Measurement of macrophage adherence and spreading with weak electric fields

Classifying contaminated cell cultures using time series features

We examine the use of time series data, derived from Electric Cell-substrate Impedance Sensing (ECIS), to differentiate between standard mammalian cell cultures and those infected with a mycoplasma organism. With the goal of easy visualization and interpretation, we perform low-dimensional feature-based classification, extracting application-relevant features from the ECIS time courses. We can achieve very high classification accuracy using only two features, which depend on the cell line under examination. Initial results also show the existence of experimental variation between plates and suggest types of features that may prove more robust to such variation. Our paper is the first to perform a broad examination of ECIS time course features in the context of detecting contamination; to combine different types of features to achieve classification accuracy while preserving interpretability; and to describe and suggest possibilities for ameliorating plate-to-plate variation.

Biomimetic in vitro respiratory system using smooth muscle cells on ECIS chips for anti-asthma TCMs screening

Airway smooth muscle (ASM) contraction is a major pathophysiological characteristic of asthma. Although β2-adrenoceptor (β2-AR) agonists are currently used as bronchodilators, they cause rapid effect and long-term agonist-induced desensitization. Thus, it is necessary to search for more effective and safer relaxant agents for ASM cells. In this work, bitter taste receptors (TAS2Rs) were demonstrated to be expressed in primary mouse ASM cells endogenously, and they were considered as new drug targets for asthma treatment. Traditional Chinese medicines (TCMs) contained a wide range of TAS2R agonists and some of them had the efficacy of relieving cough and asthma with less toxic side effects. Then the electronic cell-substrate impedance sensor (ECIS) was used for the first time to establish a method to detect the contraction/relaxation effects of ASM cells. Therefore, we introduced a biomimetic in vitro respiratory system using ASM cells on ECIS chips to screen for potential TCMs against asthma. Quinine, nobiletin, and picfeltarraenin IA screened in this study could effectively inhibit the ASM contraction in a concentration-dependent manner, showing potential value as novel anti-asthma drugs. Furthermore, the effective screening of anti-asthma drugs was realized based on 3D ASM cell arrays and gel imaging system. Consistent results were found and the reliability of the biomimetic in vitro respiratory system for the screening of TCMs against asthma was further verified. The biomimetic system designed in this study has the advantages of operation simplicity, high throughput, non-invasive, real-time, and high sensitivity, and therefore provides a promising drug screening platform for asthma disease.

In vitro assays of chemotaxis as a window into mechanisms of toxicant-induced immunomodulation

Dysregulated cell movement can lead to developmental abnormalities, neoplasia, and immune system disorders, and there are a variety of contexts in which xenobiotics (and biologic) effects on this movement are of interest. Many toxins and toxicants have been shown to disrupt controlled cell movement. Identification of compounds that affect cell movement is crucial to drug discovery. Drug components may have unexpected consequences with respect to cell motility, which would exclude these compounds in drug development. Finally, the development of drugs that target chemotactic pathways may be useful in the treatment of tumors, which often reprogram chemotactic pathways to become metastatic. The effects of these agents on cell movement can be measured using several different in vitro chemotactic assays. This review details the procedures of three in vitro measurements of chemotaxis: the Boyden chamber, the under-agarose assay, and the automated, real-time, ECIS/Taxis assay, and discusses the inferences that can be drawn from the results of such studies.

A real time chemotaxis assay unveils unique migratory profiles amongst different primary murine macrophages

Chemotaxis assays are an invaluable tool for studying the biological activity of inflammatory mediators such as CC chemokines, which have been implicated in a wide range of chronic inflammatory diseases. Conventional chemotaxis systems such as the modified Boyden chamber are limited in terms of the data captured given that the assays are analysed at a single time-point. We report the optimisation and validation of a label-free, real-time cell migration assay based on electrical cell impedance to measure chemotaxis of different primary murine macrophage populations in response to a range of CC chemokines and other chemoattractant signalling molecules. We clearly demonstrate key differences in the migratory behavior of different murine macrophage populations and show that this dynamic system measures true macrophage chemotaxis rather than chemokinesis or fugetaxis. We highlight an absolute requirement for Gαi signaling and actin cytoskeletal rearrangement as demonstrated by Pertussis toxin and cytochalasin D inhibition. We also studied the chemotaxis of CD14(+) human monocytes and demonstrate distinct chemotactic profiles amongst different monocyte donors to CCL2. This real-time chemotaxis assay will allow a detailed analysis of factors that regulate macrophage responses to chemoattractant cytokines and inflammatory mediators.

The atypical chemokine receptor D6 controls macrophage efferocytosis and cytokine secretion during the resolution of inflammation

The resolution of acute inflammation is hallmarked by the apoptotic death of inflammatory polymorphonuclear (PMN) cells, followed by their clearance by macrophages. In turn, resolution-phase macrophages exert reduced proinflammatory cytokine production, termed immune silencing. In this study, we found that the atypical chemokine receptor D6 plays an important and chemokine scavenging-independent role in promoting macrophage-mediated resolution. D6(-/-) mice displayed increased numbers of macrophages (2.2-fold increase), but not neutrophils, in their peritonea during the resolution of murine zymosan A-initiated peritonitis, in comparison to D6(+/+) animals. Moreover, D6-deficient macrophages engulfed higher numbers of apoptotic PMN cells in vivo (1.6-fold increase), and secreted higher amounts of TNF-α, CCL3, and CCL5 ex vivo than their wild-type (WT) counterparts. In addition, D6 was found to be expressed on apoptotic neutrophils from healthy humans and rodents. Moreover, the immune silencing of LPS-stimulated macrophages following their incubation with senescent PMN cells ex vivo (in terms of TNF-α, IL-1β, and CCL5 secretion) was diminished (50-65% decrease) when D6(-/-) PMN cells were applied. Accordingly, the adhesive responses induced by macrophage interactions with senescent PMN cells were reduced with D6-deficient PMN cells. Thus, our results indicate a novel mode of action for D6 during the resolution of inflammation that is instrumental to the shaping of resolving macrophage phenotypes and the completion of resolution.

Noninvasive cell-based impedance spectroscopy for real-time probing inhibitory effects of graphene derivatives

Three water-dispersible graphene derivatives, graphene oxide (GO), sulfonated graphene oxide (SGO), and sulfonated graphene (SG), were prepared and probed for their plausible cytotoxicity by non-invasive electric cell-substrate impedance sensing (ECIS). With Spodoptera frugiperda Sf9 insect cells adhered on gold microelectrodes as an active interface, it is feasible to monitor changes in impedance upon exposure to different graphene derivatives. Sf9 insect cells were then exposed to different concentrations of graphene derivatives and their spreading and viability were monitored and quantified by ECIS in real-time. On the basis of the 50% inhibition concentration (ECIS50), none of the graphene derivatives were judged to have any significant cytotoxicity with respect to the chosen cell line as the ECIS50 values were all above 100 μg/mL. However, all graphene derivatives exhibited inhibitory effects on the Sf9 response at the cell spreading level with the following order: SG (ECIS50 = 121 ± 8 μg/mL), SGO (ECIS50 = 151 ± 9 μg/mL), and GO (ECIS50 = 232 ± 27 μg/mL), reflecting differences observed in their ζ-potential and surface area. The presence of phenyl sulfonyl groups in SGO and SG improves their aqueous dispersity which enables these materials to have a greater inhibitory effect on Sf9 insect cells in comparison to GO. Such results were corroborated well with the cell count and viability by the Trypan Blue exclusion assay.

Probing inhibitory effects of nanocrystalline cellulose: inhibition versus surface charge

NCC derived from different biomass sources was probed for its plausible cytotoxicity by electric cell-substrate impedance sensing (ECIS). Two different cell lines, Spodoptera frugiperda Sf9 insect cells and Chinese hamster lung fibroblast V79, were exposed to NCC and their spreading and viability were monitored and quantified by ECIS. Based on the 50%-inhibition concentration (ECIS(50)), none of the NCC produced was judged to have any significant cytotoxicity on these two cell lines. However, NCC derived from flax exhibited the most pronounced inhibition on Sf9 compared to hemp and cellulose powder. NCCs from flax and hemp pre-treated with pectate lyase were also less inhibitory than NCCs prepared from untreated flax and hemp. Results also suggested a correlation between the inhibitory effect and the carboxylic acid contents on the NCC.

Label-Free Biosensors for Cell Biology

Label-free biosensors for studying cell biology have finally come of age. Recent developments have advanced the biosensors from low throughput and high maintenance research tools to high throughput and low maintenance screening platforms. In parallel, the biosensors have evolved from an analytical tool solely for molecular interaction analysis to powerful platforms for studying cell biology at the whole cell level. This paper presents historical development, detection principles, and applications in cell biology of label-free biosensors. Future perspectives are also discussed.

Electrical cell-substrate impedance sensing as a non-invasive tool for cancer cell study

Cell-substrate interactions are investigated in a number of studies for drug targets including angiogenesis, arteriosclerosis, chronic inflammatory diseases and carcinogenesis. One characteristic of malignant cancerous cells is their ability to invade tissue. Cell adhesion and cytoskeletal activity have served as valuable indicators for understanding the cancer cell behaviours, such as proliferation, migration and invasion. This review focuses on bio-impedance based measurement for monitoring the behaviours in real time and without using labels. Electric cell-substrate impedance sensing (ECIS) provides rich information about cell-substrate interactions, cell-cell communication and cell adhesion. High sensitivity of the ECIS method allows for observing events down to single-cell level and achieving nanoscale resolution of cell-substrate distances. Recently, its miniaturization and integration with fluorescent detection techniques have been highlighted as a new tool to deliver a high-content platform for anticancer drug development.

Noninvasive probing of inhibitory effects of cylindrospermopsin and microcystin-LR using cell-based impedance spectroscopy

In an effort to develop a noninvasive method for assessment of cyanobacterial toxins in drinking water, plausible cytotoxicity/inhibition of microcystin-LR and cylindrospermopsin was evaluated by cell-substrate impedance sensing (ECIS) using three different cell lines. Sf9 insect cells were attached to concanavalin A coated gold electrodes, whereas Chinese hamster ovary (CHO) and human embryo kidney (HEK) cells were attached to a fibronectin or laminin coated gold surface. Cytotoxic or inhibitory effects were dependent upon the cell line and the extracellular matrix (ECM) coating. Neither toxin exhibited any appreciable effect on the insect cells. In contrast, cytotoxicity of cylindrospermopsin on CHO cells was attested by both ECIS and viability tests. The half-inhibition concentration (ECIS50) of cylindrospermopsin for CHO cells was approximately 2 microg/mL (ppm) after 20 h of exposure and 4 microg/mL (ppm) after 30 h of exposure for a laminin or fibronectin coated surface. ECIS confirmed no significant effect of cylindrospermopsin on HEK cells. Microcystin-LR was also tested with CHO cells, resulting in an ECIS50 value of approximately 12 microg/mL (ppm) after 25 h of exposure for a laminin coated gold surface. The effect of microcystin-LR on CHO cells probed by ECIS was inhibitory rather than cytotoxic, as confirmed by cell viability assays.

Evaluation of doxorubicin toxicity on cardiomyocytes using a dual functional extracellular biochip

Nowadays, cardiotoxicity induced by clinical drugs presents a high prevalence and has aroused great attention onto the effective and reliable drug evaluation before clinical treatment. Doxorubicin (Adriamycin), as a type of anthracycline chemotherapy agent for cancer treatment, was restricted in the clinical use because of its cardiotoxicity. In the present work, a dual functional biochip ExCell integrated with microelectrode arrays and interdigitated electrodes was designed to study the electrophysiological function and physical state of cardiomyocytes under the treatment of doxorubicin. Extracellular field potentials and cell-substrate impedance were measured to respectively express these two functions simultaneously in the same culture. The result detected by ExCell presented a portrait of cardiotoxicity induced by doxorubicin. The amplitude of extracellular field potentials decreased to 93%, 82% and 50% at 50 min treatment of doxorubicin with concentrations of 20 μM, 100 μM and 200 μM, respectively. Successively, beating rate decrease, beat-to-beat variation and Ca(2+) flux manifested severe abnormality. The cell-substrate impedance declined continuously in the depressing process of electrophysiological function and cell death was induced in high concentration treatment. All these result indicate that the biochip ExCell has the potential to be a fast-response and subtle tool for high-throughput drug evaluation assays.

Mammalian cell-based sensor system

Use of living cells or cellular components in biosensors is receiving increased attention and opens a whole new area of functional diagnostics. The term "mammalian cell-based biosensor" is designated to biosensors utilizing mammalian cells as the biorecognition element. Cell-based assays, such as high-throughput screening (HTS) or cytotoxicity testing, have already emerged as dependable and promising approaches to measure the functionality or toxicity of a compound (in case of HTS); or to probe the presence of pathogenic or toxigenic entities in clinical, environmental, or food samples. External stimuli or changes in cellular microenvironment sometimes perturb the "normal" physiological activities of mammalian cells, thus allowing CBBs to screen, monitor, and measure the analyte-induced changes. The advantage of CBBs is that they can report the presence or absence of active components, such as live pathogens or active toxins. In some cases, mammalian cells or plasma membranes are used as electrical capacitors and cell-cell and cell-substrate contact is measured via conductivity or electrical impedance. In addition, cytopathogenicity or cytotoxicity induced by pathogens or toxins resulting in apoptosis or necrosis could be measured via optical devices using fluorescence or luminescence. This chapter focuses mainly on the type and applications of different mammalian cell-based sensor systems.

Intervention of cardiomyocyte death based on real-time monitoring of cell adhesion through impedance sensing

Cardiomyocyte death caused by proinflammatory cytokines, such as Tumor necrosis factor alpha (TNF-alpha), is one of the hot topics in cardiovascular research. TNF-alpha can induce multiple cell processes that are dependent on the treatment time although the long-term treatment definitely leads to cell death. The ability to intervene in cell death will be invaluable to reveal the effects of short-term TNF-alpha treatment to cardiomyocytes. However, a real-time monitoring technique is needed to guide the intervention of cell responses. In this work, we employed the impedance-sensing technique to real-time monitor the equivalent cell-substrate distance of cardiomyocytes via electrochemical impedance spectroscopy (EIS) and electrical cell-substrate impedance sensing (ECIS). In the stabilized cardiomyocyte culture, the sustained TNF-alpha treatment caused strengthened cell adhesion in the first 2 h which was followed by the transition to cell detachment afterwards. Considering cell detachment was an early morphological evidence of cell death, we removed TNF-alpha from the cardiomyocyte culture before the transition to achieve the intervention of cell responses. The result of this intervention showed that cell adhesion was continuously strengthened before and after the removal of TNF-alpha, indicating the short-term treated cardiomyocytes did not undergo death processes. It was also demonstrated in TUNEL and TBE tests that the percentages of apoptosis and cell death were both lowered.

Impedance-based monitoring of ongoing cardiomyocyte death induced by tumor necrosis factor-alpha

Deregulated cardiomyocyte death is a critical risk factor in a variety of cardiovascular diseases. Although various assays have been developed to detect cell responses during cell death, the capability of monitoring cell detachment will enhance the understanding of death processes by providing instant information at its early phase. In this work, we developed an impedance-sensing assay for real-time monitoring of cardiomyocyte death induced by tumor necrosis factor-alpha based on recording the change in cardiomyocyte adhesion to extracellular matrix. Electrochemical impedance spectroscopy was employed in impedance data processing, followed by calibration with the electrical cell-substrate impedance-sensing technique. The adhesion profile of cardiomyocytes undergoing cell death processes was recorded as the time course of equivalent cell-substrate distance. The cell detachment was detected with our assay and proved related to cell death in the following experiments, indicating its advantage against the conventional assays, such as Trypan blue exclusion. An optimal concentration of tumor necrosis factor-alpha (20 ng/mL) was determined to induce cardiomyocyte apoptosis rather than the combinative cell death of necrosis and apoptosis by comparing the concentration-related adhesion profiles. The cardiomyocytes undergoing apoptosis experienced an increase of cell-substrate distance from 59.1 to 89.2 nm within 24 h. The early change of cell adhesion was proved related to cardiomyocyte apoptosis in the following TUNEL test at t = 24 h, which suggested the possibility of early and noninvasive detection of cardiomyocyte apoptosis.

Impedance analysis of renal vascular smooth muscle cells

Impedance of renal vascular smooth muscle cells (VSMCs) cultured on microelectrodes was measured by electric cell-substrate impedance sensing. Changes in measured impedance as a function of frequency were compared with the calculated values obtained from an extended cell-electrode model to estimate the junctional resistance, distance between the ventral cell surface and the substratum, and apical and basolateral membrane capacitances of renal VSMCs. This cell-electrode model was derived to accommodate the slender and rectangular shape of VSMCs. The calculated changes in impedance (Z(cal)) based on the model agreed well with the experimental measurement (Z(exp)), and the percentage error defined as |(Z(cal)-Z(exp))/Z(exp)| was 1.0%. To test the sensitivity of the new model for capturing changes in cell-cell and cell-substrate interactions induced by changes in cellular environment, we then applied this model to analyze impedance changes induced by an integrin binding peptide in renal VSMCs. Our result demonstrates that integrin binding peptide decreases junctional resistance between cells, increases the distance between the basolateral cell surface and substratum, and increases the apical membrane capacitance, whereas the basolateral membrane capacitance stays relatively stable. This model provides a generic approach for impedance analysis of cell layers composed of slender, rectangular cells.

Real-time monitoring primary cardiomyocyte adhesion based on electrochemical impedance spectroscopy and electrical cell-substrate impedance sensing

The cell-substrate distance is a direct indicator of cell adhesion to extracellular matrix which is indispensable in cell culture. A real-time monitoring approach can provide a detailed profile of cell adhesion, so that enables the detecting of adhesion-related cell behavior. In this work, we report a novel real-time impedance-based method to record the adhesion profile of cardiomyocyte, overcoming its inscrutability due to the primary culture. Microfabricated biosensors are applied in cardiomyocyte culture after characterizing the cell-free system. Cyclic frequency scanning data of cell-related impedance are generated and automatically fit into the equivalent circuit model, which is established using electrochemical impedance spectroscopy. The data are displayed as the alteration of normalized cell-substrate distance and the essential parameters for manual electric cell-substrate impedance sensing calibration of absolute distance. The time course displays a significant decline in the equivalent cell-substrate distance, from 155.8 to 60.2 nm in the first 20 h of cardiomyocyte culture. Furthermore, the cardiomyocytes cultured in long-term medium and short-term medium (ACCT) for 10 h exhibit distinct difference in adhesion rate as well as cell-substrate distance (72 vs 68 nm).

Automated real-time measurements of leukocyte chemotaxis

We have previously described an automated system (ECIS/taxis) for measuring chemotactic movement of Dictyostelium amoebae in a folic acid gradient [Hadjout, N., Laevsky, G., Knecht, D.A. and Lynes, M.A., 2001. Automated real-time measurement of chemotactic cell motility. Biotechniques 31, 1130-1138.]. In the ECIS/taxis system, cells migrate in an under-agarose environment, and their position is monitored by determining the impedance change caused by cells crawling onto the surface of an electrode. In this report, we show that chemotaxis of primary and immortalized leukocytes in response to complement (C5a) could be measured using the ECIS/taxis system. Several modifications to the design of the target electrode were tested, and a linear electrode perpendicular to the direction of movement was found to increase the sensitivity and reliability of the assay. Using the optimized ECIS/taxis assay, the dose response of neutrophils and WBC 265-9C cells was established and compared to the Boyden chamber assay. The ECIS/taxis assay system can be used to compare the movement of different cell types, to assess the effect of complex chemotactic gradients, or to determine the effects of pharmaceuticals on chemotactic motility.

Embryonic stem cells as a novel cell source of cell-based biosensors

To investigate the use of embryonic stem cells as biosensor elements, mouse embryoid bodies were cultured on the surface of the light-addressable potentiometric sensor and induce to in vitro differentiate into cardiomyocytes and neurons. Extracellular potentials of the cells were recorded by sensor, to detect stem cells potential applications in drugs screening. The experimental results show that known cardiac stimulants (isoproterenol) and relaxants (carbamylcholine) have characteristic effects on the cardiomyocytes in terms of the changes of beat frequency, amplitude and duration. Thus, the embryonic stem cells potentially represent a renewable cell source for the cell-based biosensors.

Adhesion of eukaryotic cell lines on the gold surface modified with extracellular matrix proteins monitored by the piezoelectric sensor

The piezoelectric sensor (quartz crystal microbalance, QCM) was used to monitor cell adhesion in real time. Two cell lines, rat epithelial cells (WB F344) and lung melanoma cells (B16F10) were used. The cells were adhered and grown on the gold surface of the sensor pre-coated with adsorbed layer of extracellular matrix proteins as vitronectin and laminin. The process of cell attachment and spreading on the gold surface was continuously monitored and displayed by changes of the resonant frequency Deltaf and resistance DeltaR values of the piezoelectric resonators. The initial phase of cell attachment and spreading induced a decrease of frequency and increase of resistance relating viscoelastic properties of the cell monolayer on the sensing surface. The steady-state of both shifts was achieved after a few hours. The presence and state of cells on the surface was confirmed by fluorescent microscopy. The obtained results demonstrate that the piezoelectric sensor is suitable for studies of the cell adhesion processes. Thus obtained cell-based biosensor has potential for identification and screening of biologically active drugs and other biomolecules affecting cellular shape and attachment.

Adsorption and fluctuations of giant liposomes studied by electrochemical impedance measurements

The present study describes a novel approach based on electrochemical impedance measurements to follow the adsorption of giant liposomes on protein-coated solid surfaces with a time resolution in the order of seconds. The technical key features are circular gold-film electrodes as small as a few hundred micrometers in diameter and measurements of the electrode capacitance using AC signals in the kilohertz regime. Using Monte Carlo simulations, we were able to support the experiments and extract the rate constant of liposome adsorption. Besides monitoring the adsorption of liposomes on protein-coated surfaces, we also applied this technique to study shape fluctuations of the adsorbed vesicles and compared the corresponding power spectra with those recorded for hard particles and living animal cells.

On-chip micro-biosensor for the detection of human CD4+ cells based on AC impedance and optical analysis

The current study was undertaken to fabricate a small micro-electrode on-chip to rapidly detect and quantify human CD4(+) cells in a minimal volume of blood through impedance measurements made with simple electronics that could be battery operated implemented in a hand held device. The micro-electrode surface was non-covalently modified sequentially by incubation with solutions of protein G', human albumin, monoclonal mouse anti-human CD4, and mouse IgG. The anti-human CD4 antibody served as the recognition and capture molecule for CD4(+) cells present in human blood. The binding of these biomolecules to the micro-electrodes was verified by impedance and cyclic voltammetry measurements. An increase in impedance was detected for each layer of protein adsorbed onto the micro-electrode surface. This process was shown to be highly repeatable. Increased impedance was measured when CD4(+) cells were captured on the micro-electrode, and the impedance also increased as the number of captured cells increased. Fluorescence microscopy of captured cells immunolabeled with anti-human CD4, CD8, and CD19 antibodies, and the nuclear label DAPI, confirmed that only CD4(+) cells were captured. The results were highly dependent on the specimen preparation method used. We conclude that the on-chip capture system can efficiently quantify the number of CD4(+) cells.

Application of Real-Time Cell Electronic Sensing (RT-CES) Technology to Cell-Based Assays

Label-free detection emerges as a new approach in the development of technologies for cell-based screening assays. Unlike the classic detection methods that use fluorescence, radioisotope, luminescence, or light absorption, label-free detection directly measures the cell function without using a labeled molecule. The advantages of label-free detection include a simple homogeneous assay format, noninvasive measurement, less interference with normal cell function, kinetic measurement, and reduced time for assay development. Here, we have applied the electrical impedance detection method in a real-time cell electronic sensing (RT-CES trade mark ) system for cell-based assays. The cell growth rate measured by this RT-CES system was comparable to actual cell number counted manually. In addition, cell proliferation, cytotoxicity, cytoprotection, cell growth inhibition, and apoptosis data generated by this RT-CES system correlated with those determined by the classic methods. The conclusion is that the RT-CES system is a useful tool for label-free detection of certain cell-based parameters.

Shrinking the biologic world--nanobiotechnologies for toxicology

Although toxicologic effects need to be considered at the organismal level, the adverse events originate from interactions and alterations at the molecular level. Cellular structures and functions can be disrupted by modifications of the nanometer structure of critical molecules; therefore, devices used to assess biologic and toxicologic processes at the nanoscale will allow important new research pursuits. In order to properly assess alterations at these dimensions, nanofabricated tools are needed to detect, separate, analyze, and manipulate cells or biologic molecules of interest. The emergence of laser tweezers, surface plasmon resonance (SPR), laser capture microdissection (LCM), atomic force microscopy (AFM), and multi-photon microscopes have allowed for these assessments. Micro- and nanobiotechnologies will further advance biologic, clinical, and toxicologic endeavors with the aid of miniaturized, more sensitive devices. Miniaturized table-top laboratory equipment incorporating additional innovative technologies can lead to new advances, including micro total analysis systems (microTAS) or "lab-on-a-chip" and "sentinel sensor" devices. This review will highlight several devices, which have been made possible by techniques originating in the microelectronics industry. These devices can be used for toxicologic assessment of cellular structures and functions, such as cellular adhesion, signal transduction, motility, deformability, metabolism, and secretion.

Fibroblast Cells: A Sensing Bioelement for Glucose Detection by Impedance Spectroscopy

Modifying the electrical properties of fibroblasts against various glucose concentrations can serve as a basis for a new, original sensing device. The aim of the present study is to test a new biosensor based on impedancemetry measurement using eukaryote cells. Fibroblast cells were grown on a small optically transparent indium tin oxide semiconductor electrode. Electrochemical impedance spectroscopy (EIS) was used to measure the effect of D-glucose on the electrical properties of fibroblast cells. Further analyses of the EIS results were performed using equivalent circuits in order to model the electrical flow through the interface. The linear calibration curve was established in the range 0-14 mM. The specification of the biosensors was verified using cytochalasin B as an inhibitor agent of the glucose transporters. The nonreactivity to sugars other than glucose was demonstrated. Such a biosensor could be applied to a more fundamental study of cell metabolism.

Assessment of cytotoxicity using electric cell-substrate impedance sensing: concentration and time response function approach

This paper describes a simple and convenient method to measure the concentration and time response function f (C,t) of cells exposed to a toxicant by electric cell-substrate impedance sensing. Attachment and spreading of fibroblastic V79 cells cultured on small gold electrodes precoated with fibronectin were detected as electrical resistance changes. With this method, chemical cytotoxicity was easily screened by observing the response function of attached cells in the presence of inhibitor. The cytotoxicities of three test models, cadmium chloride, sodium arsenate, and benzalkonium chloride, were quantified by measuring the percentage inhibition as a function of the inhibitor concentration. The half-inhibition concentration, the required concentration to achieve 50% inhibition, derived from the response function agreed well with the results obtained using the standard neutral red assay.

An in-depth analysis of electric cell-substrate impedance sensing to study the attachment and spreading of mammalian cells

The attachment and spreading of fibroblast cells on a gold surface coated with fibronectin or ovalbumin were studied by a modified electric cell-substrate impedance sensor. In this system, cells were cultured in a well, equipped with a detecting gold electrode (surface area of 0.057 mm2) and a gold counter electrode (18 mm2). Based on a comprehensive theoretical framework, the impedance of the electrode-electrolyte interface and a cell layer was precisely obtained for frequencies ranging from 1 to 10 kHz. Surface concentrations of the protein adsorbed on the gold surface were determined by a surface plasmon resonance biosensor. The resistance change of the electrode-electrolyte interface at 4 kHz increased linearly with the number of fibroblast cells attached on the detecting electrode. The slope of the linear relationship appeared to depend on the type of coating protein. As the surface area occupied by the cells was also proportional to the cell number, the resistance change was in turn proportional to the area covered by the cells.

Monitoring motility, spreading, and mortality of adherent insect cells using an impedance sensor

An emerging sensor technology referred to as electric cell-substrate impedance sensing (ECIS) has been extended for monitoring the behavior of insect cells including attachment, motility, and mortality. In ECIS, adherent cells were cultured on an array of eight small gold electrodes deposited on the bottom of tissue culture wells and immersed in a culture medium. Upon the attachment and spreading of cells on the gold electrode, the impedance increased because the cells acted as insulating particles to restrict the current flow. Experimental data revealed that insect cells interacted differently with various proteins used to precoat the gold electrode with concanavalin A as the best promoter to accelerate the rate of cell attachment. After the cells were fully spread, the measured impedance continued to fluctuate to reflect the constant motion and metabolic activity of the cells. As the cell behavior was sensitive to external chemicals, the applicability of ECIS for inhibition assays was demonstrated with HgCl2, trinitrotoluene, trinitrobenzene (TNB), and 2-amino-4,6-dinitrotoluene as model systems. Unlike conventional assays, the quantitative data obtained in this study are taken in real time and in a continuous fashion to depict cell motility and mortality.

Direct evidence for an adhesive function in the noncholinergic role of acetylcholinesterase in neurite outgrowth

Acetylcholinesterase (AChE) can promote neurite outgrowth through a mechanism that is independent of its role in hydrolyzing the neurotransmitter acetylcholine. It has been proposed that this neuritogenic capacity of AChE may result from its intrinsic capacity to function in adhesion. In this study we directly tested this hypothesis using neuroblastoma cell lines that have been engineered for altered cell-surface expression of AChE. Using a microtiter-plate adhesion assay and the electrical cell-substrate impedance-sensing (ECIS) method, we demonstrate that the level of cell-substratum adhesion of these cells directly correlates with their level of AChE expression. Furthermore, this adhesion is blocked by either an anti-AChE antibody or a highly specific AChE inhibitor (BW284c51), both of which have also been shown to block neurite outgrowth. In addition, cells that overexpress AChE showed enhanced neurite initiation. By employing cell lines with different levels of AChE expression in two types of cell-substratum adhesion assays, our current studies provide evidence for an adhesive function for AChE. These results, together with the fact that AChE shares sequence homology and structural similarities with several known cell adhesion molecules, support the hypothesis that AChE promotes neurite outgrowth, at least in part, through an adhesive function.

Distinguishing between activated and nonactivated eosinophils by AC impedance measurements

A cellular electrical impedance device which can detect the activated state of eosinophils has been developed and tested. This impedance device consists of a small gold electrode (50 microns x 50 microns) and a large gold electrode (1.5 cm x 0.5 cm) on a glass substrate, and it was fabricated by standard photolithographic techniques. Eosinophils, which belong to the granulocytic class of white blood cells, exhibit different physical properties when they change from the nonactivated state to the activated state. Hypothetically, these changes should correspond to a change in the measured electrical impedance. In this paper, data from the measured electrical impedance of eosinophils is presented. The measurements show that the average impedance of the activated eosinophils is 26% lower than the average impedance of the nonactivated eosinophils. Statistical analysis of the measured data shows that there is a significant difference between the measured impedances of activated and nonactivated eosinophils.

A morphological biosensor for mammalian cells

An electrical biosensor is described that can continuously track morphological changes of adherent cells providing quantitative data from both sparse and confluent cultures. The method is capable of detecting vertical motion of cells of the order of 1 nm, much below the resolution of an optical microscope.

Electrical method for detection of endothelial cell shape change in real time: assessment of endothelial barrier function

We have developed an electrical method to study endothelial cell shape changes in real time in order to examine the mechanisms of alterations in the endothelial barrier function. Endothelial shape changes were quantified by using a monolayer of endothelial cells grown on a small (10(-3) cm2) evaporated gold electrode and measuring the changes in electrical impedance. Bovine pulmonary microvessel endothelial cells and bovine pulmonary artery endothelial cells were used to study the effects of alpha-thrombin on cell-shape dynamics by the impedance measurement. alpha-Thrombin produced a dose-dependent decrease in impedance that occurred within 0.5 min in both cell types, indicative of retraction of endothelial cells and widening of interendothelial junctions because of "rounding up" of the cells. The alpha-thrombin-induced decrease in impedance persisted for approximately 2 hr, after which the value recovered to basal levels. Pretreatment of endothelial cells with the protein kinase C inhibitor, calphostin C, or with 8-bromoadenosine 3',5'-cyclic monophosphate prevented the decreased impedance, suggesting that the endothelial cell change is modulated by activation of second-messenger pathways. The alpha-thrombin-induced decrease in impedance was in agreement with the previously observed increases in transendothelial albumin permeability and evidence of formation of intercellular gaps after alpha-thrombin challenge. The impedance measurement may be a valuable in vitro method for the assessment of mechanisms of decreased endothelial barrier function occurring with inflammatory mediators. Since the rapidly occurring changes in endothelial cell shape in response to mediators such as thrombin are mediated activation of second-messenger pathways, the ability to monitor endothelial cell dynamics in real time may provide insights into the signal-transduction events mediating the increased endothelial permeability.