastrous spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has induced severe public healthcare issues and weakened the global economy significantly. Although SARS-CoV-2 infection is not as fatal as the initial outbreak, many infected victims suffer from long COVID. Therefore, rapid and large-scale testing is critical in managing patients and alleviating its transmission. Herein, we review the recent advances in techniques to detect SARS-CoV-2. The sensing principles are detailed together with their application domains and analytical performances. In addition, the advantages and limits of each method are discussed and analyzed. Besides molecular diagnostics and antigen and antibody tests, we also review neutralizing antibodies and emerging SARS-CoV-2 variants. Further, the characteristics of the mutational locations in the different variants with epidemiological features are summarized. Finally, the challenges and possible strategies are prospected to develop new assays to meet different diagnostic needs. Thus, this comprehensive and systematic review of SARS-CoV-2 detection technologies may provide insightful guidance and direction for developing tools for the diagnosis and analysis of SARS-CoV-2 to support public healthcare and effective long-term pandemic management and control.

Nano-biosensor for SARS-CoV-2/COVID-19 detection: methods, mechanism and interface design

The epidemic of coronavirus disease 2019 (COVID-19) was a huge disaster to human society. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which led to COVID-19, has resulted in a large number of deaths. Even though the reverse transcription-polymerase chain reaction (RT-PCR) is the most efficient method for the detection of SARS-CoV-2, the disadvantages (such as long detection time, professional operators, expensive instruments, and laboratory equipment) limit its application. In this review, the different kinds of nano-biosensors based on surface-enhanced Raman scattering (SERS), surface plasmon resonance (SPR), field-effect transistor (FET), fluorescence methods, and electrochemical methods are summarized, starting with a concise description of their sensing mechanism. The different bioprobes (such as ACE2, S protein-antibody, IgG antibody, IgM antibody, and SARS-CoV-2 DNA probes) with different bio-principles are introduced. The key structural components of the biosensors are briefly introduced to give readers an understanding of the principles behind the testing methods. In particular, SARS-CoV-2-related RNA mutation detection and its challenges are also briefly described. We hope that this review will encourage readers with different research backgrounds to design SARS-CoV-2 nano-biosensors with high selectivity and sensitivity.

A review of current effective COVID-19 testing methods and quality control

COVID-19 is a highly infectious disease caused by the SARS-CoV-2 virus, which primarily affects the respiratory system and can lead to severe illness. The virus is extremely contagious, early and accurate diagnosis of SARS-CoV-2 is crucial to contain its spread, to provide prompt treatment, and to prevent complications. Currently, the reverse transcriptase polymerase chain reaction (RT-PCR) is considered to be the gold standard for detecting COVID-19 in its early stages. In addition, loop-mediated isothermal amplification (LMAP), clustering rule interval short palindromic repeats (CRISPR), colloidal gold immunochromatographic assay (GICA), computed tomography (CT), and electrochemical sensors are also common tests. However, these different methods vary greatly in terms of their detection efficiency, specificity, accuracy, sensitivity, cost, and throughput. Besides, most of the current detection methods are conducted in central hospitals and laboratories, which is a great challenge for remote and underdeveloped areas. Therefore, it is essential to review the advantages and disadvantages of different COVID-19 detection methods, as well as the technology that can enhance detection efficiency and improve detection quality in greater details.

An ultra-sensitive one-pot RNA-templated DNA ligation rolling circle amplification-assisted CRISPR/Cas12a detector assay for rapid detection of SARS-CoV-2

Rapid, sensitive, and one-pot diagnosis of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) plays an extremely important role in point-of-care testing (POCT). Herein, we report an ultra-sensitive and rapid one-pot enzyme-catalyzed rolling circle amplification-assisted CRISPR/FnCas12a assay, termed OPERATOR. OPERATOR employs a single well-designed single-strand padlock DNA, containing a protospacer adjacent motif (PAM) site and a sequence complementary to the target RNA which procedure converts and amplifies genomic RNA to DNA by RNA-templated DNA ligation and multiply-primed rolling circle amplification (MRCA). The MRCA amplicon of single-stranded DNA is cleaved by the FnCas12a/crRNA complex and detected via a fluorescence reader or lateral flow strip. OPERATOR presents outstanding advantages including ultra-sensitivity (1.625 copies per reaction), high specificity (100%), rapid reaction speed (∼30 min), easy operation, low cost, and on-spot visualization. Furthermore, we established a POCT platform by combining OPERATOR with rapid RNA release and a lateral flow strip without professional equipment. The high performance of OPERATOR in SARS-CoV-2 tests was confirmed using both reference materials and clinical samples, and the results suggest that is readily adaptable for point-of-care testing of other RNA viruses.

Engineering highly thermostable Cas12b via de novo structural analyses for one-pot detection of nucleic acids

CRISPR-Cas-based diagnostics have the potential to elevate nucleic acid detection. CRISPR-Cas systems can be combined with a pre-amplification step in a one-pot reaction to simplify the workflow and reduce carryover contamination. Here, we report an engineered Cas12b with improved thermostability that falls within the optimal temperature range (60°C-65°C) of reverse transcription-loop-mediated isothermal amplification (RT-LAMP). Using de novo structural analyses, we introduce mutations to wild-type BrCas12b to tighten its hydrophobic cores, thereby enhancing thermostability. The one-pot detection assay utilizing the engineered BrCas12b, called SPLENDID (single-pot LAMP-mediated engineered BrCas12b for nucleic acid detection of infectious diseases), exhibits robust trans-cleavage activity up to 67°C in a one-pot setting. We validate SPLENDID clinically in 80 serum samples for hepatitis C virus (HCV) and 66 saliva samples for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with high specificity and accuracy. We obtain results in as little as 20 min, and with the extraction process, the entire assay can be performed within an hour.

Advances in point-of-care genetic testing for personalized medicine applications

Breakthroughs within the fields of genomics and bioinformatics have enabled the identification of numerous genetic biomarkers that reflect an individual's disease susceptibility, disease progression, and therapy responsiveness. The personalized medicine paradigm capitalizes on these breakthroughs by utilizing an individual's genetic profile to guide treatment selection, dosing, and preventative care. However, integration of personalized medicine into routine clinical practice has been limited-in part-by a dearth of widely deployable, timely, and cost-effective genetic analysis tools. Fortunately, the last several decades have been characterized by tremendous progress with respect to the development of molecular point-of-care tests (POCTs). Advances in microfluidic technologies, accompanied by improvements and innovations in amplification methods, have opened new doors to health monitoring at the point-of-care. While many of these technologies were developed with rapid infectious disease diagnostics in mind, they are well-suited for deployment as genetic testing platforms for personalized medicine applications. In the coming years, we expect that these innovations in molecular POCT technology will play a critical role in enabling widespread adoption of personalized medicine methods. In this work, we review the current and emerging generations of point-of-care molecular testing platforms and assess their applicability toward accelerating the personalized medicine paradigm.

Environmental DNA/RNA for pathogen and parasite detection, surveillance, and ecology

Detection of pathogens, parasites, and other symbionts in environmental samples via eDNA/eRNA (collectively eNA) is an increasingly important source of information about their occurrence and activity. There is great potential for using such detections as a proxy for infection of host organisms in connected habitats, for pathogen monitoring and surveillance, and for early warning systems for disease. However, many factors require consideration, and appropriate methods developed and verified, in order that eNA detections can be reliably interpreted and adopted for surveillance and assessment of disease risk, and potentially inclusion in international standards, such as the World Organisation for Animal Health guidelines. Disease manifestation results from host-symbiont-environment interactions between hosts, demanding a multifactorial approach to interpretation of eNA signals.

Research progress on nucleic acid detection and genome editing of CRISPR/Cas12 system

PURPOSE

This work characterizes the applications of CRISPR/Cas12 system, including nucleic acid detection, animal, plant and microbial genome editing.

METHODS

The literature on CRISPR/Cas12 system was collected and reviewed.

RESULTS

CRISPR/Cas system is an acquired immune system derived from bacteria and archaea, which has become the most popular technology around the world because of its outstanding contribution in genome editing. Type V CRISPR/Cas systems are distinguished by a single RNA-guided RuvC nuclease domain with single effector molecule. Cas12a, the first reported type V CRISPR/Cas system, targets double-stranded DNA (dsDNA) adjacent to PAM sequences and trans-cleaves single-stranded DNA (ssDNA). We present the applications of CRISPR/Cas12 system for nucleic acid detection and genome editing in animals, plants and microorganisms. Furthermore, this review also summarizes the applications of other Cas12 proteins, such as Cas12b, Cas12c, Cas12d, and so on, which further widen the application prospects of CRISPR/Cas12 system.

CONCLUSIONS

Knowledge of the applications of CRISPR/Cas12 system is necessary for improving the understanding of the functional diversity of CRISPR/Cas12 system and also provides significant references for further research and utilization of CRISPR/Cas12 in other new fields.

Biosensing strategies for the detection of SARS-CoV-2 nucleic acids

The COVID-19 pandemic had devastating effects throughout the world, producing a severe crisis in the health systems and in the economy of a long list of countries, even developed ones. Therefore, highly sensitive and selective analytical bioplatforms that allow the descentralized and fast detection of the severe acute respiratory síndrome coronavirus 2 (SARS-CoV-2), are extremely necessary. Since 2020, several reviews have been published, most of them focused on the different strategies to detect the SARS-CoV-2, either from RNA, viral proteins or host antibodies produced due to the presence of the virus. In this review, the most relevant biosensors for the detection of SARS-CoV-2 RNA are particularly addressed, with special emphasis on the discussion of the biorecognition layers and the different schemes for transducing the hybridization event.

Development and application of DETECTR-based rapid detection for pathogenic Bacillusanthracis

Bacillus anthracis (B. anthracis) is a gram-positive bacterium responsible for the acute disease anthrax. Rapid and reliable identification of pathogenic B. anthracis is important in the detection of natural infectious disease cases or bio-threats. Herein, a DNA endonuclease targeted CRISPR trans reporter (DETECTR) detection platform based on recombinase polymerase amplification (RPA) was studied. The DETECTR system targeted three sequences from B. anthracis (the BA_5345 chromosomal specific marker, the protective antigen gene pag A from pXO1 plasmid and the capsule-biosynthesis-related gene cap A from pXO2 plasmid). We developed a rapid (<40 min), easy-to-implement and accurate identification method for of B. anthracis nucleic acid with near two-copies sensitivity. The combination of tripartite primer sets is effective for the reliable identification of B. anthracis but also for fast screening of pathogenic strains. More importantly, DETECTR correctly detected simulated clinical blood samples and firstly detected positive samples collected from the location of world War-II site, preserved at north-east China (45°36'55.940″ N, 126°38'33.738″ E) with high sensitivity and specificity. Our study provides insight into the DETECTR-based detection of B. anthracis. We present a novel screening and diagnostic option for pathogenic B. anthracis that can be performed on a user-friendly portable device. Based on its proven reliability, sensitivity, specificity and simplicity, our proposed method can be readily adapted to detect pathogenic B. anthracis, anthrax and biothreats.

Recent progress in nucleic acid detection with CRISPR

Recent advances in CRISPR-based biotechnologies have greatly expanded our capabilities to repurpose CRISPR for the development of molecular diagnostic systems. The key attribute that allows CRISPR to be widely utilized is its programmable and highly specific nature. In this review, we first illustrate the principle of the class 2 CRISPR nucleases for molecular diagnostics which originates from their immunologic defence systems. Next, we present the CRISPR-based schemes in the application of diagnostics with amplification-assisted or amplification-free strategies. By highlighting some of the recent advances we interpret how general bioengineering methodologies can be integrated with CRISPR. Finally, we discuss the challenges and exciting prospects for future CRISPR-based biosensing development. We hope that this review will guide the reader to systematically learn the start-of-the-art development of CRISPR-mediated nucleic acid detection and understand how to apply the CRISPR nucleases with different design concepts to more general applications in diagnostics and beyond.

A New Auto-RPA-Fluorescence Detection Platform for SARS-CoV-2

OBJECTIVE

The outbreak of COVID-19 caused by SARS-CoV-2 has led to a serious worldwide pandemic. Quantitative reverse transcription-polymerase chain reaction (qRT-PCR)-based methods were recommended for routine detection of SARS-CoV-2 RNA. Because the reaction time and analytical sensitivity of qRT-PCR limits the diagnosis of SARS-CoV-2, development of a quick process of SARS-CoV-2 detection technology with high analytical sensitivity remains urgent.

METHODS

We combined isothermal amplification and fluorescence detection technology to develop a new auto-recombinase polymerase amplification (RPA)-fluorescence platform that could be used in the diagnosis of SARS-CoV-2.

RESULTS

By optimization of primers and probes, the RPA platform could detect SARS-CoV-2 nucleotides within 15 min. The limits of detection and specificity of the auto-RPA-fluorescence platform were 5 copies/µL and 100%, respectively. The accuracy of detection of the auto-RPA-fluorescence platform in the 16 positive samples was 100%.

CONCLUSION

The RPA platform is a potential technology for the diagnosis of SARS-CoV-2 infection.

Promise and perils of paper-based point-of-care nucleic acid detection for endemic and pandemic pathogens

From HIV and influenza to emerging pathogens like COVID-19, each new infectious disease outbreak has highlighted the need for massively-scalable testing that can be performed outside centralized laboratory settings at the point-of-care (POC) in order to prevent, track, and monitor endemic and pandemic threats. Nucleic acid amplification tests (NAATs) are highly sensitive and can be developed and scaled within weeks while protein-based rapid tests require months for production. Combining NAATs with paper-based detection platforms are promising due to the manufacturability, scalability, and simplicity of each of these components. Typically, paper-based NAATs consist of three sequential steps: sample collection and preparation, amplification of DNA or RNA from pathogens of interest, and detection. However, these exist within a larger ecosystem of sample collection and interpretation workflow, usability, and manufacturability which can be vastly perturbed during a pandemic emergence. This review aims to explore the challenges of paper-based NAATs covering sample-to-answer procedures along with three main types of clinical samples; blood, urine, and saliva, as well as broader operational, scale up, and regulatory aspects of device development and implementation. To fill the technological gaps in paper-based NAATs, a sample-in-result-out system that incorporates the integrated sample collection, sample preparation, and integrated internal amplification control while also balancing needs of users and manufacturability upfront in the early design process is required.

SARS-CoV-2 pandemics: an update of CRISPR in diagnosis and host-virus interaction studies

Since December 2019, the Coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) has spread rapidly around the world, overburdening healthcare systems and creating significant global health concerns. Rapid detection of infected individuals via early diagnostic tests and administration of effective therapy remains vital in pandemic control, and recent advances in the CRISPR (clustered regularly interspaced short palindromic repeats)-Cas (CRISPR-associated proteins) system may support the development of novel diagnostic and therapeutic approaches. Cas-based SARS-CoV-2 detection methods (FELUDA, DETECTR, and SHERLOCK) have been developed for easier handling compared to quantitative polymerase chain reaction (qPCR) assays, with good rapidity, high specificity, and reduced need for complex instrumentation. Cas-CRISPR-derived RNA (Cas-crRNA) complexes have been shown to reduce viral loads in the lungs of infected hamsters, by degrading virus genomes and limiting viral replication in host cells. Viral-host interaction screening platforms have been developed using the CRISPR-based system to identify essential cellular factors involved in pathogenesis, and CRISPR knockout and activation screening results have revealed vital pathways in the life cycle of coronaviruses, including host cell entry receptors (ACE2, DPP4, and ANPEP), proteases involved in spike activation and membrane fusion (CTSL and TMPRSS2), intracellular traffic control routes for virus uncoating and budding, and membrane recruitment for viral replication. Several novel genes (SMARCA4, ARIDIA, and KDM6A) have also been identified via systematic data mining analysis as pathogenic factors for severe CoV infection. This review highlights how CRISPR-based systems can be applied to investigate the viral life cycle, detect viral genomes, and develop therapies against SARS-CoV-2 infection.

Elucidating the Role of CRISPR/Cas in Single-Step Isothermal Nucleic Acid Amplification Testing Assays

Developing assays that combine CRISPR/Cas and isothermal nucleic acid amplification has become a burgeoning research area due to the novelty and simplicity of CRISPR/Cas and the potential for point-of-care uses. Most current research explores various two-step assays by appending different CRISPR/Cas effectors to the end of different isothermal nucleic acid amplification methods. However, efforts in integrating both components into more ideal single-step assays are scarce, and poor-performing single-step assays have been reported. Moreover, lack of investigations into CRISPR/Cas in single-step assays results in incomplete understanding. To fill this knowledge gap, we conducted a systematic investigation by developing and comparing assays that share the identical recombinase polymerase amplification (RPA) but differ in CRISPR/Cas12a. We found that the addition of CRISPR/Cas12a indeed unlocks signal amplification but, at the same time, impedes RPA and that CRISPR/Cas12a concentration is a key parameter for attenuating RPA impediment and ensuring assay performance. Accordingly, we found that our protospacer adjacent motif (PAM)-free CRISPR/Cas12a-assisted RPA assay, which only moderately impeded RPA at its optimal CRISPR/Cas12a concentration, outperformed its counterparts in assay design, signal, sensitivity, and speed. We also discovered that a new commercial Cas12a effector could also drive our PAM-free CRISPR/Cas12a-assisted RPA assay and reduce its cost, though simultaneously lowering its signal. Our study and the new insights can be broadly applied to steer and facilitate further advances in CRISPR/Cas-based assays.

An integrated dual-layer microfluidic platform for multiple respiratory viruses screening

Currently, the coronavirus disease 2019 (COVID-19) caused by the outbreak of a novel coronavirus (SARS-CoV-2) is spreading rapidly worldwide. Due to the high incidence of influenza coinciding with SARS-CoV-2, rapid detection is crucial to prevent spreading. Here, we present an integrated dual-layer microfluidic platform for specific and highly sensitive SARS-CoV-2, influenza viruses A (FluA) H1N1, H3N2, and influenza virus B (FluB) simultaneous detection. The platform includes a dual microchip (Dμchip) and a portable detection device for real-time fluorescence detection, temperature control and online communication. The Reverse Transcription Loop-mediated Isothermal Amplification (RT-LAMP) and Cas12a cleavage were performed on the Dμchip. The limit of detection (LoD) of the Dμchip assay was 10 copies for SARS-CoV-2, FluA H1N1, H3N2, and FluB RNAs. The Dμchip assay yielded no cross-reactivity against other coronaviruses, so it was suitable for the screening of multiple viruses. Moreover, the positive percentage agreement (PPA) and negative percentage agreement (NPA) of the assay were 97.9% and 100%, respectively, in 75 clinical samples compared to data from RT-PCR-based assays. Furthermore, the assay allowed the detection SARS-CoV-2 and influenza viruses in spiked samples. Overall, the present platform would provide a rapid method for the screening of multiple viruses in hospital emergency, community and primary care settings and facilitate the remote diagnosis and outbreak control of the COVID-19.

Evaluation of an automated CRISPR-based diagnostic tool for rapid detection of COVID-19

The performance of an automated commercial CRISPR/Cas based technology was evaluated and compared with routine RT-PCR testing to diagnose COVID-19. Suspected and discharged COVID-19 cases were included and tested with CRISPR-based SARS-CoV-2 test and RT-PCR assay using throat swab and sputum specimens. The diagnostic yield was calculated and compared using the McNemar test. A total of 437 patients were included for analysis, including COVID-19 (n = 171), discharged cases (n = 155), and others (n = 111). For the diagnosis of COVID-19, the CRISPR-SARS-CoV-2 test had a sensitivity and specificity of 98.2% (168/171) and 100.0% (266/266), respectively; the RT-PCR test had a sensitivity and specificity of 100.0% (171/171) and 100.0% (266/266), respectively. No significant difference was found in the sensitivity of CRISPR-SARS-CoV-2 and RT-PCR. In conclusion, the CRISPR-SARS-CoV-2 test had a comparable performance with RT-PCR and showed several advantages, such as short assay time, low cost, and no requirement for expensive equipment.

Digital CRISPR Systems for the Next Generation of Nucleic Acid Quantification

Digital CRISPR (dCRISPR) assays are an emerging platform of molecular diagnostics. Digital platforms introduce absolute quantification and increased sensitivity to bulk CRISPR assays. With ultra-specific targeting, isothermal operation, and rapid detection, dCRISPR systems are well-prepared to lead the field of molecular diagnostics. Here we summarized the common Cas proteins used in CRISPR detection assays. The methods of digital detection and critical performance factors are examined. We formed three strategies to frame the landscape of dCRISPR systems: (1) amplification free, (2) in-partition amplification, and (3) two-stage amplification. We also compared the performance of all systems through the limit of detection (LOD), testing time, and figure of merit (FOM). This work summarizes the details of digital CRISPR platforms to guide future development. We envision that improvements to LOD and dynamic range will position dCRISPR as the leading platform for the next generation of molecular biosensing.

Advancements in CRISPR-Based Biosensing for Next-Gen Point of Care Diagnostic Application

With the move of molecular tests from diagnostic labs to on-site testing becoming more common, there is a sudden rise in demand for nucleic acid-based diagnostic tools that are selective, sensitive, flexible to terrain changes, and cost-effective to assist in point-of-care systems for large-scale screening and to be used in remote locations in cases of outbreaks and pandemics. CRISPR-based biosensors comprise a promising new approach to nucleic acid detection, which uses Cas effector proteins (Cas9, Cas12, and Cas13) as extremely specialized identification components that may be used in conjunction with a variety of readout approaches (such as fluorescence, colorimetry, potentiometry, lateral flow assay, etc.) for onsite analysis. In this review, we cover some technical aspects of integrating the CRISPR Cas system with traditional biosensing readout methods and amplification technologies such as polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), and recombinase polymerase amplification (RPA) and continue to elaborate on the prospects of the developed biosensor in the detection of some major viral and bacterial diseases. Within the scope of this article, we also discuss the recent COVID pandemic and the numerous CRISPR biosensors that have undergone development since its advent. Finally, we discuss some challenges and future prospects of CRISPR Cas systems in point-of-care testing.

In Vitro CRISPR-Cas12a-Based Detection of Cancer-Associated TP53 Hotspot Mutations Beyond the crRNA Seed Region

Cost-effective and time-efficient detection of oncogenic mutations supports improved presymptomatic cancer diagnostics and post-treatment disease monitoring. Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas12a is an RNA-guided endonuclease that, upon protospacer adjacent motif (PAM)-dependent recognition of target DNA in cis, exhibits indiscriminate ssDNase activity in trans, which can be harnessed for diagnostics. TP53, one of the most frequently mutated tumor suppressor genes in cancer, displays recurring point mutations at so-called "hotspots." In this study, we optimized Cas12a-based assay conditions for in vitro detection of six TP53 hotspot mutations at the codon for p.R273, located outside the Cas12a seed region, and evaluated the specificities of four commercial Cas12a variants. We found that nonengineered LbCas12a significantly outperformed the other tested nucleases specifically in distinguishing mutant p.R273 codons in synthetic DNA, mock cell-free DNA, and tissue biopsies, despite the suboptimal PAM-distal positioning of the corresponding mutations. Future clinical Cas12a-based applications may include point-of-care tumor analysis, cost-effective mutation screening, and improved monitoring of individual cancer patients.