Enhanced microfiltration devices configured with hydrodynamic trapping and a rain drop bypass filtering architecture for microbial cells detection

Toward waterborne protozoa detection using sensing technologies

Drought and limited sufficient water resources will be the main challenges for humankind during the coming years. The lack of water resources for washing, bathing, and drinking increases the use of contaminated water and the risk of waterborne diseases. A considerable number of waterborne outbreaks are due to protozoan parasites that may remain active/alive in harsh environmental conditions. Therefore, a regular monitoring program of water resources using sensitive techniques is needed to decrease the risk of waterborne outbreaks. Wellorganized point-of-care (POC) systems with enough sensitivity and specificity is the holy grail of research for monitoring platforms. In this review, we comprehensively gathered and discussed rapid, selective, and easy-to-use biosensor and nanobiosensor technologies, developed for the early detection of common waterborne protozoa.

Microfluidics for Environmental Applications

Microfluidic and lab-on-a-chip systems have become increasingly important tools across many research fields in recent years. As a result of their small size and precise flow control, as well as their ability to enable in situ process visualization, microfluidic systems are increasingly finding applications in environmental science and engineering. Broadly speaking, their main present applications within these fields include use as sensors for water contaminant analysis (e.g., heavy metals and organic pollutants), as tools for microorganism detection (e.g., virus and bacteria), and as platforms for the investigation of environment-related problems (e.g., bacteria electron transfer and biofilm formation). This chapter aims to review the applications of microfluidics in environmental science and engineering - with a particular focus on the foregoing topics. The advantages and limitations of microfluidics when compared to traditional methods are also surveyed, and several perspectives on the future of research and development into microfluidics for environmental applications are offered.

Microfluidics-Based Organism Isolation from Whole Blood: An Emerging Tool for Bloodstream Infection Diagnosis

The diagnosis of bloodstream infections presents numerous challenges, in part, due to the low concentration of pathogens present in the peripheral bloodstream. As an alternative to existing time-consuming, culture-based diagnostic methods for organism identification, microfluidic devices have emerged as rapid, high-throughput and integrated platforms for bacterial and fungal enrichment, detection, and characterization. This focused review serves to highlight and compare the emerging microfluidic platforms designed for the isolation of sepsis-causing pathogens from blood and suggest important areas for future research.

Functionalized electrospun poly(vinyl alcohol) nanofibers for on-chip concentration of E. coli cells

Positively and negatively charged electrospun poly(vinyl alcohol) (PVA) nanofibers were incorporated into poly(methyl methacrylate) (PMMA) microchannels in order to facilitate on-chip concentration of Escherichia coli K12 cells. The effects of fiber distribution and fiber mat height on analyte retention were investigated. The 3D morphology of the mats was optimized to prevent size-related retention of the E. coli cells while also providing a large enough surface area for analyte concentration. Positively charged nanofibers produced an 87% retention and over 80-fold concentration of the bacterial cells by mere electrostatic interaction, while negatively charged nanofibers reduced nonspecific analyte retention when compared to an empty microfluidic channel. In order to take advantage of this reduction in nonspecific retention, these negatively charged nanofibers were then modified with anti-E. coli antibodies. These proof-of-principle experiments showed that antibody-functionalized negatively charged nanofiber mats were capable of the specific capture of 72% of the E. coli cells while also significantly reducing nonspecific analyte retention within the channel as expected. The ease of fabrication and immense surface area of the functionalized electrospun nanofibers make them a promising alternative for on-chip concentration of analytes. The pore size and fiber mat morphology, as well as surface functionality of the fibers, can be tailored to allow for specific capture and concentration of a wide range of analytes.

Microfluidics for effective concentration and sorting of waterborne protozoan pathogens

We report on an inertial focussing based microfluidics technology for concentrating waterborne protozoa, achieving a 96% recovery rate of Cryptosporidium parvum and 86% for Giardia lamblia at a throughput (mL/min) capable of replacing centrifugation. The approach can easily be extended to other parasites and also bacteria.

Agarose-based microfluidic device for point-of-care concentration and detection of pathogen

Preconcentration of pathogens from patient samples represents a great challenge in point-of-care (POC) diagnostics. Here, a low-cost, rapid, and portable agarose-based microfluidic device was developed to concentrate biological fluid from micro- to picoliter volume. The microfluidic concentrator consisted of a glass slide simply covered by an agarose layer with a binary tree-shaped microchannel, in which pathogens could be concentrated at the end of the microchannel due to the capillary effect and the strong water permeability of the agarose gel. The fluorescent Escherichia coli strain OP50 was used to demonstrate the capacity of the agarose-based device. Results showed that 90% recovery efficiency could be achieved with a million-fold volume reduction from 400 μL to 400 pL. For concentration of 1 × 10(3) cells mL(-1) bacteria, approximately ten million-fold enrichment in cell density was realized with volume reduction from 100 μL to 1.6 pL. Urine and blood plasma samples were further tested to validate the developed method. In conjugation with fluorescence immunoassay, we successfully applied the method to the concentration and detection of infectious Staphylococcus aureus in clinics. The agarose-based microfluidic concentrator provided an efficient approach for POC detection of pathogens.

Focusing of sub-micrometer particles and bacteria enabled by two-dimensional acoustophoresis

Handling of sub-micrometer bioparticles such as bacteria are becoming increasingly important in the biomedical field and in environmental and food analysis. As a result, there is an increased need for less labor-intensive and time-consuming handling methods. Here, an acoustophoresis-based microfluidic chip that uses ultrasound to focus sub-micrometer particles and bacteria, is presented. The ability to focus sub-micrometer bioparticles in a standing one-dimensional acoustic wave is generally limited by the acoustic-streaming-induced drag force, which becomes increasingly significant the smaller the particles are. By using two-dimensional acoustic focusing, i.e. focusing of the sub-micrometer particles both horizontally and vertically in the cross section of a microchannel, the acoustic streaming velocity field can be altered to allow focusing. Here, the focusability of E. coli and polystyrene particles as small as 0.5 μm in diameter in microchannels of square or rectangular cross sections, is demonstrated. Numerical analysis was used to determine generic transverse particle trajectories in the channels, which revealed spiral-shaped trajectories of the sub-micrometer particles towards the center of the microchannel; this was also confirmed by experimental observations. The ability to focus and enrich bacteria and other sub-micrometer bioparticles using acoustophoresis opens the research field to new microbiological applications.

Application of microfluidics in waterborne pathogen monitoring: a review

A review of the recent advances in microfluidics based systems for the monitoring of waterborne pathogens is provided in this article. Emphasis has been made on existing, commercial and state-of-the-art systems and research activities in laboratories worldwide. The review separates sample processing systems and monitoring systems, highlighting the slow progress made in automated sample processing for monitoring of pathogens in waterworks and in the field. Future potential directions of research are also highlighted in the conclusions.

Integrated sorting, concentration and real time PCR based detection system for sensitive detection of microorganisms

The extremely low limit of detection (LOD) posed by global food and water safety standards necessitates the need to perform a rapid process of integrated detection with high specificity, sensitivity and repeatability. The work reported in this article shows a microchip platform which carries out an ensemble of protocols which are otherwise carried in a molecular biology laboratory to achieve the global safety standards. The various steps in the microchip include pre-concentration of specific microorganisms from samples and a highly specific real time molecular identification utilizing a q-PCR process. The microchip process utilizes a high sensitivity antibody based recognition and an electric field mediated capture enabling an overall low LOD. The whole process of counting, sorting and molecular identification is performed in less than 4 hours for highly dilute samples.

A Disposable Microfluidic Virus Concentration Device Based on Evaporation and Interfacial Tension

We report a disposable and highly effective polymeric microfluidic viral sample concentration device capable of increasing the concentration of virus in a human nasopharyngeal specimen more than one order of magnitude in less than 30 min without the use of a centrifuge. The device is fabricated using 3D maskless xurography method using commercially available polymeric materials, which require no cleanroom operations. The disposable components can be fabricated and assembled in five minutes. The device can concentrate a few milliliters (mL) of influenza virus in solution from tissue culture or clinical nasopharyngeal swab specimens, via reduction of the fluid volume, to tens of microliters μL). The performance of the device was evaluated by nucleic acid extraction from the concentrated samples, followed by a real-time quantitative polymerase chain reaction (qRT-PCR). The viral RNA concentration in each sample was increased on average over 10-fold for both cultured and patient specimens compared to the starting samples, with recovery efficiencies above 60% for all input concentrations. Highly concentrated samples in small fluid volumes can increase the downstream process speed of on-chip nucleic acid extraction, and result in improvements in the sensitivity of many diagnostic platforms that interrogate small sample volumes.

Cell separation based on size and deformability using microfluidic funnel ratchets

The separation of biological cells by filtration through microstructured constrictions is limited by unpredictable variations of the filter hydrodynamic resistance as cells accumulate in the microstructure. Applying a reverse flow to unclog the filter will undo the separation and reduce filter selectivity because of the reversibility of low-Reynolds number flow. We introduce a microfluidic structural ratchet mechanism to separate cells using oscillatory flow. Using model cells and microparticles, we confirmed the ability of this mechanism to sort and separate cells and particles based on size and deformability. We further demonstrate that the spatial distribution of cells after sorting is repeatable and that the separation process is irreversible. This mechanism can be applied generally to separate cells that differ based on size and deformability.

Detection of Cryptosporidium in miniaturised fluidic devices

Contamination of drinking water with the protozoan pathogen, Cryptosporidium, represents a serious risk to human health due to the low infectious dose and the resistance of this parasite to chlorine disinfection. Therefore, several countries have legislated for the frequent monitoring of drinking water for Cryptosporidium presence. Existing approved monitoring protocols are however time-consuming and do not provide essential information on the species, virulence or viability of detected oocysts. Rapid, more information-rich and automatable systems for Cryptosporidium detection are highly sought-after, and numerous miniaturised devices have been developed to address this need. This review article aims to summarise the state-of-the-art and compare the performance of these systems in terms of detection limit, ability to determine species, viability and performance in the presence of interferents. Finally, conclusions are drawn with regard to the most promising methods and directions of future research.

Rapid point-of-care concentration of bacteria in a disposable microfluidic device using meniscus dragging effect

We report a low cost, disposable polymer microfluidic sample preparation device to perform rapid concentration of bacteria from liquid samples using enhanced evaporation targeted at downstream detection using surface enhanced Raman spectroscopy (SERS). The device is composed of a poly(dimethylsiloxane) (PDMS) liquid sample flow layer, a reusable metal airflow layer, and a porous PTFE (Teflon™) membrane sandwiched in between the liquid and air layers. The concentration capacity of the device was successfully demonstrated with fluorescently tagged Escherichia coli (E. coli). The recovery concentration was above 85% for all initial concentrations lower than 1 × 10(4) CFU mL(-1). In the lowest initial concentration cases, 100 µL initial volumes of bacteria solution at 100 CFU mL(-1) were concentrated into 500 nL droplets with greater than 90% efficiency in 15 min. Subsequent tests with SERS on clinically relevant Methicillin-Sensitive Staphylococcus aureus (MSSA) after concentration in this device proved more than 100-fold enhancement in SERS signal intensity compared to the signal obtained from the unconcentrated sample. The concentration device is straightforward to design and use, and as such could be used in conjunction with a number of detection technologies.

A new method for simulating the motion of individual ellipsoidal bacteria in microfluidic devices

To successfully perform biological experiments on bacteria in microfluidic devices, control of micron-scale cell motion in the chip-sized environment is essential. Here we describe a new method for simulating the motion of individual bacterial cells in a microfluidic device using a one-way coupling Lagrangian approach combined with rigid body theory. The cell was assumed to be an elastic, solid ellipsoid, and interactions with solid wall boundaries were considered to occur in one of two collision modes, either a "standing" or "lying" collision mode on the surface. The ordinary differential equations were solved along the cell trajectory for the thirteen unknown variables of the translational cell velocity, cell location vector, rotational angular velocity, and four Euler parameters, using the Rosenbrock method based on an adaptive time-stepping technique. As selected applications, we show how this novel simulation method may be applied to the designs of efficient hydrodynamic cell traps in a microfluidic device for bacterial applications and for cell separations. Modeled designs include optimized U-shaped sieve arrays with a single aperture for the hydrodynamic cell trapping, and three kinds of staggered micropillars for cell separations.

Size-Dependent Filtration and Trapping of Microparticles in a Microfluidic Chip Using Graduated Gaps and Centrifugal Force

We proposed size-dependent microparticle filtration and trapping using graduated microchannel gaps and centrifugal force using a three-dimensional magnetically driven microtool (3D-MMT) in a microfluidic chip made of polydimethylsiloxane (PDMS). Our paper contributes the following to the field: (1) Particle filtration is robust against pressure fluctuation due to tube vibration between the chip and pump. (2) Clogging by microparticles is avoided by rotating the 3D-MMT in a microchamber. (3) Size-classified microparticles are trapped by flow control along microchannel gaps. Different-sized microparticles flow in spiral microchannels and are filtered based on size between gaps and the substrate by centrifugal force. Microparticles larger than gaps remain in the inner microchannel. Rotating the 3D-MMT using an external magnetic circuit generates swirling flow in the microchamber. Size-classified microparticles are trapped in microchannels by closing the drain port for the targeted particle. Trapped particles are measured by direct observation and treated by reagent. After experiments, trapped particles are extracted by opening drain ports. We demonstrated microparticle filtration and microparticle trapping in the microfluidic chip.

An overview of recent strategies in pathogen sensing

Pathogenic bacteria are one of the major concerns in food industries and water treatment facilities because of their rapid growth and deleterious effects on human health. The development of fast and accurate detection and identification systems for bacterial strains has long been an important issue to researchers. Although confirmative for the identification of bacteria, conventional methods require time-consuming process involving either the test of characteristic metabolites or cellular reproductive cycles. In this paper, we review recent sensing strategies based on micro- and nano-fabrication technology. These technologies allow for a great improvement of detection limit, therefore, reduce the time required for sample preparation. The paper will be focused on newly developed nano- and micro-scaled biosensors, novel sensing modalities utilizing microfluidic lab-on-a-chip, and array technology for the detection of pathogenic bacteria.

The application of on-chip optofluidic microscopy for imaging Giardia lamblia trophozoites and cysts

The optofluidic microscope (OFM) is a lensless, low-cost and highly compact on-chip device that can enable high-resolution microscopy imaging. The OFM performs imaging by flowing/scanning the target objects across a slanted hole array; by measuring the time-varying light transmission changes through the holes, we can then render images of the target objects at a resolution that is comparable to the holes' size. This paper reports the adaptation of the OFM for imaging Giardia lamblia trophozoites and cysts, a disease-causing parasite species that is commonly found in poor-quality water sources. We also describe our study of the impact of pressure-based flow and DC electrokinetic-based flow in controlling the flow motion of Giardia cysts--rotation-free translation of the parasite is important for good OFM image acquisition. Finally, we report the successful microscopy imaging of both Giardia trophozoites and cysts with an OFM that has a focal plane resolution of 0.8 microns.