Heterogeneous immunoassays using magnetic beads on a digital microfluidic platform

Redox-magnetohydrodynamics, flat flow profile-guided enzyme assay detection: toward multiple, parallel analyses

A proof-of-concept superparamagnetic microbead-enzyme complex was integrated with microfluidics pumped by redox-magneto-hydrodynamics (MHD) to take advantage of the magnet (0.56 T) beneath the chip and the uniform flat flow profile, as a first step toward developing multiple, parallel chemical analyses on a chip without the need for independent channels. The superparamagnetic beads were derivatized with alkaline phosphatase (a common enzyme label for biochemical assays) and magnetically immobilized at three different locations on the chip with one directly on the path to the detector and the other two locations adjacent to, but off the path, by a distance >5 times the detector diameter. Electroactive p-aminophenol, enzymatically generated at the bead-enzyme complex from its electroinactive precursor p-aminophenyl phosphate in a solution containing a redox species [Ru(NH3)6](3+/2+) for pumping and Tris buffer, was transported by redox-MHD and detected with square wave voltammetry at a 312 μm diameter gold microdisk stationed 2 mm downstream from the bead-complex on the flow path. Oppositely biased pumping electrodes, consisting of 2.5 cm long gold bands and separated by 5.6 mm, flanked the active flow region containing the bead-enzyme complex and detection site. The signal from adjacent paths was only 20% of that for the direct path and ≤8% when pumping electrodes were inactive.

A lab-in-a-briefcase for rapid prostate specific antigen (PSA) screening from whole blood

We present a new concept for rapid and fully portable prostate specific antigen (PSA) measurements, termed "lab-in-a-briefcase", which integrates an affordable microfluidic ELISA platform utilising a melt-extruded fluoropolymer microcapillary film (MCF) containing an array of 10 200 μm internal diameter capillaries, a disposable multi-syringe aspirator (MSA), a sample tray pre-loaded with all of the required immunoassay reagents, and a portable film scanner for colorimetric signal digital quantification. Each MSA can perform 10 replicate microfluidic immunoassays on 8 samples, allowing 80 measurements to be made in less than 15 minutes based on semi-automated operation, without the need of additional fluid handling equipment. The assay was optimised for the measurement of a clinically relevant range of PSA of 0.9 to 60.0 ng ml(-1) in 15 minutes with CVs on the order of 5% based on intra-assay variability when read using a consumer flatbed film scanner. The PSA assay performance in the MSA remained robust in undiluted or 1 : 2 diluted human serum or whole blood, and the matrix effect could simply be overcome by extending sample incubation times. The PSA "lab-in-a-briefcase" is particularly suited to a low-resource health setting, where diagnostic labs and automated immunoassay systems are not accessible, by allowing PSA measurement outside the laboratory using affordable equipment.

A fluorogenic heterogeneous immunoassay for cardiac muscle troponin cTnI on a digital microfluidic device

We describe a fluorogenic two-site noncompetitive heterogeneous immunoassay with magnetic beads on a low-voltage digital microfluidic platform using closed electrowetting-on-dielectric (EWOD). All the steps of an enzyme-linked immunosorbent assay (ELISA) were performed on the device using 9H-(1, 3-dichloro-9, 9-dimethylacridin-2-one-7-yl) phosphate as the fluorogenic substrate for the enzyme alkaline phosphatase. The performance of the system was demonstrated with cardiac marker Troponin I (cTnI) as a model analyte in phosphate-buffered saline samples. cTnI was detected within the diagnostically relevant range with a limit of detection of 2.0 ng/mL (CV = 6.47 %). Washing of magnetic beads was achieved by movement through a narrow region of buffer bridging one drop to another with minimal fluid transfer. More than 90 % of the unbound reagents were removed after five washes. Further experiments testing human blood serum on the same platform demonstrated a sample-to-answer time at ∼18.5 min detecting 6.79 ng/mL cTnI.

Phaseguide assisted liquid lamination for magnetic particle-based assays

We have developed a magnetic particle-based assay platform in which functionalised magnetic particles are transferred sequentially through laminated volumes of reagents and washing buffers. Lamination of aqueous liquids is achieved via the use of phaseguide technology; microstructures that control the advancing air-liquid interface of solutions as they enter a microfluidic chamber. This allows manual filling of the device, eliminating the need for external pumping systems, and preparation of the system requires only a few minutes. Here, we apply the platform to two on-chip strategies: (i) a one-step streptavidin-biotin binding assay, and (ii) a two-step C-reactive protein immunoassay. With these, we demonstrate how condensing multiple reaction and washing processes into a single step significantly reduces procedural times, with both assay procedures requiring less than 8 seconds.

Droplet-based microfluidic washing module for magnetic particle-based assays

In this paper, we propose a continuous flow droplet-based microfluidic platform for magnetic particle-based assays by employing in-droplet washing. The droplet-based washing was implemented by traversing functionalized magnetic particles across a laterally merged droplet from one side (containing sample and reagent) to the other (containing buffer) by an external magnetic field. Consequently, the magnetic particles were extracted to a parallel-synchronized train of washing buffer droplets, and unbound reagents were left in an original train of sample droplets. To realize the droplet-based washing function, the following four procedures were sequentially carried in a droplet-based microfluidic device: parallel synchronization of two trains of droplets by using a ladder-like channel network; lateral electrocoalescence by an electric field; magnetic particle manipulation by a magnetic field; and asymmetrical splitting of merged droplets. For the stable droplet synchronization and electrocoalescence, we optimized droplet generation conditions by varying the flow rate ratio (or droplet size). Image analysis was carried out to determine the fluorescent intensity of reagents before and after the washing step. As a result, the unbound reagents in sample droplets were significantly removed by more than a factor of 25 in the single washing step, while the magnetic particles were successfully extracted into washing buffer droplets. As a proof-of-principle, we demonstrate a magnetic particle-based immunoassay with streptavidin-coated magnetic particles and fluorescently labelled biotin in the proposed continuous flow droplet-based microfluidic platform.

Integrated lab-on-chip biosensing systems based on magnetic particle actuation--a comprehensive review

The demand for easy to use and cost effective medical technologies inspires scientists to develop innovative lab-on-chip technologies for point-of-care in vitro diagnostic testing. To fulfill medical needs, the tests should be rapid, sensitive, quantitative, and miniaturizable, and need to integrate all steps from sample-in to result-out. Here, we review the use of magnetic particles actuated by magnetic fields to perform the different process steps that are required for integrated lab-on-chip diagnostic assays. We discuss the use of magnetic particles to mix fluids, to capture specific analytes, to concentrate analytes, to transfer analytes from one solution to another, to label analytes, to perform stringency and washing steps, and to probe biophysical properties of the analytes, distinguishing methodologies with fluid flow and without fluid flow (stationary microfluidics). Our review focuses on efforts to combine and integrate different magnetically actuated assay steps, with the vision that it will become possible in the future to realize integrated lab-on-chip biosensing assays in which all assay process steps are controlled and optimized by magnetic forces.

A digital microfluidic electrochemical immunoassay

Digital microfluidics (DMF) has emerged as a popular format for implementing quantitative immunoassays for diagnostic biomarkers. All previous reports of such assays have relied on optical detection; here, we introduce the first digital microfluidic immunoassay relying on electrochemical detection. In this system, an indium tin oxide (ITO) based DMF top plate was modified to include gold sensing electrodes and silver counter/pseudoreference electrodes suitable for in-line amperometric measurements. A thyroid stimulating hormone (TSH) immunoassay procedure was developed relying on magnetic microparticles conjugated with primary antibody (Ab1). Antigen molecules are captured followed by capture of a secondary antibody (Ab2) conjugated with horseradish peroxidase enzyme (HRP). HRP catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) which can be detected amperometrically. The limit of detection of the technique (2.4 μIU mL(-1)) is compatible with clinical applications; moreover, the simplicity and the small size of the detector suggest utility in the future for portable analysis.

A novel picoliter droplet array for parallel real-time polymerase chain reaction based on double-inkjet printing

We present a double-inkjet printing method for the generation of picoliter droplet-in-oil arrays on planar substrates, efficiently addressing droplet evaporation issues without the assistance of a humidifier or glycerol.

Magnetic bead assisted labeling of antibodies at nanogram scale

There are currently several initiatives that aim to produce binding reagents for proteome-wide analysis. To enable protein detection, visualization, and target quantification, covalent coupling of reporter molecules to antibodies is essential. However, current labeling protocols recommend considerable amount of antibodies, require antibody purity and are not designed for automation. Given that small amounts of antibodies are often sufficient for downstream analysis, we developed a labeling protocol that combines purification and modification of antibodies at submicrogram quantities. With the support of magnetic microspheres, automated labeling of antibodies in parallel using biotin or fluorescent dyes was achieved.

Immunomagnetic nanoparticle-based assays for detection of biomarkers

The emergence of biomarkers as key players in the paradigm shift towards preventative medicine underscores the need for their detection and quantification. Advances made in the field of nanotechnology have played a crucial role in achieving these needs, and have contributed to recent advances in the field of medicine. Nanoparticle-based immunomagnetic assays, in particular, offer numerous advantages that utilize the unique physical properties of magnetic nanoparticles. In this review, we focus on recent developments and trends with regards to immunomagnetic assays used for detection of biomarkers. The various immunomagnetic assays are categorized into the following: particle-based multiplexing, signal control, microfluidics, microarray, and automation. Herein, we analyze each category and discuss their advantages and disadvantages.

Label-free method for cell counting in crude biological samples via paramagnetic bead aggregation

Under chaotropic conditions, DNA released from lysed cells causes the aggregation of paramagnetic beads in a rotating magnetic field in a manner that is independent of the presence of other cellular components. The extent of aggregation correlates with the mass of DNA in a quantitative manner (Leslie, D. C. et al., J. Am. Chem. Soc. 2012, 134, 5689-96), and from this, the number of DNA-containing cells in the sample can be enumerated. Microbial growth testing is demonstrated by monitoring bead aggregation with E. coli in the presence of ampicillin. Without the need for fluorescent labeling or Coulter counting, the white blood cell count can be defined directly from a microliter of crude whole blood. Specificity is brought to the process by coupling bead-based immunocapture with DNA-bead aggregation allowing for the enumeration of CD4+ T cells from human blood samples. The results of DNA-induced bead aggregation had a 95% correlation with those generated by flow cytometry. With the process requiring only inexpensive, widely available benchtop laboratory hardware, a digital camera, and a simple algorithm, this provided a highly accessible alternative to more expensive cell-counting techniques.

Recent developments in emerging microimmunoassays

Creative and novel microimmunoassay approaches continue to proliferate across many platforms originating from several fields of study. These efforts are aimed at improving one or more metrics for clinical tests, including improved sensitivity, increased speed, reduced cost, smaller sample size, the ability to analyze multiple antigens in parallel and ease of use. Many approaches focus on the production of microarrays that accomplish standard assays in parallel, or mobile solid-support formats to overcome issues of high background noise and long incubation times. In this article, innovative developments beyond existing commercial tests in the microimmunoassay arena are reviewed, covering January 2008 to April 2012. These developing experimental platforms are discussed in terms of their ability to augment or replace current commercial approaches.

A versatile automated platform for micro-scale cell stimulation experiments

Study of cells in culture (in vitro analysis) has provided important insight into complex biological systems. Conventional methods and equipment for in vitro analysis are well suited to study of large numbers of cells (≥ 10(5)) in milliliter-scale volumes (≥ 0.1 ml). However, there are many instances in which it is necessary or desirable to scale down culture size to reduce consumption of the cells of interest and/or reagents required for their culture, stimulation, or processing. Unfortunately, conventional approaches do not support precise and reproducible manipulation of micro-scale cultures, and the microfluidics-based automated systems currently available are too complex and specialized for routine use by most laboratories. To address this problem, we have developed a simple and versatile technology platform for automated culture, stimulation, and recovery of small populations of cells (100-2,000 cells) in micro-scale volumes (1-20 μl). The platform consists of a set of fibronectin-coated microcapillaries ("cell perfusion chambers"), within which micro-scale cultures are established, maintained, and stimulated; a digital microfluidics (DMF) device outfitted with "transfer" microcapillaries ("central hub"), which routes cells and reagents to and from the perfusion chambers; a high-precision syringe pump, which powers transport of materials between the perfusion chambers and the central hub; and an electronic interface that provides control over transport of materials, which is coordinated and automated via pre-determined scripts. As an example, we used the platform to facilitate study of transcriptional responses elicited in immune cells upon challenge with bacteria. Use of the platform enabled us to reduce consumption of cells and reagents, minimize experiment-to-experiment variability, and re-direct hands-on labor. Given the advantages that it confers, as well as its accessibility and versatility, our platform should find use in a wide variety of laboratories and applications, and prove especially useful in facilitating analysis of cells and stimuli that are available in only limited quantities.

A microfluidic DNA library preparation platform for next-generation sequencing

Next-generation sequencing (NGS) is emerging as a powerful tool for elucidating genetic information for a wide range of applications. Unfortunately, the surging popularity of NGS has not yet been accompanied by an improvement in automated techniques for preparing formatted sequencing libraries. To address this challenge, we have developed a prototype microfluidic system for preparing sequencer-ready DNA libraries for analysis by Illumina sequencing. Our system combines droplet-based digital microfluidic (DMF) sample handling with peripheral modules to create a fully-integrated, sample-in library-out platform. In this report, we use our automated system to prepare NGS libraries from samples of human and bacterial genomic DNA. E. coli libraries prepared on-device from 5 ng of total DNA yielded excellent sequence coverage over the entire bacterial genome, with >99% alignment to the reference genome, even genome coverage, and good quality scores. Furthermore, we produced a de novo assembly on a previously unsequenced multi-drug resistant Klebsiella pneumoniae strain BAA-2146 (KpnNDM). The new method described here is fast, robust, scalable, and automated. Our device for library preparation will assist in the integration of NGS technology into a wide variety of laboratories, including small research laboratories and clinical laboratories.

Lanthanide-doped NaScF4 nanoprobes: crystal structure, optical spectroscopy and biodetection

Trivalent lanthanide ions (Ln(3+))-doped inorganic nanoparticles (NPs) as potential luminescent bioprobes have been attracting tremendous interest because of their unique upconversion (UC) and downconversion (DC) luminescence properties. NaScF4, as an important host material, has been rarely reported and its crystal structure remains unclear. Herein, based on the single crystal X-ray diffraction, the space group of NaScF4 crystals was determined to be P31 containing multiple sites of Sc(3+) with crystallographic site symmetry of C1, which was verified by high-resolution photoluminescence spectroscopy of Eu(3+) at low temperature (10 K). Furthermore, monodisperse and size-controllable NaScF4:Ln(3+) NPs were synthesized via a facile thermal decomposition method. The biotinylated NaScF4:Er(3+)/Yb(3+) NPs were demonstrated for their applications as a heterogeneous UC luminescence bioprobe to detect avidin with a detection limit of 180 pM. After bioconjugation with amino-terminal fragment (ATF) of urokinase plasminogen activator (uPA), NaScF4:Ln(3+) NPs also exhibited specific recognition of cancer cells overexpressed with uPA receptor (uPAR, an important marker of tumor biology and metastasis), showing great potentials in tumor-targeted bioimaging.

A low cost and high throughput magnetic bead-based immuno-agglutination assay in confined droplets

Although passive immuno-agglutination assays consist of one step and simple procedures, they are usually not adapted for high throughput analyses and they require expensive and bulky equipment for quantitation steps. Here we demonstrate a low cost, multimodal and high throughput immuno-agglutination assay that relies on a combination of magnetic beads (MBs), droplets microfluidics and magnetic tweezers. Antibody coated MBs were used as a capture support in the homogeneous phase. Following the immune interaction, water in oil droplets containing MBs and analytes were generated and transported in Teflon tubing. When passing in between magnetic tweezers, the MBs contained in the droplets were magnetically confined in order to enhance the agglutination rate and kinetics. When releasing the magnetic field, the internal recirculation flows in the droplet induce shear forces that favor MBs redispersion. In the presence of the analyte, the system preserves specific interactions and MBs stay in the aggregated state while in the case of a non-specific analyte, redispersion of particles occurs. The analyte quantitation procedure relies on the MBs redispersion rate within the droplet. The influence of different parameters such as magnetic field intensity, flow rate and MBs concentration on the agglutination performances have been investigated and optimized. Although the immuno-agglutination assay described in this work may not compete with enzyme linked immunosorbent assay (ELISA) in terms of sensitivity, it offers major advantages regarding the reagents consumption (analysis is performed in sub microliter droplet) and the platform cost that yields to very cheap analyses. Moreover the fully automated analysis procedure provides reproducible analyses with throughput well above those of existing technologies. We demonstrated the detection of biotinylated phosphatase alkaline in 100 nL sample volumes with an analysis rate of 300 assays per hour and a limit of detection of 100 pM.

Full-range magnetic manipulation of droplets via surface energy traps enables complex bioassays

Manipulating droplets on an open surface promises an easier, more flexible, and more scalable platform of liquid control, than does microchannel-based fluidics. In this report, a surface-energy-trap-enabled magnetic droplet handling platform is introduced that is capable of comprehensive droplet manipulations, including droplet dispensing, transport, fusion, and particle extraction.

Characterization of the geometry of negative dielectrophoresis traps for particle immobilization in digital microfluidic platforms

This paper studies the effect of dielectrophoresis on particle manipulation and immobilization in digital microfluidic (DMF) devices. The dimensions of negative dielectrophoresis (nDEP) traps in the form of circular and square shapes are characterized using numerical and experimental approaches. These efforts will result in defining lifting and trapping zones, the ratio of which is shown to remain constant for trap sizes larger than 40 μm. As a result, a limiting constant K based on the ratio of the particle diameter to the trap size is introduced to identify the status of particle trapping prior to running numerical models or experiments. The results show that K must be less than 0.63 for trapping the particles on the nDEP traps. This study will also result in optimizing the trap size for single particle immobilization which is important for cell printing and growth applications.

Microfluidic chips for immunoassays

The use of microfluidic chips for immunoassays has been extensively explored in recent years. The combination of immunoassays and microfluidics affords a promising platform for multiple, sensitive, and automatic point-of-care (POC) diagnostics. In this review, we focus on the description of recent achievements in microfluidic chips for immunoassays categorized by their detection method. Following a brief introduction to the basic principles of each detection method, we examine current microfluidic immunosensor detection systems in detail. We also highlight interesting strategies for sensitive immunosensing configurations, multiplexed analysis, and POC diagnostics in microfluidic immunosensors.

An intelligent digital microfluidic system with fuzzy-enhanced feedback for multi-droplet manipulation

The complexity of droplet hydrodynamics on a digital microfluidic (DMF) system eventually weakens its potential for application in large-scale chemical/biological micro-reactors. We describe here an intelligent DMF technology to address that intricacy. A wide variety of control-engaged droplet manageability is proposed and demonstrated through the operation of our modular DMF prototype, which comprises: (i) rigid profiling ability of different droplet's hydrodynamics under a real-time trajectory track of droplet-derived capacitance, permitting accurate and autonomous multi-droplet positioning without visual setup and heavy image signal processing; (ii) fuzzy-enhanced controllability saving up to 21% charging time when compared with the classical approach, enhancing the throughput, fidelity and lifetime of the DMF chip, while identifying and renouncing those weakened electrodes deteriorated over time, and (iii) expert manipulability of multi-droplet routings under countermeasure decisions in real time, preventing droplet-to-droplet or task-to-task interference. Altogether, this work exhibits the first modular DMF system with built-in electronic-control software-defined intelligence to enhance the fidelity and reliability of each droplet operation, allowing future manufacturability of a wide range of life science analyses and combinatorial chemical screening applications.

Microfluidic designs and techniques using lab-on-a-chip devices for pathogen detection for point-of-care diagnostics

Effective pathogen detection is an essential prerequisite for the prevention and treatment of infectious diseases. Despite recent advances in biosensors, infectious diseases remain a major cause of illnesses and mortality throughout the world. For instance in developing countries, infectious diseases account for over half of the mortality rate. Pathogen detection platforms provide a fundamental tool in different fields including clinical diagnostics, pathology, drug discovery, clinical research, disease outbreaks, and food safety. Microfluidic lab-on-a-chip (LOC) devices offer many advantages for pathogen detection such as miniaturization, small sample volume, portability, rapid detection time and point-of-care diagnosis. This review paper outlines recent microfluidic based devices and LOC design strategies for pathogen detection with the main focus on the integration of different techniques that led to the development of sample-to-result devices. Several examples of recently developed devices are presented along with respective advantages and limitations of each design. Progresses made in biomarkers, sample preparation, amplification and fluid handling techniques using microfluidic platforms are also covered and strategies for multiplexing and high-throughput analysis, as well as point-of-care diagnosis, are discussed.

Microfluidic systems for diagnostic applications: a review

Because of intensive developments in recent years, the microfluidic system has become a powerful tool for biological analysis. Entire analytic protocols including sample pretreatment, sample/reagent manipulation, separation, reaction, and detection can be integrated into a single chip platform. A lot of demonstrations on the diagnostic applications related to genes, proteins, and cells have been reported because of their advantages associated with miniaturization, automation, sensitivity, and specificity. The aim of this article is to review recent developments in microfluidic systems for diagnostic applications. Based on the categories of various fluid-manipulating mechanisms and biological detection approaches, in-depth discussion of the microfluidic-based diagnostic systems is provided. Moreover, a brief discussion on materials and manufacturing techniques will be included. The current excellent integration of microfluidic systems and diagnostic applications suggests a solid foundation for the development of practical point-of-care devices.

Fluorinated liquid-enabled protein handling and surfactant-aided crystallization for fully in situ digital microfluidic MALDI-MS analysis

A droplet (digital) microfluidic device has been developed that enables complete protein sample preparation for MALDI-MS analysis. Protein solution dispensing, disulfide bond reduction and alkylation, tryptic digestion, sample crystallization, and mass spectrometric analysis are all performed on a single device without the need for any ex situ sample purification. Fluorinated solvents are used as an alternative to surfactants to facilitate droplet movement and limit protein adsorption onto the device surface. The fluorinated solvent is removed by evaporation and so does not interfere with the MALDI-MS analysis. Adding a small amount of perfluorooctanoic acid to the MALDI matrix solution improves the yield, quality and consistency of the protein-matrix co-crystals, reducing the need for extensive 'sweet spot' searching and improving the spectral signal-to-noise ratio. These innovations are demonstrated in the complete processing and MALDI-MS analysis of lysozyme and cytochrome c. Because all of the sample processing steps and analysis can be performed on a single digital microfluidic device without the need for ex situ sample handling, higher throughput can be obtained in proteomics applications. More generally, the results presented here suggest that fluorinated liquids could also be used to minimize protein adsorption and improve crystallization in other types of lab-on-a-chip devices and applications.

Digital microfluidics: a versatile tool for applications in chemistry, biology and medicine

Digital microfluidics (DMF) has recently emerged as a popular technology for a wide range of applications. In DMF, nanoliter to microliter droplets containing samples and reagents can be manipulated to carry out a range of discrete fluidic operations simply by applying a series of electrical potentials to an array of patterned electrodes coated with a hydrophobic insulator. DMF is distinct from microchannel-based fluidics as it allows for precise control over multiple reagent phases (liquids and solids) in heterogeneous systems with no need for complex networks of connections, microvalves, or pumps. In this review, we discuss the most recent developments in this technology with particular attention to the potential benefits and outstanding challenges for applications in chemistry, biology, and medicine.

Field-free particle focusing in microfluidic plugs

Particle concentration is a key unit operation in biochemical assays. Although there are many techniques for particle concentration in continuous-phase microfluidics, relatively few are available in multiphase (plug-based) microfluidics. Existing approaches generally require external electric or magnetic fields together with charged or magnetized particles. This paper reports a passive technique for particle concentration in water-in-oil plugs which relies on the interaction between particle sedimentation and the recirculating vortices inherent to plug flow in a cylindrical capillary. This interaction can be quantified using the Shields parameter ([Formula: see text]), a dimensionless ratio of a particle's drag force to its gravitational force, which scales with plug velocity. Three regimes of particle behavior are identified. When [Formula: see text] is less than the movement threshold (region I), particles sediment to the bottom of the plug where the internal vortices subsequently concentrate the particles at the rear of the plug. We demonstrate highly efficient concentration (∼100%) of 38 μm glass beads in 500 μm diameter plugs traveling at velocities up to 5 mm/s. As [Formula: see text] is increased beyond the movement threshold (region II), particles are suspended in well-defined circulation zones which begin at the rear of the plug. The length of the zone scales linearly with plug velocity, and at sufficiently large [Formula: see text], it spans the length of the plug (region III). A second effect, attributed to the co-rotating vortices at the rear cap, causes particle aggregation in the cap, regardless of flow velocity. Region I is useful for concentrating/collecting particles, while the latter two are useful for mixing the beads with the solution. Therefore, the two key steps of a bead-based assay, concentration and resuspension, can be achieved simply by changing the plug velocity. By exploiting an interaction of sedimentation and recirculation unique to multiphase flow, this simple technique achieves particle concentration without on-chip components, and could therefore be applied to a range of heterogeneous screening assays in discrete nl plugs.

Changes in fibrinopeptide A peptides in the sera of rats chronically exposed to low doses of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a ubiquitously distributed endocrine disruptors. To investigate peptide changes in the sera of rats chronically exposed to TCDD and to explore the association of these changes with liver morphology, TCDD was administrated to male rats at doses of 140, 350, and 875 ng/kg/week for 29 weeks. Serum was collected and proteomic analysis was performed using automated Bruker Daltonics ClinProt with matrix-assisted laser desorption/ionization time-of-flight mass spectrometer. One peptide at 1740.89 was found to be significantly decreased and further identified with nano LC-MS/MS system. The MS BLAST homology search engine reported the peptide to be a partial sequence of fibrinopeptide A. Liver fatty degeneration and necrosis were assessed by hematoxylin and eosin staining. Liver fatty degeneration and necrosis were both found to be significantly increased after TCDD exposure. Levels of fibrinopeptide A were significantly correlated with liver fatty degeneration and necrosis.

A digital microfluidic method for multiplexed cell-based apoptosis assays

Digital microfluidics (DMF), a fluid-handling technique in which picolitre-microlitre droplets are manipulated electrostatically on an array of electrodes, has recently become popular for applications in chemistry and biology. DMF devices are reconfigurable, have no moving parts, and are compatible with conventional high-throughput screening infrastructure (e.g., multiwell plate readers). For these and other reasons, digital microfluidics has been touted as being a potentially useful new tool for applications in multiplexed screening. Here, we introduce the first digital microfluidic platform used to implement parallel-scale cell-based assays. A fluorogenic apoptosis assay for caspase-3 activity was chosen as a model system because of the popularity of apoptosis as a target for anti-cancer drug discovery research. Dose-response profiles of caspase-3 activity as a function of staurosporine concentration were generated using both the digital microfluidic method and conventional techniques (i.e., pipetting, aspiration, and 96-well plates.) As expected, the digital microfluidic method had a 33-fold reduction in reagent consumption relative to the conventional technique. Although both types of methods used the same detector (a benchtop multiwell plate reader), the data generated by the digital microfluidic method had lower detection limits and greater dynamic range because apoptotic cells were much less likely to de-laminate when exposed to droplet manipulation by DMF relative to pipetting/aspiration in multiwell plates. We propose that the techniques described here represent an important milestone in the development of digital microfluidics as a useful tool for parallel cell-based screening and other applications.

Microfluidic platforms for performing surface-based clinical assays

The need for fast, specific and portable diagnostic systems for clinical assays has, in recent years, led to an explosion of research into microfluidic chip-based immunoassays towards rapid point-of-care analysis. Such devices exploit small dimensions, superior fluidic control and low reagent volumes to allow a number of clinically important procedures to be achieved with improvements on conventional methods, many of which rely on the surface-based binding of antigens to antibodies. Here, we discuss recent developments and innovations in the area of on-chip surface-based immunoassays and provide an outlook on the potential of such platforms for future diagnostics.

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.

Cytokines as potential biomarkers for Parkinson's disease: a multiplex approach

Cytokines, which are immunological messengers facilitating both intra- and inter-system communication, are considered central players in the neuroinflammatory cascades associated with the neurodegenerative process in Parkinson's disease (PD) and other neurological disorders. They have also been implicated in depression and other cognitive (e.g., memory impairment, dementia) and affective disturbances (e.g., anxiety) that show high co-morbidity with neurodegenerative diseases. As such, cytokines may hold great promise as serological biomarkers in PD, with potential applications ranging from early diagnosis and disease staging, to prognosis, drug discovery, and tracking the response to treatment. Subclassification or risk stratification in PD could be based (among other things) on reliably determined cytokine panel profiles or "signatures" of particular co-morbid disease states or at-risk groups (e.g., PD alone, PD with depression and/or dementia). Researchers and clinicians seeking to describe cytokine variations in health vs. disease will benefit greatly from technologies that allow a high degree of multiplexing and thus permit the simultaneous determination of a large roster of cytokines in single small-volume samples. The need for such highly paralleled assays is underscored by the fact that cytokines do not act in isolation but rather against a backdrop of complementary and antagonistic cytokine effects; ascribing valence to the actions of any one cytokine thus requires specific knowledge about the larger cytokine milieu. This chapter provides a technological overview of the major cytokine multiplex assay platforms before discussing the implications of such tools for biomarker discovery and related applications in PD and its depressive and cognitive co-morbidities.