Microfluidic platform versus conventional real-time polymerase chain reaction for the detection of Mycoplasma pneumoniae in respiratory specimens

An All-in-One Platform for On-Site Multiplex Foodborne Pathogen Detection Based on Channel-Digital Hybrid Microfluidics

Recently, significant progress has been made in the development of microdevices for point-of-care infectious disease detection. However, most microdevices only allow limited steps, such as DNA amplification on the chip, while sample preparation, such as lysis and DNA extraction, is conducted off the chip using the traditional method. In this study, an all-in-one platform was developed, which incorporated all necessary procedures for nucleic acid detection. Our on-chip DNA extraction method utilized the magnetic bead-based technology on a hybrid channel-digital microfluidics (C-DMF) microdevice. It yielded high recovery rates, varying from 88.43% to 95.83%, with pathogen concentrations of 103-106 CFU/mL. In particular, the on-chip method exhibited significantly higher efficacy compared to the traditional off-chip manual method, for the DNA extraction of E. coli and S. aureus, representing Gram-negative and Gram-positive bacteria, respectively, at a sample concentration of 103 CFU/mL. To address the need for rapid and accessible diagnostics, colorimetric LAMP amplification was integrated into the proposed microdevice. The results were visually detectable with the naked eye, making it user-friendly for non-specialists. In addition, this platform demonstrated impressive sensitivity in simultaneously detecting common foodborne pathogens in spiked meat samples, achieving the LOD of 102-103 CFU/mL. The entire process, from sampling to result, was fully automated and only required approximately 60 min, offering promising applicability in resource-limited and on-site testing scenarios.

Combining sensors and actuators with electrowetting-on-dielectric (EWOD): advanced digital microfluidic systems for biomedical applications

The concept of digital microfluidics (DMF) enables highly flexible and precise droplet manipulation at a picoliter scale, making DMF a promising approach to realize integrated, miniaturized "lab-on-a-chip" (LOC) systems for research and clinical purposes. Owing to its simplicity and effectiveness, electrowetting-on-dielectric (EWOD) is one of the most commonly studied and applied effects to implement DMF. However, complex biomedical assays usually require more sophisticated sample handling and detection capabilities than basic EWOD manipulation. Alternatively, combined systems integrating EWOD actuators and other fluidic handling techniques are essential for bringing DMF into practical use. In this paper, we briefly review the main approaches for the integration/combination of EWOD with other microfluidic manipulation methods or additional external fields for specified biomedical applications. The form of integration ranges from independently operating sub-systems to fully coupled hybrid actuators. The corresponding biomedical applications of these works are also summarized to illustrate the significance of these innovative combination attempts.

A Digital Microfluidic RT-qPCR Platform for Multiple Detections of Respiratory Pathogens

The coronavirus disease 2019 pandemic has spread worldwide and caused more than six million deaths globally. Therefore, a timely and accurate diagnosis method is of pivotal importance for controlling the dissemination and expansions. Nucleic acid detection by the reverse transcription-polymerase chain reaction (RT-PCR) method generally requires centralized diagnosis laboratories and skilled operators, significantly restricting its use in rural areas and field settings. The digital microfluidic (DMF) technique provides a better option for simultaneous detections of multiple pathogens with fewer specimens and easy operation. In this study, we developed a novel digital microfluidic RT-qPCR platform for multiple detections of respiratory pathogens. This method can simultaneously detect eleven respiratory pathogens, namely, mycoplasma pneumoniae (MP), chlamydophila pneumoniae (CP), streptococcus pneumoniae (SP), human respiratory syncytial virus A (RSVA), human adenovirus (ADV), human coronavirus (HKU1), human coronavirus 229E (HCoV-229E), human metapneumovirus (HMPV), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A virus (FLUA) and influenza B virus (FLUB). The diagnostic performance was evaluated using positive plasmids samples and clinical specimens compared with off-chip individual RT-PCR testing. The results showed that the limit of detections was around 12 to 150 copies per test. The true positive rate, true negative rate, positive predictive value, negative predictive value, and accuracy of DMF on-chip method were 93.33%, 100%, 100%, 99.56%, and 99.85%, respectively, as validated by the off-chip RT-qPCR counterpart. Collectively, this study reported a cost-effective, high sensitivity and specificity on-chip DMF RT-qPCR system for detecting multiple respiratory pathogens, which will greatly contribute to timely and effective clinical management of respiratory infections in medical resource-limited settings.

All-in-One Digital Microfluidics System for Molecular Diagnosis with Loop-Mediated Isothermal Amplification

In this study, an “all-in-one” digital microfluidics (DMF) system was developed for automatic and rapid molecular diagnosis and integrated with magnetic bead-based nucleic acid extraction, loop-mediated isothermal amplification (LAMP), and real-time optical signal monitoring. First, we performed on- and off-chip comparison experiments for the magnetic bead nucleic acid extraction module and LAMP amplification function. The extraction efficiency for the on-chip test was comparable to that of conventional off-chip methods. The processing time for the automatic on-chip workflow was only 23 min, which was less than that of the conventional methods of 28 min 45 s. Meanwhile, the number of samples used in on-chip experiments was significantly smaller than that used in off-chip experiments; only 5 µL of E. coli samples was required for nucleic acid extraction, and 1 µL of the nucleic acid template was needed for the amplification reaction. In addition, we selected SARS-CoV-2 nucleic acid reference materials for the nucleic acid detection experiment, demonstrating a limit of detection of 10 copies/µL. The proposed “all-in-one” DMF system provides an on-site “sample to answer” time of approximately 60 min, which can be a powerful tool for point-of-care molecular diagnostics.

A Routing-Based Repair Method for Digital Microfluidic Biochips Based on an Improved Dijkstra and Improved Particle Swarm Optimization Algorithm

Digital microfluidic biochips (DMFBs) are attractive instruments for obtaining modern molecular biology and chemical measurements. Due to the increasingly complex measurements carried out on a DMFB, such chips are more prone to failure. To compensate for the shortcomings of the module-based DMFB, this paper proposes a routing-based fault repair method. The routing-based synthesis methodology ensures a much higher chip utilization factor by removing the virtual modules on the chip, as well as removing the extra electrodes needed as guard cells. In this paper, the routing problem is identified as a dynamic path-planning problem and mixed path design problem under certain constraints, and an improved Dijkstra and improved particle swarm optimization (ID-IPSO) algorithm is proposed. By introducing a cost function into the Dijkstra algorithm, the path-planning problem under dynamic obstacles is solved, and the problem of mixed path design is solved by redefining the position and velocity vectors of the particle swarm optimization. The ID-IPSO routing-based fault repair method is applied to a multibody fluid detection experiment. The proposed design method has a stronger optimization ability than the greedy algorithm. The algorithm is applied to 8×9, 8×8, and 7×8 fault-free chips. The proposed ID-IPSO routing-based chip design method saves 13.9%, 14.3%, and 14.5% of the experiment completion time compared with the greedy algorithm. Compared with a modular fault repair method based on the genetic algorithm, the ID-IPSO routing-based fault repair method has greater advantages and can save 39.3% of the completion time on average in the completion of complex experiments. When the ratio of faulty electrodes is less than 12% and 23%, the modular and ID-IPSO routing-based fault repair methods, respectively, can guarantee a 100% failure repair rate. The utilization rate of the electrodes is 18% higher than that of the modular method, and the average electrode usage time is 17%. Therefore, the ID-IPSO routing-based fault repair method can accommodate more faulty electrodes for the same fault repair rate; the experiment completion time is shorter, the average number of electrodes is lower, and the security performance is better.

Microbioreactors for Process Development and Cell-Based Screening Studies

Microbioreactors (MBRs) have emerged as potent cultivation devices enabling automated small-scale experiments in parallel while enhancing their cost efficiency. The widespread use of MBRs has contributed to recent advances in industrial and pharmaceutical biotechnology, and they have proved to be indispensable tools in the development of many modern bioprocesses. Being predominantly applied in early stage process development, they open up new fields of research and enhance the efficacy of biotechnological product development. Their reduced reaction volume is associated with numerous inherent advantages - particularly the possibility for enabling parallel screening operations that facilitate high-throughput cultivations with reduced sample consumption (or the use of rare and expensive educts). As a result, multiple variables can be examined in a shorter time and with a lower expense. This leads to a simultaneous acceleration of research and process development along with decreased costs.MBRs range from simple miniaturized cultivations vessels (i.e., in the milliliter scale with limited possibilities for process control) to highly complex and automated small-scale microreactors with integrated sensors that allow for comprehensive screenings in very short time or a precise reflection of large-scale cultivation conditions. Progressive developments and improvements in manufacturing and automation techniques are already helping researchers to make use of the advantages that MBRs offer. This overview of current MBR systems surveys the diverse application for microbial and mammalian cell cultivations that have been developed in recent years.

Micro-Electrode-Dot-Array Digital Microfluidic Biochips: Technology, Design Automation, and Test Techniques

Digital microfluidic biochips (DMFBs) are being increasingly used for DNA sequencing, point-of-care clinical diagnostics, and immunoassays. DMFBs based on a micro-electrode-dot-array (MEDA) architecture have recently been proposed, and fundamental droplet manipulations, e.g., droplet mixing and splitting, have also been experimentally demonstrated on MEDA biochips. There can be thousands of microelectrodes on a single MEDA biochip, and the fine-grained control of nanoliter volumes of biochemical samples and reagents is also enabled by this technology. MEDA biochips offer the benefits of real-time sensitivity, lower cost, easy system integration with CMOS modules, and full automation. This review paper first describes recent design tools for high-level synthesis and optimization of map bioassay protocols on a MEDA biochip. It then presents recent advances in scheduling of fluidic operations, placement of fluidic modules, droplet-size-aware routing, adaptive error recovery, sample preparation, and various testing techniques. With the help of these tools, biochip users can concentrate on the development of nanoscale bioassays, leaving details of chip optimization and implementation to software tools.

Liquid Marble Actuator for Microfluidic Logic Systems

A mechanical flip-flop actuator has been developed that allows for the facile re-routing and distribution of liquid marbles (LMs) in digital microfluidic devices. Shaped loosely like a triangle, the actuating switch pivots from one bistable position to another, being actuated by the very low mass and momentum of a LM rolling under gravity (~4 × 10⁻⁶ kg ms⁻¹). The actuator was laser-cut from cast acrylic, held on a PTFE coated pivot, and used a PTFE washer. Due to the rocking motion of the switch, sequential LMs are distributed along different channels, allowing for sequential LMs to traverse parallel paths. This distributing effect can be easily cascaded, for example to evenly divide sequential LMs down four different paths. This lightweight, cheap and versatile actuator has been demonstrated in the design and construction of a LM-operated mechanical multiplication device — establishing its effectiveness. The actuator can be operated solely by gravity, giving it potential use in point-of-care devices in low resource areas.

Digital microfluidics comes of age: high-throughput screening to bedside diagnostic testing for genetic disorders in newborns

INTRODUCTION

Digital microfluidics (DMF) is an emerging technology with the appropriate metrics for application to newborn and high-risk screening for inherited metabolic disease and other conditions that benefit from early treatment. Areas covered: This review traces the development of electrowetting-based DMF technology toward the fulfillment of its promise to provide an inexpensive platform to conduct enzymatic assays and targeted biomarker assays at the bedside. The high-throughput DMF platform, referred to as SEEKER®, was recently authorized by the United States Food and Drug Administration to screen newborns for four lysosomal storage disorders (LSDs) and is deployed in newborn screening programs in the United States. The development of reagents and methods for LSD screening and results from screening centers are reviewed. Preliminary results from a more compact DMF device, to perform disease-specific test panels from small volumes of blood, are also reviewed. Literature for this review was sourced using principal author and subject searches in PubMed. Expert commentary: Newborn screening is a vital and highly successful public health program. DMF technology adds value to the current testing platforms that will benefit apparently healthy newborns with underlying genetic disorders and infants at-risk for conditions that present with symptoms in the newborn period.

A digital microfluidic system for loop-mediated isothermal amplification and sequence specific pathogen detection

A digital microfluidic (DMF) system has been developed for loop-mediated isothermal amplification (LAMP)-based pathogen nucleic acid detection using specific low melting temperature (T_m) Molecular Beacon DNA probes. A positive-temperature-coefficient heater with a temperature sensor for real-time thermal regulation was integrated into the control unit, which generated actuation signals for droplet manipulation. To enhance the specificity of the LAMP reaction, low-T_m Molecular Beacon probes were designed within the single-stranded loop structures on the LAMP reaction products. In the experiments, only 1 μL of LAMP reaction samples containing purified Trypanosoma brucei DNA were required, which represented over a 10x reduction of reagent consumption when comparing with the conventional off-chip LAMP. On-chip LAMP for unknown sample detection could be accomplished in 40 min with a detection limit of 10 copies/reaction. Also, we accomplished an on-chip melting curve analysis of the Molecular Beacon probe from 30 to 75 °C within 5 min, which was 3x faster than using a commercial qPCR machine. Discrimination of non-specific amplification and lower risk of aerosol contamination for on-chip LAMP also highlight the potential utilization of this system in clinical applications. The entire platform is open for further integration with sample preparation and fluorescence detection towards a total-micro-analysis system.

Digital Microfluidics for Nucleic Acid Amplification

Digital Microfluidics (DMF) has emerged as a disruptive methodology for the control and manipulation of low volume droplets. In DMF, each droplet acts as a single reactor, which allows for extensive multiparallelization of biological and chemical reactions at a much smaller scale. DMF devices open entirely new and promising pathways for multiplex analysis and reaction occurring in a miniaturized format, thus allowing for healthcare decentralization from major laboratories to point-of-care with accurate, robust and inexpensive molecular diagnostics. Here, we shall focus on DMF platforms specifically designed for nucleic acid amplification, which is key for molecular diagnostics of several diseases and conditions, from pathogen identification to cancer mutations detection. Particular attention will be given to the device architecture, materials and nucleic acid amplification applications in validated settings.

Comparison of Mycoplasma pneumoniae Genome Sequences from Strains Isolated from Symptomatic and Asymptomatic Patients

Mycoplasma pneumoniae is a common cause of respiratory tract infections (RTIs) in children. We recently demonstrated that this bacterium can be carried asymptomatically in the respiratory tract of children. To identify potential genetic differences between M. pneumoniae strains that are carried asymptomatically and those that cause symptomatic infections, we performed whole-genome sequence analysis of 20 M. pneumoniae strains. The analyzed strains included 3 reference strains, 3 strains isolated from asymptomatic children, 13 strains isolated from clinically well-defined patients suffering from an upper (n = 4) or lower (n = 9) RTI, and one strain isolated from a follow-up patient who recently recovered from an RTI. The obtained sequences were each compared to the sequences of the reference strains. To find differences between strains isolated from asymptomatic and symptomatic individuals, a variant comparison was performed between the different groups of strains. Irrespective of the group (asymptomatic vs. symptomatic) from which the strains originated, subtype 1 and subtype 2 strains formed separate clusters. We could not identify a specific genotype associated with M. pneumoniae virulence. However, we found marked genetic differences between clinical isolates and the reference strains, which indicated that the latter strains may not be regarded as appropriate representatives of circulating M. pneumoniae strains.

A review of digital microfluidics as portable platforms for lab-on a-chip applications

Following the development of microfluidic systems, there has been a high tendency towards developing lab-on-a-chip devices for biochemical applications. A great deal of effort has been devoted to improve and advance these devices with the goal of performing complete sets of biochemical assays on the device and possibly developing portable platforms for point of care applications. Among the different microfluidic systems used for such a purpose, digital microfluidics (DMF) shows high flexibility and capability of performing multiplex and parallel biochemical operations, and hence, has been considered as a suitable candidate for lab-on-a-chip applications. In this review, we discuss the most recent advances in the DMF platforms, and evaluate the feasibility of developing multifunctional packages for performing complete sets of processes of biochemical assays, particularly for point-of-care applications. The progress in the development of DMF systems is reviewed from eight different aspects, including device fabrication, basic fluidic operations, automation, manipulation of biological samples, advanced operations, detection, biological applications, and finally, packaging and portability of the DMF devices. Success in developing the lab-on-a-chip DMF devices will be concluded based on the advances achieved in each of these aspects.

Advancing rapid point-of-care viral diagnostics to a clinical setting

ABSTRACT 

We discuss here critical factors in ensuring the success of a viral diagnostic at the point of care. Molecular and immunoassay approaches are reviewed with a focus on their ability to meet the infrastructure and workflow limitations in clinical settings in both the developed and developing world. In addition to being low cost, easy-to-use, accurate and adapted for the intended laboratory and healthcare environment, viral diagnostics must also provide information that appropriately directs clinical treatment decisions. We discuss the challenges and implications of linking diagnostics to clinical decision-making at the point of care using three examples: respiratory viruses in the developed world, differential fever diagnosis in the developing world and HPV detection in resource-limited settings.

Advancing technologies for the diagnosis and management of infections

Infections remain a significant problem among surgical patients. Technological advances, especially in the arena of nano-technology, have markedly improved the ability to detect, prevent and treat surgical infections. No longer limited to culture-based methods of pathogen detection or standard antimicrobial therapies, options for management of surgical infections are rapidly expanding. Such advances are critical in this era of rapidly developing resistant and virulent strains of organisms. Further, our understanding of the host pathogen interaction grows exponentially with the development of computer-based modeling, aiding in expediting research endeavors.

Etiological analysis and predictive diagnostic model building of community-acquired pneumonia in adult outpatients in Beijing, China

BACKGROUND

Etiological epidemiology and diagnosis are important issues in adult community-acquired pneumonia (CAP), and identifying pathogens based on patient clinical features is especially a challenge. CAP-associated main pathogens in adults include viruses as well as bacteria. However, large-scale epidemiological investigations of adult viral CAP in China are still lacking. In this study, we analyzed the etiology of adult CAP in Beijing, China and constructed diagnostic models based on combinations of patient clinical factors.

METHODS

A multicenter cohort was established with 500 adult CAP outpatients enrolled in Beijing between November 2010 to October 2011. Multiplex and quantitative real-time fluorescence PCR were used to detect 15 respiratory viruses and mycoplasma pneumoniae, respectively. Bacteria were detected with culture and enzyme immunoassay of the Streptococcus pneumoniae urinary antigen. Univariate analysis, multivariate analysis, discriminatory analysis and Receiver Operating Characteristic (ROC) curves were used to build predictive models for etiological diagnosis of adult CAP.

RESULTS

Pathogens were detected in 54.2% (271/500) of study patients. Viruses accounted for 36.4% (182/500), mycoplasma pneumoniae for 18.0% (90/500) and bacteria for 14.4% (72/500) of the cases. In 182 of the patients with viruses, 219 virus strains were detected, including 166 single and 53 mixed viral infections. Influenza A virus represented the greatest proportion with 42.0% (92/219) and 9.1% (20/219) in single and mixed viral infections, respectively. Factors selected for the predictive etiological diagnostic model of viral CAP included cough, dyspnea, absence of chest pain and white blood cell count (4.0-10.0) × 10(9)/L, and those of mycoplasma pneumoniae CAP were being younger than 45 years old and the absence of a coexisting disease. However, these models showed low accuracy levels for etiological diagnosis (areas under ROC curve for virus and mycoplasma pneumoniae were both 0.61, P < 0.05).

CONCLUSIONS

Greater consideration should be given to viral and mycoplasma pneumoniae infections in adult CAP outpatients. While predictive etiological diagnostic models of viral and mycoplasma pneumoniae based on combinations of demographic and clinical factors may provide indications of etiology, diagnostic confirmation of CAP remains dependent on laboratory pathogen test results.

Real-time PCR as a diagnostic tool for bacterial diseases

In recent years, quantitative real-time PCR tests have been extensively developed in clinical microbiology laboratories for routine diagnosis of infectious diseases, particularly bacterial diseases. This molecular tool is well-suited for the rapid detection of bacteria directly in clinical specimens, allowing early, sensitive and specific laboratory confirmation of related diseases. It is particularly suitable for the diagnosis of infections caused by fastidious growth species, and the number of these pathogens has increased recently. This method also allows a rapid assessment of the presence of antibiotic resistance genes or gene mutations. Although this genetic approach is not always predictive of phenotypic resistances, in specific situations it may help to optimize the therapeutic management of patients. Finally, an approach combining the detection of pathogens, their mechanisms of antibiotic resistance, their virulence factors and bacterial load in clinical samples could lead to profound changes in the care of these infected patients.

Evaluation of a digital microfluidic real-time PCR platform to detect DNA of Candida albicans in blood

Species of Candida frequently cause life-threatening infections in neonates, transplant and intensive care unit (ICU) patients, and others with compromised host defenses. The successful management of systemic candidiasis depends upon early, rapid diagnosis. Blood cultures are the standard diagnostic method, but identification requires days and less than half of the patients are positive. These limitations may be eliminated by using real-time polymerase chain reaction (PCR) to detect Candida DNA in the blood specimens of patients at risk. Here, we optimized a PCR protocol to detect 5-10 yeasts in low volumes of simulated and clinical specimens. We also used a mouse model of systemic candidiasis and determined that candidemia is optimally detectable during the first few days after infection. However, PCR tests are often costly, labor-intensive, and inconvenient for routine use. To address these obstacles, we evaluated the innovative microfluidic real-time PCR platform (Advanced Liquid Logic, Inc.), which has the potential for full automation and rapid turnaround. Eleven and nine of 16 specimens from individual patients with culture-proven candidemia tested positive for C. albicans DNA by conventional and microfluidic real-time PCR, respectively, for a combined sensitivity of 94%. The microfluidic platform offers a significant technical advance in the detection of microbial DNA in clinical specimens.

Elderly patients with community-acquired pneumonia: optimal treatment strategies

Community-acquired pneumonia (CAP) is a common infectious disease that still causes substantial morbidity and mortality. Elderly people are frequently affected, and several issues related to care of this condition in the elderly have to be considered. This article reviews current recommendations of guidelines with a special focus on aspects of the care of elderly patients with CAP. The most common pathogen in CAP is still Streptococcus pneumoniae, followed by other pathogens such as Haemophilus influenzae, Mycoplasma pneumoniae, Chlamydophila pneumoniae and Legionella species. Antimicrobial resistance is an increasing problem, especially with regard to macrolide-resistant S. pneumoniae and fluoroquinolone-resistant strains. With regard to β-lactam antibacterials, resistance by H. influenzae and Moraxella catarrhalis is important, as is the emergence of multidrug-resistant Staphylococcus aureus. The main management decisions should be guided by the severity of disease, which can be assessed by validated clinical risk scores such as CURB-65, a tool for measuring the severity of pneumonia based on assessment of confusion, serum urea, respiratory rate and blood pressure in patients aged ≥65 years. For the treatment of low-risk pneumonia, an aminopenicillin such as amoxicillin with or without a β-lactamase inhibitor is frequently recommended. Monotherapy with macrolides is also possible, although macrolide resistance is of concern. When predisposing factors for special pathogens are present, a β-lactam antibacterial combined with a β-lactamase inhibitor, or the combination of a β-lactam antibacterial, a β-lactamase inhibitor and a macrolide, may be warranted. If possible, patients who have undergone previous antibacterial therapy should receive drug classes not previously used. For hospitalized patients with non-severe pneumonia, a common recommendation is empirical antibacterial therapy with an aminopenicillin in combination with a β-lactamase inhibitor, or with fluoroquinolone monotherapy. With proven Legionella pneumonia, a combination of β-lactams with a fluoroquinolone or a macrolide is beneficial. In severe pneumonia, ureidopenicillins with β-lactamase inhibitors, broad-spectrum cephalosporins, macrolides and fluoroquinolones are used. A combination of a broad-spectrum β-lactam antibacterial (e.g. cefotaxime or ceftriaxone), piperacillin/tazobactam and a macrolide is mostly recommended. In patients with a predisposition for Pseudomonas aeruginosa, a combination of piperacillin/tazobactam, cefepime, imipenem or meropenem and levofloxacin or ciprofloxacin is frequently used. Treatment duration of more than 7 days is not generally recommended, except for proven infections with P. aeruginosa, for which 15 days of treatment appears to be appropriate. Further care issues in all hospitalized patients are timely administration of antibacterials, oxygen supply in case of hypoxaemia, and fluid management and dose adjustments according to kidney function. The management of elderly patients with CAP is a challenge. Shifts in antimicrobial resistance and the availability of new antibacterials will change future clinical practice. Studies investigating new methods to detect pathogens, determine the optimal antimicrobial regimen and clarify the duration of treatment may assist in further optimizing the management of elderly patients with CAP.

Digital microfluidics

Digital microfluidics (DMF) is an emerging liquid-handling technology that enables individual control over droplets on an open array of electrodes. These picoliter- to microliter-sized droplets, each serving as an isolated vessel for chemical processes, can be made to move, merge, split, and dispense from reservoirs. Because of its unique advantages, including simple instrumentation, flexible device geometry, and easy coupling with other technologies, DMF is being applied to a wide range of fields. In this review, we summarize the state of the art of DMF technology from the perspective of analytical chemistry in sections describing the theory of droplet actuation, device fabrication and integration, and applications.

Particles and microfluidics merged: perspectives of highly sensitive diagnostic detection

There is a growing need for diagnostic technologies that provide laboratories with solutions that improve quality, enhance laboratory system productivity, and provide accurate detection of a broad range of infectious diseases and cancers. Recent advances in micro- and nanoscience and engineering, in particular in the areas of particles and microfluidic technologies, have advanced the "lab-on-a-chip" concept towards the development of a new generation of point-of-care diagnostic devices that could significantly enhance test sensitivity and speed. In this review, we will discuss many of the recent advances in microfluidics and particle technologies with an eye towards merging these two technologies for application in medical diagnostics. Although the potential diagnostic applications are virtually unlimited, the most important applications are foreseen in the areas of biomarker research, cancer diagnosis, and detection of infectious microorganisms.

Rapid molecular assays for specific detection and quantitation of Loa loa microfilaremia

BACKGROUND

Accurate diagnosis of Loa loa infection is essential to the success of mass drug administration efforts to eliminate onchocerciasis and lymphatic filariasis, due to the risk of fatal encephalopathic reactions to ivermectin occurring among highly microfilaremic Loa-infected individuals living in areas co-endemic for multiple filarial species.

METHODOLOGY/PRINCIPAL FINDINGS

From a pool of over 1,800 L. loa microfilaria (mf) expressed sequence tags, 18 candidate L. loa mf-specific PCR targets were identified. Real-time PCR (qPCR) assays were developed for two targets (LLMF72 and LLMF269). The qPCR assays were highly specific for L. loa compared with related filariae and also highly sensitive, with detection limits of 0.1 pg genomic DNA, or 1% of DNA extracted from normal blood spiked with a single L. loa microfilaria. Using various DNA extraction methods with dried blood spots obtained from Cameroonian subjects with parasitologically proven loiasis, the LLMF72 qPCR assay successfully estimated mf burden in 65 of 68 samples (50-96,000 mf/mL by microscopy), including all 12 samples subjected to a simple 10-minute boiling extraction. Additionally, the assay detected low-level microfilaremia among 5 of 16 samples from patients thought to be amicrofilaremic by microscopy.

CONCLUSIONS/SIGNIFICANCE

This novel, rapid, highly sensitive and specific qPCR assay is an important step forward in the laboratory diagnosis of L. loa infection.

Applications of electrowetting-based digital microfluidics in clinical diagnostics

Digital microfluidics based on electrowetting is a type of microfluidic platform in which liquids are processed as individual unit-sized droplets that are dispensed from a source, merged together, split apart or transported between locations on demand. These devices are implemented using arrays of surface electrodes to control the shape and position of droplets through the electrowetting effect. A major thrust of digital microfluidics research has been the development of integrated lab-on-a-chip devices to perform clinical in vitro diagnostic assays. A variety of preparatory and analytical processes have been implemented and feasibility has been demonstrated for test types ranging from clinical chemistries to immunoassays, nucleic acid tests and cell-based assays. In this article, the current state and future potential of digital microfluidics for clinical diagnostic testing is reviewed and evaluated.

Toward molecular parasitologic diagnosis: enhanced diagnostic sensitivity for filarial infections in mobile populations

The diagnosis of filarial infections among individuals residing in areas where the disease is not endemic requires both strong clinical suspicion and expert training in infrequently practiced parasitological methods. Recently developed filarial molecular diagnostic assays are highly sensitive and specific but have limited availability and have not been closely evaluated for clinical use outside populations residing in areas of endemicity. In this study, we assessed the performance of a panel of real-time PCR assays for the four most common human filarial pathogens among blood and tissue samples collected from a cohort of patients undergoing evaluation for suspected filarial infections. Compared to blood filtration, real-time PCR was equally sensitive for the detection of microfilaremia due to Wuchereria bancrofti (2 of 46 samples positive by both blood filtration and PCR with no discordant results) and Loa loa (24 of 208 samples positive by both blood filtration and PCR, 4 samples positive by PCR only, and 3 samples positive by blood filtration only). Real-time PCR of skin snip samples was significantly more sensitive than microscopic examination for the detection of Onchocerca volvulus microfiladermia (2 of 218 samples positive by both microscopy and PCR and 12 samples positive by PCR only). The molecular assays required smaller amounts of blood and tissue than conventional methods and could be performed by laboratory personnel without specialized parasitology training. Taken together, these data demonstrate the utility of the molecular diagnosis of filarial infections in mobile populations.