Multiplex, Real-Time, Point-of-care RT-LAMP for SARS-CoV-2 Detection Using the HFman Probe

SPECIAL: Phosphorothioate dNTP assisted RPA equipped with CRISPR/Cas12a amplifier enables high-specific nucleic acid testing

Recombinase polymerase amplification (RPA) is one of the most widely used isothermal amplification methods and considered to be a promising tool for point-of-care testing (POCT) molecular diagnosis. However, RPA is prone to have nonspecific amplification occur, due to the poor recognition accuracy of polymerase and recombinase, which severely hindered its clinical application. It is important to improve the specificity of RPA further. Herein, we developed a novel nucleic acid testing method termed phosphorothioate dNTP (dNTPαS) assisted RPA (S-RPA) that employs dNTPαS as substrates to suppress nonspecific amplification effectively. We found that dNTPαS could improve the recognition accuracy of Bsu polymerase and recombinase, thereby enhancing their amplification specificity. Our S-RPA provided much higher specificity (approximately 40 % improvement compared to classical RPA), realizing detection target with single nucleotide mutation. Based on its outstanding performance, we further combined the S-RPA with CRISPR/Cas12a to achieve highly specific and sensitive fluorescence detection, namely S-RPA equipped with CRISPR/Cas12a amplifier (SPECIAL). Our SPECIAL was more sensitive (10-fold higher) than the classical RPA-CRISPR/Cas12a assay, offering 100 % agreement with the qPCR during clinical validation. In summary, a strategy based on dNTPαS was established to enhance the specificity of RPA, thereby improving its practicability and providing a potential POCT tool for molecular diagnosis.

Development of a HiFi-LAMP Assay for Detection of Human Pegivirus Type 1 RNA

Human pegivirus (HPgV) is a blood-borne RNA virus belonging to the family Flaviviridae, and contains two types HPgV-1 and HPgV-2. HPgV-1 infection does not cause acute diseases in healthy individuals but was demonstrated to play beneficial roles in individuals coinfected with HIV-1. HPgV-1 has a high prevalence in blood donors and the general population worldwide. The long-term consequence of HPgV-1 infection in healthy individuals remains unknown. High prevalence of HPgV-1 in blood donors raises concerns about the risk of transfusion transmission. Development of rapid and accurate point-of-care testing (POCT) of HPgV-1 will facilitate the screening of HPgV-1 infection among blood donors. Here, we reported a novel high-fidelity loop-mediated isothermal amplification (HiFi-LAMP) assay for detection of HPgV-1 and evaluated its performance in 175 healthy adults from Taizhou, China. The assay exhibits high specificity and sensitivity with limits of detection (LODs) of 122.6-135.7 copies of viral RNA/25 μL reaction for various HPgV-1 variants and can be completed within 30 min. Clinical validation showed that the assay had a 100% concordance with a previously described RT-qPCR assay for 175 sera from healthy adults, showing 100% sensitivity and specificity. Furthermore, we reported a 28.0% (111/397) prevalence of HPgV-1 in healthy adults in Taizhou, China, with no significant differences between genders and ages. The prevalence is obviously higher than a pooled HPgV-1 prevalence of 3.3% in blood donors in China. The novel HPgV-1 HiFi-LAMP assay offers a robust, rapid, and cost-effective tool for HPgV-1 surveillance to mitigate transfusion risk, especially in resource-limited areas. High prevalence of HPgV-1 in healthy adults underscores its potential public health relevance.

Point-Of-Need One-Pot Multiplexed RT-LAMP Test For Detecting Three Common Respiratory Viruses In Saliva

Respiratory viral infections pose a significant global public health challenge, partly due to the difficulty in rapidly and accurately distinguishing between viruses with similar symptoms at the point of care, hindering timely and appropriate treatment and limiting effective infection control and prevention efforts. Here, we developed a multiplexed, non- invasive saliva-based, reverse transcription loop-mediated isothermal amplification (RT- LAMP) test that enables the simultaneous detection of three of the most common respiratory infections, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Influenza (Flu), and respiratory syncytial virus (RSV), in a single reaction via specific probes and monitored in real-time by a machine-learning-enabled compact analyzer. Our results demonstrate that the multiplexed assay can effectively detect three target RNAs with high accuracy. Further, testing with spiked saliva samples showed strong agreement with reverse transcription polymerase chain reaction (RT-PCR) assay, with area under the curve (AUC) values of 0.82, 0.93, and 0.96 for RSV, Influenza, and SARS-CoV-2, respectively. By enabling the rapid detection of respiratory infections from easily collected saliva samples at the point of care, the device presented here offers a practical and efficient tool for improving outcomes and helping prevent the spread of contagious diseases.

Significance

This research presents an innovative approach to respiratory infection diagnostics by combining a one-pot isothermal molecular test with machine learning-based analysis to simultaneously detect SARS-CoV-2, Influenza, and RSV in saliva samples. The battery- powered portable analyzer features novel machine-learning-assisted fluorescence detection for multiplexed reporter quantification, eliminating the need for traditional filter- based optical components and enabling adaptation to new targets without hardware changes. The test demonstrates high accuracy in detecting single and co-infections in spiked saliva samples, providing a rapid, cost-effective point-of-need solution. This tool can expand testing access, improve patient outcomes, and support more effective disease control, particularly in resource-limited or decentralized healthcare settings.

A rapid and sensitive extraction-free HiFi-LAMP assay for detecting Mycobacterium leprae

BACKGROUND

Timely and accurate detection of Mycobacterium leprae (M. leprae) is crucial for efficient treatment and early intervention of leprosy, which requires a simple and rapid extraction-free assay.

METHODS

A HiFi-loop-mediated isothermal amplification (LAMP) assay was developed for detection of M. leprae. The performance of the assay was assessed by comparing with qPCR and nested PCR assays using clinical samples. The extraction-free HiFi-LAMP assay was assessed by saliva from individuals with leprosy.

RESULTS

The M. leprae HiFi-LAMP assay has high specificity and sensitivity with a limit of detection (LOD) of 43 copies/25 µL reaction. Both sensitivity and specificity of the HiFi-LAMP assay were 100% for 130 purified DNA from nasal and oral samples, and the sensitivity was slightly higher than 50%-88.9% by the qPCR assay. A higher detection rate of M. leprae was observed in nasal swabs than oral swabs. The extraction-free assay directly using 6 µL saliva has a LOD of 11,833 M. leprae RLEP copies/mL saliva, can be completed within 30 mins, and showed 66.7% sensitivity for three saliva samples when compared with the assay using purified DNA.

CONCLUSION

The standard and/or extraction-free HiFi-LAMP assays can be used for detecting and monitoring M. leprae in endemic areas in resource-limited settings.

A Stable and Dependable Visual Technique for On-Site Nipah Virus Nucleic Acids Detection

The Nipah Virus (NiV) is a zoonotic pathogen with the mortality rate of up to 75%, recurring in Asia over the past two decades. Due to increasing the risk of human transmission mediated by various intermediate hosts such as pigs and bats, it is necessary to produce an accurate and reliable point-of-care molecular detection method for NiV field diagnosis. In this study, we designed two pairs of primers targeting the conserved G and P genes and developed a point-of-care nucleic acid detection (POC-NAD) system by integrating one-step RT-PCR, lateral flow immunoassay, and microfluidic technologies. The POC-NAD system shows high specificity and sensitivity, with a Limit of Detection (LoD) of 199.1 copies/rxn. The primers aiming to the conserved sequences enables simultaneous detection of both NiV-M and NiV-B strains. Continuous evaluation of 21 simulated clinical samples demonstrated 100% concordance with RT-PCR results. Lateral flow-based visualization improves the display time and legibility of RT-PCR results. Additionally, microfluidic chips or chambers offer disposable reagent containers and consistent PCR amplification results across various field conditions. Therefore, the diagnostic tool is suitable for real-time nucleic acid testing and NiV surveillance in resource-limited field environments.

Development of a Highly Multiplexed RT-LAMP Assay for Coverage of Genetic Sequence Diversity

Nucleic acid amplification tests (NAATs) can achieve high accuracy for diagnosing infectious diseases by targeting conserved genetic sequences specific to the target organism. Isothermal NAATs, such as reverse-transcription loop mediated isothermal amplification (RT-LAMP), simplify instrumentation requirements, facilitating point-of-care testing. However, sequence variation due to genetic variability can cause false negative results. Single-pot multiplex testing can improve sequence coverage, but RT-LAMP is complicated by requiring many primers for even a single assay, which can lead to nonspecific amplification. We implemented a process that leveraged manual primer design to develop a highly multiplexed RT-LAMP assay (Chain LAMP) targeting 7 adjacent genomic target regions of HIV, one of the most diverse clinically relevant pathogens. This process departed from standards for RT-LAMP design, including the omission of bumper primers whose activity was replaced by cooperative neighboring assays. The Chain LAMP is, to our knowledge, the highest order single-pot multiplexed RT-LAMP assay published. The assay has an analytical limit of detection of 25 copies of RNA/reaction without detectable nonspecific amplification, translating to 1000 copies of HIV/mL of plasma from a fingerstick sample, aligning with WHO standards for HIV viral load monitoring. When evaluated using 24 clinical RNA samples representative of global HIV diversity, Chain LAMP demonstrated robust coverage of sequence diversity, amplifying all samples with minimal sensitivity variation. We performed mechanistic analysis with Nanopore sequencing, identifying liftoff of multiple assay regions for each sample, indicating many initiation loci. The high level of multiplexing in the Chain LAMP effectively increases the coverage of HIV sequence diversity.

Swift and portable detection of soybean mosaic virus SC7 through RNA extraction and loop-mediated isothermal amplification using lateral flow device

The soybean mosaic disease-caused by the soybean mosaic virus (SMV)-significantly impacts soybean quality and yield. Among its various strains, SMV-SC7 is prevalent in China. Therefore, rapid and accurate diagnosis is deemed critical to mitigate the spread of SMV-SC7. In this study, a simple and rapid magnetic bead-based RNA extraction method was optimized. Furthermore, a reverse-transcription loop-mediated isothermal amplification (RT-LAMP) assay that requires no specialized equipment such as PCR Amplifier was proposed, employing a lateral flow device (LFD) for visual interpretation of SMV-SC7. The RT-LAMP-LFD approach facilitated specificity testing of SMV-SC7. Moreover, the limit of detection (LOD) of this method was as low as 10-5 ng (2.4 copies). The sensitivity of RT-LAMP-LFD was 10-fold higher than that of the colorimetric RT-LAMP method. In 194 field samples tested, the RT-LAMP-LFD detection of the SMV-SC7 had accuracy of 98.45% in comparison to RT-qPCR. In conclusion, the assay exhibited high specificity, sensitivity, and rapidity, enabling economical and portable detection of SMV-SC7 and providing technical support to identify SMV-SC7-infected soybeans.

A duplex HiFi-LAMP assay for screening of two novel human circoviruses HCirV-1 and HCirV-2

Circoviruses belong to the family Circoviridae, which is classified into two genera, Circovirus and Cyclovirus. Some circoviruses have been identified in various organisms and/or their fecal samples and might be associated with diseases in their hosts. However, few circoviruses are reported in human. Recently, two novel circoviruses HCirV-1 and HCirV-2 were identified in humans through next-generation sequencing and were defined as the species of Circovirus human in the family Circoviridae. Both viruses are suspected to be associated with liver diseases, particularly among immunosuppressed people, showing potential health implication. Investigation on the prevalence of both viruses, and identification of vulnerable population are important and need a rapid, accurate, and specific assay for detecting and screening the two viruses. In this study, we developed a duplex HiFi-LAMP assay for simultaneous detection of HCirV-1 and HCirV-2. The assay exhibits high sensitivity with LOD of 64 and 49 copies per 25 µL reaction for HCirV-1 and HCirV-2, respectively. The duplex assay was demonstrated to have a rapid reaction time within 35 min. Clinical screening tests showed that neither HCirV-1 nor HCirV-2 were detected among 875 patients with infection of HBV, HIV-1 or other viruses. Large-scale screening of both viruses in diverse populations is encouraged to enhance our understanding of their relevance to various diseases.

Multiplex competitive annealing mediated isothermal amplification with high fidelity DNA polymerase (HiFi-CAMP)

Various isothermal amplification methods have been developed for point-of-care testing (POCT) of various infectious diseases. Here, we proposed a novel isothermal amplification method, named as 5'-half complementary primers mediated isothermal amplification (HCPA). Because of the similarity of our method to the previous method competitive annealing mediated isothermal amplification (CAMP) in primer design, we also use the name CAMP for our method. We demonstrated that CAMP is mediated by both a linear isothermal amplification pattern and a loop-mediated isothermal amplification pattern. To improve the specificity and enable multiplex detection, we further developed HiFi-CAMP method that uses a small amount of high-fidelity DNA polymerase to cut HFman probe to release fluorescent signal. The HiFi-CAMP method was demonstrated to have a good specificity and sensitivity, and fast amplification speed in detection of three human respiratory viruses, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), respiratory syncytial virus A (RSV-A) and influenza A viruses (IAV). When compared with gold standard RT-qPCR assays, the HiFi-CAMP assays showed sensitivities of 90.0 %, 71.4 % and 78.1 %, specificities of 100 %, 100 % and 95.5 %, and consistencies of 93.0 %, 93.3 % and 88.2 % for SARS-CoV-2, RSV-A and IAV, respectively. Furthermore, a duplex HiFi-CAMP assay was also developed to simultaneously detect RSV-A and SARS-CoV-2. The HiFi-CAMP will provide a promising candidate for POCT diagnosis in resource-limited settings.

Evaluation of diagnostic accuracy of the wabG gene based Klebsiella pneumoniae detection by loop-mediated isothermal reaction in neonatal blood sample

Neonatal sepsis is a significant problem in developing nations, but current gold-standard diagnostic methods, such as blood culture, is slow and time-consuming. Here, we describe the development of a colorimetric loop-mediated isothermal amplification (LAMP) assay that targets the wabG gene in the lipopolysaccharide region of K. pneumoniae, offering a limit of detection (LOD) of 40 CFU/ml with specificity for K. pneumoniae compared to other non-Klebsiella strains. The sensitivity and specificity of the LAMP assay were found to be 90 % and 100 %, respectively, with a positive predictive value of 100 % and a negative predictive value of 96.47 %. The LAMP assay demonstrated a significantly shorter turnaround time of 1 h. The LAMP assay was found to be simpler, quicker, and more sensitive than traditional detection techniques such as PCR and blood culture.

Development of a Rapid Visual Detection Assay for Duck Tembusu Virus Using RT-LAMP-CRISPR/Cas12a

Duck Tembusu virus (DTMUV) is an emerging flavivirus that has inflicted significant economic losses on China's poultry industry. Rapid and accurate detection of DTMUV is crucial for effective prevention and control measures. In this study, we developed a novel, rapid visual detection assay that combines reverse transcriptase loop-mediated isothermal amplification (RT-LAMP) with the CRISPR/Cas12a system for on-site detection of DTMUV. Our results demonstrate that this assay can sensitively and specifically detect the specific DNA plasmids containing the DTMUV NS3 gene within 100 min, with a limit of detection as low as 19.3 copies/μL. We successfully applied the RT-LAMP-CRISPR/Cas12a assay to diagnose DTMUV in eight duck embryos and 11 chicken embryonic fibroblast samples, and the results obtained with direct visualization by the naked eye were consistent with those obtained using real-time RT-PCR. Overall, our RT-LAMP-CRISPR/Cas12a assay is a reliable, sensitive, specific, and user-friendly method that holds great promise for early on-site detection of DTMUV in clinical samples, facilitating timely interventions and improved disease management in the poultry industry.

Preconcentration and detection of SARS-CoV-2 in wastewater: A comprehensive review

Severe acute respiratory syndrome coronaviruses 2 (SARS-CoV-2) causing coronavirus disease 2019 (COVID-19) affected the health of human beings and the global economy. The patients with SARS-CoV-2 infection had viral RNA or live infectious viruses in feces. Thus, the possible transmission of SARS-CoV-2 through wastewater received great attentions. Moreover, SARS-CoV-2 in wastewater can serve as an early indicator of the infection within communities. We summarized the preconcentration and detection technology of SARS-CoV-2 in wastewater aiming at the complex matrices of wastewater and low virus concentration and compared their performance characteristics. We described the emerging tests that would be possible to realize the rapid detection of SARS-CoV-2 in fields and encourage academics to advance their technologies beyond conception. We concluded with a brief discussion on the outlook for integrating preconcentration and the detection of SARS-CoV-2 with emerging technologies.

Development of a Colorimetric and SERS Dual-Signal Platform via dCas9-Mediated Chain Assembly of Bifunctional Au@Pt Nanozymes for Ultrasensitive and Robust Salmonella Assay

Timely screening for harmful pathogens is a great challenge in emergencies where traditional culture methods suffer from long assay time and alternative methods are limited by poor accuracy and low robustness. Herein, we present a dCas9-mediated colorimetric and surface-enhanced Raman scattering (SERS) dual-signal platform (dCas9-CSD) to address this challenge. Strategically, the platform used dCas9 to accurately recognize the repetitive sequences in amplicons produced by loop-mediated isothermal amplification (LAMP), forming nucleic acid frameworks that assemble numerous bifunctional gold-platinum (Au@Pt) nanozymes into chains on the surface of streptavidin-magnetic beads (SA-MB). The collected Au@Pt converted colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB (oxTMB) via its Pt shell and then enhanced the Raman signal of oxTMB by its Au core. Therefore, the presence of Salmonella could be dexterously converted into cross-validated colorimetric and SERS signals, providing more reliable conclusions. Notably, dCas9-mediated secondary recognition of amplicons reduced background signal caused by nontarget amplification, and two-round signal amplification consisting of LAMP reaction and Au@Pt catalysis greatly improved the sensitivity. With this design, Salmonella as low as 1 CFU/mL could be detected within 50 min by colorimetric and SERS modes. The robustness of dCas9-CSD was further confirmed by various real samples such as lake water, cabbage, milk, orange juice, beer, and eggs. This work provides a promising point-of-need tool for pathogen detection.

Molecular Detection of Respiratory Tract Viruses in Chickens at the Point of Need by Loop-Mediated Isothermal Amplification (LAMP)

Accurate and timely molecular diagnosis of respiratory diseases in chickens is essential for implementing effective control measures, preventing the spread of diseases within poultry flocks, minimizing economic loss, and guarding food security. Traditional molecular diagnostic methods like polymerase chain reaction (PCR) require expensive equipment and trained personnel, limiting their use to centralized labs with a significant delay between sample collection and results. Loop-mediated isothermal amplification (LAMP) of nucleic acids offers an attractive alternative for detecting respiratory viruses in broiler chickens with sensitivity comparable to that of PCR. LAMP's main advantages over PCR are its constant incubation temperature (∼65 °C), high amplification efficiency, and contaminant tolerance, which reduce equipment complexity, cost, and power consumption and enable instrument-free tests. This review highlights effective LAMP methods and variants that have been developed for detecting respiratory viruses in chickens at the point of need.

A new simplified sequence-dependent loop-mediated isothermal amplification (LAMP) detection method

Fluorescence dye-based loop-mediated isothermal amplification (LAMP) is a sensitive nucleic acid detection method, but is limited to single-plex detection and may yield non-specific signals. In this study, we propose a bifunctional probe-based real-time LAMP amplification method for single-plexed or multiplexed detection. The bifunctional probe is derived by modifying the 5' end of the fluorophore and an internal quencher on one of the LAMP primers; therefore, it can simultaneously be involved in the LAMP process and signal amplification. The fluorescence intensity undergoes a cumulative exponential increase during the incorporation of the bifunctional probe into double-stranded DNA amplicons. The bifunctional probe-based LAMP method is simplified and cost-effective, as the primer design and experimental operations align entirely with the ordinary LAMP. Different from other current probe-based methods, this method does not require additional enzymes, sequences, or special probe structures. Also, it is 10 min faster than several other probe-based LAMP methods. The bifunctional probe-based LAMP method allows the simultaneous detection of the target Vibrio parahaemolyticus DNA and the internal amplification control in a one-pot reaction, demonstrating its potential for multiplexed detection.

Droplet digital molecular beacon-LAMP assay via pico-injection for ultrasensitive detection of pathogens

A pico-injection-aided digital droplet detection platform is presented that integrates loop-mediated isothermal amplification (LAMP) with molecular beacons (MBs) for the ultrasensitive and quantitative identification of pathogens, leveraging the sequence-specific detection capabilities of MBs. The microfluidic device contained three distinct functional units including droplet generation, pico-injection, and droplet counting. Utilizing a pico-injector, MBs are introduced into each droplet to specifically identify LAMP amplification products, thereby overcoming issues related to temperature incompatibility. Our methodology has been validated through the quantitative detection of Escherichia coli, achieving a detection limit as low as 9 copies/μL in a model plasmid containing the malB gene and 3 CFU/μL in a spiked milk sample. The total analysis time was less than 1.5 h. The sensitivity and robustness of this platform further demonstrated the potential for rapid pathogen detection and diagnosis, particularly when integrated with cutting-edge microfluidic technologies.

Molecular Point-of-Care Assay Development: Design and Considerations

Molecular diagnostic point-of-care (MDx POC) testing is gaining momentum and is increasingly important for infectious disease detection and monitoring, as well as other diagnostic areas such as oncology. Molecular testing has traditionally required high-complexity laboratories. Laboratory testing complexity is determined by utilizing the Clinical Laboratory Improvement Amendments of 1988 (CLIA) Categorization Criteria scorecard, utilizing seven criteria that are scored on a scale of one to three. Previously, most commercially available point-of-care (POC) tests use other analytes and technologies that were not found to be highly complex by the CLIA scoring system. However, during the COVID-19 pandemic, MDx POC testing became much more prominent. Utilization during the COVID-19 pandemic has demonstrated that MDx POC testing applications can have outstanding advantages compared to available non-molecular POC diagnostic tests. This article introduces MDx POC testing to students, technologists, researchers, and others, providing a general algorithm for MDx POC test development. This algorithm is an introductory, step-by-step decision tree for defining a molecular POC diagnostic device meeting the functional requirements for a desired application. The technical considerations driving the decision-making include nucleic acid selection method (DNA, RNA), extraction methods, sample preparation, number of targets, amplification technology, and detection method. The scope of this article includes neither higher-order multiplexing, nor quantitative molecular analysis. This article covers key application considerations, such as sensitivity, specificity, turnaround time, and shipping/storage requirements. This article provides an overall understanding of the best resources and practices to use when developing a MDx POC assay that may be a helpful resource for readers without extensive molecular testing experience as well as for those who are already familiar with molecular testing who want to increase MDx availability at the POC. © 2024 Wiley Periodicals LLC.

A novel extraction-free dual HiFi-LAMP assay for detection of methicillin-sensitive and methicillin-resistant Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a leading cause of bacteremia and blood stream infections. Methicillin-resistant S. aureus (MRSA) that first appeared in 1961 often caused hospital-acquired infections (HAIs) and community-acquired infections (CAIs) and was associated with high mortality rate. Accurate and rapid point-of-care testing (POCT) of MRSA is crucial for clinical management and treatment of MRSA infections, as well as the prevention and control of HAIs and CAIs. Here, we reported a novel extraction-free dual HiFi-LAMP assay for discriminative detection of methicillin-susceptible S. aureus and MRSA. The dual HiFi-LAMP assay can detect 30 copies/reaction of nuc and mecA genes with detection limits of 147 and 158 copies per 25 µL reaction, respectively. A retrospective clinical evaluation with 107 clinical S. aureus isolates showed both sensitivity and specificity of 100%. A prospective clinical evaluation with 35 clinical samples revealed a specificity of 100% and a sensitivity of 92.3%. The dual HiFi-LAMP assay can detect almost all S. aureus samples (141/142; 99.3%) within 20 min, implying that the entire HiFi-LAMP assay (including sample process) can be completed within 40 min, extremely significantly shorter than 3-5 days by the traditional clinical microbial culture and antibiotic susceptibility testing. The novel extraction-free dual HiFi-LAMP assay can be used as a robust POCT tool to promote precise diagnosis and treatment of MRSA infections in hospitals and to facilitate surveillance of MRSA at hospital and community settings.IMPORTANCEMethicillin-resistant Staphylococcus aureus (MRSA) was associated with high mortality rate and listed as a "priority pathogen" by the World Health Organization. Accurate and rapid point-of-care testing (POCT) of MRSA is critically required for clinical management and treatment of MRSA infections. Some previous LAMP-based POCT assays for MRSA might be questionable due to their low specificity and the lack of appropriate evaluation directly using clinical samples. Furthermore, they are relatively tedious and time-consuming because they require DNA extraction and lack multiplex detection capacity. Here, we reported a novel extraction-free dual HiFi-LAMP assay for discriminative detection of MRSA and methicillin-susceptible S. aureus. The assay has high specificity and sensitivity and can be completed within 40 min. Clinical evaluation with real clinical samples and clinical isolates showed excellent performance with 100% specificity and 92.3%-100% sensitivity. The novel extraction-free assay may be a robust POCT tool to promote precise diagnosis of MRSA infections and facilitate surveillance of MRSA at hospital and community settings.

Visual, rapid, and cost-effective BK virus detection system for renal transplanted patients using gold nanoparticle coupled loop-mediated isothermal amplification (nanoLAMP)

A substantial percentage of kidney transplant recipients show transplant failure due to BK virus-induced nephropathy. This can be clinically controlled by the rapid and timely detection of BK virus infection in immune-compromised patients. We report a rapid (two hours from sample collection, processing, and detection), cost-effective (< 2$), highly sensitive and BKV-specific nanoLAMP (loop-mediated isothermal amplification) diagnostic methodology using novel primers and gold nanoparticles complex-based visual detection. The standardized nanoLAMP showed an analytical sensitivity of 25 copies/µl and did not cross-react with closely related JC and SV40 viruses. This nanoLAMP showed diagnostic sensitivity and specificity as 91% and 96%, respectively, taking 50 BK virus-negative (confirmed by qPCR from the plasma of healthy donors) and 57 positive BKV patient samples (confirmed by clinical parameters and qPCR assay). This simple two-step, low-cost, and quick (1-2 h/test) detection would be advantageous over the currently used diagnostic methodology. It may change the paradigm for polyomavirus infection-based failure of renal transplant.

Direct TAMRA-dUTP labeling of M. tuberculosis genes using loop-mediated isothermal amplification (LAMP)

Fluorescent molecule-based direct labeling of amplified DNA is a sensitive method employed across diverse DNA detection and diagnostics systems. However, using pre-labeled primers only allows for the attachment of a single fluorophore to each DNA strand and any modifications of the system are less flexible, requiring new sets of primers. As an alternative, direct labeling of amplified products with modified nucleotides is available, but still poorly characterized. To address these limitations, we sought a direct and adaptable approach to label amplicons produced through Loop-mediated isothermal amplification (LAMP), using labeled nucleotides (dUTPs) rather than primers. The focus of this study was the development and examination of a direct labeling technique of specific genes, including those associated with drug resistance in Mycobacterium tuberculosis. We used 5-(3-Aminoallyl)-2'-deoxyuridine-5'triphosphate, tagged with 5/6-TAMRA (TAMRA-dUTP) for labeling LAMP amplicons during the amplification process and characterized amplification and incorporation efficiency. The optimal TAMRA-dUTP concentration was first determined based on amplification efficiency (0.5% to total dNTPs). Higher concentrations of modified nucleotides reduced or completely inhibited the amplification yield. Target size also showed to be determinant to the success of amplification, as longer sequences showed lower amplification rates, thus less TAMRA incorporated amplicons. Finally, we were able to successfully amplify all four M. tuberculosis target genes using LAMP and TAMRA-modified dUTPs.

Enhancing Loop-Mediated Isothermal Amplification through Nonpowered Nanoelectric Preconcentration

The global threat posed by the COVID-19 pandemic has catalyzed the development of point-of-care (POC) molecular diagnostics. While loop-mediated isothermal amplification (LAMP) stands out as a promising technique among FDA-approved methods, it is occasionally susceptible to a high risk of false positives due to nonspecific amplification of a primer dimer. In this work, we report an enhancing LAMP technique in terms of assay sensitivity and reliability through streamlined integration with a nonpowered nanoelectric preconcentration (NPP). The NPP, serving as a sample preparation tool, enriched the virus concentration in samples prior to the subsequent LAMP assay. This enrichment enabled not only to achieve more sensitive assay but also to shorten the assay time for all tested clinical samples by ∼10 min compared to the conventional LAMP. The shortened assay time suppresses the occurrence of nonspecific amplification by not providing the necessary incubation time, effectively suppressing misidentification by false positives. Utilizing this technique, we also developed a prototype of the POC NPP-LAMP kit. This kit offers a streamlined diagnostic process for nontrained individuals, from the sample enrichment, transfer of the enriched sample to LAMP assays, which facilitates on-site/on-demand diagnosis of SARS-CoV-2. This development holds the potential to contribute toward preventing not only the current outbreak but also future occurrences of pandemic viruses.

Rapid detection of four major HFMD-associated enteroviruses by multiplex HiFi-LAMP assays

Hand, foot, and mouth disease (HFMD) caused by various enteroviruses is a major public health concern globally. Human enterovirus 71(EVA71), coxsackievirus A16 (CVA16), coxsackievirus A6 (CVA6), and coxsackievirus A10 (CVA10) are four major enteroviruses responsible for HFMD. Rapid, accurate, and specific point-of-care (POC) detection of the four enteroviruses is crucial for the prevention and control of HFMD. Here, we developed two multiplex high-fidelity DNA polymerase loop-mediated isothermal amplification (mHiFi-LAMP) assays for simultaneous detection of EVA71, CVA16, CVA6, and CVA10. The assays have good specificity and exhibit high sensitivity, with limits of detection (LOD) of 11.2, 49.6, 11.4, and 20.5 copies per 25 μL reaction for EVA71, CVA16, CVA6, and CVA10, respectively. The mHiFi-LAMP assays showed an excellent clinical performance (sensitivity 100.0%, specificity 83.3%, n = 47) when compared with four singleplex RT-qPCR assays (sensitivity 93.1%, specificity 100%). In particular, the HiFi-LAMP assays exhibited better performance (sensitivity 100.0%, specificity 100%) for CVA16 and CVA6 than the RT-qPCR assays (sensitivity 75.0-92.3%, specificity 100%). Furthermore, the mHiFi-LAMP assays detected all clinical samples positive for the four enteroviruses within 30 min, obviously shorter than about 1-1.5 h by the RT-qPCR assays. The new mHiFi-LAMP assays can be used as a robust point-of-care testing (POCT) tool to facilitate surveillance of HFMD at rural and remote communities and resource-limited settings.

Current Trends in RNA Virus Detection via Nucleic Acid Isothermal Amplification-Based Platforms

Ribonucleic acid (RNA) viruses are one of the major classes of pathogens that cause human diseases. The conventional method to detect RNA viruses is real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), but it has some limitations. It is expensive and time-consuming, with infrastructure and trained personnel requirements. Its high throughput requires sophisticated automation and large-scale infrastructure. Isothermal amplification methods have been explored as an alternative to address these challenges. These methods are rapid, user-friendly, low-cost, can be performed in less specialized settings, and are highly accurate for detecting RNA viruses. Microfluidic technology provides an ideal platform for performing virus diagnostic tests, including sample preparation, immunoassays, and nucleic acid-based assays. Among these techniques, nucleic acid isothermal amplification methods have been widely integrated with microfluidic platforms for RNA virus detection owing to their simplicity, sensitivity, selectivity, and short analysis time. This review summarizes some common isothermal amplification methods for RNA viruses. It also describes commercialized devices and kits that use isothermal amplification techniques for SARS-CoV-2 detection. Furthermore, the most recent applications of isothermal amplification-based microfluidic platforms for RNA virus detection are discussed in this article.

Pipette-free field-deployable molecular diagnostic kit for bimodal visual detection of infectious RNA viruses

Here, we developed a field-deployable molecular diagnostic kit for the detection of RNA viruses that operates in a pipette-free manner. The kit is composed of acrylic sticks, PCR tubes, and palm-sized three-dimensional(3D)-printed heaters operated by batteries. The kit performs RNA extraction, reverse transcriptase loop-mediated isothermal amplification (RT-LAMP), and visual detection in one kit. An acrylic stick was engraved with one shallow and one deep cylindrical chamber at each end for the insertion of an FTA card and ethidium homodimer-1 (EthD-1), respectively, to perform RNA extraction/purification and bimodal visual detection of the target amplicons. First, an intercalation of EthD-1 into the target DNA initially produces fluorescence upon UV illumination. Next, the addition of a strong oxidant, in this case sodium (meta) periodate (NaIO4 ), produces intense aggregates in the presence of EthD-1-intercalated DNA, realized by electrostatic interaction. In the absence of the target amplicon, no fluorescence or aggregates are observed. Using this kit, two major infectious viruses-severe fever with thrombocytopenia syndrome virus (SFTSV) and severe acute respiratory syndrome coronavirus (SARS-CoV-2)-were successfully detected in 1 h, and the limits of detection (LOD) were approximately 1 virus μL-1 for SFTSV and 103 copies μL-1 for SARS-CoV-2 RNA. The introduced kit is portable, end-user-friendly, and can be operated in a pipette-free manner, paving the way for simple and convenient virus detection in resource-limited settings.

UbiNAAT: a multiplexed point-of-care nucleic acid diagnostic platform for rapid at-home pathogen detection

The COVID-19 pandemic increased demands for respiratory disease testing to facilitate treatment and limit transmission, demonstrating in the process that most existing test options were too complex and expensive to perform in point-of-care or home scenarios. Lab-based molecular techniques can detect viral RNA in respiratory illnesses but are expensive and require trained personnel, while affordable antigen-based home tests lack sensitivity for early detection in newly infected or asymptomatic individuals. The few home RNA detection tests deployed were prohibitively expensive. Here, we demonstrate a point-of-care, paper-based rapid analysis device that simultaneously detects multiple viral RNAs; it is demonstrated on two common respiratory viruses (COVID-19 and influenza A) spiked onto a commercial nasal swab. The automated device requires no sample preparation by the user after insertion of the swab, minimizing user operation steps. We incorporated lyophilized amplification reagents immobilized in a porous matrix, a novel thermally actuated valve for multiplexed fluidic control, a printed circuit board that performs on-device lysis and amplification within a cell-phone-sized disposable device. Reverse transcription loop-mediated isothermal amplification (RT-LAMP) products are visualized via fluorescent dyes using a modified cell phone, resulting in detection of as few as 104 viral copies per swab across both pathogens within 30 minutes. This integrated platform could be commercialized in a form that would be inexpensive, portable, and sensitive; it can readily be multiplexed to detect as many as 8 different RNA or DNA sequences, and adapted to any desired RNA or DNA detection assays.

Ultrasensitive and fast detection of SARS-CoV-2 using RT-LAMP without pH-dependent dye

This study investigates the performance of reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for the colorimetric detection of SARS-CoV-2 using fluorometric dye, namely, calcein. The detection limit (LoD) with the N-ID1 primer set resulted in superior performance, corresponding to ~ 2 copies/reaction or ~ 0.1 copies/μL of the RNA sample. The color development can be observed by the naked eye, using an ultraviolet (UV) transilluminator or a hand-UV light without the requirement of expensive devices. The average time-to-reaction (TTR) value was 26.2 min in high-copy number samples, while it was about 50 min in rRT-PCR. A mobile application was proposed to quantify the positive and negative results based on the three-color spaces (RGB, Lab, and HSB). Compared to rRT-PCR (n = 67), this assay allows fast and sensitive visual detection of SARS-CoV-2, with high sensitivity (90.9%), selectivity (100%), and accuracy (94.03%). Besides, the assay was sensitive regardless of variants. Since this assay uses a fluorescent dye for visual observation, it can be easily adapted in RT-LAMP assays with high sensitivity. Thus, it can be utilized in low-source centers and field testing such as conferences, sports meetings, refugee camps, companies, and schools.

Revolutionizing SARS-CoV-2 omicron variant detection: Towards faster and more reliable methods

The emergence of the highly contagious Omicron variant of SARS-CoV-2 has inflicted significant damage during the ongoing COVID-19 pandemic. This new variant's significant sequence changes and mutations in both proteins and RNA have rendered many existing rapid detection methods ineffective in identifying it accurately. As the world races to control the spread of the virus, researchers are urgently exploring new diagnostic strategies to specifically detect Omicron variants with high accuracy and sensitivity. In response to this challenge, we have compiled a comprehensive overview of the latest reported rapid detection techniques. These techniques include strategies for the simultaneous detection of multiple SARS-CoV-2 variants and methods for selectively distinguishing Omicron variants. By categorizing these diagnostic techniques based on their targets, which encompass protein antigens and nucleic acids, we aim to offer a comprehensive understanding of the utilization of various recognition elements in identifying these targets. We also highlight the advantages and limitations of each approach. Our work is crucial in providing a more nuanced understanding of the challenges and opportunities in detecting Omicron variants and emerging variants.

Rapid detection of human influenza A viruses by HFman probe-based loop-mediated isothermal amplification assays

Since China abandoned the zero-COVID policy at the end of 2022, a wave of severe Flu pandemic emerged in China. Rapid and accurate diagnosis of Influenza A virus (IAV) is critical for clinical management and therapeutic decision-making of patients with fever. Here, we reported a novel IAV HF-LAMP assay, which can be performed with purified RNA or directly using clinical samples. The assays with purified RNA and clinical samples have high sensitivity with limit of detection (LOD) of 9.6 copies/reaction, 9900 copies/mL, and short sample-to-answer times of 36 and 50 min, respectively. Both assays showed high specificity and significantly higher IAV detection rate than the rapid antigen detection (RAD) assays. Furthermore, we found the vast majority (91.2 %) of children with fever during the pandemic were infected by IAV, and current IAV infection has a very narrow detectable window. The novel IVA HF-LAMP assays will provide robust tools to facilitate early diagnosis of IAV infection in current and future seasonal influenza epidemics.

Multiple thermocycles followed by LAMP with only two primers for ultrasensitive colorimetric viral RNA testing and tracking at single-base resolution

Rapid, accurate and high throughput measurement of infectious viruses is an urgent need to prevent viral transmission. Loop-mediated isothermal amplification (LAMP) is an attractive isothermal amplification method for nucleic acid detection, especially for point-of-care (POC) testing, but it needs at least four primers and its sensitivity is also limited when integrating with visual detection methods. Herein, by designing only two primers to precisely recognize the four regions of the target, we developed a multiple thermocycles-based LAMP method (MTC-LAMP) for sensitive and specific testing and tracking of viral RNA. We also introduced a novel SYBR Green I (SG)-assisted stable colorimetric assay induced by the amplification products through the charge neutralization effect of positively charged SG toward gold nanoparticles (AuNPs). The ultralow nonspecific background of the double exponential amplification improved the detection sensitivity to near single-molecule level (1 aM, 3 copies in 5 μL solution), which was higher than RT-PCR and RT-LAMP. After adding AuNPs, a significant color difference between target and blank was immediately observed by naked eye. By introducing a peptide nucleic acid (PNA) clamp into our colorimetric MTC-LAMP assay, the specific distinguish of virus variants at single-base resolution was observed without the requirement of any equipment. This assay shows great potential for large-scale screening and tracking of the threatening viruses with ultrahigh sensitivity and pronounced colorimetric output, which is of great importance for pandemic control.

Mobile Efficient Diagnostics of Infectious Diseases via On-Chip RT-qPCR: MEDIC-PCR

The COVID-19 outbreak has caused public and global health crises. However, the lack of on-site fast, reliable, sensitive, and low-cost reverse transcription polymerase chain reaction (RT-PCR) testing limits early detection, timely isolation, and epidemic prevention and control. Here, the authors report a rapid mobile efficient diagnostics of infectious diseases via on-chip -RT-quantitative PCR (RT-qPCR): MEDIC-PCR. First, the authors use a roll-to-roll printing process to accomplish low-cost carbon-black-based disposable PCR chips that enable rapid LED-induced photothermal PCR cycles. The MEDIC-PCR can perform RT (3 min), and PCR (9 min) steps. Further, the cohort of 89 COVID-19 and 103 non-COVID-19 patients testing is completed by the MEDIC-PCR to show excellent diagnostic accuracy of 97%, sensitivity of 94%, and specificity of 98%. This MEDIC-PCR can contribute to the preventive global health in the face of a future pandemic.

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.

RART-LAMP: One-Step Extraction-Free Method for Genotyping within 40 min

Loop-mediated isothermal amplification (LAMP) is a commonly used alternative to PCR for point-of-care detection of nucleic acids due to its rapidity, sensitivity, specificity, and simpler instrumentation. While dual-labeled TaqMan probes are widely used in PCR for single-nucleotide polymorphism (SNP) genotyping, real-time LAMP primarily relies on turbidimetry or intercalator fluorescence measurements, which can be non-specific and generate false-positive results. In this study, we propose a closed-tube, dual-labeled RNA-modified probes and RNase H II-assisted real-time LAMP (RART-LAMP) method for SNP genotyping. Our findings indicate that (1) fluorescence signals were predominantly derived from probe hydrolysis rather than hybridization, (2) temperature-controlled hybridization between the probe and template ensured the specificity of SNP analysis, and (3) RNase H II hydrolysis between the target containing SNP sites and probes did not exhibit sequence specificity. Our RART-LAMP approach demonstrated excellent performance in genotyping C677T clinical samples, including gDNA extracted from blood, saliva, and swabs. More importantly, saliva and swab samples could be directly analyzed without any pretreatment, indicating promising prospects for nucleic acid analysis at the point of care in resource-limited settings.

SARS-Cov-2 Spike-S1 Antigen Test Strip with High Sensitivity Endowed by High-Affinity Antibodies and Brightly Fluorescent QDs/Silica Nanospheres

The extensive research into developing novel strategies for detecting respiratory syndrome coronavirus 2 (SARS-CoV-2) antigens in clinical specimens, especially the sensitive point-of-care testing method, is still urgently needed to reach rapid screening of viral infections. Herein, a new lateral flow immunoassay (LFIA) platform was reported for the detection of SARS-CoV-2 spike-S1 protein antigens, in which four sensitive and specific SARS-CoV-2 mouse monoclonal antibodies (MmAbs) were tailored by using quantum dot (QD)-loaded dendritic mesoporous silica nanoparticles modified further for achieving the -COOH group surface coating (named Q/S-COOH nanospheres). Importantly, compact QD adsorption was achieved in mesoporous channels of silica nanoparticles on account of highly accessible central-radial pores and electrostatic interactions, leading to significant signal amplification. As such, a limit of detection for SARS-CoV-2 spike-S1 testing was found to be 0.03 ng/mL, which is lower compared with those of AuNPs-LFIA (traditional colloidal gold nanoparticles, Au NPs) and enzyme-linked immunosorbent assay methods. These results show that optimizing the affinity of antibody and the intensity of fluorescent nanospheres simultaneously is of great significance to improve the sensitivity of LFIA.

Recent development of surface-enhanced Raman scattering for biosensing

Surface-Enhanced Raman Scattering (SERS) technology, as a powerful tool to identify molecular species by collecting molecular spectral signals at the single-molecule level, has achieved substantial progresses in the fields of environmental science, medical diagnosis, food safety, and biological analysis. As deepening research is delved into SERS sensing, more and more high-performance or multifunctional SERS substrate materials emerge, which are expected to push Raman sensing into more application fields. Especially in the field of biological analysis, intrinsic and extrinsic SERS sensing schemes have been widely used and explored due to their fast, sensitive and reliable advantages. Herein, recent developments of SERS substrates and their applications in biomolecular detection (SARS-CoV-2 virus, tumor etc.), biological imaging and pesticide detection are summarized. The SERS concepts (including its basic theory and sensing mechanism) and the important strategies (extending from nanomaterials with tunable shapes and nanostructures to surface bio-functionalization by modifying affinity groups or specific biomolecules) for improving SERS biosensing performance are comprehensively discussed. For data analysis and identification, the applications of machine learning methods and software acquisition sources in SERS biosensing and diagnosing are discussed in detail. In conclusion, the challenges and perspectives of SERS biosensing in the future are presented.

Water-soluble polythiophene-based colorimetry for the quick and accurate detection of SARS-CoV-2 RNA

The SARS-CoV-2-related Corona Virus Disease 2019 (COVID-19) epidemic has had a significant negative impact on society and endangered global health. To quickly stop and constrain the pandemic, a SARS-CoV-2 detection technology that is sensitive, quick and reasonably priced is urgently required. The widely used reverse-transcription polymerase chain reaction (RT-PCR) requires complex equipment and a fair amount of time. Reverse transcription-loop-mediated isothermal amplification (RT-LAMP) exhibits significant advantage for early detection of COVID-19 without the requirement for expensive equipment by amplifying a little amount of RNA to a detectable level at isothermal condition. Here, a water-soluble polythiophene-based colorimetric method by combining with RT-LAMP is established for fast and sensitive detection of SARS-CoV-2 RNA. The proposed assay has benefits for the quick detection of SARS-CoV-2 RNA at concentrations as low as 10 aM, or 6 copies/μL.

Evolution of the Probe-Based Loop-Mediated Isothermal Amplification (LAMP) Assays in Pathogen Detection

Loop-mediated isothermal amplification (LAMP), as the rank one alternative to a polymerase chain reaction (PCR), has been widely applied in point-of-care testing (POCT) due to its rapid, simple, and cost-effective characteristics. However, it is difficult to achieve real-time monitoring and multiplex detection with the traditional LAMP method. In addition, these approaches that use turbidimetry, sequence-independent intercalating dyes, or pH-sensitive indicators to indirectly reflect amplification can result in false-positive results if non-specific amplification occurs. To fulfill the needs of specific target detection and one-pot multiplex detection, a variety of probe-based LAMP assays have been developed. This review focuses on the principles of these assays, summarizes their applications in pathogen detection, and discusses their features and advantages over the traditional LAMP methods.

Portable Paper-Based Nucleic Acid Enrichment for Field Testing

Point-of-care testing (POCT) can be the method of choice for detecting infectious pathogens; these pathogens are responsible for not only infectious diseases such as COVID-19, but also for certain types of cancers. For example, infections by human papillomavirus (HPV) or Helicobacter pylori (H. pylori) are the main cause of cervical and stomach cancers, respectively. COVID-19 and many cancers are treatable with early diagnoses using POCT. A variety of nucleic acid testing have been developed for use in resource-limited environments. However, questions like unintegrated nucleic acid extraction, open detection systems increase the risk of cross-contamination, and dependence on expensive equipment and alternating current (AC) power supply, significantly limit the application of POCT, especially for on-site testing. In this paper, a simple portable platform is reported capable of rapid sample-to-answer testing within 30 min based on recombinase polymerase amplification (RPA) at a lower temperature, to detect SARS-CoV-2 virus and H. pylori bacteria with a limit of detection as low as 4 × 102 copies mL-1 . The platform used a battery-powered portable reader for on-chip one-pot amplification and fluorescence detection, and can test for multiple (up to four) infectious pathogens simultaneously. This platform can provide an alternative method for fast and reliable on-site diagnostic testing.

Research progress of severe acute respiratory syndrome coronavirus 2 on aerosol collection and detection

The outbreak of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in late 2019 has negatively affected people's lives and productivity. Because the mode of transmission of SARS-CoV-2 is of great concern, this review discusses the sources of virus aerosols and possible transmission routes. First, we discuss virus aerosol collection methods, including natural sedimentation, solid impact, liquid impact, centrifugal, cyclone and electrostatic adsorption methods. Then, we review common virus aerosol detection methods, including virus culture, metabolic detection, nucleic acid-based detection and immunology-based detection methods. Finally, possible solutions for the detection of SARS-CoV-2 aerosols are introduced. Point-of-care testing has long been a focus of attention. In the near future, the development of an instrument that integrates sampling and output results will enable the real-time, automatic monitoring of patients.

A hairpin probe-mediated exponential amplification reaction for highly sensitive and specific detection of microRNAs

In this work, we propose a hairpin probe-mediated exponential amplification reaction (HEAR) strategy that combines DNA strand displacement with a "who triggers, who gets generated" mode, providing excellent single-base discrimination and a reduced background signal. The detection limit is 19 aM, which is reduced by 3 orders of magnitude compared to traditional exponential amplification approaches. This one-pot strategy also exhibits a wide dynamic range, high specificity and short detection time. It is expected to become a powerful tool for clinical diagnosis.

Strategies for the Voltammetric Detection of Loop-Mediated Isothermal Amplification

Loop-mediated isothermal amplification (LAMP) is rapidly developing into an important tool for the point-of-use detection of pathogens for both clinical and environmental samples, largely due to its sensitivity, rapidity, and adaptability to portable devices. Many methods are used to monitor LAMP, but not all are amenable to point-of-use applications. Common methods such as fluorescence often require bulky equipment, whereas colorimetric and turbidimetric methods can lack sensitivity. Electrochemical biosensors are becoming increasingly important for these applications due to their potential for low cost, high sensitivity, and capacity for miniaturization into integrated devices. This review provides an overview of the use of voltammetric sensors for monitoring LAMP, with a specific focus on how electroactive species are used to interface between the biochemical products of the LAMP reaction and the voltammetric sensor. Various strategies for the voltammetric detection of DNA amplicons as well as pyrophosphate and protons released during LAMP are presented, ranging from direct DNA binding by electroactive species to the creative use of pyrophosphate-detecting aptamers and pH-sensitive oligonucleotide structures. Hurdles for adapting these devices to point-of-use applications are also discussed.

Rapid point-of-care detection of BK virus in urine by an HFman probe-based loop-mediated isothermal amplification assay and a finger-driven microfluidic chip

Background

BK virus (BKV)-associated nephropathy (BKVN) is one of the leading causes of renal dysfunction and graft loss in renal transplant recipients. Early monitoring of BKV in urine is crucial to minimize the deleterious effects caused by this virus on preservation of graft function.

Methods

We report a simple, rapid, sensitive loop-mediated isothermal amplification (LAMP) assay using an HFman probe for detecting BKV in urine. To evaluate the performance of the assay, a comparison of the HFman probe-based LAMP (HF-LAMP) assay with two qPCR assays was performed using urine samples from 132 HIV-1 infected individuals. We further evaluated the performance of HF-LAMP directly using the urine samples from these HIV-1 infected individuals and 30 kidney transplant recipients without DNA extraction. Furthermore, we combined the HF-LAMP assay with a portable finger-driven microfluidic chip for point-of-care testing (POCT).

Results

The assay has high specificity and sensitivity with a limit of detection (LOD) of 12 copies/reaction and can be completed within 30 min. When the DNA was extracted, the HF-LAMP assay showed an equivalent and potentially even higher sensitivity (93.5%) than the qPCR assays (74.2-87.1%) for 132 urine samples from HIV-1 infected individuals. The HF-LAMP assay can be applied in an extraction-free format and can be completed within 45 min using a simple heat block. Although some decreased performance was seen on urine samples from HIV-1 infected individuals, the sensitivity, specificity, and accuracy of the extraction-free BKV HF-LAMP assay were 95%, 100%, and 96.7% for 30 clinical urine samples from kidney transplant recipients, respectively.

Conclusion

The assay has high specificity and sensitivity. Combined with a portable finger-driven microfluidic chip for easy detection, this method shows great potential for POCT detection of BKV.

Current trends in COVID-19 diagnosis and its new variants in physiological fluids: Surface antigens, antibodies, nucleic acids, and RNA sequencing

Rapid, highly sensitive, and accurate virus circulation monitoring techniques are critical to limit the spread of the virus and reduce the social and economic burden. Therefore, point-of-use diagnostic devices have played a critical role in addressing the outbreak of COVID-19 (SARS-CoV-2) viruses. This review provides a comprehensive overview of the current techniques developed for the detection of SARS-CoV-2 in various body fluids (e.g., blood, urine, feces, saliva, tears, and semen) and considers the mutations (i.e., Alpha, Beta, Gamma, Delta, Omicron). We classify and comprehensively discuss the detection methods depending on the biomarker measured (i.e., surface antigen, antibody, and nucleic acid) and the measurement techniques such as lateral flow immunoassay (LFIA), enzyme-linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP), microarray analysis, clustered regularly interspaced short palindromic repeats (CRISPR) and biosensors. Finally, we addressed the challenges of rapidly identifying emerging variants, detecting the virus in the early stages of infection, the detection sensitivity, selectivity, and specificity, and commented on how these challenges can be overcome in the future.

Emerging Multiplex Nucleic Acid Diagnostic Tests for Combating COVID-19

The COVID-19 pandemic caused by SARS-CoV-2 has drawn attention to the need for fast and accurate diagnostic testing. Concerns from emerging SARS-CoV-2 variants and other circulating respiratory viral pathogens further underscore the importance of expanding diagnostic testing to multiplex detection, as single-plex diagnostic testing may fail to detect emerging variants and other viruses, while sequencing can be too slow and too expensive as a diagnostic tool. As a result, there have been significant advances in multiplex nucleic-acid-based virus diagnostic testing, creating a need for a timely review. This review first introduces frequent nucleic acid targets for multiplex virus diagnostic tests, then proceeds to a comprehensive and up-to-date overview of multiplex assays that incorporate various detection reactions and readout modalities. The performances, advantages, and disadvantages of these assays are discussed, followed by highlights of platforms that are amenable for point-of-care use. Finally, this review points out the remaining technical challenges and shares perspectives on future research and development. By examining the state of the art and synthesizing existing development in multiplex nucleic acid diagnostic tests, this review can provide a useful resource for facilitating future research and ultimately combating COVID-19.

Reverse Transcription-Loop-Mediated Isothermal Amplification-CRISPR-Cas13a Technology as a Promising Diagnostic Tool for SARS-CoV-2

At the end of 2019, a new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), caused a pandemic that persists to date and has resulted in more than 6.2 million deaths. In the last couple of years, researchers have made great efforts to develop a diagnostic technique that maintains high levels of sensitivity and specificity, since an accurate and early diagnosis is required to minimize the prevalence of SARS-CoV-2 infection. In this context, CRISPR-Cas systems are proposed as promising tools for development as diagnostic techniques due to their high specificity, highlighting that Cas13 endonuclease discriminates single nucleotide changes and displays collateral activity against single-stranded RNA molecules. With the aim of improving the sensitivity of diagnosis, this technology is usually combined with isothermal preamplification reactions (SHERLOCK, DETECTR). Based on this, we developed a reverse transcription-loop-mediated isothermal amplification (RT-LAMP)-CRISPR-Cas13a method for SARS-CoV-2 virus detection in nasopharyngeal samples without using RNA extraction that exhibits 100% specificity and 83% sensitivity, as well as a positive predictive value (PPV) of 100% and negative predictive values (NPVs) of 100%, 81%, 79.1%, and 66.7% for cycle threshold (CT) values of <20, 20 to 30, >30 and overall, respectively. IMPORTANCE The coronavirus disease 2019 (COVID-19) crisis has driven the development of innovative molecular diagnosis methods, including CRISPR-Cas technology. In this work, we performed a protocol, working with RNA extraction kit-free samples and using RT-LAMP-CRISPR-Cas13a technology; our results place this method at the forefront of rapid and specific diagnostic methods for COVID-19 due to the high specificity (100%), sensitivity (83%), PPVs (100%), and NPVs (81% for high viral loads) obtained with clinical samples.

A one-tube rapid visual CRISPR assay for the field detection of Japanese encephalitis virus

Early and rapid detection of Japanese encephalitis virus (JEV) is necessary for timely preventive and control measures. However, JEV RNA detection remains challenging due to the low level of viremia. In this study, a RApid VIsual CRISPR (RAVI-CRISPR) assay based on reverse transcription loop-mediated isothermal amplification (RT-LAMP) and CRISPR/Cas12a targeting was developed for easy detection of JEV in the field. We showed successful detection of 8.97 or more copies of the C gene sequence of JEV RNA within approximately 60 min. This assay also displayed no cross-reactivity with other porcine pathogens. We applied our one-tube RAVI-CRISPR assay to 18 brain tissue sample for JE diagnosis. The results from both fluorescence intensity measurements and directly naked-eye visualization were consistent with those from real-time PCR analysis. Taken together, our results showed that one-tube RAVI-CRISPR assay is robust, convenient, sensitive, specific, affordable, and potentially adaptable to on-site detection or surveillance of JEV in clinical and vector samples.

Amine-Functionalized Quantum Dots as a Universal Fluorescent Nanoprobe for a One-Step Loop-Mediated Isothermal Amplification Assay with Single-Copy Sensitivity

Loop-mediated isothermal amplification (LAMP) has received considerable attention for decentralized (point-of-care and on-site) nucleic acid testing in view of its simple temperature control (60-65 °C) and short assay time (15-60 min). There remains a challenge in its wide adoption and acceptance due to the limitations of the existing amplification result reporter probes, e.g., photobleaching of organic fluorophore and reduced sensitivity of the pH-sensitive colorimetric dye. Herein, we demonstrate CdSeS/ZnS quantum dots (semiconductor fluorescent nanocrystals with superior photostability than organic fluorophore) with surface modification of cysteamine (amine-QDs) as a new reporter probe for LAMP that enabled single-copy sensitivity (limit of detection of 83 zM; 20 μL reaction volume). For a negative LAMP sample (absence of target sequence), positively charged amine-QDs remained dispersed due to interparticle electrostatic repulsion. While for a positive LAMP sample (presence of target sequence), amine-QDs became precipitated. The characterization data showed that amine-QDs were embedded in magnesium pyrophosphate crystals (generated during positive LAMP), thus leading to their coprecipitation. This amine-QD-based one-step LAMP assay advances the field of QD-based nucleic acid amplification assays in two aspects: (1) compatibility─one-step amplification and detection (versus separation of amplification and detection steps); and (2) universality─the same amine-QDs for different target sequences (versus different oligonucleotide-modified QDs for different target sequences).

An HFman Probe-Based Multiplex Reverse Transcription Loop-Mediated Isothermal Amplification Assay for Simultaneous Detection of Hantaan and Seoul Viruses

Hantaviruses are zoonotic pathogens that are widely distributed worldwide. Hantaan virus (HTNV) and Seoul virus (SEOV) are two most common hantaviruses that infect humans and cause hemorrhagic fever with renal syndrome (HFRS). Rapid and sensitive detection of HTNV and SEOV are crucial for surveillance, clinical treatment and management of HFRS. This study aimed to develop a rapid HFman probe-based mulstiplex reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay to simultaneously detect HTNV and SEOV. A novel multiplex RT-LAMP assay was developed, and 46 serum samples obtained from clinically suspected patients were used for evaluation. The novel RT-LAMP assay can detect as low as 3 copies/reaction of hantaviruses with a detection limit of 41 and 73 copies per reaction for HTNV and SEOV, respectively. A clinical evaluation showed that the consistencies of the multiplex RT-LAMP with RT-qPCR assay were 100% and 97.8% for HTNV and SEOV, respectively. In view of the high prevalence of HTNV and SEOV in rural areas with high rodent density, a colorimetric visual determination method was also developed for point-of-care testing (POCT) for the diagnosis of the two viruses. The novel multiplex RT-LAMP assay is a sensitive, specific, and efficient method for simultaneously detecting HTNV and SEOV.