Multiplex detection of blood-borne pathogens on a self-driven microfluidic chip using loop-mediated isothermal amplification

Enhanced Point-of-Care SARS-CoV-2 Detection: Integrating RT-LAMP with Microscanning

The COVID-19 pandemic has highlighted the urgent need for rapid and accurate diagnostic methods for various infectious diseases, including SARS-CoV-2. Traditional RT-PCR methods, while highly sensitive and specific, require complex equipment and skilled personnel. In response, we developed an integrated RT-LAMP-MS assay, which combines rapid reverse transcription loop-mediated isothermal amplification (RT-LAMP) with microscanning (MS) technology for detecting SARS-CoV-2. The assay uses magnesium pyrophosphate formed during LAMP amplification as a visual marker, allowing direct observation via microscopy without the need for additional chemical indicators or probes. For the SARS-CoV-2/IC RT-LAMP-MS assay, the sample-LAMP reagent mixture was added to a microchip with SARS-CoV-2 primers and internal controls, then incubated at 62 °C for 30 min in a heat block, followed by amplification analysis using a microscanner. In clinical tests, the RT-LAMP-MS assay showed 99% sensitivity and 100% specificity, which is identical to the RT-LAMP results and comparable to the commercial AllplexTM SARS-CoV-2 assay results. Additionally, the limit of detection (LOD) was determined to be 10-1 PFU mL-1 (dynamic range: 103~10-1 PFU mL-1). The assay delivers results in 30 min, uses low-cost equipment, and demonstrates 100% reproducibility in repeated tests, making it suitable for point-of-care use in resource-limited settings.

Microfluidic systems for infectious disease diagnostics

Microorganisms, encompassing both uni- and multicellular entities, exhibit remarkable diversity as omnipresent life forms in nature. They play a pivotal role by supplying essential components for sustaining biological processes across diverse ecosystems, including higher host organisms. The complex interactions within the human gut microbiota are crucial for metabolic functions, immune responses, and biochemical signalling, particularly through the gut-brain axis. Viruses also play important roles in biological processes, for example by increasing genetic diversity through horizontal gene transfer when replicating inside living cells. On the other hand, infection of the human body by microbiological agents may lead to severe physiological disorders and diseases. Infectious diseases pose a significant burden on global healthcare systems, characterized by substantial variations in the epidemiological landscape. Fast spreading antibiotic resistance or uncontrolled outbreaks of communicable diseases are major challenges at present. Furthermore, delivering field-proven point-of-care diagnostic tools to the most severely affected populations in low-resource settings is particularly important and challenging. New paradigms and technological approaches enabling rapid and informed disease management need to be implemented. In this respect, infectious disease diagnostics taking advantage of microfluidic systems combined with integrated biosensor-based pathogen detection offers a host of innovative and promising solutions. In this review, we aim to outline recent activities and progress in the development of microfluidic diagnostic tools. Our literature research mainly covers the last 5 years. We will follow a classification scheme based on the human body systems primarily involved at the clinical level or on specific pathogen transmission modes. Important diseases, such as tuberculosis and malaria, will be addressed more extensively.

Point-of-Care Testing for Hepatitis Viruses: A Growing Need

Viral hepatitis, caused by hepatitis A virus (HAV), hepatitis B virus (HBV), hepatitis C virus (HCV), hepatitis D virus (HDV), or hepatitis E virus (HEV), is a major global public health problem. These viruses cause millions of infections each year, and chronic infections with HBV, HCV, or HDV can lead to severe liver complications; however, they are underdiagnosed. Achieving the World Health Organization's viral hepatitis elimination goals by 2030 will require access to simpler, faster, and less expensive diagnostics. The development and implementation of point-of-care (POC) testing methods that can be performed outside of a laboratory for the diagnosis of viral hepatitis infections is a promising approach to facilitate and expedite WHO's elimination targets. While a few markers of viral hepatitis are already available in POC formats, tests for additional markers or using novel technologies need to be developed and validated for clinical use. Potential methods and uses for the POC testing of antibodies, antigens, and nucleic acids that relate to the diagnosis, monitoring, or surveillance of viral hepatitis infections are discussed here. Unmet needs and areas where additional research is needed are also described.

Isothermal nucleic acid amplification technology in HIV detection

Nucleic acid testing for HIV plays an important role in the early diagnosis and monitoring of antiretroviral therapy outcomes in HIV patients and HIV-infected infants. Currently, the main molecular diagnostic methods employed are complex, time-consuming, and expensive to operate in resource-limited areas. Isothermal nucleic acid amplification technology overcomes some of the shortcomings of traditional assays and makes it possible to use point-of-care tests for molecular HIV detection. Here, we summarize and discuss the latest technological advances in isothermal nucleic acid amplification for HIV detection, with the intent of providing guidance for the development of subsequent HIV assays with high sensitivity and specificity.

Visualized RNA detection of SARS-CoV-2 in a closed tube by coupling RT-PCR with nested invasive reaction

A simple, cost-effective and reliable diagnosis of pathogen nucleic acids assay is much required for controlling a pandemic of a virus disease, such as COVID-19. Our previously developed visualized detection of pathogen DNA in a single closed tube is very suitable for POCT. However, virus RNA could not be detected directly and should be reverse-transcribed into cDNA in advance. To enable this visualized assay to detect virus RNA directly, various types of reverse transcriptase were investigated, and finally we found that HiScript II reverse transcriptase could keep active and be well adapted to the one-pot visualized assay in optimized conditions. Reverse transcription, template amplification and amplicon identification by PCR coupled with invasive reaction, as well as visualization by self-assembling of AuNP probes could be automatically and sequentially performed in a closed tube under different temperature conditions, achieving "sample (RNA)-in-result (red color)-out" only by a simple PCR engine plus the naked eye. The visualized RT-PCR is sensitive to unambiguous detection of 5 copies of the N and ORFlab genes of SARS-CoV-2 RNA comparing favourably with qPCR methods (commercialized kit), is specific to genotype 3 variants (Alpha, Beta and Omicron) of SARS-CoV-2, and is very accurate for picking up 0.01% Omicron variant from a large amount of sequence-similar backgrounds. The method is employed in detecting 50 clinical samples, and 10 of them were detected as SARS-CoV-2 positive samples, identical to those by conventional RT-PCR, indicating that the method is cost-effective and labor-saving for pathogen RNA screening in resource-limited regions.

Rapid on-site nucleic acid testing: On-chip sample preparation, amplification, and detection, and their integration into all-in-one systems

As nucleic acid testing is playing a vital role in increasingly many research fields, the need for rapid on-site testing methods is also increasing. The test procedure often consists of three steps: Sample preparation, amplification, and detection. This review covers recent advances in on-chip methods for each of these three steps and explains the principles underlying related methods. The sample preparation process is further divided into cell lysis and nucleic acid purification, and methods for the integration of these two steps on a single chip are discussed. Under amplification, on-chip studies based on PCR and isothermal amplification are covered. Three isothermal amplification methods reported to have good resistance to PCR inhibitors are selected for discussion due to their potential for use in direct amplification. Chip designs and novel strategies employed to achieve rapid extraction/amplification with satisfactory efficiency are discussed. Four detection methods providing rapid responses (fluorescent, optical, and electrochemical detection methods, plus lateral flow assay) are evaluated for their potential in rapid on-site detection. In the final section, we discuss strategies to improve the speed of the entire procedure and to integrate all three steps onto a single chip; we also comment on recent advances, and on obstacles to reducing the cost of chip manufacture and achieving mass production. We conclude that future trends will focus on effective nucleic acid extraction via combined methods and direct amplification via isothermal methods.

Collection, nucleic acid release, amplification, and visualization platform for rapid field detection of rice false smut

Rice false smut (RFS) has brought serious food safety problems to the world. Reliable diagnostic tools are needed for the field detection of RFS. Traditional polymerase chain reaction (PCR) is inefficient due to sample transport and preparation, which cannot adapt to the needs of field detection. Herein, we successfully developed a simple, portable microfluidic test platform to rapidly detect RFS. To simplify the operation, we integrated spore purification, nucleic acid release, and amplification into one chip. A micro air pump was used to separate the spores from the impurities and complete the collection of the spores through the airflow. We rapidly lysed spores and released nucleic acids by the benzyl chloride method. The loop-mediated isothermal amplification (LAMP) products could be combined with SYBR Green I to observe the results visually. On-chip sample tests showed that the spore collection efficiency was approximately 78%. By providing on-chip detection results, the chip had 100% specificity and a detection limit of 100 copies/reaction. At the same time, the stability (CV < 5%) and quantitative ability (R² = 0.989) of the chip were also guaranteed. Through the visual detection of large samples, the on-chip detection results were highly concordant with the classical RT-PCR detection results, and the detection timeliness was greatly enhanced. Compared with RT-PCR, the single-sample detection time was shortened by about twenty minutes. The proposed micro-diagnostic tool did not require any large end-point detection instruments and avoided the complicated operation of nucleic acid extraction. As a result, in the future, our microfluidic chip could be used for rapid and real-time monitoring and early warning of rice false smut spores in rice paddies.

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.

A microfluidic fully paper-based analytical device integrated with loop-mediated isothermal amplification and nano-biosensors for rapid, sensitive, and specific quantitative detection of infectious diseases

Bacterial meningitis, an infection of the membranes (meninges) and cerebrospinal fluid (CSF) surrounding the brain and spinal cord, is one of the major causes of death and disability worldwide. Higher case-fatality rates and short survival times have been reported in developing countries. Hence, a quick, straightforward, and low-cost approach is in great demand for the diagnosis of meningitis. In this research, a microfluidic fully paper-based analytical device (μFPAD) integrated with loop-mediated isothermal amplification (LAMP) and ssDNA-functionalized graphene oxide (GO) nano-biosensors was developed for the first time for a simple, rapid, low-cost, and quantitative detection of the main meningitis-causing bacteria, Neisseria meningitidis (N. meningitidis). The results can be successfully read within 1 hour with the limit of detection (LOD) of 6 DNA copies per detection zone. This paper device also offers versatile functions by providing a qualitative diagnostic analysis (i.e., a yes or no answer), confirmatory testing, and quantitative analysis. These features make the presented μFPAD capable of a simple, highly sensitive, and specific diagnosis of N. meningitis. Furthermore, this microfluidic approach has great potential in the rapid detection of a wide variety of different other pathogens in low-resource settings.

Flap Endonuclease-Induced Steric Hindrance Change Enables the Construction of Multiplex and Versatile Lateral Flow Strips for DNA Detection

A lateral flow strip (LFS) is an ideal tool for point-of-care testing (POCT), but traditional LFSs cannot be used for multiplex detection. Herein, a multiplex and versatile LFS based on flap endonuclease 1 (FEN1)-induced steric hindrance change (FISH-LFS) is proposed. In this method, multiplex PCR coupled with cascade invasive reactions was employed to yield single-stranded flaps, which were target-specific but independent of target sequences. Then, the amplicons were applied for FISH-LFS, and the single-stranded flaps would be efficiently captured by the complementary LFS-probes at different test lines. As flaps were cleaved from the specially designed hairpin probes, competition among flaps and hairpin probes would occur in capturing the probes at test lines. We enabled the hairpin probes to flow through the test lines while the flaps to stay at the test lines by making use of the difference in steric hindrance between hairpin probes and flaps. The assay is able to detect as low as two copies of blood pathogens (HBV, HCV, and HIV), to pick up as low as 0.1% mutants from wild-type gDNA, and to genotype 200 copies of SARS-CoV-2 variants α and β within 75 min at a conventional PCR engine. As the method is free of dye, a portable PCR engine could be used for a cost-effective multiplex detection on site. Results using an ultrafast mobile PCR system for FISH-LFS showed that as fast as 30 min was achieved for detecting three pathogens (HBV, HCV, and HIV) in blood, very suitable for POCT of pathogen screening. The method is convenient in operation, simple in instrumentation, specific in genotyping, and very easy in setting up multiplex POCT assays.

Principles and Applications of Loop-Mediated Isothermal Amplification to Point-of-Care Tests

For the identification of nucleic acids, which are important biomarkers of pathogen-mediated diseases and viruses, the gold standard for NA-based diagnostic applications is polymerase chain reaction (PCR). However, the requirements of PCR limit its application as a rapid point-of-care diagnostic technique. To address the challenges associated with regular PCR, many isothermal amplification methods have been developed to accurately detect NAs. Isothermal amplification methods enable NA amplification without changes in temperature with simple devices, as well as faster amplification times compared with regular PCR. Of the isothermal amplifications, loop-mediated isothermal amplification (LAMP) is the most studied because it amplifies NAs rapidly and specifically. This review describes the principles of LAMP, the methods used to monitor the process of LAMP, and examples of biosensors that detect the amplicons of LAMP. In addition, current trends in the application of LAMP to smartphones and self-diagnosis systems for point-of-care tests are also discussed.

A carbon-black-embedded poly(dimethylsiloxane)-paper hybrid device for energy-efficient nucleic-acid amplification in point-of-care testing

A paper-based device patterned with a carbon-black-poly(dimethylsiloxane) (PDMS) mixture is developed as a heating platform for nucleic-acid amplification tests. The photothermal effect of carbon black under 808 nm laser irradiation is used to conduct loop-mediated isothermal amplification (LAMP) to detect Escherichia coli (E. coli) O157:H7, a foodborne pathogen. We characterize the heat generation of carbon black by changing its concentration and the hardness of PDMS. Then, we optimize the minimum laser power required to perform LAMP. The proposed paper-based device requires less than 15 min to perform LAMP, and the result can be confirmed based on the color change observed by the naked eye. The rfbE gene of E. coli O157:H7 is specifically amplified, with a detection limit of 10² CFU mL^-1. Amplification is also performed by using a laboratory-made laser-diode device, which consumes only 2 W h during its operation. The low cost, disposability, and easy fabrication of the paper-based device make it a powerful tool for point-of-care testing.

An HFman probe-based reverse transcription loop-mediated isothermal amplification (RT-LAMP) assay for HIV-1 detection

Loop-mediated isothermal amplification (LAMP) is suitable for the development of a rapid and cost-effective nucleic acid technique for point of care (POC) applications. However, LAMP methods often generate non-specific amplification, therefore inevitably resulting in false positive results especially when sequence-independent dyes are used to indirectly reflect the results. In this study, we established and optimized a reverse transcription LAMP (RT-LAMP) assay with a high-fidelity DNA polymerase-mediated fluorescent probe (HFman probe) for human immunodeficiency virus-1 (HIV-1) detection. The assay showed high sensitivity and specificity. Using 101 plasma samples with different HIV-1 viral load, we demonstrated that our assay can detect the major HIV-1 subtypes circulating in China, including CRF01_AE, CRF07_BC, CRF08_BC, CRF55_01B, and unique recombinant forms (URFs). We also compared our assay with an approved commercial real-time quantitative polymerase chain reaction (RT-qPCR) kit and found the sensitivity, specificity and consistency was 88.8%, 100% and 89.1%, respectively. The HFman probe-based RT-LAMP assay is a high specific detection method that is rapid, variant-tolerant and simple to operate, and thus is of great significance for timely disclosure of HIV status and rapid POC diagnosis.

SMART-LAMP: A Smartphone-Operated Handheld Device for Real-Time Colorimetric Point-of-Care Diagnosis of Infectious Diseases via Loop-Mediated Isothermal Amplification

Nucleic acid amplification diagnostics offer outstanding features of sensitivity and specificity. However, they still lack speed and robustness, require extensive infrastructure, and are neither affordable nor user-friendly. Thus, they have not been extensively applied in point-of-care diagnostics, particularly in low-resource settings. In this work, we have combined the loop-mediated isothermal amplification (LAMP) technology with a handheld portable device (SMART-LAMP) developed to perform real-time isothermal nucleic acid amplification reactions, based on simple colorimetric measurements, all of which are Bluetooth-controlled by a dedicated smartphone app. We have validated its diagnostic utility regarding different infectious diseases, including Schistosomiasis, Strongyloidiasis, and COVID-19, and analyzed clinical samples from suspected COVID-19 patients. Finally, we have proved that the combination of long-term stabilized LAMP master mixes, stored and transported at room temperature with our developed SMART-LAMP device, provides an improvement towards true point-of-care diagnosis of infectious diseases in settings with limited infrastructure. Our proposal could be easily adapted to the diagnosis of other infectious diseases.

Analysis and validation of silica-immobilised BST polymerase in loop-mediated isothermal amplification (LAMP) for malaria diagnosis

Bacillus stearothermophilus large fragment (BST_LF) DNA polymerase is reported, isolated on silica via a fused R5 silica-affinity peptide and used in nucleic acid diagnostics. mCherry (mCh), included in the fusion construct, was shown as an efficient fluorescent label to follow the workflow from gene to diagnostic. The R5 immobilisation on silica from cell lysate was consistent with cooperative R5-specific binding of R5₂-mCh-FL-BST_LF or R5₂-mCh-H10-BST_LF fusion proteins followed by non-specific protein binding (including E. coli native proteins). Higher R5-binding could be achieved in the presence of phosphate, but phosphate residue reduced loop-mediated isothermal amplification (LAMP) performance, possibly blocking sites on the BST_LF for binding of β- and γ-phosphates of the dNTPs. Quantitative assessment showed that cations (Mg²⁺ and Mn²⁺) that complex the PPi product optimised enzyme activity. In malaria testing, the limit of detection depended on Plasmodium species and primer set. For example, 1000 copies of P. knowlesi 18S rRNA could be detected with the P.KNO-LAU primer set with Si-R5₂-mCh-FL-BST_LF , but 10 copies of P. ovale 18S rRNA could be detected with the P.OVA-HAN primer set using the same enzyme. The Si-immobilised BST_LF outperformed the commercial enzyme for four of the nine Plasmodium LAMP primer sets tested. Si-R5₂-mCh-FL-BST_LF production was transferred from Cambridge to Accra and set up de novo for a trial with clinical samples. Different detection limits were found, targeting the mitochondrial DNA or the 18S rRNA gene for P. falciparum. The results are discussed in comparison with qPCR and sampling protocol and show that the Si-BST_LF polymerase can be optimised to meet the WHO recommended guidelines.

Visualized Genotyping from "Sample to Results" Within 25 Minutes by Coupling Recombinase Polymerase Amplification (RPA) With Allele-Specific Invasive Reaction Assisted Gold Nanoparticle Probes Assembling

A simple and rapid genotyping method with less-instrumentation is essential for realizing point-of-care detection of personalized medicine-related gene biomarkers. Herein, we developed a rapid and visualized genotyping method by coupling recombinase polymerase amplification (RPA) with allele-specific invader reaction assisted gold nanoparticle probes assembling. In the method, the DNA targets were firstly amplified by using RPA, which is a rapid isothermal amplification technology. Then an allele-specific invasion reaction was performed to recognize the single nucleotide polymorphisms (SNPs) site in the amplicons, to produce signal molecules that caused discoloration of gold nanoparticle probes. As a result, genotyping was achieved by observing the color change of the reaction by using naked eye without the requirement for any expensive instrument. In order to achieve rapid genotyping detection, the genomic DNA from oral swab lysate samples were used for the RPA templates amplification. In this way, a visualized genotyping from "samples to results" within 25 min was realized. Two clopidogrel related SNPs CYP2C19*2 and CYP2C19*3 of 56 clinical samples were correctly genotyped by using this rapid visualized genotyping assay. In addition, the feasibility for this pathogen genotyping method was also verified by detecting plasmid DNA containing three SARS-COV-2 gene mutation sites, indicating that this method has the potential for clinical sample detection.

Postsynthetic Modification of the Magnetic Zirconium-Organic Framework for Efficient and Rapid Solid-Phase Extraction of DNA

In recent years, several approaches have been applied to modify metal-organic frameworks (MOFs) owing to their excellent structural tunability such as higher extraction efficiency than that of primitive crystals. Herein, Zr-based MOFs (UiO-66-NH₂) with a suitable size modulated by acetic acid were successfully synthesized for effective DNA extraction. The bonding conformations and adsorption mechanism indicated a high affinity between UiO-66-NH₂ and the DNA molecules. Furthermore, Fe₃O₄ nanoparticles were immobilized on the UiO-66-NH₂ surface to allow MOFs with magnetism. The magnetic zirconium-organic framework (MZMOF) retained the intact structure of MOFs and simplified subsequent extraction operations. In the DNA recovery investigation, MZMOF showed high recovery efficiency for both short-stranded DNA (90.4%) and pseudovirus DNA (95.1%). In addition, it showed superior DNA extraction efficiency from plasma (57.6%) and swab preservation solution (86.5%). The prepared MZMOF was employed for highly specific extraction of viral DNA and cfDNA from samples. To further simplify the extraction process, MZMOF was applied to immiscible phase filtration assisted by a surface tension (IFAST) chip for facilitating rapid DNA extraction with sensitive point-of-care testing. The developed MZMOF-based extraction method has significant potential for increasing the demand for rapid and efficient nucleic acid extraction.