Real-time Impedance Measurements Research Articles

Mitochondrial dysfunction increases pro-inflammatory cytokine production and impairs repair and corticosteroid responsiveness in lung epithelium

COPD is characterized by chronic lung inflammation and irreversible lung tissue damage. Inhaled noxious gases, including cigarette smoke, are the major risk factor for COPD. Inhaled smoke first encounters the epithelial lining of the lungs, causing oxidative stress and mitochondrial dysfunction. We investigated whether a mitochondrial defect may contribute to increased lung epithelial pro-inflammatory responses, impaired epithelial repair and reduced corticosteroid sensitivity as observed in COPD. We used wild-type alveolar epithelial cells A549 and mitochondrial DNA-depleted A549 cells (A549 Rho-0) and studied pro-inflammatory responses using (multiplex) ELISA as well as epithelial barrier function and repair (real-time impedance measurements), in the presence and absence of the inhaled corticosteroid budesonide. We observed that A549 Rho-0 cells secrete higher levels of pro-inflammatory cytokines than wild-type A549 cells and display impaired repair upon wounding. Budesonide strongly suppressed the production of neutrophil attractant CXCL8, and promoted epithelial integrity in A549 wild-type cells, while A549 Rho-0 cells displayed reduced corticosteroid sensitivity compared to wild-type cells. The reduced corticosteroid responsiveness may be mediated by glycolytic reprogramming, specifically glycolysis-associated PI3K signaling, as PI3K inhibitor LY294002 restored the sensitivity of CXCL8 secretion to corticosteroids in A549 Rho-0 cells. In conclusion, mitochondrial defects may lead to increased lung epithelial pro-inflammatory responses, reduced epithelial repair and reduced corticosteroid responsiveness in lung epithelium, thus potentially contributing to the pathogenesis of COPD.

Intrapleural Impedance Sensor Real-Time Tracking of Pneumothorax in a Porcine Model of Air Leak

In patients with alveolar-to-pleural air leak due to recent surgery or trauma, clinicians tend to manage chest tubes with suction therapy. Nonsuction therapy is associated with shorter chest tube duration but also a higher risk of pneumothorax. We sought to develop an intrapleural electrical impedance sensor for continuous, real-time monitoring of pneumothorax development in a porcine model of air leak as a means of promoting nonsuction therapy. Using thoracoscopy, 2 chest tubes and the pleural impedance sensor were introduced into the pleural space of 3 pigs. Continuous air leak was introduced through 1 chest tube by carbon dioxide insufflation. The second chest tube was placed to suction then transitioned to no suction at increasingly higher air leaks until pneumothorax developed. Simultaneously, real-time impedance measurements were obtained from the pleural sensor. Fluoroscopy spot images were captured to verify the presence or absence of pneumothorax. Statistical Analysis Software was used throughout. With the chest tube on suction, a fully expanded lung was identified by a distinct pleural electrical impedance respiratory waveform. With transition of the chest tube to water seal, loss of contact of the sensor with the lung resulted in an immediate measurement of infinite electrical impedance. Pneumothorax resolution by restoring suction therapy was detected in real time by a return of the normal respiratory impedance waveform. Pleural electrical impedance monitoring detected pneumothorax development and resolution in real time. This simple technology has the potential to improve the safety and quality of chest tube management.

Linalool attenuates oxidative stress and mitochondrial dysfunction mediated by glutamate and NMDA toxicity

Mitochondrial dysfunction and inflammation contribute to the initiation and development of several brain pathological conditions, including Alzheimer’s disease and cerebral ischemia. Linalool is an aromatic plant-derived monoterpene alcohol with reported anti-inflammatory, and anti-oxidant properties. We investigated the role of linalool on glutamate-induced mitochondrial oxidative stress in immortalized neuronal HT-22 cells. Glutamate induced oxidative stress in neuronal cells, as detected by real-time cell impedance measurements, MTT assay, and analysis of Annexin V/PI. Administration of linalool 100 μM reduced cell death mediated by glutamate. Staining of glutamate-stimulated mitochondria by MitoTracker revealed improved morphology in the presence of linalool. Furthermore, we demonstrated a potential neuroprotective effect of linalool in conditions of oxidative stress by a reduction of mitochondrial ROS and mitochondrial calcium levels, and by preserving mitochondrial membrane potential. Experiments using both high-resolution respirometry and Seahorse Extracellular flux analyzer showed that linalool was able to promote an increase in uncoupled respiration that could contribute to its neuroprotective capacity. Linalool protection was validated using organotypic hippocampal slices as ex vivo model with NMDA as a stimulus to induce excitotoxity cell damage. These results demonstrate that linalool is protective in an in vitro model of glutamate-induced oxidative stress and in an ex-vivo model for excitotoxity, proposing linalool as a potential therapeutic agent against neurodegenerative brain diseases where oxidative stress contributes to the pathology of the disease.

Real-time cellular impedance monitoring and imaging of biological barriers in a dual-flow membrane bioreactor

The generation of physiologically relevant in-vitro models of biological barriers can play a key role in understanding human diseases and in the development of more predictive methods for assessing toxicity and drug or nutrient absorption. Here, we present an advanced cell culture system able to mimic the dynamic environment of biological barriers while monitoring cell behaviour through real-time impedance measurements and imaging. It consists of a fluidic device with an apical and a basal flow compartment separated by a semi-permeable membrane. The main features of the device are the integration of sensing through transepithelial electrical impedance (TEEI) measurements and transparent windows for optical monitoring within a dual flow system.Caco-2 cells were cultured in the TEEI bioreactor under both flow and static conditions. Although no differences in the expression of peripheral actin and occludin were visible, the cells in dynamic conditions developed higher impedance values at low frequencies, indicative of a higher paracellular electrical impedance with respect to the static cultures. TEEI measurements at high frequency also enabled monitoring monolayer formation, which can be correlated with the observation of an RC behaviour in the impedance spectra. In particular, the cells subject to flow showed accelerated barrier formation and increased vitality with respect to the static controls, again highlighting the importance of dynamic conditions for epithelial cells.

Characterization of the Electrosurgical Tissue Joining Process Using Dynamic Impedance and Energy Efficiency

Electrosurgical tissue joining is an effective way to create hemostasis, especially in surgical procedures performed in the minimally invasive manner. The quality of tissue joints and potential thermal damages to the surroundings are the two main concerns when using electrosurgical tissue joining tools. A more robust method for quality control is still needed. The goal of this study is to characterize the joining process using dynamic impedance and energy efficiency. Three joining times (4, 6, and 8 s) and three compression levels (80%, 90%, and 95%) were used to join porcine arterial tissues while the process parameters including voltage, current, and impedance were monitored. Tensile tests were performed to evaluate the quality of tissue joints. A new index, the strength-energy coefficient (mmHg/J), which is defined as the tensile strength divided by the consumed energy, is introduced to evaluate the energy efficiency of the joining process. Strength-energy coefficient offers a new way to estimate the required joining time to achieve sufficient joining strength while minimizing the energy consumption to reduce thermal damages. The 95% compression level has the highest strength-energy coefficient for 4- and 6-s joining times. This indicates that the 95% compression level has higher energy efficiency and can form a good tissue joint with less energy and time in comparison with those required by a lower compression level. The progression of the tissue joining process was characterized by the real-time impedance measurement, which can be used as a tool for quality control.

(Invited) Dielectrophoretic Capture and Detection of Microbial Pathogens Using Nanoelectrode Arrays

Rapid and highly sensitive detection of pathogenic microbes is critical for food safety and environmental protection. To achieve this, it requires combining novel sample preparation techniques and extremely sensitive detection methods. In this presentation, I summarize a series of studies in my lab on developing a nanoscale dielectrophoresis (DEP) device for effective capturing and concentrating pathogenic particles such as viral and bacterial particles in a fluidic chip. This technique was then integrated with various detection methods such as fluorescence imaging, surface enhanced Raman spectroscopy (SERS) and real-time impedance measurements for quantitative assessment of the pathogen concentration. Due to the small size (~1 micron for bacterial cells and ~100 nm for viral particles), it is challenging to capture and concentrating these pathogenic particles from dilute solutions. Here we demonstrate that the highly focused electric field at the tip of an embedded nanoelectrode array can be utilized to generate a large DEP force to effectively manipulate pathogenic particles. The nanoelectrode array was made of vertically aligned carbon nanofibers (VACNFs), about 5 micron in length and 100 nm in diameter, and embedded in a SiO2 film. It was placed at the bottom of a microfluidic channel against a macroscopic indium tin oxide (ITO) top electrode, forming a DEP device in “points-and-lid” configuration. We have shown that E. coli DHα5 cells flowing through the channel can be effectively captured and concentrated at the desired microscale areas inside the channel using a small AC voltage (~6-10 Vpp). This device is particularly effective in capturing viral particles (such as bacteriophage T4r) due to the comparable size between the viral particles and the exposed VACNF tip. To achieve specific detection, the DEP chip has been integrated with a Raman probe for SERS measurements of nanotag-labelled E. coli DHα5 cells. The SERS nanotags are based on iron oxide-gold (IO-Au) core-shell nanoovals (NOVs) of ~50 nm in size, which are coated with QSY21 Raman reporters and attached to E. coli cells through specific antibodies. The combination of the greatly enhanced Raman signal by the SERS nanotags and the effective DEP concentration significantly improves the detection limit and speed. The SERS signal has been fully validated with fluorescence microscopy measurements under all DEP conditions. A concentration detection limit as low as 210 cfu/mL using a portable Raman system has been obtained with a DEP capture time of only ~50 s. The detection has been validated in purified solutions as well as complex samples including chicken broth, soil solution and apple juice. Real-time impedance measurements has also been demonstrated as a feedback during DEP capture of vaccinia viral particles. By controlling the proper AC voltage, the nucleic acid contents in the viral particles can be released by opening the envelope with electroporation under the high electric field at the VACNF tips. These results demonstrate the potential to develop a compact portable system for rapid and highly sensitive detection of specific pathogens. Furthermore, this technique is based on physical method and the pathogenic particles are fully released after the AC voltage is turned off, making it a robust device that can be repeatedly used.

A similarity based prognostics approach for real time health management of electronics using impedance analysis and SVM regression

In electronic assemblies, interconnects provide connections between electrical components both mechanically and electrically. During their use conditions, interconnects encounter multiple stress conditions such as temperature extremes, corrosion, and vibration. When these stress conditions are applied repeatedly, interconnects may lose their functionality, and the assemblies may eventually fail during the operation. As the consequence of electronics failure becomes critical, the need for reliable interconnects will grow.This paper demonstrates a prognostic approach for predicting remaining lifetime of solder joints in real-time. During stress testing, impedance has been reported to respond to early stages of solder joint degradation in the form of non-linear increases. These early responses were trended using support vector machine and compared with real-time impedance measurements for solder joint remaining life prediction. To evaluate the prediction performance, the impedance of a degrading solder joint was collected during mechanical fatigue testing, and the proposed approach was applied in real-time. During fatigue testing, the proposed approach successfully predicted solder joint failures over multiple trials. These results imply this prognostic approach can be an effective means for real-time health management of electronics and can be applied to systems whose performance variable demonstrates gradual changes prior to their end of life.

Real-Time Impedance Characterization Method for RFID-Type Backscatter Communication Devices

This paper presents a radio frequency (RF) measurement method that allows to determine electrical characteristics such as scattering parameters or impedance of contactless passive chips, using common measurement devices such as oscilloscope, personal computer, and directional coupler. The measurements obtained using this method are as accurate as those obtained with vector network analyzer (VNA) measurements, while providing several improvements. First, the method makes it possible to measure a chip’s impedance in activation state, which requires large input power, not compatible with VNA measurements. Second, this method realizes a real-time measurement, which consists in impedance measurement as a function of time. Therefore, this real-time measurement makes it possible to detect and measure the impedance changes of an actual contactless smart card’s integrated circuit during a load modulation communication at different powers. Finally, this real-time impedance measurement gives important information on chips’ electrical characteristics that can be used to optimize near-field communication devices design in order to reduce the power losses within an RF identification tag.

Dihydrotestosterone induces pro-angiogenic factors and assists homing of MSC into the cardiac tissue.

The use of mesenchymal stem cells (MSC) as a therapeutic tool in cardiovascular diseases is promising. Since androgens exert some beneficial actions on the cardiovascular system, we tested our hypothesis that this hormone could promote MSC-mediated repair processes, also. Cultured MSCs isolated from Wharton's jelly were exposed to 30 nM dihydrotestosterone (DHT) for 1 or 4 days and the effects of the hormone on their growth/migration/adhesion and the underlying mechanisms were assessed. Results were obtained by real-time cell impedance measurements, and DNA quantification showed that DHT increased MSC proliferation by ~30%. As determined by xCELLigence system, DHT augmented (~2 folds) the migration of MSC toward cardiac tissue slices (at 12 h), and this effect was blocked by flutamide, an androgen receptor (AR) antagonist. Exposure of cells to DHT, upregulated the gene and protein expression of AR, EMMPRIN and MMP-9 and downregulated the expression of MMP-2 DHT significantly induced the release of nitric oxide by MSC (≥2-fold) and flutamide blocked this effect. When MSCs were co-cultured with cardiac slices, immunohistochemical analysis and qRT-PCR showed that the integration of DHT-stimulated MSC was significantly higher than that of in controls. In conclusion, our findings provide the first evidence that DHT promotes MSC growth, migration and integration into the cardiac slices. The modulating effects of DHT were associated with upregulation of ARs and of key molecules known to promote tissue remodeling and angiogenesis. Our findings suggest that priming of MSC with DHT may potentially increase their capability to regenerate cardiac tissue; in vivo studies are needed to confirm our in vitro findings.

Dasatinib Reversibly Disrupts Endothelial Vascular Integrity by Increasing Non-Muscle Myosin II Contractility in a ROCK-Dependent Manner.

Purpose: Dasatinib is a short-acting dual ABL/SRC family tyrosine kinase inhibitor (TKI), which is frequently used to treat chronic myeloid leukemia. Although very effective, patients taking dasatinib often display severe adverse effects, including pleural effusions and increased risk of bleeding primarily in the gastrointestinal tract. The actual causes of these side effects are currently undetermined. We hypothesize that endothelial cells (ECs) that line the inner walls of blood vessels and control the traffic to the underlying tissues might be involved.Experimental Design: The effects of TKIs on ECs were studied by various assays, such as real-time cell impedance measurements, live-cell microscopy, wound healing, Western blot, and an in vivo model.Results: Dasatinib uniquely causes a profound, dose-dependent disorganization of the EC monolayers. Dasatinib promoted the disassembly of cell-cell contacts, altered cell-matrix contacts, and further altered the wound healing. A key observation is that this effect is fully reversible after drug washout. In line with these in vitro observations, intraperitoneal administration of dasatinib to mice caused significant vascular leakage in the intestine. The underlying molecular mechanism of dasatinib-induced reorganization of the actin involves ROCK activation, which increases the amount of the phosphorylation of myosin light chain and consequently activates the non-muscle myosin II.Conclusions: Our data are consistent with a scenario in which dasatinib triggers a transient increase in vascular leakage that probably contributes to adverse effects such as bleeding diathesis and pleural effusions. Clin Cancer Res; 23(21); 6697-707. ©2017 AACR.

Impact of Mycotoxins Secreted by Aspergillus Molds on the Inflammatory Response of Human Corneal Epithelial Cells

Exposure to molds and mycotoxins not only contributes to the onset of respiratory disease, it also affects the ocular surface. Very few published studies concern the evaluation of the effect of mycotoxin exposure on ocular cells. The present study investigates the effects of aflatoxin B1 (AFB1) and gliotoxin, two mycotoxins secreted by Aspergillus molds, on the biological activity of the human corneal epithelial (HCE) cells. After 24, 48, and 72 h of exposure, cellular viability and inflammatory response were assessed. Both endpoint cell viability colorimetric assays and continuous cell impedance measurements, providing noninvasive real-time assessment of the effect on cells, were performed. Cytokine gene expression and interleukin-8 release were quantified. Gliotoxin appeared more cytotoxic than AFB1 but, at the same time, led to a lower increase of the inflammatory response reflecting its immunosuppressive properties. Real-time cell impedance measurement showed a distinct profile of cytotoxicity for both mycotoxins. HCE cells appeared to be a well-suited in vitro model to study ocular surface reactivity following biological contaminant exposure. Low, but persistent inflammation, caused by environmental factors, such as fungal toxins, leads to irritation and sensitization, and could be responsible for allergic manifestations which, in turn, could lead to mucosal hyper-reactivity.

A general method to regenerate arrayed gold microelectrodes for label-free cell assay

We developed a method to regenerate arrayed gold microelectrodes equipped for a commercial label-free cell analyzer. The regeneration process includes efficient treatment of the gold surface with trypsin (0.25%, v/v) digestion, rinsing with ethanol and deionized water and spinning steps. The proposed method ensured complete regeneration and repeated usage of gold microchips up to 4 times for the real-time electric impedance measurement of anti-cancer drug cytotoxicity.

Controllable in-situ cell electroporation with cell positioning and impedance monitoring using micro electrode array.

This paper reports a novel microarray chip for in-situ, real-time and selective electroporation on individual cells integrated with cell positioning and impedance monitoring. An array of quadrupole-electrode units (termed positioning electrodes) and pairs of planar center electrodes located at the centers of each quadrupole-electrode unit were fabricated on the chip. The positioning electrodes are used to trap and position living cells onto the center electrodes based on negative dielectrophoresis (nDEP). The center electrodes are used for in-situ cell electroporation, and also used to measure cell impedance for monitoring cellular dynamics in real time. Controllably selective electroporation and electrical measurement on the cells in array are realized. We present an evidence of selective electroporation through use of fluorescent dyes. Subsequently we use in-situ and real-time impedance measurement to monitor the process, which demonstrates the dynamic behavior of the cell electroporation. Finally, we show the use of this device to perform successful transfection onto individual HeLa cells with vector DNA encoding a green fluorescent.

Real-time monitoring of hypertrophy in HL-1 cardiomyocytes by impedance measurements reveals different modes of growth.

Hypertrophic growth is a response of the heart to increased mechanical load or physiological stress. Thereby, cardiomyocytes grow in length and/or width to maintain cardiac pump function. Major signaling pathways involved in cardiomyocyte growth and remodeling have been identified during recent years including calcineurin-NFAT and PI3K-Akt signaling. Modulation of these pathways is of certain interest for therapeutic treatment of cardiac hypertrophy. However, quantification and characterization of hypertrophy in response to different stimuli or modulators is difficult. This study aims to test different read-out systems for detection and quantification of differences in hypertrophic growth in response to prohypertrophic stimuli. Real-time impedance measurements allowed the detection of distinct differences in hypertrophic growth in response to endothelin, norepinephrine, phenylephrine or BIO, which were not observable by other methods such as flow cytometry. Endothelin treatment induced a rapid and strong peak in the impedance signal concomitant with a massive reorientation of the actin cytoskeleton. Changes in expression of hypertrophy-associated genes were detected and stabilization of β-catenin was identified as a common response to all hypertrophic stimuli used in this study. Hypertrophic growth was blocked by the PI3K/mTOR inhibitor PI-103.

Dynamic monitoring of single cell lysis in an impedance-based microfluidic device.

A microfluidic device that is capable of trapping and sensing dynamic variations in the electrical properties of individual cells is demonstrated. The device is applied to the real-time recording of impedance measurements of mouse embryonic stem cells (mESCs) during the process of membrane lysis, with the resulting changes in the electrical properties of cells during this process being quantitatively tracked over time. It is observed that the impedance magnitude decreases dramatically after cell membrane lysis. A significant shift in the phase spectrum is also observed during the time course of this process. By fitting experimental data to physical models, the electrical parameters of cells can be extracted and parameter variations quantified during the process. In the cell lysis experiments, the equivalent conductivity of the cell membrane is found to increase significantly due to pore formation in the membrane during lysis. An increase in the specific capacitance of the membrane is also observed. On the other hand, the conductivity of the cytoplasm is observed to decrease, which may be explained the fact that excess water enters the cell through the gradual permeabilization of the membrane during lysis. Cells can be trapped in the device for periods up to several days, and their electrical response can be monitored by real-time impedance measurements in a label-free and non-invasive manner. Furthermore, due to the highly efficient single cell trapping capacity of the device, a number of cells can be trapped and held in separate wells for concurrent parallel experiments, allowing for the possibility of stepped parametric experiments and studying cell heterogeneity by combining measurements across the array.

Dosimetric Characteristics of an EMF Delivery System Based on a Real-Time Impedance Measurement Device

In this paper, the dosimetric characterization of an EMF exposure setup compatible with real-time impedance measurements of adherent biological cells is proposed. The EMF are directly delivered to the 16-well format plate used by the commercial xCELLigence apparatus. Experiments and numerical simulations were carried out for the dosimetric analysis. The reflection coefficient was less than -10dB up to 180MHz and this exposure system can be matched at higher frequencies up to 900 and 1800MHz. The specific absorption rate (SAR) distribution within the wells containing the biological medium was calculated by numerical finite-difference time domain simulations and results were verified by temperature measurements at 13.56MHz. Numerical SAR values were obtained at the microelectrode level where the biological cells were exposed to EMF including 13.56, 900, and 1800MHz. At 13.56MHz, the SAR values, within the cell layer and the 270-μL volume of medium, are 1.9e3 and 3.5W/kg/incident mW, respectively.

Microelectrical Impedance Spectroscopy for the Differentiation between Normal and Cancerous Human Urothelial Cell Lines: Real-Time Electrical Impedance Measurement at an Optimal Frequency.

Purpose. To distinguish between normal (SV-HUC-1) and cancerous (TCCSUP) human urothelial cell lines using microelectrical impedance spectroscopy (μEIS). Materials and Methods. Two types of μEIS devices were designed and used in combination to measure the impedance of SV-HUC-1 and TCCSUP cells flowing through the channels of the devices. The first device (μEIS-OF) was designed to determine the optimal frequency at which the impedance of two cell lines is most distinguishable. The μEIS-OF trapped the flowing cells and measured their impedance at a frequency ranging from 5 kHz to 1 MHz. The second device (μEIS-RT) was designed for real-time impedance measurement of the cells at the optimal frequency. The impedance was measured instantaneously as the cells passed the sensing electrodes of μEIS-RT. Results. The optimal frequency, which maximized the average difference of the amplitude and phase angle between the two cell lines (p < 0.001), was determined to be 119 kHz. The real-time impedance of the cell lines was measured at 119 kHz; the two cell lines differed significantly in terms of amplitude and phase angle (p < 0.001). Conclusion. The μEIS-RT can discriminate SV-HUC-1 and TCCSUP cells by measuring the impedance at the optimal frequency determined by the μEIS-OF.

Cultured cells of the blood-brain barrier from apolipoprotein B-100 transgenic mice: effects of oxidized low-density lipoprotein treatment.

BackgroundThe apolipoprotein B-100 (ApoB-100) transgenic mouse line is a model of human atherosclerosis. Latest findings suggest the importance of ApoB-100 in the development of neurodegenerative diseases and microvascular/perivascular localization of ApoB-100 protein was demonstrated in the cerebral cortex of ApoB-100 transgenic mice. The aim of the study was to characterize cultured brain endothelial cells, pericytes and glial cells from wild-type and ApoB-100 transgenic mice and to study the effect of oxidized low-density lipoprotein (oxLDL) on these cells.MethodsMorphology of cells isolated from brains of wild type and ApoB-100 transgenic mice was characterized by immunohistochemistry and the intensity of immunolabeling was quantified by image analysis. Toxicity of oxLDL treatment was monitored by real-time impedance measurement and lactate dehydrogenase release. Reactive oxygen species and nitric oxide production, barrier permeability in triple co-culture blood–brain barrier model and membrane fluidity were also determined after low-density lipoprotein (LDL) or oxLDL treatment.ResultsThe presence of ApoB-100 was confirmed in brain endothelial cells, while no morphological change was observed between wild type and transgenic cells. Oxidized but not native LDL exerted dose-dependent toxicity in all three cell types, induced barrier dysfunction and increased reactive oxygen species (ROS) production in both genotypes. A partial protection from oxLDL toxicity was seen in brain endothelial and glial cells from ApoB-100 transgenic mice. Increased membrane rigidity was measured in brain endothelial cells from ApoB-100 transgenic mice and in LDL or oxLDL treated wild type cells.ConclusionThe morphological and functional properties of cultured brain endothelial cells, pericytes and glial cells from ApoB-100 transgenic mice were characterized and compared to wild type cells for the first time. The membrane fluidity changes in ApoB-100 transgenic cells related to brain microvasculature indicate alterations in lipid composition which may be linked to the partial protection against oxLDL toxicity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12987-015-0013-y) contains supplementary material, which is available to authorized users.

Electrical/ Electrochemical Impedance Measurement for Biological Applications

As a principle of transduction, the impedance technique has been applied in the field of biological study ranging from microbiology to cancer cell/tissue studies. This paper summarizes the applications of electrical/electrochemical impedance spectroscopy that have been practiced in our research in the past several years, mainly including two distinct fields--the detection of foodborne bacterial pathogens and the study of oral cancer cells. Foodborne diseases caused by foodborne pathogens have been a serious threat to public health for decades and remain one of the major concerns of our society. The development of rapid, sensitive, and specific methods is central to implementing effective practice to ensure food safety and security. We have been using impedance technique as a means to detect and/or quantify foodborne pathogenic bacteria. This paper will particular introduce the recent significant development in this field, including the use of microfabricated microelectrodes, microfluidic chip-based devices, nanoparticles and integration with other techniques such as dielectrophoresis. Based on the fundamental impedance microbiology, which is a technique based on the measurement of changes in electrical impedance of a culture medium or a reaction solution resulting from the bacterial growth, we have added some new aspects to this subject that have made the impedance technique a more valuable technique for detection of foodborne bacterial pathogens. These aspects include the use of different electrode systems and the analysis of impedance components using equivalent circuits for better improvement on the detection systems. The advances in microfabrication technologies have launched the use of microfabricated microarray electrodes in impedance detection and the miniaturization of impedance microbiology into a chip format, which has shown great promising in rapid detection of bacterial growth. Further, the integration of impedance technique with biosensor technology has led to the development of impedance biosensors that is expending rapidly for bacteria detection in recent years. Impedance biosensors for bacteria detection are based on the analysis of electrical properties of bacterial cells when they are attached to or associated with the electrodes. Such impedance biosensor methods have substantially reduced the assay time down to 30 min~2 h compared with growth-based impedance methods. The dimensional compatibility of those microfabricated biosensors with the target bacterial cells has enabled them to detect the binding of bacterial cells on its surface without any amplification step. On the other hand, electrical impedance spectroscopy (EIS) enables direct sensing of cellular activities occurring on an electrode surface by measuring the induced capacitance and/or resistance changes by cells attached on the electrode. Particular, EIS is capable of distinguishing different types of cells based on the cellular activity-induced electrical signals. We have demonstrated the use of real-time impedance technique to study the cellular activities of oral cancer cells in a label-free manner, including cell proliferation, adhesion, spreading, and apoptosis induced by drug treatments. Furthermore, it is known that during transformation from non-cancer cells to caner cells, the cellular morphology, structure, and function are altered, which may includes, but are not limited to changes in the nuclei, composition of the cytoplasm, structure of the cell membrane, changes in the nuclei, composition of the cytoplasm, structure of the cell membrane, and expression levels of ion channels, etc. These changes may result in alterations in cancer cell properties that could be detected by the EIS well before these morphological features that normally used in detection can be seen or biomarkers are developed. We have explored the use of real-time impedance measurements to distinguish oral cancer cells from normal oral epithelial cells in label-free manner by studying the kinetics of cell spreading and attachment of the two cell types.

Microfluidic platform for assessing pancreatic islet functionality through dielectric spectroscopy.

Human pancreatic islets are seldom assessed for dynamic responses to external stimuli. Thus, the elucidation of human islet functionality would provide insights into the progression of diabetes mellitus, evaluation of preparations for clinical transplantation, as well as for the development of novel therapeutics. The objective of this study was to develop a microfluidic platform for in vitro islet culture, allowing the multi-parametric investigation of islet response to chemical and biochemical stimuli. This was accomplished through the fabrication and implementation of a microfluidic platform that allowed the perifusion of islet culture while integrating real-time monitoring using impedance spectroscopy, through microfabricated, interdigitated electrodes located along the microchamber arrays. Real-time impedance measurements provide important dielectric parameters, such as cell membrane capacitance and cytoplasmic conductivity, representing proliferation, differentiation, viability, and functionality. The perifusion of varying glucose concentrations and monitoring of the resulting impedance of pancreatic islets were performed as proof-of-concept validation of the lab-on-chip platform. This novel technique to elucidate the underlying mechanisms that dictate islet functionality is presented, providing new information regarding islet function that could improve the evaluation of islet preparations for transplantation. In addition, it will lead to a better understanding of fundamental diabetes-related islet dysfunction and the development of therapeutics through evaluation of potential drug effects.