Detection of SARS-CoV-2 and the L452R spike mutation using reverse transcription loop-mediated isothermal amplification plus bioluminescent assay in real-time (RT-LAMP-BART)

Unravelling the diagnostic methodologies for SARS-CoV-2; the Indispensable need for developing point-of-care testing

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-caused COVID-19 pandemic that continues to be a global menace and since its emergence in the late 2019, SARS-CoV-2 has been vigorously spreading throughout the globe putting the whole world into a multidimensional calamity. The suitable diagnosis strategies are on the front line of the battle against preventing the spread of infections. Since the clinical manifestation of COVID-19 is shared between various diseases, detection of the unique impacts of the pathogen on the host along with the diagnosis of the virus itself should be addressed. Employing the most suitable approaches to specifically, sensitively and effectively recognize the infected cases may be a real game changer in controlling the outbreak and the crisis management. In that matter, point-of-care assays (POC) appears to be the potential option, due to sensitivity, specificity, affordable, and availability. Here we brief the most recent findings about the virus, its variants, and the conventional methods that have been used for its detection, along with the POC strategies that have been applied to the virus diagnosis and the developing technologies which can accelerate the diagnosis procedure yet maintain its efficiency.

Versatility of reverse transcriptase loop-mediated isothermal amplification (RT-LAMP) from diagnosis of early pathological infection to mutation detection in organisms

Loop-mediated isothermal amplification (LAMP) is a rapid, state-of-the-art DNA amplification technology, used primarily for the quick diagnosis and early identification of microbial infection, caused by pathogens such as virus, bacteria and malaria. A target DNA can be amplified within 30 min using the LAMP reaction, taking place at a steady temperature. The LAMP method uses four or six primers to bind eight regions of a target DNA and has a very high specificity. The devices used for conducting LAMP are usually simple since the LAMP method is an isothermal process. When LAMP is coupled with Reverse Transcription (RT), it allows direct detection of RNA in a sample. This greatly enhances the efficiency of diagnosis of RNA viruses in a sample. Recently, the rampant spread of COVID-19 demanded such a rapid, simple, and cost-effective Point of Care Test (PoCT) for the accurate diagnosis of this pandemic. Loop-mediated isothermal amplification (LAMP) assays are not only used for the detection of microbial pathogens, but there are various other applications such as detection of genetic mutations in food and various organisms. In this review, various implementations of RT-LAMP techniques would be discussed.

Rapid assays of SARS-CoV-2 virus and noble biosensors by nanomaterials

The COVID-19 outbreak caused by SARS-CoV-2 in late 2019 has spread rapidly across the world to form a global epidemic of respiratory infectious diseases. Increased investigations on diagnostic tools are currently implemented to assist rapid identification of the virus because mass and rapid diagnosis might be the best way to prevent the outbreak of the virus. This critical review discusses the detection principles, fabrication techniques, and applications on the rapid detection of SARS-CoV-2 with three categories: rapid nuclear acid augmentation test, rapid immunoassay test and biosensors. Special efforts were put on enhancement of nanomaterials on biosensors for rapid, sensitive, and low-cost diagnostics of SARS-CoV-2 virus. Future developments are suggested regarding potential candidates in hospitals, clinics and laboratories for control and prevention of large-scale epidemic.

Fluorometric Detection of SARS-CoV-2 Single-Nucleotide Variant L452R Using Ligation-Based Isothermal Gene Amplification

Since the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant was first discovered, several variants showing different infectivity and immune responses have emerged globally. As the conventional method, whole-genome sequencing following polymerase chain reaction (PCR) is currently used for diagnosis of SARS-CoV-2 mutations. However, these conventional PCR-based direct DNA sequencing methods are time-consuming, complicated, and require expensive DNA sequencing modules. Here, we developed a fluorometric method for the accurate detection of a single missense mutation of U to G in the spike (S) gene that changes leucine to arginine (L452R) in SARS-CoV-2 genomic RNA. Our method for the detection of single-nucleotide mutations (SNM) in the viral RNA genome includes RNA sequence-dependent DNA ligation and tandem isothermal gene amplification methods, such as strand displacement amplification (SDA) and rolling circle amplification (RCA) generating G-quadruplex (GQ). In the presence of SNM in the viral RNA, ligation of both ends of the probe DNAs occurs between 5'-phosphorylated hairpin DNA and linear probe DNA that can discriminate a single base mismatch. The ligated DNAs were then extended to generate long-stem hairpin DNAs that are subjected to the first isothermal gene amplification (SDA). SDA produces multitudes of short ssDNA from the long-stem hairpin DNAs, which then serve as primers by annealing to circular padlock DNA for the second isothermal gene amplification (RCA). RCA produces a long stretch of ssDNA containing GQ structures. Thioflavin T (ThT) is then intercalated into GQ and emits green fluorescence, which allows the fluorometric identification of SARS-CoV-2 variants. This fluorometric analysis sensitively distinguished SNM in the L452R variant of SARS-CoV-2 RNA as low as 10 pM within 2 h. Hence, this fluorometric detection method using ligation-assisted tandem isothermal gene amplification can be applied for the diagnosis of SARS-CoV-2 SNM variants with high accuracy and sensitivity, without the need for cumbersome whole-genome DNA sequencing.

A New Method to Detect Variants of SARS-CoV-2 Using Reverse Transcription Loop-Mediated Isothermal Amplification Combined with a Bioluminescent Assay in Real Time (RT-LAMP-BART)

Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), of which there are several variants. The three major variants (Alpha, Delta, and Omicron) carry the N501Y, L452R, and Q493R/Q498R mutations, respectively, in the S gene. Control of COVID-19 requires rapid and reliable detection of not only SARS-CoV-2 but also its variants. We previously developed a reverse transcription loop-mediated isothermal amplification assay combined with a bioluminescent assay in real time (RT-LAMP-BART) to detect the L452R mutation in the SARS-CoV-2 spike protein. In this study, we established LAMP primers and peptide nucleic acid probes to detect N501Y and Q493R/Q498R. The LAMP primer sets and PNA probes were designed for the N501Y and Q493R/Q498R mutations on the S gene of SARS-CoV-2. The specificities of RT-LAMP-BART assays were evaluated using five viral and four bacterial reference strains. The sensitivities of RT-LAMP-BART assays were evaluated using synthetic RNAs that included the target sequences, together with RNA-spiked clinical nasopharyngeal and salivary specimens. The results were compared with those of conventional real-time reverse transcription-polymerase chain reaction (RT-PCR) methods. The method correctly identified N501Y and Q493R/Q498R. Within 30 min, the RT-LAMP-BART assays detected up to 100-200 copies of the target genes; conventional real-time RT-PCR required 130 min and detected up to 500-3000 copies. Surprisingly, the real-time RT-PCR for N501Y did not detect the BA.1 and BA.2 variants (Omicron) that exhibited the N501Y mutation. The novel RT-LAMP-BART assay is highly specific and more sensitive than conventional real-time RT-PCR. The new assay is simple, inexpensive, and rapid; thus, it can be useful in efforts to identify SARS-CoV-2 variants of concern.

Multiplexed Reverse Transcription Loop-Mediated Isothermal Amplification Coupled with a Nucleic Acid-Based Lateral Flow Dipstick as a Rapid Diagnostic Method to Detect SARS-CoV-2

Due to the high reproduction rate of COVID-19, it is important to identify and isolate infected patients at the early stages of infection. The limitations of current diagnostic methods are speed, cost, and accuracy. Furthermore, new viral variants have emerged with higher rates of infectivity and mortality, many with mutations at various primer binding sites, which may evade detection via conventional PCR kits. Therefore, a rapid method that is sensitive, specific, and cost-effective is needed for a point-of-care molecular test. Accordingly, we developed a rapid molecular SARS-CoV-2 detection kit with high specificity and sensitivity, RT-PCR, taking advantage of the loop-mediated isothermal amplification (LAMP) technique. Four sets of six primers were designed based on conserved regions of the SARS-CoV-2 genome: two outer, two inner and two loop primers. Using the optimized protocol, SARS-CoV-2 genes were detected as quickly as 10 min but were most sensitive at 30 min, detecting as little as 100 copies of template DNA. We then coupled the RT-LAMP with a lateral flow dipstick (LFD) for multiplex detection. The LFD could detect two genic amplifications on a single strip, making it suitable for multiplexed detection. The development of a multiplexed RT-LAMP-LFD reaction on crude VTM samples would be suitable for the point-of-care diagnosis of COVID-19 in diagnostic laboratories as well as in private homes.

A loop-mediated isothermal amplification-enabled analytical assay for the detection of SARS-CoV-2: A review

The number of words: 4645, the number of figures: 4, the number of tables: 1The outbreak of COVID-19 in December 2019 caused a global pandemic of acute respiratory disease, and with the increasing virulence of mutant strains and the number of confirmed cases, this has resulted in a tremendous threat to global public health. Therefore, an accurate diagnosis of COVID-19 is urgently needed for rapid control of SARS-CoV-2 transmission. As a new molecular biology technology, loop-mediated isothermal amplification (LAMP) has the advantages of convenient operation, speed, low cost and high sensitivity and specificity. In the past two years, rampant COVID-19 and the continuous variation in the virus strains have demanded higher requirements for the rapid detection of pathogens. Compared with conventional RT-PCR and real-time RT-PCR methods, genotyping RT-LAMP method and LAMP plus peptide nucleic acid (PNA) probe detection methods have been developed to correctly identified SARS-CoV-2 variants, which is also why LAMP technology has attracted much attention. LAMP detection technology combined with lateral flow assay, microfluidic technology and other sensing technologies can effectively enhance signals by nucleic acid amplification and help to give the resulting output in a faster, more convenient and user-friendly way. At present, LAMP plays an important role in the detection of SARS-CoV-2.

Rapid and Sensitive Genotyping of SARS-CoV-2 Key Mutation L452R with an RPA-PfAgo Method

In the two years of COVID-19 pandemic, the SARS-CoV-2 variants have caused waves of infections one after another, and the pandemic is not ending. The key mutations on the S protein enable the variants with enhanced viral infectivity, immune evasion, and/or antibody neutralization resistance, bringing difficulties to epidemic prevention and control. In support of precise epidemic control and precision medicine of the virus, a fast and simple genotyping method for the key mutations of SARS-CoV-2 variants needs to be developed. By utilizing the specific recognition and cleavage property of the nuclease Argonaute from Pyrococcus furiosus (PfAgo), we developed a recombinase polymerase amplification (RPA) and PfAgo combined method for a rapid and sensitive genotyping of SARS-CoV-2 key mutation L452R. With a delicate design of the strategy, careful screening of the RPA primers and PfAgo gDNA, and optimization of the reaction, the method achieves a high sensitivity of a single copy per reaction, which is validated with the pseudovirus. This is the highest sensitivity that can be achieved theoretically and the highest sensitivity as compared to the available SARS-CoV-2 genotyping assays. Using RPA, the procedure of the method is finished within 1.5 h and only needs a minimum laboratorial support, suggesting that the method can be easily applied locally or on-site. The RPA-PfAgo method established in this study provides a strong support to the precise epidemic control and precision medicine of SARS-CoV-2 variants and can be readily developed for the simultaneous genotyping of multiple SARS-CoV-2 mutations.

The Future of Point-of-Care Nucleic Acid Amplification Diagnostics after COVID-19: Time to Walk the Walk

Since the onset of the COVID-19 pandemic, over 610 million cases have been diagnosed and it has caused over 6.5 million deaths worldwide. The crisis has forced the scientific community to develop tools for disease control and management at a pace never seen before. The control of the pandemic heavily relies in the use of fast and accurate diagnostics, that allow testing at a large scale. The gold standard diagnosis of viral infections is the RT-qPCR. Although it provides consistent and reliable results, it is hampered by its limited throughput and technical requirements. Here, we discuss the main approaches to rapid and point-of-care diagnostics based on RT-qPCR and isothermal amplification diagnostics. We describe the main COVID-19 molecular diagnostic tests approved for self-testing at home or for point-of-care testing and compare the available options. We define the influence of specimen selection and processing, the clinical validation, result readout improvement strategies, the combination with CRISPR-based detection and the diagnostic challenge posed by SARS-CoV-2 variants for different isothermal amplification techniques, with a particular focus on LAMP and recombinase polymerase amplification (RPA). Finally, we try to shed light on the effect the improvement in molecular diagnostics during the COVID-19 pandemic could have in the future of other infectious diseases.