Detection of Zika virus using reverse-transcription LAMP coupled with reverse dot blot analysis in saliva.

In recent years, there have been increasing numbers of infectious disease outbreaks that spread rapidly to population centers resulting from global travel, population vulnerabilities, environmental factors, and ecological disasters such as floods and earthquakes. Some examples of the recent outbreaks are the Ebola epidemic in West Africa, Middle East respiratory syndrome coronavirus (MERS-Co) in the Middle East, and the Zika outbreak through the Americas. We have created a generic protocol for detection of pathogen RNA and/or DNA using loop-mediated isothermal amplification (LAMP) and reverse dot-blot for detection (RDB) and processed automatically in a microfluidic device. In particular, we describe how a microfluidic assay to detect HIV viral RNA was converted to detect Zika virus (ZIKV) RNA. We first optimized the RT-LAMP assay to detect ZIKV RNA using a benchtop isothermal amplification device. Then we implemented the assay in a microfluidic device that will allow analyzing 24 samples simultaneously and automatically from sample introduction to detection by RDB technique. Preliminary data using saliva samples spiked with ZIKV showed that our diagnostic system detects ZIKV RNA in saliva. These results will be validated in further experiments with well-characterized ZIKV human specimens of saliva. The described strategy and methodology to convert the HIV diagnostic assay and platform to a ZIKV RNA detection assay provides a model that can be readily utilized for detection of the next emerging or re-emerging infectious disease.

A modifiable microarray-based universal sensor: providing sample-to-results automation.

A microfluidic system consisting of generic single use cartridges which interface with a workstation allows the automatic performance of all necessary sample preparation, PCR analysis and interpretation of multiplex PCR assays. The cartridges contain a DNA array with 20 different 16mer DNA "universal" probes immobilized at defined locations. PCR amplicons can be detected via hybridization of user-defined "reporter" probes that are complementary at their 3' termini to one or more of the universal probes and complementary to the target amplicons at their 5' termini. The system was able to detect single-plex and multiplex PCR amplicons from various infectious agents as well as wild type and mutant alleles of single nucleotide polymorphisms. The system's ease of use was further demonstrated by converting a published PCR assay for the detection of Mycobacterium genitalium in a fully automated manner. Excellent correlation between traditional manual methods and the automated analysis performed by the workstation suggests that the system can provide a means to easily design and implement a variety of customized PCR-based assays. The system will be useful to researchers or clinical investigators seeking to develop their own user defined assays. As the U.S. FDA continues to pursue regulatory oversight of LDTs, the system would also allow labs to continue to develop compliant assays.

A Rapid, Self-confirming Assay for HIV: Simultaneous Detection of Anti-HIV Antibodies and Viral RNA.

OBJECTIVE: We developed a microfluidic system to simultaneously detect host anti-HIV antibodies and viral RNA in the same specimen in order to satisfy two important diagnostic criteria, especially within resource-limited settings. First, the system can detect acute HIV infection and allow immediate confirmation of a seropositive screening result by detection of HIV RNA. It also addresses the well-known "seroconversion window" during early HIV infection when antibodies are not yet detectable and viral loads are at their highest. METHODS: We first developed and optimized two separate manual assays for the detection of host anti-HIV antibodies and viral RNA and then converted them to the microfluidic system. We optimized a commercially available serologic assay to run within the microfluidic device while we incorporated the isothermal LAMP assay to detect the presence of viral RNA. The microfluidic device and instrumentation were developed to simultaneously perform both assays without any user intervention. RESULTS: The finalized system consists of a disposable injection molded and film-laminated microfluidic CARD disposable device and a portable, software controlled instrument, which together can automatically perform all steps of both assays without any user intervention after the initial loading of samples and reagents. The microfluidic CARD cartridge has multiple microchannels, valves, pumps and reservoirs, which perform the immunoassay, isolates viral RNA for detection by magnetic bead based purification, and Reverse Transcriptase loop-mediated isothermal amplification (RT-LAMP). The microfluidic system was able to detect host anti-HIV antibodies and viral RNA in either a blood or saliva sample. CONCLUSION: The ability to detect antibodies and simultaneously confirm a seropositive HIV-RNA result provides healthcare workers with a complete and accurate appraisal of a patient's infection status in the earliest stages of the disease and represents an important tool for the "Test and Treat" and "Treatment as Prevention" approaches for controlling the HIV epidemic.

Determination of genotypes using a fully automated molecular detection system.

CONTEXT: Although the value of pharmacogenomics to improve patient outcomes has become increasingly clear, adoption in medical practice has been slow, which can be attributed to several factors, including complicated and expensive testing procedures and required equipment, lack of training by private practice physicians, and reluctance of both private and commercial payers to reimburse for such testing. OBJECTIVES: To evaluate a fully automated molecular detection system for human genotyping assays, starting with anticoagulated whole blood samples, and to perform all sample preparation, assay, and analysis steps automatically with actionable results reported by the system's software. DESIGN: The genotypes of 254 random individuals were determined by performing bidirectional DNA sequencing, and that information was used to statistically train the imaging software of the automated molecular detection system to distinguish the 3 possible genotypes (ie, homozygous wild type, heterozygous, and homozygous mutant) at each of 3 different loci (CYP2C9*2, CYP2C9*3, and VKORC1). RESULTS: The resulting software algorithm was able to correctly identify the genotypes of all 254 individuals (100%) evaluated without any further user analysis. CONCLUSIONS: The EncompassMDx workstation (Rheonix, Inc, Ithaca, New York) is a molecular detection system that can automatically determine the genotypes of individuals in an unattended manner. Considerably less technical expertise was required to achieve results identical to those obtained using more complex, time-consuming, and expensive bidirectional DNA sequencing. This optimized system may dramatically simplify and reduce the costs of pharmacogenomics testing, thus leading to more-widespread use.

Prion protein detection in serum using micromechanical resonator arrays.

Prion proteins that have transformed from their normal cellular counterparts (PrP(c)) into infectious form (PrP(res)) are responsible for causing progressive neurodegenerative diseases in numerous species, such as bovine spongiform encephalopathy (BSE) in cattle (also known as mad cow disease), scrapie in sheep, and Creutzfeldt-Jakob disease (CJD) in humans. Due to a possible link between BSE and CJD it is highly desirable to develop non-invasive and ante mortem tests for the detection of prion proteins in bovine samples. Such ante mortem tests of all cows prior to slaughter will help to prevent the introduction of PrP(res) into the human food supply. Furthermore, detection of PrP(res) in donated blood will also help to prevent the transmission of CJD among humans through blood transfusion. In this study, we have continued development of a micromechanical resonator array that is capable of detecting PrP(c) in bovine blood serum. The sensitivity of the resonators for the detection of PrP(c) is further enhanced by the use of secondary mass labels. A pair of antibodies is used in a sandwich immunoassay format to immobilize PrP(c) on the surface of resonators and attach nanoparticles as secondary mass labels to PrP(c). Secondary mass labeling is optimized in terms of incubation time to maximize the frequency shifts that correspond to the presence of PrP(c) on the surface of resonators. Our results show that a minimum of 200 pg mL(-1) of PrP(c) in blood serum can be detected using micromechanical resonator arrays.

Human pathogenic Cryptosporidium species bioanalytical detection method with single oocyst detection capability.

A bioanalytical detection method for specific detection of viable human pathogenic Cryptosporidium species, C. parvum, C. hominis, and C. meleagridis is described. Oocysts were isolated from water samples via immunomagnetic separation, and mRNA was extracted with oligo-dT magnetic beads, amplified using nucleic acid sequence-based amplification (NASBA), and then detected in a nucleic acid hybridization lateral flow assay. The amplified target sequence employed was hsp70 mRNA, production of which is stimulated via a brief heat shock. The described method was capable of detecting one oocyst in 10 µL using flow-cytometer-counted samples. Only viable oocysts were detected, as confirmed using 4',6-diamidino-2-phenylindole and propidium iodide (DAPI/PI) staining. The detection system was challenged by detecting oocysts in the presence of large numbers of common waterborne microorganisms and packed pellet material filtered from environmental water samples. When the method was compared with EPA Method 1622 for C. parvum detection, highly comparable results were obtained. Since the described detection system yields unambiguous results within 4.5 h, it is an ideal method for monitoring the safety of drinking water.

Prion protein detection using nanomechanical resonator arrays and secondary mass labeling.

Nanomechanical resonators have shown potential application for mass sensing and have been used to detect a variety of biomolecules. In this study, a dynamic resonance-based technique was used to detect prion proteins (PrP), which in conformationally altered forms are known to cause neurodegenerative diseases in animals as well as humans. Antibodies and nanoparticles were used as mass labels to increase the mass shift and thus amplify the frequency shift signal used in PrP detection. A sandwich assay was used to immobilize PrP between two monoclonal antibodies, one of which was conjugated to the resonator's surface while the other was either used alone or linked to the nanoparticles as a mass label. Without additional mass labeling, PrP was not detected at concentrations below 20 microg/mL. In the presence of secondary antibodies the analytical sensitivity was improved to 2 microg/mL. With the use of functionalized nanoparticles, the sensitivity improved an additional 3 orders of magnitude to 2 ng/mL.

Microfluidic biosensor for the serotype-specific detection of dengue virus RNA.

The development of a microfluidic biosensor with fluorescence detection for the rapid, sensitive, and serotype-specific detection of Dengue virus is presented. The biosensor chip consists of poly(dimethylsiloxane) (PDMS) substrate with fabricated microchannels and a glass substrate used to seal the microchannels. These two substrates are packaged within a pressure-closed Plexiglas housing to provide a watertight reversible sealing at the PDMS-glass interface. The ability to reversibly seal the device permits easy disassembly and quick interchange of the device parts, which is ideal for developmental purposes. The biosensor employs a magnetic bead-based sandwich hybridization system in conjugation with liposome amplification for the specific detection of nucleic acids. The concentrations of the various biosensor components were optimized using a synthesized fragment of Dengue virus RNA. To evaluate the sensitivity of the assay, two detection systems, based on fluorescence measurements of intact and lysed liposomes, were analyzed. The entire analysis was complete within 20 min (including incubation time) with RNA detection limits of 0.125 nM and 50 pM for intact and lysed liposome detection systems, respectively. Subsequently, the biosensor was applied to the analysis of actual RNA obtained from Dengue virus serotypes 1-4. The resulting signals were compared to those obtained using standard electrochemiluminescence detection and shown to correspond perfectly with respect to serotype identification.

Development of a microfluidic biosensor module for pathogen detection.

The development of a microfluidic biosensor module with fluorescence detection for the identification of pathogenic organisms and viruses is presented in this article. The microfluidic biosensor consists of a network of microchannels fabricated in polydimethylsiloxane (PDMS) substrate. The microchannels are sealed with a glass substrate and packed in a Plexiglas housing to provide connection to the macro-world and ensure leakage-free flow operation. Reversible sealing permits easy disassembly for cleaning and replacing the microfluidic channels. The fluidic flow is generated by an applied positive pressure gradient, and the module can be operated under continuous solution flow of up to 80 microL min(-1). The biosensor recognition principle is based on DNA/RNA hybridization and liposome signal amplification. Superparamagnetic beads are incorporated into the system as a mobile solid support and are an essential part of the analysis scheme. In this study, the design, fabrication and the optimization of concentrations and amounts of the different biosensor components are carried out. The total time required for an assay is only 15 min including sample incubation time. The biosensor module is designed so that it can be easily integrated with a micro total analysis system, which will combine sample preparation and detection steps onto a single chip.

Development of an immunomagnetic bead-immunoliposome fluorescence assay for rapid detection of Escherichia coli O157:H7 in aqueous samples and comparison of the assay with a standard microbiological method.

The objective of this study was to develop and optimize a protocol for the rapid detection of Escherichia coli O157:H7 in aqueous samples by a combined immunomagnetic bead-immunoliposome (IMB/IL) fluorescence assay. The protocol consisted of the filtration or centrifugation of 30- to 100-ml samples followed by incubation of the filter membranes or pellet with anti-E. coli O157:H7 immunomagnetic beads in growth medium specific for E. coli O157:H7. The resulting E. coli O157:H7-immunomagnetic bead complexes were isolated by magnetic separation, washed, and incubated with sulforhodamine B-containing immunoliposomes specific for E. coli O157:H7; the final immunomagnetic bead-E. coli O157:H7-immunoliposome complexes were again isolated by magnetic separation, washed, and lysed with a n-octyl-beta-d-glucopyranoside to release sulforhodamine B. The final protocol took less than 8 h to complete and had a detection limit of less than 1 CFU of E. coli O157:H7 per ml in various aqueous matrices, including apple juice and cider. To validate the protocol at an independent facility, 100-ml samples of groundwater with and without E. coli O157:H7 (15 CFU) were analyzed by a public health laboratory using the optimized protocol and a standard microbiological method. While the IMB/IL fluorescence assay was able to identify E. coli O157:H7-containing samples with 100% accuracy, the standard microbiological method was unable to distinguish E. coli O157:H7-spiked samples from negative controls without further extensive workup. These results demonstrate the feasibility of using immunomagnetic beads in combination with sulforhodamine B-encapsulating immunoliposomes for the rapid detection of E. coli O157:H7 in aqueous samples.

Multi-analyte single-membrane biosensor for the serotype-specific detection of Dengue virus.

A multi-analyte biosensor based on nucleic acid hybridization and liposome signal amplification was developed for the rapid serotype-specific detection of Dengue virus. After RNA amplification, detection of Dengue virus specific serotypes can be accomplished using a single analysis within 25 min. The multi-analyte biosensor is based on single-analyte assays (see Baeumner et al (2002) Anal Chem 74:1442-1448) developed earlier in which four analyses were required for specific serotype identification of Dengue virus samples. The multi-analyte biosensor employs generic and serotype-specific DNA probes, which hybridize with Dengue RNA that is amplified by the isothermal nucleic acid sequence based amplification (NASBA) reaction. The generic probe (reporter probe) is coupled to dye-entrapping liposomes and can hybridize to all four Dengue serotypes, while the serotype-specific probes (capture probes) are immobilized through biotin-streptavidin interaction on the surface of a polyethersulfone membrane strip in separate locations. A mixture of amplified Dengue virus RNA sequences and liposomes is applied to the membrane and allowed to migrate up along the test strip. After the liposome-target sequence complexes hybridize to the specific probes immobilized in the capture zones of the membrane strip, the Dengue serotype present in the sample can be determined. The amount of liposomes immobilized in the various capture zones directly correlates to the amount of viral RNA in the sample and can be quantified by a portable reflectometer. The specific arrangement of the capture zones and the use of unlabeled oligonucleotides (cold probes) enabled us to dramatically reduce the cross-reactivity of Dengue virus serotypes. Therefore, a single biosensor can be used to detect the exact Dengue serotype present in the sample. In addition, the biosensor can simultaneously detect two serotypes and so it is useful for the identification of possible concurrent infections found in clinical samples. The various biosensor components have been optimized with respect to specificity and sensitivity, and the system has been ultimately tested using blind coded samples. The biosensor demonstrated 92% reliability in Dengue serotype determination. Following isothermal amplification of the target sequences, the biosensor had a detection limit of 50 RNA molecules for serotype 2, 500 RNA molecules for serotypes 3 and 4, and 50,000 molecules for serotype 1. The multi-analyte biosensor is portable, inexpensive, and very easy to use and represents an alternative to current detection methods coupled with nucleic acid amplification reactions such as electrochemiluminescence, or those based on more expensive and time consuming methods such as ELISA or tissue culture.

A rapid biosensor for viable B. anthracis spores.

A simple membrane-strip-based biosensor assay has been combined with a nucleic acid sequence-based amplification (NASBA) reaction for rapid (4 h) detection of a small number (ten) of viable B. anthracis spores. The biosensor is based on identification of a unique mRNA sequence from one of the anthrax toxin genes, the protective antigen ( pag), encoded on the toxin plasmid, pXO1, and thus provides high specificity toward B. anthracis. Previously, the anthrax toxins activator ( atxA) mRNA had been used in our laboratory for the development of a biosensor for the detection of a single B. anthracis spore within 12 h. Changing the target sequence to the pag mRNA provided the ability to shorten the overall assay time significantly. The vaccine strain of B. anthracis (Sterne strain) was used in all experiments. A 500-microL sample containing as few as ten spores was mixed with 500 microL growth medium and incubated for 30 min for spore germination and mRNA production. Thus, only spores that are viable were detected. Subsequently, RNA was extracted from lysed cells, selectively amplified using NASBA, and rapidly identified by the biosensor. While the biosensor assay requires only 15 min assay time, the overall process takes 4 h for detection of ten viable B. anthracis spores, and is shortened significantly if more spores are present. The biosensor is based on an oligonucleotide sandwich-hybridization assay format. It uses a membrane flow-through system with an immobilized DNA probe that hybridizes with the target sequence. Signal amplification is provided when the target sequence hybridizes to a second DNA probe that has been coupled to liposomes encapsulating the dye sulforhodamine B. The amount of liposomes captured in the detection zone can be read visually or quantified with a hand-held reflectometer. The biosensor can detect as little as 1 fmol target mRNA (1 nmol L(-1)). Specificity analysis revealed no cross-reactivity with 11 organisms tested, among them closely related species such as B. cereus, B. megaterium, B. subtilis, B. thuringiensis, Lactococcus lactis, Lactobacillus plantarum, and Chlostridium butyricum. Also, no false positive signals were obtained from nonviable spores. We suggest that this inexpensive biosensor is a viable option for rapid, on-site analysis providing highly specific data on the presence of viable B. anthracis spores.

Biosensor for dengue virus detection: sensitive, rapid, and serotype specific.

A serotype-specific RNA biosensor was developed for the rapid detection of Dengue virus (serotypes 1-4) in blood samples. After RNA amplification, the biosensor allows the rapid detection of Dengue virus RNA in only 15 min. In addition, the biosensor is portable, inexpensive, and very easy to use, making it an ideal detection system for point-of-care and field applications. The biosensor is coupled to the isothermal nucleic acid sequence-based amplification (NASBA) technique with which small amounts of virus RNA are amplified using a simple water bath. During the NASBA reaction, a generic sequence is attached to all RNA molecules as described earlier (Wu, S. J.; Lee, E. M.; Putvatana, R.; Shurtliff, R. N.; Porter, K R.; Suharyono, W.; Watt, D. M.; King, C. C.; Murphy, G. S.; Hayes, C. G.; Romano, J. W. J. Clin. Microbiol. 2001, 39, 2794-2798.). It has been shown earlier that Dengue virus can be detected specifically using two DNA probes: a first probe hybridized with the attached generic sequence and, therefore, bound to every amplified RNA molecule; and a second probe either bound to all four Dengue virus serotypes or chosen to be specific for only one serotype. These probes were utilized in the biosensor described in this publication. For a generic Dengue virus biosensor, the second probe is complementary to a conserved region found in all Dengue serotypes. For identification of the individual Dengue virus serotypes, four serotype-specific probes were developed (Wu, S. J.; Lee, E. M.; Putvatana, R.; Shurtiff, R. N.; Porter, K. R.; Suharyono, W.; Watt, D. M.; King, C. C.; Murphy, G. S.; Hayes, C. G.; Romano, J. W. J. Clin. Microbiol. 2001, 39, 2794-2798.). The biosensor is a membrane-based DNA/RNA hybridization system using liposome amplification. The generic DNA probe (reporter probe) is coupled to the outside of dye-encapsulating liposomes. The conserved or Dengue serotype specific probes (capture probes) are immobilized on a polyethersulfone membrane strip. Liposomes are mixed with amplified target sequence and are then applied to the membrane. The mixture is allowed to migrate along the test strip, and the liposome-target sequence complexes are immobilized in the capture zone via hybridization of the capture probe with target sequence. The amount of liposomes present in the immobilized complex is directly proportional to the amount of target sequence present in the sample and can be quantified using a portable reflectometer. The different biosensor components have been optimized with respect to sensitivity and, foremost, specificity toward the different serotypes. An excellent correlation to a laboratory-based detection system was demonstrated. Finally, the assay was tested using a limited number of clinical human serum samples. Although Dengue serotypes 1, 2 and 4 were identified correctly, serotype 3 displayed low cross-reactivity with biosensors designed for detection of serotypes 1 and 4.