Showing papers in "Lab on a Chip in 2013"

Paper-based microfluidic point-of-care diagnostic devices

Abstract: Dipstick and lateral-flow formats have dominated rapid diagnostics over the last three decades. These formats gained popularity in the consumer markets due to their compactness, portability and facile interpretation without external instrumentation. However, lack of quantitation in measurements has challenged the demand of existing assay formats in consumer markets. Recently, paper-based microfluidics has emerged as a multiplexable point-of-care platform which might transcend the capabilities of existing assays in resource-limited settings. However, paper-based microfluidics can enable fluid handling and quantitative analysis for potential applications in healthcare, veterinary medicine, environmental monitoring and food safety. Currently, in its early development stages, paper-based microfluidics is considered a low-cost, lightweight, and disposable technology. The aim of this review is to discuss: (1) fabrication of paper-based microfluidic devices, (2) functionalisation of microfluidic components to increase the capabilities and the performance, (3) introduction of existing detection techniques to the paper platform and (4) exploration of extracting quantitative readouts via handheld devices and camera phones. Additionally, this review includes challenges to scaling up, commercialisation and regulatory issues. The factors which limit paper-based microfluidic devices to become real world products and future directions are also identified.

Surface acoustic wave microfluidics

Abstract: The recent introduction of surface acoustic wave (SAW) technology onto lab-on-a-chip platforms has opened a new frontier in microfluidics. The advantages provided by such SAW microfluidics are numerous: simple fabrication, high biocompatibility, fast fluid actuation, versatility, compact and inexpensive devices and accessories, contact-free particle manipulation, and compatibility with other microfluidic components. We believe that these advantages enable SAW microfluidics to play a significant role in a variety of applications in biology, chemistry, engineering and medicine. In this review article, we discuss the theory underpinning SAWs and their interactions with particles and the contacting fluids in which they are suspended. We then review the SAW-enabled microfluidic devices demonstrated to date, starting with devices that accomplish fluid mixing and transport through the use of travelling SAW; we follow that by reviewing the more recent innovations achieved with standing SAW that enable such actions as particle/cell focusing, sorting and patterning. Finally, we look forward and appraise where the discipline of SAW microfluidics could go next.

Engineering of functional, perfusable 3D microvascular networks on a chip

Abstract: Generating perfusable 3D microvessels in vitro is an important goal for tissue engineering, as well as for reliable modelling of blood vessel function. To date, in vitro blood vessel models have not been able to accurately reproduce the dynamics and responses of endothelial cells to grow perfusable and functional 3D vascular networks. Here we describe a microfluidic-based platform whereby we model natural cellular programs found during normal development and angiogenesis to form perfusable networks of intact 3D microvessels as well as tumor vasculatures based on the spatially controlled co-culture of endothelial cells with stromal fibroblasts, pericytes or cancer cells. The microvessels possess the characteristic morphological and biochemical markers of in vivo blood vessels, and exhibit strong barrier function and long-term stability. An open, unobstructed microvasculature allows the delivery of nutrients, chemical compounds, biomolecules and cell suspensions, as well as flow-induced mechanical stimuli into the luminal space of the endothelium, and exhibits faithful responses to physiological shear stress as demonstrated by cytoskeleton rearrangement and increased nitric oxide synthesis. This simple and versatile platform provides a wide range of applications in vascular physiology studies as well as in developing vascularized organ-on-a-chip and human disease models for pharmaceutical screening.

Microfluidic heart on a chip for higher throughput pharmacological studies

Abstract: We present the design of a higher throughput “heart on a chip” which utilizes a semi-automated fabrication technique to process sub millimeter sized thin film cantilevers of soft elastomers. Anisotropic cardiac microtissues which recapitulate the laminar architecture of the heart ventricle are engineered on these cantilevers. Deflection of these cantilevers, termed Muscular Thin Films (MTFs), during muscle contraction allows calculation of diastolic and systolic stresses generated by the engineered tissues. We also present the design of a reusable one channel fluidic microdevice completely built out of autoclavable materials which incorporates various features required for an optical cardiac contractility assay: metallic base which fits on a heating element for temperature control, transparent top for recording cantilever deformation and embedded electrodes for electrical field stimulation of the tissue. We employ the microdevice to test the positive inotropic effect of isoproterenol on cardiac contractility at dosages ranging from 1 nM to 100 μM. The higher throughput fluidic heart on a chip has applications in testing of cardiac tissues built from rare or expensive cell sources and for integration with other organ mimics. These advances will help alleviate translational barriers for commercial adoption of these technologies by improving the throughput and reproducibility of readout, standardization of the platform and scalability of manufacture.

A dynamic multi-organ-chip for long-term cultivation and substance testing proven by 3D human liver and skin tissue co-culture

Abstract: Current in vitro and animal tests for drug development are failing to emulate the systemic organ complexity of the human body and, therefore, to accurately predict drug toxicity. In this study, we present a multi-organ-chip capable of maintaining 3D tissues derived from cell lines, primary cells and biopsies of various human organs. We designed a multi-organ-chip with co-cultures of human artificial liver microtissues and skin biopsies, each a 1/100 000 of the biomass of their original human organ counterparts, and have successfully proven its long-term performance. The system supports two different culture modes: i) tissue exposed to the fluid flow, or ii) tissue shielded from the underlying fluid flow by standard Transwell® cultures. Crosstalk between the two tissues was observed in 14-day co-cultures exposed to fluid flow. Applying the same culture mode, liver microtissues showed sensitivity at different molecular levels to the toxic substance troglitazone during a 6-day exposure. Finally, an astonishingly stable long-term performance of the Transwell®-based co-cultures could be observed over a 28-day period. This mode facilitates exposure of skin at the air–liquid interface. Thus, we provide here a potential new tool for systemic substance testing.

Fundamentals of inertial focusing in microchannels

Abstract: Inertial microfluidics has been attracting considerable interest in recent years due to immensely promising applications in cell biology. Despite the intense attention, the primary focus has been on development of inertial microfluidic devices with less emphasis paid to elucidation of the inertial focusing mechanics. The incomplete understanding, and sometimes confusing experimental results that indicate a different number of focusing positions in square or rectangular microchannels under similar flow conditions, have led to poor guidelines and difficulties in design of inertial microfluidic systems. In this work, we describe and experimentally validate a two-stage model inertial focusing in microchannels. Our analysis and experimental results show that not only the well-accepted shear-induced and wall-induced lift forces act on particles within flow causing equilibration near microchannel sidewalls, but the rotation-induced lift force influences the position of these equilibria. In addition, for the first time, we experimentally measure lift coefficients, which previously could only be obtained from numerical simulations. More importantly, insights offered by our two-stage model of inertial focusing are broadly applicable to cross-sectional geometries beyond rectangular. With elucidation of the equilibration mechanism, we envision better guidelines for the inertial microfluidics community, ultimately leading to improved performance and broader acceptance of the inertial microfluidic devices in a wide range of applications, from filtration to cell separations.

Smartphone based health accessory for colorimetric detection of biomarkers in sweat and saliva

Abstract: The mobile health market is rapidly expanding and portable diagnostics tools offer an opportunity to decrease costs and increase the availability of healthcare. Here we present a smartphone based accessory and method for the rapid colorimetric detection of pH in sweat and saliva. Sweat pH can be correlated to sodium concentration and sweat rate in order to indicate to users the proper time to hydrate during physical exercise and avoid the risk of muscle cramps. Salivary pH below a critical threshold is correlated with enamel decalcification, an acidic breakdown of calcium in the teeth. We conduct a number of human trials with the device on a treadmill to demonstrate the ability to monitor changes in sweat pH due to exercise and electrolyte intake and predict optimal hydration. Additionally, we perform trials to measure salivary pH over time to monitor the effects of diet on oral health risks.

Microfluidic methods for forming liposomes

Abstract: Liposome structures have a wide range of applications in biology, biochemistry, and biophysics. As a result, several methods for forming liposomes have been developed. This review provides a critical comparison of existing microfluidic technologies for forming liposomes and, when applicable, a comparison with their analogous macroscale counterparts. The properties of the generated liposomes, including size, size distribution, lamellarity, membrane composition, and encapsulation efficiency, form the basis for comparison. We hope that this critique will allow the reader to make an informed decision as to which method should be used for a given biological application.

Label-free biodetection using a smartphone

Abstract: Utilizing its integrated camera as a spectrometer, we demonstrate the use of a smartphone as the detection instrument for a label-free photonic crystal biosensor. A custom-designed cradle holds the smartphone in fixed alignment with optical components, allowing for accurate and repeatable measurements of shifts in the resonant wavelength of the sensor. Externally provided broadband light incident upon an entrance pinhole is subsequently collimated and linearly polarized before passing through the biosensor, which resonantly reflects only a narrow band of wavelengths. A diffraction grating spreads the remaining wavelengths over the camera's pixels to display a high resolution transmission spectrum. The photonic crystal biosensor is fabricated on a plastic substrate and attached to a standard glass microscope slide that can easily be removed and replaced within the optical path. A custom software app was developed to convert the camera images into the photonic crystal transmission spectrum in the visible wavelength range, including curve-fitting analysis that computes the photonic crystal resonant wavelength with 0.009 nm accuracy. We demonstrate the functionality of the system through detection of an immobilized protein monolayer, and selective detection of concentration-dependent antibody binding to a functionalized photonic crystal. We envision the capability for an inexpensive, handheld biosensor instrument with web connectivity to enable point-of-care sensing in environments that have not been practical previously.

Ciliated micropillars for the microfluidic-based isolation of nanoscale lipid vesicles

Abstract: We fabricated a microfluidic device consisting of ciliated micropillars, forming a porous silicon nanowire-on-micropillar structure. We demonstrated that the prototype device can preferentially trap exosome-like lipid vesicles, while simultaneously filtering out proteins and cell debris. Trapped lipid vesicles can be recovered intact by dissolving the porous nanowires in PBS buffer.

SyM-BBB: A Microfluidic Blood Brain Barrier Model

Abstract: Current techniques for mimicking the Blood-Brain Barrier (BBB) largely use incubation chambers (Transwell) separated with a filter and matrix coating to represent and to study barrier permeability. These devices have several critical shortcomings: (a) they do not reproduce critical microenvironmental parameters, primarily anatomical size or hemodynamic shear stress, (b) they often do not provide real-time visualization capability, and (c) they require a large amount of consumables. To overcome these limitations, we have developed a microfluidics based Synthetic Microvasculature model of the Blood-Brain Barrier (SyM-BBB). The SyM-BBB platform is comprised of a plastic, disposable and optically clear microfluidic chip with a microcirculation sized two-compartment chamber. The chamber is designed in such a way as to permit the realization of side-by-side apical and basolateral compartments, thereby simplifying fabrication and facilitating integration with standard instrumentation. The individually addressable apical side is seeded with endothelial cells and the basolateral side can support neuronal cells or conditioned media. In the present study, an immortalized Rat Brain Endothelial cell line (RBE4) was cultured in SyM-BBB with a perfusate of Astrocyte Conditioned Media (ACM). Biochemical analysis showed upregulation of tight junction molecules while permeation studies showed an intact BBB. Finally, transporter assay was successfully demonstrated in SyM-BBB indicating a functional model.

Optical imaging techniques for point-of-care diagnostics

Abstract: Improving access to effective and affordable healthcare has long been a global endeavor. In this quest, the development of cost-effective and easy-to-use medical testing equipment that enables rapid and accurate diagnosis is essential to reduce the time and costs associated with healthcare services. To this end, point-of-care (POC) diagnostics plays a crucial role in healthcare delivery in both developed and developing countries by bringing medical testing to patients, or to sites near patients. As the diagnosis of a wide range of diseases, including various types of cancers and many endemics, relies on optical techniques, numerous compact and cost-effective optical imaging platforms have been developed in recent years for use at the POC. Here, we review the state-of-the-art optical imaging techniques that can have a significant impact on global health by facilitating effective and affordable POC diagnostics.

Simple, distance-based measurement for paper analytical devices

Abstract: Paper-based analytical devices (PADs) represent a growing class of elegant, yet inexpensive chemical sensor technologies designed for point-of-use applications. Most PADs, however, still utilize some form of instrumentation such as a camera for quantitative detection. We describe here a simple technique to render PAD measurements more quantitative and straightforward using the distance of colour development as a detection motif. The so-called distance-based detection enables PAD chemistries that are more portable and less resource intensive compared to classical approaches that rely on the use of peripheral equipment for quantitative measurement. We demonstrate the utility and broad applicability of this technique with measurements of glucose, nickel, and glutathione using three different detection chemistries: enzymatic reactions, metal complexation, and nanoparticle aggregation, respectively. The results show excellent quantitative agreement with certified standards in complex sample matrices. This work provides the first demonstration of distance-based PAD detection with broad application as a class of new, inexpensive sensor technologies designed for point-of-use applications.

Cost-effective and rapid blood analysis on a cell-phone

Abstract: We demonstrate a compact and cost-effective imaging cytometry platform installed on a cell-phone for the measurement of the density of red and white blood cells as well as hemoglobin concentration in human blood samples. Fluorescent and bright-field images of blood samples are captured using separate optical attachments to the cell-phone and are rapidly processed through a custom-developed smart application running on the phone for counting of blood cells and determining hemoglobin density. We evaluated the performance of this cell-phone based blood analysis platform using anonymous human blood samples and achieved comparable results to a standard bench-top hematology analyser. Test results can either be stored on the cell-phone memory or be transmitted to a central server, providing remote diagnosis opportunities even in field settings.

A PDMS/paper/glass hybrid microfluidic biochip integrated with aptamer-functionalized graphene oxide nano-biosensors for one-step multiplexed pathogen detection

Abstract: Infectious pathogens often cause serious public health concerns throughout the world. There is an increasing demand for simple, rapid and sensitive approaches for multiplexed pathogen detection. In this paper we have developed a polydimethylsiloxane (PDMS)/paper/glass hybrid microfluidic system integrated with aptamer-functionalized graphene oxide (GO) nano-biosensors for simple, one-step, multiplexed pathogen detection. The paper substrate used in this hybrid microfluidic system facilitated the integration of aptamer biosensors on the microfluidic biochip, and avoided complicated surface treatment and aptamer probe immobilization in a PDMS or glass-only microfluidic system. Lactobacillus acidophilus was used as a bacterium model to develop the microfluidic platform with a detection limit of 11.0 cfu mL−1. We have also successfully extended this method to the simultaneous detection of two infectious pathogens - Staphylococcus aureus and Salmonella enterica. This method is simple and fast. The one-step ‘turn on’ pathogen assay in a ready-to-use microfluidic device only takes ∼10 min to complete on the biochip. Furthermore, this microfluidic device has great potential in rapid detection of a wide variety of different other bacterial and viral pathogens.

Scaling and systems biology for integrating multiple organs-on-a-chip

Abstract: Coupled systems of in vitro microfabricated organs-on-a-chip containing small populations of human cells are being developed to address the formidable pharmacological and physiological gaps between monolayer cell cultures, animal models, and humans that severely limit the speed and efficiency of drug development. These gaps present challenges not only in tissue and microfluidic engineering, but also in systems biology: how does one model, test, and learn about the communication and control of biological systems with individual organs-on-chips that are one-thousandth or one-millionth of the size of adult organs, or even smaller, i.e., organs for a milliHuman (mHu) or microHuman (μHu)? Allometric scaling that describes inter-species variation of organ size and properties provides some guidance, but given the desire to utilize these systems to extend and validate human pharmacokinetic and pharmacodynamic (PK/PD) models in support of drug discovery and development, it is more appropriate to scale each organ functionally to ensure that it makes the suitable physiological contribution to the coupled system. The desire to recapitulate the complex organ–organ interactions that result from factors in the blood and lymph places a severe constraint on the total circulating fluid (∼5 mL for a mHu and ∼5 μL for a μHu) and hence on the pumps, valves, and analytical instruments required to maintain and study these systems. Scaling arguments also provide guidance on the design of a universal cell-culture medium, typically without red blood cells. This review presents several examples of scaling arguments and discusses steps that should ensure the success of this endeavour.

Dissolvable fluidic time delays for programming multi-step assays in instrument-free paper diagnostics

Abstract: Lateral flow tests (LFTs) are an ingenious format for rapid and easy-to-use diagnostics, but they are fundamentally limited to assay chemistries that can be reduced to a single chemical step. In contrast, most laboratory diagnostic assays rely on multiple timed steps carried out by a human or a machine. Here, we use dissolvable sugar applied to paper to create programmable flow delays and present a paper network topology that uses these time delays to program automated multi-step fluidic protocols. Solutions of sucrose at different concentrations (10-70% of saturation) were added to paper strips and dried to create fluidic time delays spanning minutes to nearly an hour. A simple folding card format employing sugar delays was shown to automate a four-step fluidic process initiated by a single user activation step (folding the card); this device was used to perform a signal-amplified sandwich immunoassay for a diagnostic biomarker for malaria. The cards are capable of automating multi-step assay protocols normally used in laboratories, but in a rapid, low-cost, and easy-to-use format.

A personalized food allergen testing platform on a cellphone.

Abstract: We demonstrate a personalized food allergen testing platform, termed iTube, running on a cellphone that images and automatically analyses colorimetric assays performed in test tubes toward sensitive and specific detection of allergens in food samples This cost-effective and compact iTube attachment, weighing approximately 40 grams, is mechanically installed on the existing camera unit of a cellphone, where the test and control tubes are inserted from the side and are vertically illuminated by two separate light-emitting-diodes The illumination light is absorbed by the allergen assay, which is activated within the tubes, causing an intensity change in the acquired images by the cellphone camera These transmission images of the sample and control tubes are digitally processed within 1 s using a smart application running on the same cellphone for detection and quantification of allergen contamination in food products We evaluated the performance of this cellphone-based iTube platform using different types of commercially available cookies, where the existence of peanuts was accurately quantified after a sample preparation and incubation time of ∼20 min per test This automated and cost-effective personalized food allergen testing tool running on cellphones can also permit uploading of test results to secure servers to create personal and/or public spatio-temporal allergen maps, which can be useful for public health in various settings

Recent advances in microfluidic techniques for single-cell biophysical characterization

Abstract: Biophysical (mechanical and electrical) properties of living cells have been proven to play important roles in the regulation of various biological activities at the molecular and cellular level, and can serve as promising label-free markers of cells' physiological states. In the past two decades, a number of research tools have been developed for understanding the association between the biophysical property changes of biological cells and human diseases; however, technical challenges of realizing high-throughput, robust and easy-to-perform measurements on single-cell biophysical properties have yet to be solved. In this paper, we review emerging tools enabled by microfluidic technologies for single-cell biophysical characterization. Different techniques are compared. The technical details, advantages, and limitations of various microfluidic devices are discussed.

Rapid electrochemical detection on a mobile phone

Abstract: We present a compact mobile phone platform for rapid, quantitative biomolecular detection. This system consists of an embedded circuit for signal processing and data analysis, and disposable microfluidic chips for fluidic handling and biosensing. Capillary flow is employed for sample loading, processing, and pumping to enhance operational portability and simplicity. Graphical step-by-step instructions displayed on the phone assists the operator through the detection process. After the completion of each measurement, the results are displayed on the screen for immediate assessment and the data is automatically saved to the phone's memory for future analysis and transmission. Validation of this device was carried out by detecting Plasmodium falciparum histidine-rich protein 2 (PfHRP2), an important biomarker for malaria, with a lower limit of detection of 16 ng mL(-1) in human serum. The simple detection process can be carried out with two loading steps and takes 15 min to complete each measurement. Due to its compact size and high performance, this device offers immense potential as a widely accessible, point-of-care diagnostic platform, especially in remote and rural areas. In addition to its impact on global healthcare, this technology is relevant to other important applications including food safety, environmental monitoring and biosecurity.

Spheroid-based three-dimensional liver-on-a-chip to investigate hepatocyte-hepatic stellate cell interactions and flow effects.

Abstract: We have developed a three-dimensional (3D) liver-on-a-chip to investigate the interaction of hepatocytes and hepatic stellate cells (HSCs) in which primary 3D hepatocyte spheroids and HSCs are co-cultured without direct cell–cell contact. Here, we show that the 3D liver chip offers substantial advantages for the formation and harvesting of spheroids. The most important feature of this liver chip is that it enables continuous flow of medium to the cells through osmotic pumping, and thus requires only minimal handling and no external power source. We also demonstrate that flow assists the formation and long-term maintenance of spheroids. Additionally, we quantitatively and qualitatively investigated the paracrine effects of HSCs, demonstrating that HSCs assist in the maintenance of hepatocyte spheroids and play an important role in the formation of tight cell–cell contacts, thereby improving liver-specific function. Spheroids derived from co-cultures exhibited improved albumin and urea secretion rates compared to mono-cultured spheroids after 9 days. Immunostaining for cytochrome P450 revealed that the enzymatic activity of spheroids co-cultured for 8 days was greater than that of mono-cultured spheroids. These results indicate that this system has the potential for further development as a unique model for studying cellular interactions or as a tool that can be incorporated into other models aimed at creating hepatic structure and prolonging hepatocyte function in culture.

Probing cellular heterogeneity in cytokine-secreting immune cells using droplet-based microfluidics

Abstract: Here, we present a platform to detect cytokine (IL-2, IFN-γ, TNF-α) secretion of single, activated T-cells in droplets over time. We use a novel droplet-based microfluidic approach to encapsulate cells in monodisperse agarose droplets together with functionalized cytokine-capture beads for subsequent binding and detection of secreted cytokines from single cells. This method allows high-throughput detection of cellular heterogeneity and maps subsets within cell populations with specific functions.

Microfluidic platforms for mechanobiology

Abstract: Mechanotransduction has been a topic of considerable interest since early studies demonstrated a link between mechanical force and biological response. Until recently, studies of fundamental phenomena were based either on in vivo experiments with limited control or direct access, or on large-scale in vitro studies lacking many of the potentially important physiological factors. With the advent of microfluidics, many of the previous limitations of in vitro testing were eliminated or reduced through greater control or combined functionalities. At the same time, imaging capabilities were tremendously enhanced. In this review, we discuss how microfluidics has transformed the study of mechanotransduction. This is done in the context of the various cell types that exhibit force-induced responses and the new biological insights that have been elucidated. We also discuss new microfluidic studies that could produce even more realistic models of in vivo conditions by combining multiple stimuli or creating a more realistic microenvironment.

Skin and hair on-a-chip: in vitro skin models versus ex vivo tissue maintenance with dynamic perfusion

Abstract: Substantial progress has been achieved over the last few decades in the development of skin equivalents to model the skin as an organ. However, their static culture still limits the emulation of essential physiological properties crucial for toxicity testing and compound screening. Here, we describe a dynamically perfused chip-based bioreactor platform capable of applying variable mechanical shear stress and extending culture periods. This leads to improvements of culture conditions for integrated in vitro skin models, ex vivo skin organ cultures and biopsies of single hair follicular units.

Microfabricated Mammalian Organ Systems and Their Integration into Models of Whole Animals and Humans

Abstract: While in vitro cell based systems have been an invaluable tool in biology, they often suffer from a lack of physiological relevance. The discrepancy between the in vitro and in vivo systems has been a bottleneck in drug development process and biological sciences. The recent progress in microtechnology has enabled manipulation of cellular environment at a physiologically relevant length scale, which has led to the development of novel in vitro organ systems, often termed ‘organ-on-a-chip’ systems. By mimicking the cellular environment of in vivo tissues, various organ-on-a-chip systems have been reported to reproduce target organ functions better than conventional in vitro model systems. Ultimately, these organ-on-a-chip systems will converge into multi-organ ‘body-on-a-chip’ systems composed of functional tissues that reproduce the dynamics of the whole-body response. Such microscale in vitro systems will open up new possibilities in medical science and in the pharmaceutical industry.

An acoustofluidic micromixer based on oscillating sidewall sharp-edges.

Abstract: Rapid and homogeneous mixing inside a microfluidic channel is demonstrated via the acoustic streaming phenomenon induced by the oscillation of sidewall sharp-edges. By optimizing the design of the sharp-edges, excellent mixing performance and fast mixing speed can be achieved in a simple device, making our sharp-edge-based acoustic micromixer a promising candidate for a wide variety of applications.

Development of automated paper-based devices for sequential multistep sandwich enzyme-linked immunosorbent assays using inkjet printing

Abstract: To the best of our knowledge, this is the first report on paper-based devices for automating the sequential multistep procedures of a sandwich-type enzyme-linked immunosorbent assay (ELISA) that require only a single-step application of the sample solution. The device was based on a piece of nitrocellulose (NC) membrane with specially designed channels, where all the reagents are applied at different locations in order to control the fluid travel to the detection region. The inkjet printing method, a simple and low-cost process, was used to create the flow channel and device barrier patterns. The fabricated barrier was found to be an efficient boundary for the liquid along the printed design in the NC membrane, enabling direct control of the reagent flow time. ELISA results were obtained with a single-step sample application. The developed devices (so-called automated paper-based devices) provided a simple procedure for the sandwich ELISA, while reducing assay time and reagent consumption. Colorimetric results were measured using digital camera imaging with software processing. The capability of the method developed herein was successfully used to determine the levels of human chorionic gonadotropin (hCG) by ELISA.

Smartphone quantifies Salmonella from paper microfluidics

Abstract: Smartphone-based optical detection is a potentially easy-to-use, handheld, true point-of-care diagnostic tool for the early and rapid detection of pathogens. Paper microfluidics is a low-cost, field-deployable, and easy-to-use alternative to conventional microfluidic devices. Most paper-based microfluidic assays typically utilize dyes or enzyme–substrate binding, while bacterial detection on paper microfluidics is rare. We demonstrate a novel application of smartphone-based detection of Salmonella on paper microfluidics. Each paper microfluidic channel was pre-loaded with anti-Salmonella Typhimurium and anti-Escherichia coli conjugated submicroparticles. Dipping the paper microfluidic device into the Salmonella solutions led to the antibody-conjugated particles that were still confined within the paper fibers to immunoagglutinate. The extent of immunoagglutination was quantified by evaluating Mie scattering from the digital images taken at an optimized angle and distance with a smartphone. A smartphone application was designed and programmed to allow the user to position the smartphone at an optimized angle and distance from the paper microfluidic device, and a simple image processing algorithm was implemented to calculate and display the bacterial concentration on the smartphone. The detection limit was single-cell-level and the total assay time was less than one minute.

Liver-cell patterning lab chip: mimicking the morphology of liver lobule tissue.

Abstract: A lobule-mimetic cell-patterning technique for on-chip reconstruction of centimetre-scale liver tissue of heterogeneous hepatic and endothelial cells via an enhanced field-induced dielectrophoresis (DEP) trap is demonstrated and reported. By mimicking the basic morphology of liver tissue, the classic hepatic lobule, the lobule-mimetic-stellate-electrodes array was designed for cell patterning. Through DEP manipulation, well-defined and enhanced spatial electric field gradients were created for in-parallel manipulation of massive individual cells. With this liver-cell patterning labchip design, the original randomly distributed hepatic and endothelial cells inside the microfluidic chamber can be manipulated separately and aligned into the desired pattern that mimicks the morphology of liver lobule tissue. Experimental results showed that both hepatic and endothelial cells were orderly guided, snared, and aligned along the field-induced orientation to form the lobule-mimetic pattern. About 95% cell viability of hepatic and endothelial cells was also observed after cell-patterning demonstration via a fluorescent assay technique. The liver function of CYP450-1A1 enzyme activity showed an 80% enhancement for our engineered liver tissue (HepG2+HUVECs) compared to the non-patterned pure HepG2 for two-day culturing.

Microfluidic electroporation for cellular analysis and delivery

Abstract: Electroporation is a simple yet powerful technique for breaching the cell membrane barrier. The applications of electroporation can be generally divided into two categories: the release of intracellular proteins, nucleic acids and other metabolites for analysis and the delivery of exogenous reagents such as genes, drugs and nanoparticles with therapeutic purposes or for cellular manipulation. In this review, we go over the basic physics associated with cell electroporation and highlight recent technological advances on microfluidic platforms for conducting electroporation. Within the context of its working mechanism, we summarize the accumulated knowledge on how the parameters of electroporation affect its performance for various tasks. We discuss various strategies and designs for conducting electroporation at the microscale and then focus on analysis of intracellular contents and delivery of exogenous agents as two major applications of the technique. Finally, an outlook for future applications of microfluidic electroporation in increasingly diverse utilities is presented.