Isothermal nucleic acid amplification technologies for point-of-care diagnostics: a critical review

Rapid and highly sensitive colorimetric LAMP assay and integrated device for visual detection of monkeypox virus

BACKGROUND

The monkeypox virus (MPXV) is a linear double-stranded DNA virus with a large genome that causes tens of thousands of infections and hundreds of deaths in at least 40 countries and regions worldwide. Therefore, timely and accurate diagnostic testing could be an important measure to prevent the ongoing spread of MPXV and widespread epidemics.

RESULTS

Here, we designed multiple sets of primers for the target region of MPXV for loop-mediated isothermal amplification (LAMP) detection and identified the optimal primer set. Then, the specificity in fluorescent LAMP detection was verified using the plasmids containing the target gene, pseudovirus and other DNA/RNA viruses. We also evaluated the sensitivity of the colorimetric LAMP detection system using the plasmid and pseudovirus samples, respectively. Besides, we used monkeypox pseudovirus to simulate real samples for detection. Subsequent to the establishment and introduction of a magnetic beads (MBs)-based nucleic acid extraction technique, an integrated device was developed, characterized by rapidity, high sensitivity, and remarkable specificity. This portable system demonstrated a visual detection limit of 137 copies/mL, achieving sample-to-answer detection within 1 h.

SIGNIFICANCE

The device has the advantages of integration, simplicity, miniaturization, and visualization, which help promote the realization of accurate, rapid, portable, and low-cost testing. Meanwhile, this platform could facilitate efficient, cost-effective and easy-operable point-of-care testing (POCT) in diverse resource-limited settings in addition to the laboratory.

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.

A highly integrated digital PCR system with on-chip heating for accurate DNA quantitative analysis

Digital polymerase chain reaction (dPCR) is extensively used for highly sensitive disease diagnosis due to its single-molecule detection ability. However, current dPCR systems require intricate DNA sample distribution, rely on cumbersome external heaters, and exhibit sluggish thermal cycling, hampering efficiency and speed of the dPCR process. Herein, we presented the development of a microwell array based dPCR system featuring an integrated self-heating dPCR chip. By utilizing hydrodynamic and electrothermal simulations, the chip's structure is optimized, resulting in improved partitioning within microwells and uniform thermal distribution. Through strategic hydrophilic/hydrophobic modifications on the chip's surface, we effectively secured the compartmentalization of sample within the microwells by employing an overlaying oil phase, which renders homogeneity and independence of samples in the microwells. To achieve precise, stable, uniform, and rapid self-heating of the chip, the ITO heating layer and the temperature control algorithm are deliberately designed. With a capacity of 22,500 microwells that can be easily expanded, the system successfully quantified EGFR plasmid solutions, exhibiting a dynamic linear range of 105 and a detection limit of 10 copies per reaction. To further validate its performance, we employed the dPCR platform for quantitative detection of BCR-ABL1 mutation gene fragments, where its performance was compared against the QuantStudio 3D, and the self-heating dPCR system demonstrated similar analytical accuracy to the commercial dPCR system. Notably, the individual chip is produced on a semiconductor manufacturing line, benefiting from mass production capabilities, so the chips are cost-effective and conducive to widespread adoption and accessibility.

Label-free and portable detection of HIV-DNA by a handheld luminometer

BACKGROUND

The human immunodeficiency virus (HIV) remains a major worldwide health problem. Nowadays, many methods have been developed for quantitative detecting human immunodeficiency virus DNA (HIV-DNA), such as fluorescence and colorimetry. However, these methods still have the disadvantages of being expensive and requiring professional technicians. Early diagnosis of pathogens is increasingly dependent on portable instruments and simple point-of-care testing (POCT). Therefore, it is meaningful and necessary to develop portable and cheap methods for detecting disease markers.

RESULTS

In this work, a label-free chemiluminescence (CL) method was developed for detecting HIV-DNA via a handheld luminometer. To achieve label-free target detection, the CL catalyst, G-triplex-hemin DNAzyme (G3-hemin DNAzyme), was in-situ assembled in the presence of HIV-DNA. For improving sensitivity, HIV-DNA induced the cyclic strand displacement reaction (SDR), which can form three G3-hemin DNAzymes in one cycle. So, the chemiluminescence reaction between luminol and H2O2 was highly effectively catalyzed, and the CL intensity was linearly related with the concentration of HIV-DNA in the range of 0.05-10 nM with a detection limit of 29.0 pM. Due to the high specificity of hairpin DNA, single-base mismatch can be discriminated, which ensured the specific detection of HIV-DNA.

SIGNIFICANCE

In-situ formation of G3-hemin DNAzyme led to label-free and selective detection without complex synthesis and functionalization. Therefore, it offers a cheap, selective, sensitive and portable method for detecting disease-related genes, which is promising for POCT of clinical diagnosis in resource-limited settings.

C. difficile biomarkers, pathogenicity and detection

BACKGROUND

Clostridioides difficile infection (CDI) is the main etiologic agent of antibiotic-associated diarrhea. CDI contributes to gut inflammation and can lead to disruption of the intestinal epithelial barrier. Recently, the rate of CDI cases has been increased. Thus, early diagnosis of C. difficile is critical for controlling the infection and guiding efficacious therapy.

APPROACH

A search strategy was set up using the terms C. difficile biomarkers and diagnosis. The found references were classified into two general categories; conventional and advanced methods.

RESULTS

The pathogenicity and biomarkers of C. difficile, and the collection manners for CDI-suspected specimens were briefly explained. Then, the conventional CDI diagnostic methods were subtly compared in terms of duration, level of difficulty, sensitivity, advantages, and disadvantages. Thereafter, an extensive review of the various newly proposed techniques available for CDI detection was conducted including nucleic acid isothermal amplification-based methods, biosensors, and gene/single-molecule microarrays. Also, the detection mechanisms, pros and cons of these methods were highlighted and compared with each other. In addition, approximately complete information on FDA-approved platforms for CDI diagnosis was collected.

CONCLUSION

To overcome the deficiencies of conventional methods, the potential of advanced methods for C. difficile diagnosis, their direction, perspective, and challenges ahead were discussed.

A Diagnostic Chip for the Colorimetric Detection of Legionella pneumophila in Less than 3 h at the Point of Need

Legionella pneumophila has been pinpointed by the World Health Organization as the highest health burden of all waterborne pathogens in the European Union and is responsible for many disease outbreaks around the globe. Today, standard analysis methods (based on bacteria culturing onto agar plates) need several days (~12) in specialized analytical laboratories to yield results, not allowing for timely actions to prevent outbreaks. Over the last decades, great efforts have been made to develop more efficient waterborne pathogen diagnostics and faster analysis methods, requiring further advancement of microfluidics and sensors for simple, rapid, accurate, inexpensive, real-time, and on-site methods. Herein, a lab-on-a-chip device integrating sample preparation by accommodating bacteria capture, lysis, and DNA isothermal amplification with fast (less than 3 h) and highly sensitive, colorimetric end-point detection of L. pneumophila in water samples is presented, for use at the point of need. The method is based on the selective capture of viable bacteria on on-chip-immobilized and -lyophilized antibodies, lysis, the loop-mediated amplification (LAMP) of DNA, and end-point detection by a color change, observable by the naked eye and semiquantified by computational image analysis. Competitive advantages are demonstrated, such as low reagent consumption, portability and disposability, color change, storage at RT, and compliance with current legislation.

Entropy-driven catalysis-based lateral flow assay for sensitive detection of Alzheimer 's-associated MicroRNA

Alzheimer's disease (AD) is a degenerative disease of the brain worldwide. Currently, there is no effective cure. But accurate and early diagnosis of AD is critical to the development of patient care and future treatments. MiRNA-16 has been considered as an effective diagnostic biomarker for AD because of its regulatory effect on key proteins of AD. Herein, a colorimetric lateral flow assay (LFA) was developed for sensitive detection of miRNA-16 based on entropy-driven catalysis (EDC) amplification strategy. MiRNA-16 triggered EDC and released more linker DNAs (LDNA) of sandwich structure. Thus, AuNPs were enriched at the T-line to enhance the colorimetric signal and improve the sensitivity of visual assay. It showed good specificity and sensitivity for detecting miRNA-16 with a detection limit of 1.01 pM. The practical detection of miRNA-16 in human serum obtained satisfactory result. Significantly, EDC achieved signal amplification in homogeneous solution without enzyme and DNA labeling, leading to a cheap and easy detection of miRNA-16. Therefore, it provided a portable and rapid assay for AD-related nucleic acid, which holds a potential for point-of-care testing (POCT) of AD.

Mesoporous Gold: Substrate-Dependent Growth Dynamics, Strain Accumulation, and Electrocatalytic Activity for Biosensing

Understanding the growth of mesoporous crystalline materials, such as mesoporous metals, on different substrates can provide valuable insights into the crystal growth dynamics and the redox reactions that influence their electrochemical sensing performance. Herein, it is demonstrated how the amorphous nature of the glass substrate can suppress the typical <111> oriented growth in mesoporous Au (mAu) films. The suppressed <111> growth is manifested as an accumulation of strain, leading to the generation of abundant surface defects, which are beneficial for enhancing the electrochemical activity. The fine structuring attained enables dramatically accelerated diffusion and enhances the electrochemical sensing performance for disease-specific biomolecules. As a proof-of-concept, the as-fabricated glass-grown mAu film demonstrates high sensitivity in electrochemical detection of SARS-CoV-2-specific RNA with a limit of detection (LoD) as low as 1 attomolar (aM).

Integrating Recombinase Polymerase Amplification and Photosensitization Colorimetric Detection in One Tube for Fast Screening of C. sakazakii in Formula Milk Powder

Cronobacter sakazakii (C. sakazakii) is a widely existing opportunistic pathogen and thus threatens people with low immunity, especially infants. To prevent the outbreak, a rapid and accurate on-site testing method is required. The current standard culture-based method is time-consuming (3-4 days), while the nucleic acid amplification (PCR)-based detection is mostly carried out in central laboratories. Herein, isothermal recombinase polymerase amplification (RPA) coupled with a photosensitization colorimetric assay (PCA) was adopted for the on-site detection of C. sakazakii in powdered infant formulas (PIFs). The lowest visual detection concentration of C. sakazakii is 800 cfu/mL and 2 cfu/g after 8 h bacteria pre-enrichment. Furthermore, to avoid typical cap opening-resulted aerosol pollution, the PCA reagents were lyophilized onto the cap of the RPA tube (containing lyophilized RPA reagents). After amplification, the tube was subjected to simple shaking to mix the PCA reagents with the amplification products for light-driven color development. Such a one-tube assay offered a lowest concentration of 1000 copies of genomic DNA of C. sakazakii within 1 h. After 8 h of bacterial enrichment, the lowest detecting concentration could be pushed down to 5 cfu/g bacteria in PIF. To facilitate on-site monitoring, a portable, battery-powered PCA device was designed to mount the typical RPA 8-tube strip, and a color analysis cellphone APP was further employed for facile readout.

CRISPR-Cas12a assisted recombinase based strand invading isothermal amplification platform designed for targeted detection of Bacillus anthracis Sterne

Detection of a pathogen is crucial prior to all prophylaxis and post exposure treatment, as it can prevent further disease manifestation. In this study, we have developed a nucleic acid pre-amplification based CRISPR diagnostic for detection and surveillance of Bacillus anthracis Sterne. Strand Invasion Based isothermal Amplification (SIBA) platform and Cas12a (CRISPR endo-nuclease) was used to develop CRISPR-SIBA, a multifaceted diagnostic platform. SIBA was employed as the isothermal pre-amplification platform. CRISPR-Cas12a based collateral trans-cleavage reaction was used to ensure and enhance the specificity of the system. Efficiency of the detection system was evaluated by detecting Bacillus anthracis Sterne in complex wastewater sample backgrounds. Previously reported, Prophage 3, Cya and Pag genes of Bacillus anthracis were used as targets for this assay. The amplification system provided reliable and specific detection readout, with a sensitivity limit of 100 colony forming units in 40 min. The endpoint fluorescence from CRISPR collateral cleavage reactions gave a detection limit of 105 to 106 CFUs. The experiments conducted in this study provide the evidence for SIBA's applicability and compatibility with CRISPR-Cas system and its efficiency to specifically detect Bacillus anthracis Sterne. CRISPR-SIBA can be translated into developing cost-effective diagnostics for pathogens in resource constrained settings.

Rapid Detection of Measles Virus Using Reverse Transcriptase/Recombinase Polymerase Amplification Coupled with CRISPR/Cas12a and a Lateral Flow Detection: A Proof-of-Concept Study

The measles virus is highly contagious, and efforts to simplify its diagnosis are essential. A reverse transcriptase/recombinase polymerase amplification assay coupled with CRISPR/Cas12a and an immunochromatographic lateral flow detection (RT-RPA-CRISPR-LFD) was developed for the simple visual detection of measles virus. The assay was performed in less than 1 h at an optimal temperature of 42 °C. The detection limit of the assay was 31 copies of an RNA standard in the reaction tube. The diagnostic performances were evaluated on a panel of 27 measles virus RT-PCR-positive samples alongside 29 measles virus negative saliva samples. The sensitivity and specificity were 96% (95% CI, 81-99%) and 100% (95% CI, 88-100%), respectively, corresponding to an accuracy of 98% (95% CI, 94-100%; p < 0.0001). This method will open new perspectives in the development of the point-of-care testing diagnosis of measles.

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.

A multiplex recombinase polymerase amplification assay combined with CRISPR/Cas12a for the detection of respiratory syncytial virus and respiratory adenovirus

OBJECTIVE

Respiratory syncytial virus (RSV) and respiratory adenovirus (ADV) are two common pathogens that cause acute respiratory tract infections in children. We aimed to develop a rapid method for detecting both pathogens simultaneously.

METHODS

The recombinase polymerase isothermal amplification (RPA) method was combined with the CRISPR/Cas detection system. The assay's specificity and sensitivity were explored by designing RPA primers and CRISPR RNAs (crRNAs) through multi-sequence comparisons, optimizing the reaction conditions, and using a fluorescent reading device. The consistency of the test results of 160 clinical pharyngeal swab samples was studied using quantitative polymerase chain reaction (qPCR) results as a comparative control.

RESULTS

RSV and ADV could be detected at levels as low as 104 copies/mL and 103 copies/mL, respectively, within 50 minutes with no cross-reactivity with other similar pathogens. For the clinical samples, compared with the qPCR method, the sensitivities for RSV and ADV were 98.1% and 91.4%, respectively, and the detection specificities were both 100%. The Kappa values were greater than 0.95, suggesting a high degree of consistency.

CONCLUSION

This method for detecting RSV and ADV is rapid, sensitive, and specific. It can accurately detect mixed infections in a timely manner, making it suitable for use in areas with scarce healthcare resources.

Self-Powered Microfluidics for Point-of-Care Solutions: From Sampling to Detection of Proteins and Nucleic Acids

Self-powered microfluidics presents a revolutionary approach to address the challenges of healthcare in decentralized and point-of-care settings where limited access to resources and infrastructure prevails or rapid clinical decision-making is critical. These microfluidic systems exploit physical and chemical phenomena, such as capillary forces and surface tension, to manipulate tiny volumes of fluids without the need for external power sources, making them cost-effective and highly portable. Recent technological advancements have demonstrated the ability to preprogram complex multistep liquid operations within the microfluidic circuit of these standalone systems, which enabled the integration of sensitive detection and readout principles. This chapter first addresses how the accessibility to in vitro diagnostics can be improved by shifting toward decentralized approaches like remote microsampling and point-of-care testing. Next, the crucial role of self-powered microfluidic technologies to enable this patient-centric healthcare transition is emphasized using various state-of-the-art examples, with a primary focus on applications related to biofluid collection and the detection of either proteins or nucleic acids. This chapter concludes with a summary of the main findings and our vision of the future perspectives in the field of self-powered microfluidic technologies and their use for in vitro diagnostics applications.

A dual signal amplification system with specific signal identification for rapid and sensitive detection of miRNA

False positive which is mostly caused by the nonspecific amplification has severely hindered the development of nucleic acid detection and it is hard to avoid. Therefore, specific signals recognition and output in nucleic acid amplification are crucial to reliability of clinical diagnosis. Herein, we proposed a one-step and rapid miRNA detection strategy with specific signal identification, dual amplification and output. And this strategy was named as high-temperature hybridization chain reaction coupled with strand displacement amplification (HSA). In HSA, we well designed a target signal recognition, replication, and output probe (RRO probe). If the target miRNA exists, RRO probe can initiate a strand displacement amplification and output a target-related special single-stranded DNA (trigger). And the trigger can be identified by a high-temperature hybridization chain reaction and initiate a secondary signal amplification. As a result, the quantitative determination of HSA for miRNA-21 was in the range of 100 fM to 100 pM in 30 min, and with a detection limit of 82 fM. Moreover, with high sensitivity and rapidity, HSA has been successfully used to detect miRNA-21 in real samples.

Low-tech vs. high-tech approaches in μPADs as a result of contrasting needs and capabilities of developed and developing countries focusing on diagnostics and point-of-care testing

Paper-based analysis has captivated scientists' attention in the field of analytical chemistry and related areas for the last two decades. Arguably no other area of modern chemical analysis is so broad and diverse in its approaches spanning from simple 'low-tech' low-cost paper-based analytical devices (PADs) requiring no or simple instrumentation, to sophisticated PADs and microfluidic paper-based analytical devices (μPADs) featuring elements of modern material science and nanomaterials affording high selectivity and sensitivity. Correspondingly diverse is the applicability, covering resource-limited scenarios on the one hand and most advanced approaches on the other. Herein we offer a view reflecting this diversity in the approaches and types of devices. The core idea of this article rests in dividing μPADs according to their type into two groups: A) instrumentation-free μPADs for resource-limited scenarios or developing countries and B) instrumentation-based μPADs as futuristic POC devices for e-diagnostics mainly aimed at developed countries. Each of those two groups is presented and discussed with the view of the main requirements in the given area, the most common targets, sample types and suitable detection approaches either implementing high-tech elements or low-tech low-cost approaches. Finally, a socioeconomic perspective is offered in discussing the fabrication and operational costs of μPADs, and, future perspectives are offered.

Manually pressurized droplet digital PCR chip for rapid SARS-CoV-2 diagnostics

Droplet digital PCR (ddPCR) is a technique in which PCR reaction is divided into thousands of nanoliter-sized droplets and has proven to be a great tool in virus diagnostics. Compared to the gold standard system quantitative real-time PCR (RT-qPCR), ddPCR functions particularly well when dealing with samples with low template counts, such as viral concentration. This feature makes the technique suitable for early detection of the virus. In this study, a novel portable PDMS ddPCR chip is introduced. The chip functions without external pumps using manual pressurization with a multichannel pipet. The created droplets are monodispersed and form a monolayer on the chip's collection chamber, from where they can be effortlessly imaged. Droplets were analyzed and counted using artificial intelligence. The use of the manually pressurized chip was demonstrated for a SARS-CoV-2 assay, which takes advantage of isothermal strand invasion-based amplification (SIBA) technology, allowing quick and accurate, even point-of-care analysis of the sample. The results demonstrate that SIBA assays can be divided into nanoliter-sized droplets and used as quantitative assays, giving an approximation of the samples' viral count.

Rapid and accurate detection of SARS-CoV-2 using the RHAM technology

Rapid and sensitive detection of pathogens is of utmost importance in interrupting the transmission chain of infectious diseases. In recent years, this has proven to be vital during the coronavirus disease (COVID-19) global pandemic that put countless lives at risk. Numerous molecular diagnostic methods were used, including RT-PCR, NASBA, E-SDA, E-RCA, LAMP, and RPA. However, these technologies potentially require primer optimization and complex instruments. Here, we propose the RHAM (RNase Hybridization-Assisted amplification) system as a rapid, specific, and sensitive molecular diagnosis platform. Combining the LAMP and RNase HII-mediated fluorescent reporter, the RHAM system can amplify and visualize the target in one isothermal system with high sensitivity (5 × 102 copies/mL). There was no cross-reactivity with other common respiratory viruses. Analysis of clinical samples revealed the RHAM system to generate positive signals within 15 min without false positive or negative results. The present study shows that RHAM is not only an ideal platform for detecting pathogens, such as SARS-CoV-2 but can be potentially applied in POCT settings.

Digital Recombinase Polymerase Amplification, Digital Loop-Mediated Isothermal Amplification, and Digital CRISPR-Cas Assisted Assay: Current Status, Challenges, and Perspectives

Digital nucleic acid detection based on microfluidics technology can quantify the initial amount of nucleic acid in the sample with low equipment requirements and simple operations, which can be widely used in clinical and in vitro diagnosis. Recently, isothermal amplification technologies such as recombinase polymerase amplification (RPA), loop-mediated isothermal amplification (LAMP), and clustered regularly interspaced short palindromic repeats-CRISPR associated proteins (CRISPR-Cas) assisted technologies have become a hot spot of attention and state-of-the-art digital nucleic acid chips have provided a powerful tool for these technologies. Herein, isothermal amplification technologies including RPA, LAMP, and CRISPR-Cas assisted methods, based on digital nucleic acid microfluidics chips recently, have been reviewed. Moreover, the challenges of digital isothermal amplification and possible strategies to address them are discussed. Finally, future directions of digital isothermal amplification technology, such as microfluidic chip and device manufacturing, multiplex detection, and one-pot detection, are outlined.

Development of a novel integrated isothermal amplification system for detection of bacteria-spiked blood samples

Bloodstream infection (BSI) caused by bacteria is highly pathogenic and lethal, and easily develops whole-body inflammatory state. Immediate identification of disease-causing bacteria can improve patient prognosis. Traditional testing methods are not only time-consuming, but such tests are limited to laboratories. Recombinase polymerase amplification combined with lateral flow dipstick (RPA-LFD) holds great promise for rapid nucleic acid detection, but the uncapping operation after amplification easily contaminates laboratories. Therefore, the establishment of a more effective integrated isothermal amplification system has become an urgent problem to be solved. In this study, we designed and fabricated a hermetically sealed integrated isothermal amplification system. Combining with this system, a set of RPA-LFD assays for detecting S. aureus, K. peneumoniae, P. aeruginosa, and H. influenza in BSI were established and evaluated. The whole process could be completed in less than 15 min and the results can be visualized by the naked eye. The developed RPA-LFD assays displayed a good sensitivity, and no cross-reactivity was observed in seven similar bacterial genera. The results obtained with 60 clinical samples indicated that the developed RPA-LFD assays had high specifcity and sensitivity for identifying S. aureus, K. peneumoniae, P. aeruginosa, and H. influenza in BSI. In conclusion, our results showed that the developed RPA-LFD assay is an alternative to existing PCR-based methods for detection of S. aureus, K. peneumoniae, P. aeruginosa, and H. influenza in BSI in primary hospitals.

Infectious Disease Diagnosis and Pathogen Identification Platform Based on Multiplex Recombinase Polymerase Amplification-Assisted CRISPR-Cas12a System

Controlling and mitigating infectious diseases caused by multiple pathogens or pathogens with several subtypes require multiplex nucleic acid detection platforms that can detect several target genes rapidly, specifically, sensitively, and simultaneously. Here, we develop a detection platform, termed Multiplex Assay of RPA and Collateral Effect of Cas12a-based System (MARPLES), based on multiplex nucleic acid amplification and Cas12a ssDNase activation to diagnose these diseases and identify their pathogens. We use the clinical specimens of hand, foot, and mouth disease (HFMD) and influenza A to evaluate the feasibility of MARPLES in diagnosing the disease and identifying the pathogen, respectively, and find that MARPLES can accurately diagnose the HFMD associated with enterovirus 71, coxsackievirus A16 (CVA16), CVA6, or CVA10 and identify the exact types of H1N1 and H3N2 in an hour, showing high sensitivity and specificity and 100% predictive agreement with qRT-PCR. Collectively, our findings demonstrate that MARPLES is a promising multiplex nucleic acid detection platform for disease diagnosis and pathogen identification.

Self-assembly of DNA-gold nanoaggregate for visual detection of thymidine kinase 1 (TK1) mRNA via lateral flow assay

Nucleic acid lateral flow assay (NALFA) with gold nanoparticles (AuNPs) as colorimetric probes have been extensively adopted for point-of-care testing (POCT). However, the sensitivity of NALFA still needs to be improved. Herein, DNA-gold nanoaggregate (DNA-AuNA) was assembled as a signal amplification probe of NALFA for sensitive detection of tumor marker TK1 mRNA. Four functional oligonucleotides with complementary pairs were assembled to form DNA-AuNA that coupled more AuNPs to improve sensitivity. Thus, the limit of detection (LOD) was 0.36 pM, which is lower than that of conventional AuNPs-based NALFA. Moreover, the bioassay showed good reproducibility, stability, and specificity for detecting TK1 mRNA. The detection of TK1 mRNA in human serum was also satisfactory. Therefore, DNA-AuNA-based NALFA provides a sensitive method for portable detection of TK1 mRNA.

Establishment and application of a point-of-care testing and diagnosis method for early immediate expression gene IE1 of cytomegalovirus in maternal urine based on isothermal amplification

BACKGROUND

Human Cytomegalovirus virus (HCMV) is a worldwide virus that causes no serious symptoms in most adults. However, HCMV infection during pregnancy, it may lead to a series of serious complications, such as hearing loss, mental retardation, visual impairment, microcephaly and developmental retardation.

AIM

The aim of this study was to develop a simple, low dependence on equipment and accurate method for HCMV detection based on the recombinase polymerase amplification (RPA) and lateral flow chromatography strip (LFS) reading.

METHODS

In order to meet the feasibility of HCMV early screening, three pairs of RPA primers were designed based on the UL123 gene encoding IE1, which was expressed immediately in the early stage of HCMV. In order to improve the specificity of the reaction and satisfy the visual detection, a specific probe was designed to insert THF site between upstream and downstream primers, fluorescein isothiocyanate (FITC) and C3spacer were used to modify the 5' end and the 3' end respectively, and Biotin was used to modify the 5' end of the reverse primer. HCMV standard strain AD169 was enriched by ARPE-19 cells culture, and its genome was extracted. The primers and probes were screened by RPA-LFS test, and the optimal reaction temperature and time were determined The specificity was verified in different viruses, bacteria and parasites. The standard curve was drawn based on the constructed recombinant plasmid of pMD18T-HCMV-UL123 and used for HCMV genomic DNA quantification and determination of the detection sensitivity. Urine samples from artificial HCMV contamination or clinical collection were prepared to evaluate the consistency with the results of real-time quantitative PCR.

RESULTS

The results showed that the primers and probes for HCMV RPA-LFS detection based on UL123 gene were successfully screened, the amplification of HCMV genomic DNA with as low as 30 copies could be completed at 37 °C within 15 min, it did not react with Human herpesvirus 1, Streptococcus pyogenes, Candida albicans, Listeria monocytogenes, Y. enterocolitica, Klebsiella Pneumoniae, Enterobacter cloacae, Citrobacter freundii, Vibrio alginnolyfificus, Vibrio parahaemolyticus, S. typhimurium, Staphylococcus aureus, Pseudomonas aeruginosa and Trichomonas vaginalis. The positive rate of PCR was 96.67 % in 30 simulated urine samples and 100 % in 127 clinical urine samples with the same UL123 gene detection.

CONCLUSIONS

To sum up, we developed a diagnostic method for HCMV based on UL123 gene combined with RPA and LFS, which is low dependent on equipment, fast, sensitive and specific, provide reference for point-of-care testing HCMV in grass-roots laboratories and remote areas.

Field-deployable assay based on CRISPR-Cas13a coupled with RT-RPA in one tube for the detection of SARS-CoV-2 in wastewater

CRISPR-based nucleic acid detection is easy to implement, field deployable, and always coupled with isothermal amplification to improve the sensitivity. However, the conventional detection requires two separate steps, which can cause long-lasting amplicon aerosol contaminants, hence leading to false-positive results. To address this problem, we proposed a one-tube assay based on CRISPR-Cas13a coupled with reverse transcription-recombinase polymerase amplification to avoid aerosol pollution. The one-tube assay could be completed within 40 min with a sensitivity of up to 180 copies of RNA per reaction, and exhibited no cross reactivity with two related coronaviruses. Our technology showed reproducibility with relative standard deviation of 4.6% responding to 1 fM nucleic acid for three times. It could be used to detect SARS-CoV-2 nucleic acids in raw wastewater with a limit of detection of 103 copies/mL. We also validated the practicability of this technique for viral detection in environmental water samples by detecting SARS-CoV-2 in wastewater, which were not detectable by RT-qPCR technology, showing resistance of this technology to wastewater matrix. It is anticipated that the robustness and high sensitivity will significantly promote the development of a point-of-care method in environmental virus monitoring.

Label-free DNA quantification using isothermal amplification on an exposed core optical fiber microfluidic platform

Isothermal amplification technology has triggered a surge in research due to its compatibility with small and portable equipment, simplicity, and high efficiency, especially in light of the COVID-19 pandemic where reliable widescale testing is critical to outbreak management. In this paper, a label-free isothermal deoxyribonucleic acid (DNA) amplification method based on refractive index (RI) quantification is proposed and demonstrated for the first time by combining optical fiber sensing, microfluidics, and isothermal amplification. A highly RI-sensitive Mach-Zehnder (MZ) interference is formed by splicing a short length of an exposed-core fiber between two lengths of a single-mode fiber while the microfluidic liquid channel on the exposed side of the ECF is filled with target DNA and the amplification solution. Real-time quantitative measurement of the target DNA is then realized by monitoring the change in RI of the solution during the isothermal DNA amplification process. The experimental results show that the platform successfully realizes real-time label-free monitoring of isothermal amplification of 0.16 aM DNA samples. This method is a breakthrough for applications in the fields of DNA detection and quantification where simple operation, rapid detection, portability, small size, high selectivity, and high sensitivity are required.

Specific biomarker mining and rapid detection of Burkholderia cepacia complex by recombinase polymerase amplification

Objective

To mine specific proteins and their protein-coding genes as suitable molecular biomarkers for the Burkholderia cepacia Complex (BCC) bacteria detection based on mega analysis of microbial proteomic and genomic data comparisons and to develop a real-time recombinase polymerase amplification (rt-RPA) assay for rapid isothermal screening for pharmaceutical and personal care products.

Methods

We constructed an automatic screening framework based on Python to compare the microbial proteomes of 78 BCC strains and 263 non-BCC strains to identify BCC-specific protein sequences. In addition, the specific protein-coding gene and its core DNA sequence were validated in silico with a self-built genome database containing 158 thousand bacteria. The appropriate methodology for BCC detection using rt-RPA was evaluated by 58 strains in pure culture and 33 batches of artificially contaminated pharmaceutical and personal care products.

Results

We identified the protein SecY and its protein-coding gene secY through the automatic comparison framework. The virtual evaluation of the conserved region of the secY gene showed more than 99.8% specificity from the genome database, and it can distinguish all known BCC species from other bacteria by phylogenetic analysis. Furthermore, the detection limit of the rt-RPA assay targeting the secY gene was 5.6 × 102 CFU of BCC bacteria in pure culture or 1.2 pg of BCC bacteria genomic DNA within 30 min. It was validated to detect <1 CFU/portion of BCC bacteria from artificially contaminated samples after a pre-enrichment process. The relative trueness and sensitivity of the rt-RPA assay were 100% in practice compared to the reference methods.

Conclusion

The automatic comparison framework for molecular biomarker mining is straightforward, universal, applicable, and efficient. Based on recognizing the BCC-specific protein SecY and its gene, we successfully established the rt-RPA assay for rapid detection in pharmaceutical and personal care products.

Mayaro virus detection by integrating sample preparation with isothermal amplification in portable devices

Mayaro virus (MAYV) is an emerging mosquito-borne alphavirus that causes clinical symptoms similar to those caused by Chikungunya virus (CHIKV), Dengue virus (DENV), and Zika virus (ZIKV). To differentiate MAYV from these viruses diagnostically, we have developed a portable device that integrates sample preparation with real-time, reverse-transcription, loop-mediated isothermal amplification (rRT-LAMP). First, we designed a rRT-LAMP assay targeting MAYV's non-structural protein (NS1) gene and determined the limit of detection of at least 10 viral genome equivalents per reaction. The assay was specific for MAYV, without cross-reactions with CHIKV, DENV, or ZIKV. The rRT-LAMP assay was integrated with a sample preparation device (SPD) wherein virus lysis and RNA enrichment/purification were carried out on the spot, without requiring pipetting, while subsequent real-time amplification device (RAD) enables virus detection at the point of care (POC). The functions of our platform were demonstrated using purified MAYV RNA or blood samples containing viable viruses. We have used the devices for detection of MAYV in as short as 13 min, with limit of detection to as low as 10 GEs/reaction.

RNA-Cleaving DNAzyme-Based Amplification Strategies for Biosensing and Therapy

Since their first discovery in 1994, DNAzymes have been extensively applied in biosensing and therapy that act as recognition elements and signal generators with the outstanding properties of good stability, simple synthesis, and high sensitivity. One subset, RNA-cleaving DNAzymes, is widely employed for diverse applications, including as reporters capable of transmitting detectable signals. In this review, the recent advances of RNA-cleaving DNAzyme-based amplification strategies in scaled-up biosensing are focused, the application in diagnosis and disease treatment are also discussed. Two major types of RNA-cleaving DNAzyme-based amplification strategies are highlighted, namely direct response amplification strategies and combinational response amplification strategies. The direct response amplification strategies refer to those based on novel designed single-stranded DNAzyme, and the combinational response amplification strategies mainly include two-part assembled DNAzyme, cascade reactions, CHA/HCR/RCA, DNA walker, CRISPR-Cas12a and aptamer. Finally, the current status of DNAzymes, the challenges, and the prospects of DNAzyme-based biosensors are presented.

Programmable magnetic robot (ProMagBot) for automated nucleic acid extraction at the point of need

Upstream sample preparation remains the bottleneck for point-of-need nucleic acid testing due to its complexity and time-consuming nature. Sample preparation involves extracting, purifying, and concentrating nucleic acids from various matrices. These processes are critical for ensuring the accuracy and sensitivity of downstream nucleic acid amplification and detection. However, current sample preparation methods are often laboratory-based, requiring specialized equipment, trained personnel, and several hours of processing time. As a result, sample preparation often limits the speed, portability, and cost-effectiveness of point-of-need nucleic acid testing. A universal, field-deployable sample preparation device is highly desirable for this critical need and unmet challenge. Here we reported a handheld, battery-powered, reconfigurable, and field-deployable nucleic acid sample preparation device. A programmable electromagnetic actuator was developed to drive a magnetic robot (ProMagBot) in X/Y 2D space, such that various magnetic bead-based sample preparations can be readily translated from the laboratory to point-of-need settings. The control of the electromagnetic actuator requires only a 3-phase unipolar voltage in X and Y directions, and therefore, the motion space is highly scalable. We validated the ProMagBot device with a model application by extracting HIV viral RNAs from plasma samples using two widely used magnetic bead kits: ChargeSwitch and MagMAX beads. In both cases, the ProMagBot could successfully extract viral RNAs from 50 μL plasma samples containing as low as 102 copies of viral RNAs in 20 minutes. Our results demonstrated the ability of ProMagBot to prepare samples from complex mediums at the point of need. We believe such a device would enable rapid and robust sample preparation in various settings, including resource-limited or remote environments, and accelerate the development of next-generation point-of-need nucleic acid testing.

Isothermal nucleic acid amplification and its uses in modern diagnostic technologies

Nucleic acids are prominent biomarkers for diagnosing infectious pathogens using nucleic acid amplification techniques (NAATs). PCR, a gold standard technique for amplifying nucleic acids, is widely used in scientific research and diagnosis. Efficient pathogen detection is a key to adequate food safety and hygiene. However, using bulky thermal cyclers and costly laboratory setup limits its uses in developing countries, including India. The isothermal amplification methods are exploited to develop miniaturized sensors against viruses, bacteria, fungi and other pathogenic organisms and have been applied for in situ diagnosis. Isothermal amplification techniques have been found suitable for POC techniques and follow WHO's ASSURED criteria. LAMP, NASBA, SDA, RCA and RPA are some of the isothermal amplification techniques which are preferable for POC diagnostics. Furthermore, methods such as WGA, CPA, HDA, EXPAR, SMART, SPIA and DAMP were introduced for even more accuracy and robustness. Using recombinant polymerases and other nucleic acid-modifying enzymes has dramatically broadened the detection range of target pathogens under the scanner. The coupling of isothermal amplification methods with advanced technologies such as CRISPR/Cas systems, fluorescence-based chemistries, microfluidics and paper-based sensors has significantly influenced the biosensing and diagnosis field. This review comprehensively analyzed isothermal nucleic acid amplification methods, emphasizing their advantages, disadvantages and limitations.

Point-of-Care Testing of the MTF1 Osteoarthritis Biomarker Using Phenolphthalein-Soaked Swabs

Osteoarthritis (OA) is the most common joint disease, which accompanies pain and inconvenience in daily life owing to degradation of cartilage and adjacent tissues. In this study, we propose a simple point-of-care testing (POCT) kit for the detection of the MTF1 OA biomarker to achieve on-site clinical diagnosis of OA. The kit contains an FTA card for patient sample treatments, a sample tube for loop-mediated isothermal amplification (LAMP), and a phenolphthalein-soaked swab for naked eye detection. The MTF1 gene was isolated from synovial fluids using an FTA card and amplified using the LAMP method at 65 °C for 35 min. A test part of the phenolphthalein-soaked swab was decolorized in the presence of the MTF1 gene due to the pH change after the LAMP, but the color remained pink in the absence of the MTF1 gene. The control part of the swab served as a reference color in relation to the test part. When real-time LAMP (RT-LAMP), gel electrophoresis, and colorimetric detection of the MTF1 gene were performed, the limit of detection (LOD) was confirmed at 10 fg/μL, and the overall processes were completed in 1 h. The detection of an OA biomarker in the form of POCT was reported for the first time in this study. The introduced method is expected to serve as a POCT platform directly applicable by clinicians for easy and rapid identification of OA.

Current and emerging trends in techniques for plant pathogen detection

Plant pathogenic microorganisms cause substantial yield losses in several economically important crops, resulting in economic and social adversity. The spread of such plant pathogens and the emergence of new diseases is facilitated by human practices such as monoculture farming and global trade. Therefore, the early detection and identification of pathogens is of utmost importance to reduce the associated agricultural losses. In this review, techniques that are currently available to detect plant pathogens are discussed, including culture-based, PCR-based, sequencing-based, and immunology-based techniques. Their working principles are explained, followed by an overview of the main advantages and disadvantages, and examples of their use in plant pathogen detection. In addition to the more conventional and commonly used techniques, we also point to some recent evolutions in the field of plant pathogen detection. The potential use of point-of-care devices, including biosensors, have gained in popularity. These devices can provide fast analysis, are easy to use, and most importantly can be used for on-site diagnosis, allowing the farmers to take rapid disease management decisions.

Horizon scan of DNA-based methods for quality control and monitoring of herbal preparations

Herbal medicines and preparations are widely used in healthcare systems globally, but concerns remain about their quality and safety. New herbal products are constantly being introduced to the market under varying regulatory frameworks, with no global consensus on their definition or characterization. These biologically active mixtures are sold through complex globalized value chains, which create concerns around contamination and profit-driven adulteration. Industry, academia, and regulatory bodies must collaborate to develop innovative strategies for the identification and authentication of botanicals and their preparations to ensure quality control. High-throughput sequencing (HTS) has significantly improved our understanding of the total species diversity within DNA mixtures. The standard concept of DNA barcoding has evolved over the last two decades to encompass genomic data more broadly. Recent research in DNA metabarcoding has focused on developing methods for quantifying herbal product ingredients, yielding meaningful results in a regulatory framework. Techniques, such as loop-mediated isothermal amplification (LAMP), DNA barcode-based Recombinase Polymerase Amplification (BAR-RPA), DNA barcoding coupled with High-Resolution Melting (Bar-HRM), and microfluidics-based methods, offer more affordable tests for the detection of target species. While target capture sequencing and genome skimming are considerably increasing the species identification resolution in challenging plant clades, ddPCR enables the quantification of DNA in samples and could be used to detect intended and unwanted ingredients in herbal medicines. Here, we explore the latest advances in emerging DNA-based technologies and the opportunities they provide as taxa detection tools for evaluating the safety and quality of dietary supplements and herbal medicines.

Recent advances in cascade isothermal amplification techniques for ultra-sensitive nucleic acid detection

Nucleic acid amplification techniques have always been one of the hot spots of research, especially in the outbreak of COVID-19. From the initial polymerase chain reaction (PCR) to the current popular isothermal amplification, each new amplification techniques provides new ideas and methods for nucleic acid detection. However, limited by thermostable DNA polymerase and expensive thermal cycler, PCR is difficult to achieve point of care testing (POCT). Although isothermal amplification techniques overcome the defects of temperature control, single isothermal amplification is also limited by false positives, nucleic acid sequence compatibility, and signal amplification capability to some extent. Fortunately, efforts to integrating different enzymes or amplification techniques that enable to achieve intercatalyst communication and cascaded biotransformations may overcome the corner of single isothermal amplification. In this review, we systematically summarized the design fundamentals, signal generation, evolution, and application of cascade amplification. More importantly, the challenges and trends of cascade amplification were discussed in depth.

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.

Superior possibilities and upcoming horizons for nanoscience in COVID-19: noteworthy approach for effective diagnostics and management of SARS-CoV-2 outbreak

The outbreak of COVID-19 has caused great havoc and affected many parts of the world. It has imposed a great challenge to the medical and health fraternity with its ability to continue mutating and increasing the transmission rate. Some challenges include the availability of current knowledge of active drugs against the virus, mode of delivery of the medicaments, its diagnosis, which are relatively limited and do not suffice for further prognosis. One recently developed drug delivery system called nanoparticles is currently being utilized in combating COVID-19. This article highlights the existing methods for diagnosis of COVID-19 such as computed tomography scan, reverse transcription-polymerase chain reaction, nucleic acid sequencing, immunoassay, point-of-care test, detection from breath, nanotechnology-based bio-sensors, viral antigen detection, microfluidic device, magnetic nanosensor, magnetic resonance platform and internet-of-things biosensors. The latest detection strategy based on nanotechnology, biosensor, is said to produce satisfactory results in recognizing SARS-CoV-2 virus. It also highlights the successes in the research and development of COVID-19 treatments and vaccines that are already in use. In addition, there are a number of nanovaccines and nanomedicines currently in clinical trials that have the potential to target COVID-19.

A fully integrated nucleic acid analysis system for multiplex detection of genetic polymorphisms related to folic acid metabolism

A sufficient intake of folic acid is essential during pregnancy, but several genetic polymorphisms reduce its absorption, threaten the lives of pregnant women and cause congenital disabilities in newborns. Traditional laboratory detection of genetic variants related to folic acid metabolism is time-consuming and labor-intensive. Microfluidics-based molecular diagnosis integrates sample pre-processing and nucleic acid amplification on-chip to achieve rapid, sensitive, high-throughput, and automated detection. Here, we developed a fully integrated microfluidic system for the detection of genetic polymorphisms related to folic acid metabolism in a "sample in-answer out" style. The system consists of nucleic acid extraction and amplification modules. During nucleic acid extraction, blood cells are lysed, and DNA is captured and eluted through a silica-gel membrane. After that, multiple gene loci are detected using loop-mediated isothermal amplification (LAMP) and the color of the reaction chamber indicates whether genetic mutations are present. The experimental results demonstrate that the system can accurately detect gene polymorphisms associated with folic acid metabolism in blood samples with high sensitivity and no cross-contamination between chambers. The blood samples of five patients were tested for mutant alleles on this system, and the test results were consistent with qPCR and DNA sequencing observations. The operation is fully automated, and the detection is completed in approximately 70 minutes. The proposed system has great potential in prenatal diagnosis and other types of nucleic acid detection.

Molecular Computation for Molecular Classification

DNA as an informational polymer has, for the past 30 years, progressively become an essential molecule to rationally build chemical reaction networks endowed with powerful signal-processing capabilities. Whether influenced by the silicon world or inspired by natural computation, molecular programming has gained attention for diagnosis applications. Of particular interest for this review, molecular classifiers have shown promising results for disease pattern recognition and sample classification. Because both input integration and computation are performed in a single tube, at the molecular level, this low-cost approach may come as a complementary tool to molecular profiling strategies, where all biomarkers are quantified independently using high-tech instrumentation. After introducing the elementary components of molecular classifiers, some of their experimental implementations are discussed either using digital Boolean logic or analog neural network architectures.

An Accurate, Rapid and Cost-Effective Method for T-nos Detection Based on CRISPR/Cas12a

CRISPR/Cas12a technology is used for nucleic acid detection due to its specific recognition function and non-specific single-stranded DNA cleavage activity. Here, we developed a fluorescence visualisation detection method based on PCR and CRISPR/Cas12a approaches. The method was used to detect the nopaline synthase terminator (T-nos) of genetically modified (GM) crops, circumventing the need for expensive instruments and technicians. For enhanced sensitivity and stability of PCR-CRISPR/Cas12a detection, we separately optimised the reaction systems for PCR amplification and CRISPR/Cas12a detection. Eleven samples of soybean samples were assessed to determine the applicability of the PCR-CRISPR/Cas12a method. The method could specifically detect target gene levels as low as 60 copies in the reaction within 50 min. In addition, accurate detection of all 11 samples confirmed the applicability. The method is not limited by large-scale instruments, making it suitable for mass detection of transgenic components in plants in the field. In conclusion, we developed a new, accurate, rapid, and cost-effective method for GM detection.

Biosensors based on functional nucleic acids and isothermal amplification techniques

In the past few years, with the in-depth research of functional nucleic acids and isothermal amplification techniques, their applications in the field of biosensing have attracted great interest. Since functional nucleic acids have excellent flexibility and convenience in their structural design, they have significant advantages as recognition elements in biosensing. At the same time, isothermal amplification techniques have higher amplification efficiency, so the combination of functional nucleic acids and isothermal amplification techniques can greatly promote the widespread application of biosensors. For the purpose of further improving the performance of biosensors, this review introduces several widely used functional nucleic acids and isothermal amplification techniques, as well as their classification, basic principles, application characteristics, and summarizes their important applications in the field of biosensing. We hope to provide some references for the design and construction of new tactics to enhance the detection sensitivity and detection range of biosensing.

Rapid isothermal point-of-care test for screening of SARS-CoV-2 (COVID-19)

Rapid on-site diagnosis of emerging pathogens is key for early identification of infected individuals and for prevention of further spreading in a population. Currently available molecular diagnostic tests are instrument-based whereas rapid antibody and antigen tests are often not sufficiently sensitive for detection in pre-symptomatic subjects. There is a need for rapid point of care molecular screening tests that can be easily adapted to emerging pathogens and are selective, sensitive, reliable in different settings around the world. We have developed a simple, rapid (<30 ​min), and inexpensive test for SARS-CoV-2 that is based on combination of isothermal reverse transcription recombinase polymerase amplification (RT-RPA) using modified primers and visual detection with paper-based microfluidics. Our test (CoRapID) is specific for SARS-CoV-2 (alpha to omicron variants) and does not detect other coronaviruses and pathogens by in silico and in vitro analysis. A two-step test protocol was developed with stable lyophilized reagents that reduces handling by using portable and disposable components (droppers, microapplicators/swabs, paper-strips). After optimization of assay components and conditions, we have achieved a limit of detection (LoD) of 1 copy/reaction by adding a blocking primer to the lateral flow assay. Using a set of 138 clinical samples, a sensitivity of 88.1% (P ​< ​0.05, CI: 78.2-93.8%) and specificity of 93.9% (P ​< ​0.05, CI: 85.4-97.6%) was determined. The lack of need for instrumentation for our CoRapID makes it an ideal on-site primary screening tool for local hospitals, doctors' offices, senior homes, workplaces, and in remote settings around the world that often do not have access to clinical laboratories.

Enzyme-Assisted Nucleic Acid Amplification in Molecular Diagnosis: A Review

Infectious diseases and tumors have become the biggest medical challenges in the 21st century. They are driven by multiple factors such as population growth, aging, climate change, genetic predispositions and more. Nucleic acid amplification technologies (NAATs) are used for rapid and accurate diagnostic testing, providing critical information in order to facilitate better follow-up treatment and prognosis. NAATs are widely used due their high sensitivity, specificity, rapid amplification and detection. It should be noted that different NAATs can be selected according to different environments and research fields; for example, isothermal amplification with a simple operation can be preferred in developing countries or resource-poor areas. In the field of translational medicine, CRISPR has shown great prospects. The core component of NAAT lies in the activity of different enzymes. As the most critical material of nucleic acid amplification, the key role of the enzyme is self-evident, playing the upmost important role in molecular diagnosis. In this review, several common enzymes used in NAATs are compared and described in detail. Furthermore, we summarize both the advances and common issues of NAATs in clinical application.

Multiple ligation–Assisted recombinase polymerase amplification for highly sensitive and selective colorimetric detection of SARS-CoV-2

In this paper we present a new method for the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), targeting a specific region “N gene.” Under isothermal reaction conditions, we integrated ligation (Lig; high selectivity) and recombinase polymerase amplification (RPA; high sensitivity) processes, obtaining a robust method of detection. For point-of-care testing, we incorporated our laboratory-produced pyrophosphate ion (PPi)–sensing probe (PK-probe) for colorimetric analysis of the reaction. The total detection system was efficient and effective at diagnosing this RNA virus–mediated disease rapidly (30 min). In a full-genome SARS-CoV-2 study, our PK-probe/Lig-RPA system functioned with a limit of detection of 1160 copies/ml, with a single-mismatch level of selectively, and it was highly selective even in the presence of bacterial genomes commonly found in the human mouth and nose. This robust, straightforward, selective, efficient, and ultrasensitive colorimetric detection method, with potential for point-of-care analysis, should also be effective in detecting a diverse range of other RNA-based diseases.

Rapid On-Site Detection of Extensively Drug-Resistant Genes in Enterobacteriaceae via Enhanced Recombinase Polymerase Amplification and Lateral Flow Biosensor

The widespread emergence of transferable extensively drug-resistant (XDR) genes, including blaNDM and blaKPC for carbapenem resistance, mcr-1 for colistin resistance, and tet(X4) and tet(X6) for tigecycline resistance, in Enterobacteriaceae poses a major threat to public health. Thus, rapid on-site detection of these XDR genes is urgently needed. We developed a cascade system with a unitary polyethylene glycol (PEG) 200-enhanced recombinase polymerase amplification (RPA) as the core, combined with a modified Chelex-100 lysis method and a horseradish peroxidase (HRP)-catalyzed lateral flow immunoassay (LFIA) biosensor, to accurately detect these genes in Enterobacteriaceae. The conventional Chelex-100 lysis method was modified to allow in situ extraction of bacterial DNA in 20 min without requiring bulky high-speed centrifuges. Using PEG 200 increased the amplification efficiency of the RPA by 13%, and the HRP-catalyzed LFIA biosensor intensified the colorimetric signal of the test line. Following optimization, the sensitivity of the cascade system was <10 copies/μL with satisfactory specificity, allowing for highly sensitive detection of these XDR genes in Enterobacteriaceae. The complete detection procedure can be completed in less than 1 h without using large-scale instruments. This assay is conducive to rapid on-site visual detection of these XDR genes in Enterobacteriaceae in practical applications, thus providing better technical support for clinical surveillance of these genes and better treatment of XDR pathogens. IMPORTANCE Carbapenem, colistin, and tigecycline are considered the last resorts for treating severe bacterial infections caused by extensively drug-resistant (XDR) pathogens. A major threat to public health is the emergence and prevalence of transferable XDR genes in Enterobacteriaceae, such as blaNDM and blaKPC for carbapenem resistance, mcr-1 for colistin resistance, and tet(X4) and tet(X6) for tigecycline resistance. Therefore, it is imperative to develop rapid on-site methods to detect these XDR genes. In this study, we constructed a cascade system for detecting these genes based on PEG 200-enhanced recombinase polymerase amplification combined with a modified Chelex-100 lysis method and HRP-catalyzed lateral flow immunoassay. The current method is capable of detecting the above-mentioned XDR genes in situ with satisfactory specificity and sensitivity, which could provide technical support for the surveillance of these genes and provide medication recommendations for the treatment of relevant clinical infections.

Paper-Based Biosensors for the Detection of Nucleic Acids from Pathogens

Paper-based biosensors are microfluidic analytical devices used for the detection of biochemical substances. The unique properties of paper-based biosensors, including low cost, portability, disposability, and ease of use, make them an excellent tool for point-of-care testing. Among all analyte detection methods, nucleic acid-based pathogen detection offers versatility due to the ease of nucleic acid synthesis. In a point-of-care testing context, the combination of nucleic acid detection and a paper-based platform allows for accurate detection. This review offers an overview of contemporary paper-based biosensors for detecting nucleic acids from pathogens. The methods and limitations of implementing an integrated portable paper-based platform are discussed. The review concludes with potential directions for future research in the development of paper-based biosensors.

Point-of-care testing in companion and food animal disease diagnostics

Laboratory diagnoses of animal diseases has advanced tremendously in recent decades with the advent of cutting-edge technologies such as real-time polymerase chain reaction, next generation sequencing (NGS), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and others However, most of these technologies need sophisticated equipment, laboratory space and highly skilled workforce. Therefore, there is an increasing market demand for point-of-care testing (POCT) in animal health and disease diagnostics. A wide variety of assays based on antibodies, antigens, nucleic acid, and nanopore sequencing are currently available. Each one of these tests have their own advantages and disadvantages. However, a number of research and developmental activities are underway in both academia and industry to improve the existing tests and develop newer and better tests in terms of sensitivity, specificity, turnaround time and affordability. In both companion and food animal disease diagnostics, POCT has an increasing role to play, especially in resource-limited settings. It plays a critical role in improving animal health and wellbeing in rural communities in low- and middle-income countries. At the same time, ensuring high standard of quality through proper validation, quality assurance and regulation of these assays are very important for accurate diagnosis, surveillance, control and management of animal diseases. This review addresses the different types of POCTs currently available for companion and food animal disease diagnostics, tests in the pipeline and their advantages and disadvantages.

LAMP-Based Point-of-Care Biosensors for Rapid Pathogen Detection

Seeking optimized infectious pathogen detection tools is of primary importance to lessen the spread of infections, allowing prompt medical attention for the infected. Among nucleic-acid-based sensing techniques, loop-mediated isothermal amplification is a promising method, as it provides rapid, sensitive, and specific detection of microbial and viral pathogens and has enormous potential to transform current point-of-care molecular diagnostics. In this review, the advances in LAMP-based point-of-care diagnostics assays developed during the past few years for rapid and sensitive detection of infectious pathogens are outlined. The numerous detection methods of LAMP-based biosensors are discussed in an end-point and real-time manner with ideal examples. We also summarize the trends in LAMP-on-a-chip modalities, such as classical microfluidic, paper-based, and digital LAMP, with their merits and limitations. Finally, we provide our opinion on the future improvement of on-chip LAMP methods. This review serves as an overview of recent breakthroughs in the LAMP approach and their potential for use in the diagnosis of existing and emerging diseases.

MINI: A high-throughput point-of-care device for performing hundreds of nucleic acid tests per day

There are a variety of infectious diseases with a high incidence and mortality in limited resource settings that could benefit from rapid point of care molecular diagnosis. Global health efforts have sought to implement mass-screening programs to provide earlier detection and subsequent treatment in an effort to control transmission and improve health outcomes. However, many of the current diagnostic technologies under development are limited to fewer than 10 samples per run, which inherently restricts the screening throughput of these devices. We have developed a high throughput device called "MINI" that is capable of testing hundreds of samples per day at the point-of-care. MINI can utilize multiple energy sources - electricity, flame, or solar - to perform loop-mediated isothermal amplification (LAMP) in a portable and robust device which is ideal for use in limited resource settings. The unique opto-electronic design of MINI minimizes the energy and space requirements of the device and maximizes the optical isolation and signal clarity, enabling point-of-care analysis of 96 unique samples at once. We show comparable performance to a commercial instrument using two different LAMP assays for Kaposi's sarcoma-associated herpesvirus and a common housekeeping gene, GAPDH. With a single device capable of running hundreds of samples per day, increased access to modern molecular diagnostics could improve health outcomes for a variety of diseases common in limited resource settings.