Electrochemical detection in a microfluidic device of oxidative stress generated by macrophage cells

In Vitro Electrochemical Detection of Hydrogen Peroxide in Activated Macrophages via a Platinum Microelectrode Array

Oxidative stress, an excess of endogenous or exogenous reactive oxygen species (ROS) in the human body, is closely aligned with inflammatory responses. ROS such as hydrogen peroxide (H₂O₂), superoxide, and radical hydroxyl ions serve essential functions in fighting infection; however, chronic elevation of these species irreversibly damages cellular components. Given the central role of inflammation in a variety of diseases, including Alzheimer’s disease and rheumatoid arthritis, a low-cost, extracellular, non-invasive assay of H₂O₂ measurement is needed. This work reports the use of a platinum microelectrode array (Pt MEA)-based ceramic probe to detect time- and concentration-dependent variations in H₂O₂ production by activated RAW 264.7 macrophages. First, these cells were activated by lipopolysaccharide (LPS) to induce oxidative stress. Chronoamperometry was then employed to detect the quantity of H₂O₂ released by cells at various time intervals up to 48 h. The most stimulatory concentration of LPS was identified. Further experiments assessed the anti-inflammatory effect of dexamethasone (Dex), a commonly prescribed steroid medication. As expected, the probe detected significantly increased H₂O₂ production by LPS-doped macrophages, subsequently diminishing the pro-inflammatory effect in LPS-doped cells treated with Dex. These results strongly support the use of this probe as a non-invasive, robust, point-of-care test of inflammation, with a high potential for multiplexing in further studies.

Recent Progress in Lab-On-a-Chip Systems for the Monitoring of Metabolites for Mammalian and Microbial Cell Research

Lab-on-a-chip sensing technologies have changed how cell biology research is conducted. This review summarises the progress in the lab-on-a-chip devices implemented for the detection of cellular metabolites. The review is divided into two subsections according to the methods used for the metabolite detection. Each section includes a table which summarises the relevant literature and also elaborates the advantages of, and the challenges faced with that particular method. The review continues with a section discussing the achievements attained due to using lab-on-a-chip devices within the specific context. Finally, a concluding section summarises what is to be resolved and discusses the future perspectives.

Measuring and regulating oxygen levels in microphysiological systems: design, material, and sensor considerations

As microfabrication techniques and tissue engineering methods improve, microphysiological systems (MPS) are being engineered that recapitulate complex physiological and pathophysiological states to supplement and challenge traditional animal models. Although MPS provide unique microenvironments that transcend common 2D cell culture, without proper regulation of oxygen content, MPS often fail to provide the biomimetic environment necessary to activate and investigate fundamental pathways of cellular metabolism and sub-cellular level. Oxygen exists in the human body in various concentrations and partial pressures; moreover, it fluctuates dramatically depending on fasting, exercise, and sleep patterns. Regulating oxygen content inside MPS necessitates a sensitive biological sensor to quantify oxygen content in real-time. Measuring oxygen in a microdevice is a non-trivial requirement for studies focused on understanding how oxygen impacts cellular processes, including angiogenesis and tumorigenesis. Quantifying oxygen inside a microdevice can be achieved via an array of technologies, with each method having benefits and limitations in terms of sensitivity, limits of detection, and invasiveness that must be considered and optimized. This article will review oxygen physiology in organ systems and offer comparisons of organ-specific MPS that do and do not consider oxygen microenvironments. Materials used in microphysiological models will also be analyzed in terms of their ability to control oxygen. Finally, oxygen sensor technologies are critically compared and evaluated for use in MPS.

Electric field assisted multicomponent reaction in a microfluidic reactor for superior conversion and yield

We explore the improvements in yield and conversion of a chemical reaction inside a two-phase microfluidic reactor when subjected to an externally applied alternating current (AC) electric field. A computational fluid dynamic (CFD) framework has been developed to incorporate the descriptions of the two-phase flow, multicomponent transport and reaction, and the Maxwell's stresses generated at oil-water interface owing to the presence of the externally applied electric field. The CFD model ensures that the reactants are flown into a microchannel together with the oil and water phases before the reaction takes place at the interface and products diffuse back to the bulk phases. The study unveils that the variation in the intensity of the AC field helps in converting a two-phase stratified flow into an oil-in-water microemulsion composed of oil slugs, plugs, or droplets. Importantly, the results also suggest that harnessing the vortices inside or outside these flow patterns helps in the improvement in mass transfer across the interface, which can be employed to improve the yield and conversion of a reaction. We have shown an example case of a pseudo-first order reaction for which the variation in frequency and intensity of AC field is found to form higher surface-to-volume-ratio flow patterns having a higher throughput. The convective recirculation in and around these miniaturized flow morphologies increase the rate of mass transfer, mixing of reactant and products, conversion of reactant, and yield of products. The results reported can be of significance in the design and development of future advanced-flow rector technologies.

Downstream Simultaneous Electrochemical Detection of Primary Reactive Oxygen and Nitrogen Species Released by Cell Populations in an Integrated Microfluidic Device

An innovative microfluidic platform was designed to monitor electrochemically four primary reactive oxygen (ROS) and reactive nitrogen species (RNS) released by aerobic cells. Taking advantage of the space confinement and electrode performances under flow conditions, only a few experiments were sufficient to directly provide significant statistical data relative to the average behavior of cells during oxidative-stress bursts. The microfluidic platform comprised an upstream microchamber for cell culture and four parallel microchannels located downstream for separately detecting H₂O₂, ONOO^-, NO^·, and NO₂^-. Amperometric measurements were performed at highly sensitive Pt-black electrodes implemented in the microchannels. RAW 264.7 macrophage secretions triggered by a calcium ionophore were used as a way to assess the performance, sensitivity, and specificity of the integrated microfluidic device. In comparison with some previous evaluations achieved from single-cell measurements, reproducible and relevant determinations validated the proof of concept of this microfluidic platform for analyzing statistically significant oxidative-stress responses of various cell types.

Glucose and Lactate Miniaturized Biosensors for SECM-Based High-Spatial Resolution Analysis: A Comparative Study

With the aim of developing miniaturized enzymatic biosensors suitable for in vitro diagnostic applications, such as monitoring of metabolites at single cell level, glucose and lactate biosensors were fabricated by immobilizing enzymes (glucose oxidase and lactate oxidase, respectively) on 10 μm Pt ultramicroelectrodes. These electrodes are meant to be employed as probes for scanning electrochemical microscopy (SECM), which is a unique technique for high-spatial-resolution electrochemical-based analysis. The use of enzymatic moieties improves sensitivity, time scale response, and information content of the microprobes; however, protein immobilization is a key step in the biosensor preparation that greatly affects the overall performance. A crucial aspect is the miniaturization of the sensing, preserving their sensitivity. In this work, we investigated the most common enzyme immobilization techniques. Several fabrication routes are reported and the main figures of merit, such as sensitivity, detection limit, response time, reproducibility, spatial resolution, biosensor efficiency, permeability, selectivity, and the ability to block electro-active interfering species, are investigated and compared. With the intent of using the microprobes for in vitro functional imaging of single living cells, we carefully evaluate the spatial resolution achieved by our modified electrodes on 2D SECM imaging. Metabolic activity of single MCF10A cells were obtained by monitoring the glucose concentrations in close proximity of single living cell, using the UME-based biosensor probes prepared. A voltage-switch approach was implemented to disentangle the topographical contribution of the cells enabling quantitative measurements of cellular uptakes.

Simultaneous Real-Time Monitoring of Oxygen Consumption and Hydrogen Peroxide Production in Cells Using Our Newly Developed Chip-Type Biosensor Device

All living organisms bear its defense mechanism. Immune cells during invasion by foreign body undergoes phagocytosis during which monocyte and neutrophil produces reactive oxygen species (ROS). The ROS generated in animal cells are known to be involved in several diseases and ailments, when generated in excess. Therefore, if the ROS generated in cells can be measured and analyzed precisely, it can be employed in immune function evaluation and disease detection. The aim of the current study is to introduce our newly developed chip-type biosensor device with high specificity and sensitivity. It comprises of counter electrode and working electrodes I and II. The counter electrode is a platinum plate while the working electrodes I and II are platinum microelectrode and osmium-horseradish peroxidase modified gold electrode, respectively which acts as oxygen and hydrogen peroxide (H₂O₂) detection sensors. Simultaneous measurement of oxygen consumption and H₂O₂ generation were measured in animal cells under the effect of exogenous addition of differentiation inducer, phorbol 12-myristate 13-acetate. The results obtained showed considerable changes in reduction currents in the absence and presence of inducer. Our newly developed chip-type biosensor device is claimed to be a useful tool for real-time monitoring of the respiratory activity and precise detection of H₂O₂ in cells. It can thus be widely applied in biomedical research and in clinical trials being an advancement over other H₂O₂ detection techniques.

Fast, Ultrasensitive Detection of Reactive Oxygen Species Using a Carbon Nanotube Based-Electrocatalytic Intracellular Sensor

Herein, we report a highly sensitive electrocatalytic sensor-cell construct that can electrochemically communicate with the internal environment of immune cells (e.g., macrophages) via the selective monitoring of a particular reactive oxygen species (ROS), hydrogen peroxide. The sensor, which is based on vertically aligned single-walled carbon nanotubes functionalized with an osmium electrocatalyst, enabled the unprecedented detection of a local intracellular "pulse" of ROS on a short second time scale in response to bacterial endotoxin (lipopolysaccharide-LPS) stimulation. Our studies have shown that this initial pulse of ROS is dependent on NADPH oxidase (NOX) and toll like receptor 4 (TLR4). The results suggest that bacteria can induce a rapid intracellular pulse of ROS in macrophages that initiates the classical innate immune response of these cells to infection.

Multianalyte Microphysiometry of Macrophage Responses to Phorbol Myristate Acetate, Lipopolysaccharide, and Lipoarabinomannan

This study examined the hypothesis that mycobacterial antigens generate different metabolic responses in macrophages as compared to gram-negative effectors and macrophage activators. The metabolic activation of macrophages by PMA is a useful tool for studying virulent agents and can be compared to other effectors. While phorbol myristate acetate (PMA) is commonly used to study macrophage activation, the concentration used to create this physiological response varies. The response of RAW-264.7 macrophages is concentration-dependent, where the metabolic response to high concentrations of PMA decreases suggesting deactivation. The gram-negative effector, lipopolysaccharide (LPS), was seen to promote glucose and oxygen production which were used to produce a delayed onset of oxidative burst. Pre-incubation with interferon-γ (IFN-γ) increased the effect on cell metabolism, where the synergistic effects of IFN-γ and LPS immediately initiated oxidative burst. These studies exhibited a stark contrast with lipoarabinomannan (LAM), an antigenic glycolipid component associated with the bacterial genus Mycobacterium. The presence of LAM effectively inhibits any metabolic response preventing consumption of glucose and oxygen for the promotion of oxidative burst and to ensure pathogenic proliferation. This study demonstrates for the first time the immediate inhibitory metabolic effects LAM has on macrophages, suggesting implications for future intervention studies with Mycobacterium tuberculosis.

Fabrication of two-layer poly(dimethyl siloxane) devices for hydrodynamic cell trapping and exocytosis measurement with integrated indium tin oxide microelectrodes arrays

The design, fabrication and test of a microfluidic cell trapping device to measure single cell exocytosis were reported. Procedures on the patterning of double layer template based on repetitive standard photolithography of AZ photoresist were investigated. The replicated poly(dimethyl siloxane) devices with 2.5 μm deep channels were proved to be efficient for stopping cells. Quantal exocytosis measurement can be achieved by targeting single or small clumps of chromaffin cells on top of the 10 μm × 10 μm indium tin oxide microelectrodes arrays with the developed microdevice. And about 72 % of the trapping sites can be occupied by cells with hydrodynamic trapping method and the recorded amperometric signals are comparable to the results with traditional carbon fiber microelectrodes. The method of manufacturing the microdevices is simple, low-cost and easy to perform. The manufactured device offers a platform for the high throughput detection of quantal catecholamine exocytosis from chromaffin cells with sufficient sensitivity and broad application.

Electrochemistry at the Edge of Reason: Chalcogen-Based Redox Systems in Biochemistry and Drug Design

In Biology, numerous cellular signalling and control networks are centred around redox active chalcogen species, such as the thiol group of cysteine, the sulfide of methionine and the selenol(ate) of the unusual amino acid selenocysteine. These amino acids form part of peptides, proteins and enzymes, which they endow with a distinct (i.e. chalcogen) redox activity. Compared to the biological redox chemistry of metal ions (e.g. iron, copper, manganese), the redox behaviour of such chalcogen-based systems is considerably more diverse, complex and difficult to study. Not surprisingly, there have been few interactions between electrochemists and biological chalcogen redox chemists in the past. Nonetheless, electrochemistry provides several interesting leads: Impedance measurements enable cell biologists to ‘watch cells grow’ in real time and in a continuous manner, which forms the basis for innovative drug profiling. Voltammetry can be used to monitor the formation of (oxygen and nitrogen based) reactive species at the level of individual macrophages without the need of elaborate staining techniques. At the same time, Cyclic Voltammetry provides access to the redox properties of various cysteine proteins and enzymes, and hence may assist in unravelling some of the remaining mysteries of the cellular thiolstat. And finally, electrochemical methods are extraordinarily powerful and useful in the characterization and ultimately also the design of redox-modulating natural products and drugs, including potential antioxidants and anticancer agents.

Microfluidic systems for studying neurotransmitters and neurotransmission

Neurotransmitters and neuromodulators are molecules within the nervous system that play key roles in cell-to-cell communication. Upon stimulation, neurons release these signaling molecules, which then act at local or distant locations to elicit a physiological response. Ranging from small molecules, such as diatomic gases and amino acids, to larger peptides, these chemical messengers are involved in many functional processes including growth, reproduction, memory and behavior. Understanding signaling molecules and the conditions that govern their release in healthy or damaged networks promises to deliver insights into neural network formation and function. Microfluidic devices can provide optimal cell culture conditions, reduced volume systems, and precise control over the chemical and physical nature of the extracellular environment, making them well-suited for studying neurotransmission and other forms of cell-to-cell signaling. Here we review selected microfluidic approaches that are suitable for monitoring cell-to-cell signaling molecules. We highlight devices that improve in vivo sample collection as well as compartmentalized devices designed to isolate individual neurons or co-cultures in vitro, including a focus on systems used for studying neural injury and regeneration, and devices that allow selective chemical stimulations and the characterization of released molecules.

Miniature enzyme-based electrodes for detection of hydrogen peroxide release from alcohol-injured hepatocytes

Alcohol insult to the liver sets off a complex sequence of inflammatory and fibrogenic responses. There is increasing evidence that hepatocytes play a key role in triggering these responses by producing inflammatory signals such as cytokines and reactive oxygen species (ROS). In the present study, we employed a cell culture/biosensor platform consisting of electrode arrays integrated with microfluidics to monitor extracellular H(2)O(2), one of the major ROS types, produced by primary rat hepatocytes during alcohol injury. The biosensor consisted of hydrogel microstructures with entrapped horseradish peroxidase (HRP) immobilized on an array of miniature gold electrodes. These arrays of sensing electrodes were integrated into microfluidic devices and modified with collagen (I) to promote hepatocyte adhesion. Once seeded into the microfluidic devices, hepatocytes were exposed to 100 mM ethanol and the signal at the working electrode was monitored by cyclic voltammetry (CV) over the course of 4 h. The CV experiments revealed that hepatocytes secreted up to 1.16 μM H(2)O(2) after 3 h of stimulation. Importantly, when hepatocytes were incubated with antioxidants or alcohol dehydrogenase inhibitor prior to alcohol exposure, the H(2)O(2) signal was decreased by ~5-fold. These experiments further confirmed that the biosensor was indeed monitoring oxidative stress generated by the hepatocytes and also pointed to one future use of this technology for screening hepatoprotective effects of antioxidants.

Metabolic impact of 4-hydroxynonenal on macrophage-like RAW 264.7 function and activation

Metabolic profiling of macrophage metabolic response upon exposure to 4-hydroxynonenal (HNE) demonstrates that HNE does not simply inactivate superoxide-generating enzymes but also could be responsible for the impairment of downfield signaling pathways. Multianalyte microphysiometry (MAMP) was employed to simultaneously measure perturbations in extracellular acidification, lactate production, and oxygen consumption for the examination of aerobic and anaerobic pathways. Combining the activation of oxidative burst with phorbol myristate acetate (PMA) and the immunosuppression with HNE, the complex nature of HNE toxicity was determined to be concentration- and time-dependent. Further analysis was utilized to assess the temporal effect of HNE on reactive oxygen species (ROS) production and on protein kinase C (PKC). Increased levels of HNE with decreasing PKC activity suggest that PKC is a target for HNE adductation prior to oxidative burst. Additionally, localization of PKC to the cell membrane was prevented with the introduction of HNE, demonstrating a consequence of HNE adductation on NADPH activation. The impairment of ROS by HNE suggests that HNE has a greater role in foam cell formation and tissue damage than is already known. Although work has been performed to understand the effect of HNE's regulation of specific signaling pathways, details regarding its involvement in cellular metabolism as a whole are generally unknown. This study examines the impact of HNE on macrophage oxidative burst and identifies PKC as a key protein for HNE suppression and eventual metabolic response.

Affinity and enzyme-based biosensors: recent advances and emerging applications in cell analysis and point-of-care testing

The applications of biosensors range from environmental testing and biowarfare agent detection to clinical testing and cell analysis. In recent years, biosensors have become increasingly prevalent in clinical testing and point-of-care testing. This is driven in part by the desire to decrease the cost of health care, to shift some of the analytical tests from centralized facilities to "frontline" physicians and nurses, and to obtain more precise information more quickly about the health status of a patient. This article gives an overview of recent advances in the field of biosensors, focusing on biosensors based on enzymes, aptamers, antibodies, and phages. In addition, this article attempts to describe efforts to apply these biosensors to clinical testing and cell analysis.

Quantification of noise sources for amperometric measurement of quantal exocytosis using microelectrodes

Electrochemical microelectrodes are commonly used to record amperometric spikes of current that result from oxidation of transmitter released from individual vesicles during exocytosis. Whereas the exquisite sensitivity of these measurements is well appreciated, a better understanding of the noise sources that limit the resolution of the technique is needed to guide the design of next-generation devices. We measured the current power spectral density (S(I)) of electrochemical microelectrodes to understand the physical basis of dominant noise sources and to determine how noise varies with the electrode material and geometry. We find that the current noise is thermal in origin in that S(I) is proportional to the real part of the admittance of the electrode. The admittance of microelectrodes is well described by a constant phase element model such that both the real and imaginary admittance increase with frequency raised to a power of 0.84-0.96. Our results demonstrate that the current standard deviation is proportional to the square root of the area of the working electrode, increases ∼linearly with the bandwidth of the recording, and varies with the choice of the electrode material with Au ≈ carbon fiber > nitrogen-doped diamond-like carbon > indium-tin-oxide. Contact between a cell and a microelectrode does not appreciably increase noise. Surface-patterned microchip electrodes can have a noise performance that is superior to that of carbon-fiber microelectrodes of the same area.

A printed superoxide dismutase coated electrode for the study of macrophage oxidative burst

The miniaturization of electrochemical sensors allows for the minimally invasive and cost effective examination of cellular responses at a high efficacy rate. In this work, an ink-jet printed superoxide dismutase electrode was designed, characterized, and utilized as a novel microfluidic device to examine the metabolic response of a 2D layer of macrophage cells. Since superoxide production is one of the first indicators of oxidative burst, macrophage cells were exposed within the microfluidic device to phorbol myristate acetate (PMA), a known promoter of oxidative burst, and the production of superoxide was measured. A 46 ± 19% increase in current was measured over a 30 min time period demonstrating successful detection of sustained macrophage oxidative burst, which corresponds to an increase in the superoxide production rate by 9 ± 3 attomoles/cell/s. Linear sweep voltammetry was utilized to show the selectivity of this sensor for superoxide over hydrogen peroxide. This novel controllable microfluidic system can be used to study the impact of multiple effectors from a large number of bacteria or other invaders along a 2D layer of macrophages, providing an in vitro platform for improved electrochemical studies of metabolic responses.

On-chip multi-electrochemical sensor array platform for simultaneous screening of nitric oxide and peroxynitrite

In this work we report on the design, microfabrication and analytical performances of a new electrochemical sensor array (ESA) which allows for the first time the simultaneous amperometric detection of nitric oxide (NO) and peroxynitrite (ONOO(-)), two biologically relevant molecules. The on-chip device includes individually addressable sets of gold ultramicroelectrodes (UMEs) of 50 µm diameter, Ag/AgCl reference electrode and gold counter electrode. The electrodes are separated into two groups; each has one reference electrode, one counter electrode and 110 UMEs specifically tailored to detect a specific analyte. The ESA is incorporated on a custom interface with a cell culture well and spring contact pins that can be easily interconnected to an external multichannel potentiostat. Each UME of the network dedicated to the detection of NO is electrochemically modified by electrodepositing thin layers of poly(eugenol) and poly(phenol). The detection of NO is performed amperometrically at 0.8 V vs. Ag/AgCl in phosphate buffer solution (PBS, pH = 7.4) and other buffers adapted to biological cell culture, using a NO-donor. The network of UMEs dedicated to the detection of ONOO(-) is used without further chemical modification of the surface and the uncoated gold electrodes operate at -0.1 V vs. Ag/AgCl to detect the reduction of ONOOH in PBS. The selectivity issue of both sensors against major biologically relevant interfering analytes is examined. Simultaneous detection of NO and ONOO(-) in PBS is also achieved.

Advances in embryo culture platforms: novel approaches to improve preimplantation embryo development through modifications of the microenvironment

BACKGROUND

The majority of research aimed at improving embryo development in vitro has focused on manipulation of the chemical environment, examining details such as energy substrate composition and impact of various growth factors or other supplements. In comparison, relatively little work has been done examining the physical requirements of preimplantation embryos and the role culture platforms or devices can play in influencing embryo development.

METHODS

Electronic searches were performed using keywords centered on embryo culture techniques using PUBMED through June 2010 and references were searched for additional research articles.

RESULTS

Various approaches to in vitro embryo culture that involve manipulations of the physical culture environment are emerging. Novel culture platforms being developed examine issues such as media volume and embryo spacing. Furthermore, methods to permit dynamic embryo culture with fluid flow and embryo movement are now available, and novel culture surfaces are being tested.

CONCLUSIONS

Although several factors remain to be studied to optimize efficiency, manipulations of the embryo culture microenvironment through novel culture devices may offer a means to improve embryo development in vitro. Reduced volume systems that reduce embryo spacing, such as the well-of-the-well approach, appear beneficial, although more work is needed to verify the source of their true benefit in human embryos. Emerging microfluidic technology appears to be a promising approach. However, along with the work on specialized culture surfaces, more information is required to determine the impact on human embryo development.

Salmonella detoxifying enzymes are sufficient to cope with the host oxidative burst

The oxidative burst produced by the NADPH oxidase (Phox) is an essential weapon used by host cells to eradicate engulfed pathogens. In Salmonella typhimurium, oxidative stress resistance has been previously proposed to be mediated by the pathogenicity island 2 type III secretion system (T3SS-2), periplasmic superoxide dismutases and cytoplasmic catalases/peroxidases. Here, we fused an OxyR-dependent promoter to the gfp to build the ahpC-gfp transcriptional fusion. This reporter was used to monitor hydrogen peroxide levels as sensed by Salmonella during the course of an infection. We showed that the expression of this fusion was under the exclusive control of reactive oxygen species produced by the host. The ahpC-gfp expression was noticeably modified in the absence of bacterial periplasmic superoxide dismutases or cytoplasmic catalases/peroxidases. Surprisingly, inactivation of the T3SS-2 had no effect on the ahpC-gfp expression. All together, these results led to a model in which Salmonella resistance relies on its arsenal of detoxifying enzymes to cope with Phox-mediated oxidative stress.

Release monitoring of single cells on a microfluidic device coupled with fluorescence microscopy and electrochemistry

A method for monitoring the biological exocytotic phenomena on a microfluidic system was proposed. A microfluidic device coupled with functionalities of fluorescence imaging and amperometric detection has been developed to enable the real-time monitoring of the exocytotic events. Exocytotic release of single SH-SY5Y neuroblastoma cells was studied. By staining the cells located on integrated microelectrodes with naphthalene-2,3-dicarboxaldehyde, punctuate fluorescence consistent with localization of neurotransmitters stored in vesicles was obtained. The stimulated exocytotic release was successfully observed at the surface of SH-SY5Y cells without refitting the commercial inverted fluorescence microscope. Spatially and temporally resolved exocytotic events from single cells on a microfluidic device were visualized in real time using fluorescence microscopy and were amperometrically recorded by the electrochemical system simultaneously. This coupled technique is simple and is hoped to provide new insights into the mechanisms responsible for the kinetics of exocytosis.

Microfluidic perfusion system for maintaining viable heart tissue with real-time electrochemical monitoring of reactive oxygen species

A microfluidic device has been developed to maintain viable heart tissue samples in a biomimetic microenvironment. This device allows rat or human heart tissue to be studied under pseudo in vivo conditions. Effluent levels of lactate dehydrogenase and hydrogen peroxide were used as markers of damaged tissue in combination with in situ electrochemical measurement of the release of reactive oxygen species (ROS). The parameters for perfusion were optimized to maintain biopsies of rat right ventricular or human right atrial tissue viable for up to 5 and 3.5 hours, respectively. Electrochemical assessment of the oxidation current of total ROS, employing cyclic voltammetry, gave results in real-time that were in good agreement to biochemical assessment using conventional, off-chip, commercial assays. This proof-of-principle, integrated microfluidic device, may be exploited in providing a platform technology for future cardiac research, offering an alternative approach for investigating heart pathophysiology and facilitating the development of new therapeutic strategies.

Redox reactions of reactive oxygen species in aqueous solutions as the probe for scanning electrochemical microscopy of single live T24 cells

The redox reactions of two main components of reactive oxygen species (ROS), superoxide and hydrogen peroxide, along with oxygen in aqueous solutions were investigated using a conventional electrochemical technique, differential pulse voltammetry (DPV). Superoxide undergoes oxidation at a Pt working electrode biased at 0.055 V versus Ag/AgCl, while hydrogen peroxide can be oxidized and reduced at 0.817 and –0.745 V, respectively. Oxygen in the solutions is reduced at the electrode with an applied potential of –0.455 V. Based on these results, hydrogen peroxide and superoxide released from live cells can be successfully monitored, identified, and mapped using scanning electrochemical microscopy (SECM) at different potentials. Single human bladder (T24) cells were imaged using a 5 μm diameter SECM probe biased at –0.400, –0.600, and –0.800 V. Oxygen reduction that seems an interference can be discriminated from that of hydrogen peroxide by means of SECM.

Finding out egyptian gods' secret using analytical chemistry: biomedical properties of egyptian black makeup revealed by amperometry at single cells

Lead-based compounds were used during antiquity as both pigments and medicines in the formulation of makeup materials. Chemical analysis of cosmetics samples found in Egyptians tombs and the reconstitution of ancient recipes as reported by Greco-Roman authors have shown that two non-natural lead chlorides (laurionite Pb(OH)Cl and phosgenite Pb(2)Cl(2)CO(3)) were purposely synthesized and were used as fine powders in makeup and eye lotions. According to ancient Egyptian manuscripts, these were essential remedies for treating eye illness and skin ailments. This conclusion seems amazing because today we focus only on the well-recognized toxicity of lead salts. Here, using ultramicroelectrodes, we obtain new insights into the biochemical interactions between lead(II) ions and cells, which support the ancient medical use of sparingly soluble lead compounds. Submicromolar concentrations of Pb(2+) ions are shown to be sufficient for eliciting specific oxidative stress responses of keratinocytes. These consist essentially of an overproduction of nitrogen monoxide (NO degrees ). Owing to the biological role of NO degrees in stimulating nonspecific immunological defenses, one may argue that these lead compounds were deliberately manufactured and used in ancient Egyptian formulations to prevent and treat eye illnesses by promoting the action of immune cells.

Separation and detection of peroxynitrite using microchip electrophoresis with amperometric detection

Peroxynitrite (ONOO(-)) is a highly reactive species implicated in the pathology of several cardiovascular and neurodegenerative diseases. It is generated in vivo by the diffusion-limited reaction of nitric oxide (NO(*)) and superoxide anion ((*)O(2)(-)) and is known to be produced during periods of inflammation. Detection of ONOO(-) is made difficult by its short half-life under physiological conditions (approximately 1 s). Here we report a method for the separation and detection of ONOO(-) from other electroactive species utilizing a microchip electrophoresis device incorporating an amperometric detection scheme. Microchip electrophoresis permits shorter separation times (approximately 25 s for ONOO(-)) and higher temporal resolution than conventional capillary electrophoresis (several minutes). This faster analysis allows ONOO(-) to be detected before substantial degradation occurs, and the increased temporal resolution permits more accurate tracking of dynamic changes in chemical systems.

Microfluidic tools for cell biological research

Microfluidic technology is creating powerful tools for cell biologists to control the complete cellular microenvironment, leading to new questions and new discoveries. We review here the basic concepts and methodologies in designing microfluidic devices, and their diverse cell biological applications.

Investigation of Localized Catalytic and Electrocatalytic Processes and Corrosion Reactions with Scanning Electrochemical Microscopy (SECM)

Scanning electrochemical microscopy (SECM) has developed into a very versatile tool for the investigation of solid-liquid, liquid-liquid and liquid-gas interfaces. The arrangement of an ultramicroelectrode (UME) in close proximity to the interface under study allows the application of a large variety of different experimental schemes. The most important have been named feedback mode, generation-collection mode, redox competition mode and direct mode. Quantitative descriptions are available for the UME signal, depending on different sample properties and experimental variables. Therefore, SECM has been established as an indispensible tool in many areas of fundamental electrochemical research. Currently, it also spreads as an important new method to solve more applied problems, in which inhomogeneous current distributions are typically observed on different length scales. Prominent examples include devices for electrochemical energy conversion such as fuel cells and batteries as well as localized corrosion phenomena. However, the direct local investigation of such systems is often impossible. Instead, suitable reaction schemes, sample environments, model samples and even new operation modes have to be introduced in order to obtain results that are relevant to the practical application. This review outlines and compares the theoretical basis of the different SECM working modes and reviews the application in the area of electrochemical energy conversion and localized corrosion with a special emphasis on the problems encountered when working with practical samples.

Nuclear translocation kinetics of NF-kappaB in macrophages challenged with pathogens in a microfluidic platform

We have developed a microfluidic platform for real-time imaging of host-pathogen interactions and cellular signaling events. Host cells are immobilized in a controlled environment for optical interrogation of the kinetics and stochasticity of immune response to pathogenic challenges. Here, we have quantitatively measured activation of the toll-like receptor 4 (TLR4) pathway in RAW264.7 murine macrophage-like cells. This was achieved by measuring the cytoplasm-to-nucleus translocation kinetics of a green fluorescent protein fusion construct to the NF-kappaB transcription factor subunit RelA (GFP-RelA). Translocation kinetics in response to live bacteria and purified lipopolysaccharide (LPS) challenges were measured, and this work presents the first demonstration of live imaging of host cell infection on a microfluidic platform with quantitative analysis of an early (<0.5 h from infection) immune signaling event. Our data show that a 1,000x increase in the LPS dose led to a ~10x increase in a host cell activation metric we developed in order to describe NF-kappaB translocation kinetics. Using this metric, live bacteria challenges were assigned an equivalent LPS dose as a first step towards comparing NF-kappaB translocation kinetics between TLR4-only pathway signaling (activated by LPS) and multiple pathway signaling (activated by whole bacteria). The device also contains a unique architecture for capturing and fluidically isolating single host cells for the purpose of differentiating between primary and secondary immune signaling.