A reverse transcription loop-mediated isothermal amplification assay optimized to detect multiple HIV subtypes

Development of a LAMP-Based Diagnostic for the Detection of Multiple HIV-1 Strains

Since its first appearance in 1981, HIV-1 has remained a global concern. Current methods for diagnosing HIV-1, while effective, are mostly specific to a given subtype of HIV-1 and often require expensive equipment and highly trained individuals to collect and process the sample. It is necessary to develop a sensitive diagnostic method that can be administered with minimal equipment to provide better care in low-resource settings. Loop-mediated isothermal amplification is a rapid and sensitive method for detecting the presence of specific nucleic acid sequences. Herein we report the development and comparison of two different HIV LAMP assays, integrase and VPR, as well as the comparison between TRIZol and magnetic beads RNA extraction methods for each assay. Our analysis shows that the integrase assay was able to detect the virus from multiple subtypes in under 30 min with a variable limit of detection (LOD) that was dependent on the HIV-1 subtype.

Rapid and visual identification of HIV-1 using reverse transcription loop-mediated isothermal amplification integrated with a gold nanoparticle-based lateral flow assay platform

Human immunodeficiency virus type one (HIV-1) infection remains a major public health problem worldwide. Early diagnosis of HIV-1 is crucial to treat and control this infection effectively. Here, for the first time, we reported a novel molecular diagnostic assay called reverse transcription loop-mediated isothermal amplification combined with a visual gold nanoparticle-based lateral flow assay (RT-LAMP-AuNPs-LFA), which we devised for rapid, specific, sensitive, and visual identification of HIV-1. The unique LAMP primers were successfully designed based on the pol gene from the major HIV-1 genotypes CRF01_AE, CRF07_BC, CRF08_BC, and subtype B, which are prevalent in China. The optimal HIV-1-RT-LAMP-AuNPs-LFA reaction conditions were determined to be 68°C for 35 min. The detection procedure, including crude genomic RNA isolation (approximately 5 min), RT-LAMP amplification (35 min), and visual result readout (<2 min), can be completed within 45 min. Our assay has a detection limit of 20 copies per test, and we did not observe any cross-reactivity with any other pathogen in our testing. Hence, our preliminary results indicated that the HIV-1-RT-LAMP-AuNPs-LFA assay can potentially serve as a useful point-of-care diagnostic tool for HIV-1 detection in a clinical setting.

Vivid COVID-19 LAMP is an ultrasensitive, quadruplexed test using LNA-modified primers and a zinc ion and 5-Br-PAPS colorimetric detection system

Sensitive and rapid point-of-care assays have been crucial in the global response to SARS-CoV-2. Loop-mediated isothermal amplification (LAMP) has emerged as an important diagnostic tool given its simplicity and minimal equipment requirements, although limitations exist regarding sensitivity and the methods used to detect reaction products. We describe the development of Vivid COVID-19 LAMP, which leverages a metallochromic detection system utilizing zinc ions and a zinc sensor, 5-Br-PAPS, to circumvent the limitations of classic detection systems dependent on pH indicators or magnesium chelators. We make important strides in improving RT-LAMP sensitivity by establishing principles for using LNA-modified LAMP primers, multiplexing, and conducting extensive optimizations of reaction parameters. To enable point-of-care testing, we introduce a rapid sample inactivation procedure without RNA extraction that is compatible with self-collected, non-invasive gargle samples. Our quadruplexed assay (targeting E, N, ORF1a, and RdRP) reliably detects 1 RNA copy/µl of sample (=8 copies/reaction) from extracted RNA and 2 RNA copies/µl of sample (=16 copies/reaction) directly from gargle samples, making it one of the most sensitive RT-LAMP tests and even comparable to RT-qPCR. Additionally, we demonstrate a self-contained, mobile version of our assay in a variety of high-throughput field testing scenarios on nearly 9,000 crude gargle samples. Vivid COVID-19 LAMP can be an important asset for the endemic phase of COVID-19 as well as preparing for future pandemics.

Use of whole blood and dried blood spot for detection of HIV-1 nucleic acids using reverse transcription loop-mediated isothermal amplification

For monitoring viral load (VL) or Early Infant Diagnosis (EID) of HIV-1, real-time Polymerase Chain Reaction (qPCR) is used to perform on plasma or Dried Blood Spot (DBS) sample. The qPCR method is expensive and requires sophisticated equipment. Therefore, there is a requirement for newer and cheaper technology for VL measurement or EID. In this analytical study, a Reverse Transcription-Loop-Mediated Isothermal Amplification (RT-LAMP) assay was optimized and applied for amplification of HIV nucleic acids (NA) extracted from plasma, heat-treated plasma, heat-treated whole blood and lysis buffer-treated dried blood spot (DBS). The amplified product of RT-LAMP assay was detected by color change of Hydroxy naphthol blue (HNB) dye, step ladder pattern band on agarose gel after electrophoresis and sigmoid-shaped curve in the real-time thermal cycler. Comparing the results from RT-LAMP testing of all conditions with the results obtained by RT-qPCR results, viewed as the gold standard; a relative analytical sensitivity and specificity of RT-LAMP was calculated as 100 % and 90 % respectively. The corresponding positive predictive value (PPV) and negative predictive value (NPV) were 93.75 % and 100 %, respectively. The percentage of agreement between the RT-LAMP and RT-qPCR was 88.46% and Cohen's kappa value was 0.75 shows a substantial agreement between the two tests. This study suggests that whole blood or DBS may be useful specimens for analysis by HIV-1 specific RT-LAMP, to provide a cost effective alternative to RT-qPCR for the detection of HIV-1 nucleic acid at the point of care, or in early infant diagnoses.

Microfluidic Devices for HIV Diagnosis and Monitoring at Point-of-Care (POC) Settings

Human immunodeficiency virus (HIV) is a global epidemic; however, many individuals are able to obtain treatment and manage their condition. Progression to acquired immunodeficiency syndrome (AIDS) occurs during late-stage HIV infection, which compromises the immune system, making it susceptible to infections. While there is no cure, antiretroviral therapy can be used provided that detection occurs, preferably during the early phase. However, the detection of HIV is expensive and resource-intensive when tested with conventional methods, such as flow cytometry, polymerase chain reaction (PCR), or enzyme-linked immunosorbent assays (ELISA). Improving disease detection in resource-constrained areas requires equipment that is affordable, portable, and can deliver rapid results. Microfluidic devices have transformed many benchtop techniques to on-chip detection for portable and rapid point-of-care (POC) testing. These devices are cost-effective, sensitive, and rapid and can be used in areas lacking resources. Moreover, their functionality can rival their benchtop counterparts, making them efficient for disease detection. In this review, we discuss the limitations of currently used conventional HIV diagnostic assays and provide an overview of potential microfluidic technologies that can improve HIV testing in POC settings.

Fingerpick Blood-Based Nucleic Acid Testing on A USB Interfaced Device towards HIV self-testing

HIV self-testing is an emerging innovative approach that allows individuals who want to know their HIV status to collect their own specimen, perform a test, and interpret the results privately. Existing HIV self-testing methods rely on rapid diagnostic tests (RDTs) to detect the presence of HIV-1/2 antibodies, which could miss a significant portion of asymptomatic carriers during the window period. In this work, we present a fully integrated nucleic acid testing (NAT) device towards streamlined HIV self-testing using 100 μL finger-prick whole blood. The device consists of a ready-to-use microfluidic reagent cartridge and an ultra-compact NAT-on-USB analyzer. The test requires simple steps from the user to drop the finger-prick blood sample into a collection tube with lysis buffer and load the lysate onto the microfluidic cartridge, and the testing result can be easily read out by a custom-built graphical user interface (GUI). The microfluidic cartridge and the analyzer automatically handle the complexity of sample preparation, purification, and real-time reverse-transcription loop-mediated isothermal amplification (RT-LAMP). With a turnaround time of ∼60 min, we achieved a limit of detection (LoD) of 214 viral RNA copies/mL of whole blood at a 95% confidence level. Due to its ease of use and high sensitivity, we anticipate the HIV NAT-on-USB device would be particularly useful for the high-risk populations seeking private self-testing at the early stages of exposure.

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.

A magnet-actuated microfluidic array chip for high-throughput pretreatment and amplification and detection of multiple pathogens

The outbreak of global infectious diseases has posed a significant threat to public health, requiring the rapid and accurate diagnosis of pathogens promptly for society to implement immediate control measures to prevent widespread pandemics.

Loop-Mediated Isothermal Amplification (LAMP): The Better Sibling of PCR?

In 1998, when the PCR technique was already popular, a Japanese company called Eiken Chemical Co., Ltd. designed a method known as the loop-mediated isothermal amplification of DNA (LAMP). The method can produce up to 109 copies of the amplified DNA within less than an hour. It is also highly specific due to the use of two to three pairs of primers (internal, external, and loop), which recognise up to eight specific locations on the DNA or RNA targets. Furthermore, the Bst DNA polymerase most used in LAMP shows a high strand displacement activity, which eliminates the DNA denaturation stage. One of the most significant advantages of LAMP is that it can be conducted at a stable temperature, for instance, in a dry block heater or an incubator. The products of LAMP can be detected much faster than in standard techniques, sometimes only requiring analysis with the naked eye. The following overview highlights the usefulness of LAMP and its effectiveness in various fields; it also considers the superiority of LAMP over PCR and presents RT-LAMP as a rapid diagnostic tool for SARS-CoV-2.

A rapid variant-tolerant reverse transcription loop-mediated isothermal amplification assay for the point of care detection of HIV-1

Human immunodeficiency virus (HIV) continues to be a major burden on public health globally with on-going increases in the number of new infections each year. Rapid and sensitive point-of-care tests allow timely interventions and are essential to control the spread of the disease. However the highly variable nature of the virus, resulting in the evolution of many subtypes and inter-subtype recombinants, poses important challenges for its diagnosis. Here we describe a variant-tolerant reverse-transcription RT-LAMP amplification of the virus's INT gene, providing a simple to use, rapid (<30 min) in vitro point-of-care diagnostic test with a limit of detection <18 copies/reaction. The assay was first validated in clinical studies of patient samples, using both established RT-LAMP and RT-qPCR assays for reference, with results showing that this new variant-tolerant HIV-1 RT-LAMP diagnostic test is highly sensitive without compromising its high specificity for HIV-1 subtypes. The diagnostic test was subsequently configured within an easy-to-read paper microfluidic lateral flow test and was validated clinically using patient samples, demonstrating its future potential for use in timely, effective, low cost HIV diagnostics in global regions where healthcare resources may be limited.

Urinary exosomal mRNA detection using novel isothermal gene amplification method based on three-way junction

Exosomal messenger RNA (mRNA) has emerged as a valuable biomarker for liquid biopsy-based disease diagnosis and prognosis due to its stability in body fluids and its biological regulatory function. Here, we report a rapid one-step isothermal gene amplification reaction based on three-way junction (3WJ) formation and the successful detection of urinary exosomal mRNA from tumor-bearing mice. The 3WJ structure can be formed by the association of 3WJ probes (3WJ-template and 3WJ-primer) in the presence of target RNA. After 3WJ structure formation, the 3WJ primer is repeatedly extended and cleaved by a combination of DNA polymerase and nicking endonuclease, producing multiple signal primers. Subsequently, the signal primers promote a specially designed network reaction pathway to produce G-quadruplex probes under isothermal conditions. Finally, G-quadruplex structure produces highly enhanced fluorescence signal upon binding to thioflavin T. This method provides a detection limit of 1.23 pM (24.6 amol) with high selectivity for the target RNA. More importantly, this method can be useful for the sensing of various kinds of mRNA, including breast cancer cellular mRNA, breast cancer exosomal mRNA, and even urinary exosomal mRNA from breast cancer mice. We anticipate that the developed RNA detection assay can be used for various biomedical applications, such as disease diagnosis, prognosis, and treatment monitoring.

Advances in HIV diagnosis and monitoring

Although highly active antiretroviral therapy (HAART) has been introduced over twenty years ago to treat Human Immunodeficiency Virus (HIV) positive patients, acquired immunodeficiency syndrome (AIDS) is still one of the deadliest diseases found worldwide. AIDS prevalence and mortality rates are usually more pronounced in resource-constrained countries than in the developed world. The lack of trained medical technicians, sophisticated diagnostic equipment, and the overall scarcity of medical infrastructures have severely impacted HIV/AIDS diagnostics, which hinders the initiation and periodic monitoring of antiretroviral therapy (ART). Currently, available HIV viral load assays are not well-suited for resource-limited settings due to their high cost and a requirement for medical/technical infrastructures. In this paper, we review current and emerging diagnostic assays for HIV detection, with a focus on point-of-care (POC) based immunoassays for viral load measurement, drug resistance, and HIV recurrence. We also discuss the limitations of the available HIV assays and highlight the technological advancements in cellphone, paper, and flexible material-based assays which have the potential to improve HIV diagnosis and monitoring, thus assisting with the management of the disease.

A Mismatch-tolerant RT-LAMP Method for Molecular Diagnosis of Highly Variable Viruses

Loop-mediated isothermal amplification (LAMP) has been widely used in the detection of pathogens. However, there are usually numerous variants in one viral pathogen and primers employed in LAMP can hardly match all these variants. The mismatches between the primers and the viral genomes, especially those at the 3'-end of the primers, hinder LAMP reactions, leading to failure of the detection. Here, we present a mismatch-tolerant RT-LAMP protocol, which utilizes the 3'-5' exonuclease activity of the Q5 high-fidelity DNA polymerase to remove potential mismatched bases at the 3'-end of the primers during LAMP amplification. Using HIV-1 as a proof-of-principle, we showed that this protocol could represent a promising tool for accurate detection of genetically unstable viruses in laboratory, hospital and field.

Classification of Multiple DNA Dyes Based on Inhibition Effects on Real-Time Loop-Mediated Isothermal Amplification (LAMP): Prospect for Point of Care Setting

LAMP has received great interest and is widely utilized in life sciences for nucleic acid analysis. To monitor a real-time LAMP assay, a fluorescence DNA dye is an indispensable component and therefore the selection of a suitable dye for real-time LAMP is a need. To aid this selection, we investigated the inhibition effects of twenty-three DNA dyes on real-time LAMP. Threshold time (T_t) values of each real-time LAMP were determined and used as an indicator of the inhibition effect. Based on the inhibition effects, the dyes were classified into four groups: (1) non-inhibition effect, (2) medium inhibition effect, (3) high inhibition effect, and (4) very high inhibition effect. The signal to noise ratio (SNR) and the limit of detection (LOD) of the dyes in groups 1, 2, and 3 were further investigated, and possible inhibition mechanisms of the DNA dyes on the real-time LAMP are suggested and discussed. Furthermore, a comparison of SYTO 9 in different LAMP reactions and different systems is presented. Of the 23 dyes tested, SYTO 9, SYTO 82, SYTO 16, SYTO 13, and Miami Yellow were the best dyes with no inhibitory effect, low LOD and high SNR in the real-time LAMP reactions. The present classification of the dyes will simplify the selection of fluorescence dye for real-time LAMP assays in point of care setting.

Point-of-Care HIV Viral Load Testing: an Essential Tool for a Sustainable Global HIV/AIDS Response

The global public health community has set ambitious treatment targets to end the HIV/AIDS pandemic. With the notable absence of a cure, the goal of HIV treatment is to achieve sustained suppression of an HIV viral load, which allows for immunological recovery and reduces the risk of onward HIV transmission. Monitoring HIV viral load in people living with HIV is therefore central to maintaining effective individual antiretroviral therapy as well as monitoring progress toward achieving population targets for viral suppression. The capacity for laboratory-based HIV viral load testing has increased rapidly in low- and middle-income countries, but implementation of universal viral load monitoring is still hindered by several barriers and delays. New devices for point-of-care HIV viral load testing may be used near patients to improve HIV management by reducing the turnaround time for clinical test results. The implementation of near-patient testing using these new and emerging technologies may be an essential tool for ensuring a sustainable response that will ultimately enable an end to the HIV/AIDS pandemic. In this report, we review the current and emerging technology, the evidence for decentralized viral load monitoring by non-laboratory health care workers, and the additional considerations for expanding point-of-care HIV viral load testing.

A Mismatch-Tolerant Reverse Transcription Loop-Mediated Isothermal Amplification Method and Its Application on Simultaneous Detection of All Four Serotype of Dengue Viruses

Loop-mediated isothermal amplification (LAMP) has been widely used in the detection of pathogens causing infectious diseases. However, mismatches between primers (especially in the 3′-end) and templates significantly reduced the amplification efficiency of LAMP, and limited its application to genetically diverse viruses. Here, we reported a novel mismatch-tolerant LAMP assay and its application in the detection of dengue viruses (DENV). The novel method features the addition of as little as 0.15 U of high-fidelity DNA polymerase to the standard 25 μl LAMP reaction mixture. This amount was sufficient to remove the mismatched bases at the 3′-end of primers, thereby resulting in excellent tolerance for various mismatches occurring at the 3′-end of the LAMP primers during amplification. This novel LAMP assay has a markedly improved amplification efficiency especially for the mutants forming mismatches with internal primers (FIP/BIP) and loop primers (FLP/BLP). The reaction time of the novel method was about 5.6–22.6 min faster than the conventional LAMP method regardless of the presence or absence of mismatches between primers and templates. Using the novel method, we improved a previously established pan-serotype assay for DENV, and demonstrated greater sensitivity for detection of four DENV serotypes than the previous one. The limit of detection (LOD) of the novel assay was 74, 252, 78, and 35 virus RNA copies per reaction for DENV-1, DENV-2, DENV-3, and DENV-4, respectively. Among 153 clinical samples from patients with suspected DENV infection, the novel assay detected 94.8% samples being DENV positive, higher than that detected by the commercial NS1 antigen assay (92.2%), laboratory-based RT-PCR method (78.4%), and the conventional RT-LAMP assay (86.9%). Furthermore, the novel RT-LAMP assay has been developed into a visual determination method by adding colorimetric dyes. Because of its simplicity, all LAMP-based diagnostic assays may be easily updated to the newly improved version. The novel mismatch-tolerant LAMP method represents a simple, sensitive and promising approach for molecular diagnosis of highly variable viruses, and it is especially suited for application in resource-limited settings.

A multiplexed RT-LAMP assay for detection of group M HIV-1 in plasma or whole blood

Isothermal nucleic acid amplification techniques, such as reverse-transcription loop-mediated isothermal amplification (RT-LAMP), exhibit characteristics that are suitable for the development of a rapid, low-cost NAT that can be used at the POC. For demonstration of utility for global use, studies are needed to validate the performance of RT-LAMP for the detection of divergent subtypes. In this study, we designed and evaluated multiplexed HIV-1 integrase RT-LAMP primers to detect subtypes within group M, along with an RNase P positive internal processing and amplification control. Using a panel of 26 viral isolates representing the major circulating subtypes, we demonstrated detection of all isolates of subtypes A1, C, D, F1, F2, G, CRF01_AE, CRF02_AG, and two unique recombinant forms (URFs). A whole blood panel created with one representative isolate of each subtype was successfully amplified with the group M HIV-1 integrase and RNase P internal control primers. The group M HIV-1 RT-LAMP assay was further evaluated on 61 plasma specimens obtained from persons from Cameroon and Uganda. The sequence-conserved group M HIV-1 RT-LAMP primers, coupled to a low-cost amplification device, may improve diagnosis of acute infection at the POC and provide timely confirmation of HIV status.

Loop-mediated isothermal amplification (LAMP): a versatile technique for detection of micro-organisms

Loop‐mediated isothermal amplification (LAMP) amplifies DNA with high specificity, efficiency and rapidity under isothermal conditions by using a DNA polymerase with high displacement strand activity and a set of specifically designed primers to amplify targeted DNA strands. Following its first discovery by Notomi et al. (2000Nucleic Acids Res 28: E63), LAMP was further developed over the years which involved the combination of this technique with other molecular approaches, such as reverse transcription and multiplex amplification for the detection of infectious diseases caused by micro‐organisms in humans, livestock and plants. In this review, available types of LAMP techniques will be discussed together with their applications in detection of various micro‐organisms. Up to date, there are varieties of LAMP detection methods available including colorimetric and fluorescent detection, real‐time monitoring using turbidity metre and detection using lateral flow device which will also be highlighted in this review. Apart from that, commercialization of LAMP technique had also been reported such as lyophilized form of LAMP reagents kit and LAMP primer sets for detection of pathogenic micro‐organisms. On top of that, advantages and limitations of this molecular detection method are also described together with its future potential as a diagnostic method for infectious disease.

A Multifunctional Reactor with Dry-Stored Reagents for Enzymatic Amplification of Nucleic Acids

To enable inexpensive molecular detection at the point-of-care and at home with minimal or no instrumentation, it is necessary to streamline unit operations and store reagents refrigeration-free. To address this need, a multifunctional enzymatic amplification reactor that combines solid-phase nucleic acid extraction, concentration, and purification; refrigeration-free storage of reagents with just-in-time release; and enzymatic amplification is designed, prototyped, and tested. A nucleic acid isolation membrane is placed at the reactor's inlet, and paraffin-encapsulated reagents are prestored within the reactor. When a sample mixed with chaotropic agents is filtered through the nucleic acid isolation membrane, the membrane binds nucleic acids from the sample. Importantly, the sample volume is decoupled from the reaction volume, enabling the use of relatively large sample volumes for high sensitivity. When the amplification reactor's temperature increases to its operating level, the paraffin encapsulating the reagents melts and moves out of the way. The reagents are hydrated, just-in-time, and the polymerase reaction proceeds. The amplification process can be monitored, in real-time. We demonstrate our reactors' ability to amplify both DNA and RNA targets using polymerase with both reverse-transcriptase and strand displacement activities to obtain sensitivities on-par with benchtop equipment and a shelf life exceeding 6 months.

Loop-Mediated Isothermal Amplification on Crude DNA as a Point-of-Care Test for the Diagnosis of Mycoplasma-Related Vaginitis During Early Pregnancy

Background

Mycoplasma-related vaginitis gradually has been growing as a threat in adults-genitourinary infection contributes to funisitis, spontaneous abortion, and low birth weight. Until now, use of loop-mediated isothermal amplification (LAMP) to detect Ureaplasma urealyticum (UU), Mycoplasma hominis (MH), or Mycoplasma genitalium (MG) has been reported by some researchers. However, previous studies focused on purified DNA as the template for LAMP assay, which is usually extracted via commercial kit.

Methods

We developed a LAMP assay for rapid detection of UU, MH, and MG genital mycoplasmas using a simple boiling method for DNA extraction, in a cohort of pregnant women with mycoplasma-related vaginitis. We monitored amplicons with the naked eye using SYBR Green I.

Results

The cohort in our study showed a prevalence of 22.6% in pregnant women, as detected by UU-LAMP assay. Compared to the polymerase chain reaction (PCR) test with purified DNA, the sensitivity of the UU-LAMP in clinical specimens with crude DNA was 87.5% (95% confidence interval [CI], 64.6%->99.9). For crude DNA specimens, UU-LAMP was more sensitive and reliable than PCR, with a higher agreement rate (96.8%) and Youden index value (0.88).

Conclusions

As a point-of-care test, LAMP is a useful, specific, and efficient way to detect genital mycoplasmas in resource-limited settings, especially for crude DNA.

Miniaturized devices for point of care molecular detection of HIV

The HIV pandemic affects 36.7 million people worldwide, predominantly in resource-poor settings. Nucleic acid-based molecular detection of HIV plays a significant role in antiretroviral treatment monitoring for HIV patients, as well as diagnosis of HIV infection in infants. Currently available molecular diagnostic methods are complex, time-consuming and relatively expensive, thus limiting their use in resource-poor settings. Recent advances in microfluidics technology have made possible low-cost integrated miniaturized devices for molecular detection and quantification of HIV at the point of care. We review recent technical advances in molecular testing of HIV using microfluidic technology, with a focus on assays based on isothermal nucleic acid amplification. Microfluidic components for sample preparation, isothermal amplification and result detection are discussed and compared. We also discuss the challenges and future directions for developing an integrated "sample-to-result" microfluidic platform for HIV molecular detection.

Instrument-Free Point-of-Care Molecular Detection of Zika Virus

The recent outbreak of Zika virus (ZIKV) infection in the Americas and its devastating impact on fetal development have prompted the World Health Organization (WHO) to declare the ZIKV pandemic as a Public Health Emergency of International Concern. Rapid and reliable diagnostics for ZIKV are vital because ZIKV-infected individuals display no symptoms or nonspecific symptoms similar to other viral infections. Because immunoassays lack adequate sensitivity and selectivity and are unable to identify active state of infection, molecular diagnostics are an effective means to detect ZIKV soon after infection and throughout pregnancy. We report on a highly sensitive reverse-transcription loop-mediated, isothermal amplification (RT-LAMP) assay for rapid detection of ZIKV and its implementation in a simple, easy-to-use, inexpensive, point-of-care (POC) disposable cassette that carries out all the unit operations from sample introduction to detection. For thermal control of the cassette, we use a chemically heated cup without a need for electrical power. Amplification products are detected with leuco crystal violet (LCV) dye by eye without a need for instrumentation. We demonstrated the utility of our POC diagnostic system by detecting ZIKV in oral samples with sensitivity of 5 plaque-forming units (PFU) in less than 40 min. Our system is particularly suitable for resource-poor settings, where centralized laboratory facilities, funds, and trained personnel are in short supply, and for use in doctors' offices, clinics, and at home.