Electrical Properties Of Cells Research Articles

An electrochemical surface plasmon resonance imaging system targeting cell analysis

This paper presents an electrochemical-surface plasmon resonance imaging (EC-SPRI) system, enabling the characterization of optical and electrical properties of cells, simultaneously. The developed surface plasmon resonance (SPR) imaging system was capable of imaging micro cavities with a dimension of 10 μm × 10 μm and differentiated glycerol solutions with a group of refractive indices (RIs). Furthermore, the EC-SPRI system was used to image A549 cells, suggesting corresponding RI and morphology changes during the cell death process. In the end, electrochemical and SPR methods were used in combination, recording oxidation peaks of A549 cells in the cyclic voltage curves and SPR response unit increase, simultaneously.

Rapid dielectrophoretic characterization of single cells using the dielectrophoretic spring

Dielectrophoresis-based cell separation has significant promise for separation of cells from heterogeneous mixtures based on their electrical properties and is used in diverse areas ranging from hematopoietic stem cell purification to cancer cell isolation. The electrical properties of cells in heterogeneous populations determine if and how well cell subpopulations are separable, and therefore the utility of dielectrophoretic separation is fundamentally determined by our ability to measure electrical properties of cell populations on a cell-by-cell basis. We developed an automated system for electrical characterization of cells that can characterize 1000's of individual cells across a range of conditions (>30 conditions/h). The system uses a continuous-flow microfluidic device and a method termed the dielectrophoretic spring that uses the force balance between dielectrophoresis and fluid drag to measure electrical properties of cells independent of size. We present characterization of the method with beads and cells as well as its application to rapidly find conditions that can discriminate neutrophils with different activation states.

Microfluidic genome-wide profiling of intrinsic electrical properties in Saccharomyces cerevisiae

Methods to analyze the intrinsic physical properties of cells - for example, size, density, rigidity, or electrical properties - are an active area of interest in the microfluidics community. Although the physical properties of cells are determined at a fundamental level by gene expression, the relationship between the two remains exceptionally complex and poorly characterized, limiting the adoption of intrinsic separation technologies. To improve our current understanding of how a cell's genotype maps to a measurable physical characteristic and quantitatively investigate the potential of using these characteristics as biomarkers, we have developed a novel screen that combines microfluidic cell sorting with high-throughput sequencing and the haploid yeast deletion library to identify genes whose functions modulate one such characteristic - intrinsic electrical properties. Using this screen, we are able to establish a high-content electrical profile of the haploid yeast gene deletion strains. We find that individual genetic deletions can appreciably alter the electrical properties of cells, affecting ~10% of the 4432 gene deletion strains screened. Additionally, we find that gene deletions affecting electrical properties in specific ways (i.e. increasing or decreasing effective conductivity at higher or lower electric field frequencies) are strongly associated with an enriched subset of fundamental biological processes that can be traced to specific pathways and complexes. The screening approach demonstrated here and the attendant results are immediately applicable to the intrinsic separations community.

Recordings from Cultured Newt Olfactory Receptor Cells

Freshly dissociated olfactory receptor cells (ORCs) are commonly used in electrophysiological research investigations of the physicochemical mechanisms of olfactory signal transduction. Because the morphology of cultured cells clearly becomes worse over time, the ORCs are examined traditionally within several days after dissociation. However, there has been a major concern that cells are affected soon after dissociation. To gain a better understanding of the reliability of data obtained from solitary cells, we obtained electrical data during the lifetime of single ORCs dissociated from the newt. The time course for the deterioration could be revealed by monitoring the membrane properties during culture. Although the number of living cells that were identified by trypan blue extrusion declined day by day, the remaining cells retained morphology and their fundamental electrical features until day 19. In some cells, the cilia and dendrite were observed until day 21, and the bipolar morphology until day 31. The fundamental features of cell excitation were maintained during culture without showing remarkable changes when they retained morphological features. The results suggest that electrical properties of cells are almost unchanged within several days. Furthermore, the dissociated newt ORCs can be used for several weeks that are almost comparable to the intrinsic lifetime of the ORCs in vivo.

Capacitance-based assay for real-time monitoring of endocytosis and cell viability

Label-free cell-based assays have emerged as a promising means for high-throughput screening. Most label-free sensors are based on impedance measurements that reflect the passive electrical properties of cells. Here we introduce a capacitance-based assay that measures the dielectric constant (capacitance) of biological cells, and demonstrate the feasibility of analyzing endocytosis and screening chemotherapeutic agents with this assay. Endocytosis induces a change in the zeta potential, leading to a change in the dielectric constant which enables real-time endocytosis monitoring using the capacitance sensor. Additionally, since the dielectric constant is proportional to cell radius and cell volume, cell viability can be estimated from the change in capacitance. Therefore, the capacitance sensor array can also be used for cytotoxicity testing for large-scale chemotherapeutic screening.

Viability and membrane potential analysis of Bacillus megaterium cells by impedance flow cytometry

Single cell analysis is an important tool to gain deeper insights into microbial physiology for the characterization and optimization of bioprocesses. In this study a novel single cell analysis technique was applied for estimating viability and membrane potential (MP) of Bacillus megaterium cells cultured in minimal medium. Its measurement principle is based on the analysis of the electrical cell properties and is called impedance flow cytometry (IFC). Comparatively, state-of-the-art fluorescence-based flow cytometry (FCM) was used to verify the results obtained by IFC. Viability and MP analyses were performed with cells at different well-defined growth stages, focusing mainly on exponential and stationary phase cells, as well as on dead cells. This was done by PI and DiOC(2)(3) staining assays in FCM and by impedance measurements at 0.5 and 10 MHz in IFC. In addition, transition growth stages of long-term cultures and agar plate colonies were characterized with both methods. FCM and IFC analyses of all experiments gave comparable results, quantitatively and qualitatively, indicating that IFC is an equivalent technique to FCM for the study of physiological cell states of bacteria.

Efficient Semi‐Transparent Organic Solar Cells with Good Transparency Color Perception and Rendering Properties

AbstractWindow integrated photovoltaics for automotive and building applications are a promising market segment for organic solar modules. Besides semi‐transparency, window integrated applications require a reasonable transparency perception and good color rendering properties in order to be suitable for realistic scene illumination. Here, the transmitted light through semi‐transparent organic solar cells comprising the polymer/fullerene blend poly[(4,4'‐bis(2‐ethylhexyl)dithieno[3,2‐b:2',3'‐d]silole)‐2,6‐diyl‐alt‐(2,1,3‐benzothiadiazole)‐4,7‐diyl]: [6,6]‐phenyl C71‐butric acid methyl ester (PSBTBT:PC70BM) as active layer and a sputtered aluminum doped zinc oxide cathode were found to exhibit a color neutral perception for the human eye and very good color rendering properties. Moreover, the electrical cell properties allow for efficient energy harvesting with an overall power conversion efficiency η ≈ 3%.

G030082 細胞の電気的特性を評価するマイクロ波原子間力顕微鏡プローブの開発([G03008]材料力学部門一般セッション(8):材料の電気的特性)

G030082 細胞の電気的特性を評価するマイクロ波原子間力顕微鏡プローブの開発([G03008]材料力学部門一般セッション(8):材料の電気的特性)

Multiscale Modeling of Dye Solar Cells and Comparison With Experimental Data

In this paper, we investigate the electrical properties of dye solar cells (DSCs) under illumination and in dark conditions when an external bias is applied. The measurements performed on the cells will be compared with theoretical calculations. The modeling is made using two approaches: a finite-element code based on Tiber computer-aided design (CAD) software to describe in detail the electrical properties of the cell and a circuital model implemented on PSpice. The latter has been developed in the perspective of simulating larger systems, such as modules and panels. It should be a phenomenological model to fit I-V characteristics of real cells. The CAD instead allows to calculate steady-state properties and I-V characteristics of the cell, solving a set of differential equations on meshes in one, two, and three dimensions. The two models are compared to experimental values, and the microscopic model is used to shine light over the fitting parameters of the circuital model.

Local device parameter extraction of a concentrator photovoltaic cell under solar spot illumination

Focused sunlight can act as a localized source of excess minority carriers in a solar cell. Current signal generated by these carriers gives considerable information about the electrical properties of the cell's material. Point by point current–voltage data were measured for a back point-contact concentrator photovoltaic cell when illuminated by focused sunlight. Two numerical curve fitting procedures: a non-linear two-point interval division and particle swarm optimization algorithm were then applied to extract local parameters (i.e. as function of position) from the current–voltage data at each measurement point. Extracted parameters plotted yields relative spatial information about the electrical properties of a solar cell in a two or three dimensional mapping. The curve fitting routines applied to current–voltage data reveal that performance parameters: short circuit current, open circuit voltage, maximum power and fill factor show distinct variations in the vicinity of the observed current reducing feature. The relative values of the diode ideality factors, series resistance, shunt resistance and reverse saturation currents from both methods showed no significant measurable features that could be distinguished. This shows that the observed reduction in photo-induced current was due to severe recombination in the bulk or around the highly diffused point contacts and not the quality of the multiple p–n junctions of the cell. These approaches allow one to obtain a set of parameters at each local point on the cell which are reasonable and representative of the physical system.

DC microelectrode array for investigating the intracellular ion changes

Microelectrode arrays (MEAs) are extensively being used to study the electrical properties of cells. Most of the MEAs use metal electrodes which are in direct contact with the cells. When using DC currents, this leads to undesirable chemical influencing of the cell. Also, metal electrodes are unsuitable for the measuring of constant potentials. A new kind of MEA is developed which replaces the metal electrodes by electrolyte-filled microchannels with Ag/AgCl-electrodes at their ends. The surface of the DCMEA consists of a nanoporous membrane that acts as a homogenous cell substrate, thus avoiding any topographical guidance of the cells. It is adhered to a polydimethylsiloxane layer with four electrode channels embedded in it, using a novel plasma bonding method. A transparent polymer ground plate connects the channels to the silver electrodes as shown in Fig. 1. This MEA allows for the stimulation of the cells with stationary, non-homogenous electric fields, e.g. to simulate the electrical environment near wounds in vitro. It has been proposed in the literature that intracellular ions are involved during cell migration. The DCMEA can be used to simulate in vitro electric fields to investigate intracellular ion changes. By loading cells with ion specific fluorescence dyes, real-time ion kinetic changes can directly be carried out on DCMEA. These studies will be performed by using a time lapse video microscope. In this paper we present the detailed fabrication and testing of the new DCMEA. Results on intracellular ion flows will be presented using this DCMEA.

Electrical properties of breast cancer cells from impedance measurement of cell suspensions

Impedance spectroscopy of biological cells has been used to monitor cell status, e.g. cell proliferation, viability, etc. It is also a fundamental method for the study of the electrical properties of cells which has been utilised for cell identification in investigations of cell behaviour in the presence of an applied electric field, e.g. electroporation. There are two standard methods for impedance measurement on cells. The use of microelectrodes for single cell impedance measurement is one method to realise the measurement, but the variations between individual cells introduce significant measurement errors. Another method to measure electrical properties is by the measurement of cell suspensions, i.e. a group of cells within a culture medium or buffer. This paper presents an investigation of the impedance of normal and cancerous breast cells in suspension using the Maxwell-Wagner mixture theory to analyse the results and extract the electrical parameters of a single cell. The results show that normal and different stages of cancer breast cells can be distinguished by the conductivity presented by each cell.

Transient Characteristics of the Reset Programming of a Phase-Change Line Cell and the Effect of the Reset Parameters on the Obtained State

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, we investigate the effect of the reset-pulse parameters of a phase-change memory line cell on the electrical cell properties. By means of electrothermal finite-element simulations and measurements, the characteristics of the reset state (resistance after switching, threshold voltage, and stability of the state) are related to the physical parameters during reset switching (the temporal and spatial distribution of the temperature during switching, the evolution of the melting and molten phases, and the time that the line is molten). From a device point of view, we emphasize the following aspects: 1) Due to good thermal isolation, the line cell can be reset using a 5-ns short current pulse of limited amplitude; 2) longer pulsewidths allow lower reset current amplitudes due to the gradual heating of surrounding dielectric; 3) the reset resistance has no direct relation with the threshold voltage but is strongly related to the number of reset pulses applied to the cell; and 4) shorter pulsewidths allow extended endurance lifetimes. </para>

On‐chip non‐invasive and label‐free cell discrimination by impedance spectroscopy

Many flow-cytometric cell characterization methods require costly markers and colour reagents. We present here a novel device for cell discrimination based on impedance measurement of electrical cell properties in a microfluidic chip, without the need of extensive sample preparation steps and the requirement of labelling dyes. We demonstrate that in-flow single cell measurements in our microchip allow for discrimination of various cell line types, such as undifferentiated mouse fibroblasts 3T3-L1 and adipocytes on the one hand, or human monocytes and in vitro differentiated dendritic cells and macrophages on the other hand. In addition, viability and apoptosis analyses were carried out successfully for Jurkat cell models. Studies on several species, including bacteria or fungi, demonstrate not only the capability to enumerate these cells, but also show that even other microbiological life cycle phases can be visualized. These results underline the potential of impedance spectroscopy flow cytometry as a valuable complement to other known cytometers and cell detection systems.

Cell electrophoresis on a chip: what can we know from the changes in electrophoretic mobility?

An overview of both experimental and theoretical studies of cell electrophoresis mobility (EPM) over the past fifty years and the relevance of cell EPM measurement are presented and discussed from the viewpoint of exploring the potential use of cell EPM as an index of the biological condition of cells. Physical measurements of the optical and/or electrical properties of cells have been attracting considerable attention as noninvasive cell-evaluation methods that are essential for the future of cell-based application technologies such as cell-based drug screening and cell therapy. Cell EPM, which can be measured in a noninvasive manner by cell electrophoresis, reflects the electrical and mechanical properties of the cell surface. Although the importance of cell EPM has been underestimated for a long time, mostly owing to the technical difficulties associated with its measurement, recent improvements in measurement technology using microcapillary chips have been changing the situation: cell EPM measurement has become more reliable and faster. Recent studies using the automated microcapillary cell electrophoresis system have revealed the close correlation between cell EPM and important biological phenomena including cell cycle, apoptosis, enzymatic treatment, and immune reaction. In particular, the converged EPM distribution observed for synchronized cells has altered the conventional belief that cell EPMs vary considerably. Finding a new significance of cell EPM is likely to lead to noninvasive cell evaluation methods essential for the next-generation of cell engineering.

Broadband excitation for short-time impedance spectroscopy

Frequency domain impedance measurements are still the common approach in assessing passive electrical properties of cells and tissues. However, due to the time requirements for sweeping over a frequency range for performing spectroscopy, they are not suited for recovering fast impedance changes of biological objects. The use of broad bandwidth excitation and monitoring the response as a function of time will greatly reduce the measurement time. The widespread usage of a square wave excitation is simple but not always the best choice. Here we consider different waveforms for excitation and discuss not only the advantages but also their limitations. Measurements in a miniaturized chamber where frequency and time domain measurements are compared show the suitability of different waveforms as excitation signals for the measurements of bio-impedance. The chirp excitation has been found to be most promising in terms of frequency range, signal-to-noise ratio and crest factor.

Comparison of Electrical Properties of Viruses Studied by AC Capacitance Scanning Probe Microscopy

Capacitances of five types of viruses, adenovirus type 5 (AV5), herpes simplex virus type 1 (HSV1), simian virus 40 (SV40), vaccinia (MVA), and cowpea mosaic virus (CPMV), were compared by AC capacitance scanning probe microscopy. This technique, using a Pt-coated AFM tip as an electrode to probe capacitance of materials between the tip and a bottom electrode, has been applied to study surface structures of semiconductors and polymers with nanometer spatial resolution; however, biological samples at the nanoscale have not been explored by this technique yet. Because most biological cells are poor conductors, this approach to probe electric properties of cells by capacitance is logical. This scanning probe technique showed that each virus has distinguishable and characteristic capacitance. A series of control experiments were carried out using mutant viruses to validate the origin of the characteristic capacitance responses for different viruses. A mutation on the capsid in HSV1 with green fluorescence proteins increased capacitance from 9 x 10(-6) to 1 x 10(-5) F/cm2 at the frequency of 10(4) Hz. Herpes simplex virus type 2 (HSV2) decreased capacitance when its envelope and glycoproteins were chemically extracted. These control experiments indicate that dielectric properties of capsid proteins and envelope glycoproteins significantly influence overall dielectric constants of viruses. Because those capsid proteins and glycoproteins are characteristic of the virus strain, this technique could be applied to detect and identify viruses at the single viron level using their distinct capacitance spectra as fingerprints without labeling.

The enhancement of HCN channel instantaneous current facilitated by slow deactivation is regulated by intracellular chloride concentration

The hyperpolarization-activated cation current I (f) plays a key role in the modulation of rhythmic activity in cardiac pacemaker cells and spontaneously firing neurons. I (f) is generated by hyperpolarization-activated cyclic nucleotide-gated channels (HCN1-HCN4) and comprises two components: the fast instantaneous current (I (INS)) and the slowly developing steady-state current (I (SS)). We found that in I (f) traces evoked by consecutive hyperpolarization, the I (INS) amplitude of the second trace was up to 50% larger than the first. I (SS) was identical. This pre-hyperpolarization mediated enhancement of I (INS) was maximal in channels displaying slow kinetics (sinoatrial I (f), HCN3, and HCN4), while it was almost negligible for fast channels (HCN1 and HCN2). The enhancement quantitatively correlated with the frequency of hyperpolarization. Analysis of HCN4 currents suggested that enhancement was facilitated by incomplete deactivation, confirmed by HCN2-HCN4 chimeric studies. It is important to note that intracellular Cl(-) was found to be a cellular suppressor of I (INS) enhancement. Cl(-) inhibited the enhancement with an IC(50) around 25 mM and Hill coefficients between 2 and 6. Cl(-) shifted V (0.5) by +7 mV when [Cl(-)](i) was increased from 11 to 141 mM. In conclusion, I (INS) represents a quantitatively important component of I (f) at low Cl(-) (as found in most cell types). Moreover, an increase in cellular Cl(-) will suppress enhancement of I (INS) and, hence, potentially affect the electrical properties of cells.

Validating the Need to Validate Code

Douglass Post and Lawrence Votta’s article admirably stresses the need for validation of computation. If I understand their main point correctly, it’s that computation is science, not mathematics.The article motivates me to contrast two fields I work between that use very different paradigms to describe the electrodiffusion of charge. In computational electronics, 1,2 1. C. Jacoboni, P. Lugli, The Monte Carlo Method for Semiconductor Device Simulation, Springer-Verlag, New York (1989) https://doi.org/10.1007/978-3-7091-6963-6.2. S. Selberherr, Analysis and Simulation of Semiconductor Devices, Springer-Verlag, New York (1984) https://doi.org/10.1007/978-3-7091-8752-4. the electric field is traditionally calculated by solving Poisson’s equation with far-field boundary conditions but at relatively low resolution. Poisson is solved anew whenever charges move. Computational chemistry, starting more or less with computer simulation of fluids 3 3. M. P. Allen, D. J. Tildesley, Computer Simulation of Liquids, Oxford U. Press, New York (1987). and computational biology, 4 4. T. Schlick, Molecular Modeling and Simulation, Springer-Verlag, New York (2002). computes the electric field at high resolution and does not deal clearly with far-field boundary conditions. Electrodiffusion, which has been at the center of electro- and physical chemistry since Michael Faraday’s time, is also at the center of electronics, where it describes the movement of charge in semiconductors and most of our digital devices. Electrodiffusion is no less important in biophysics, where it is responsible for the electrical properties of cells and tissues, and controls many biological functions.It seems to me that these different treatments of similar physics are distinct and unlikely to be equally precise under all conditions. I hope the article helps motivate workers in each tradition to discuss other treatments beyond their own and try to understand the differences. I hope such workers can determine the conditions under which each treatment is accurate. That way we may learn to use each computational tradition of electrodiffusion only in appropriate situations.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. C. Jacoboni, P. Lugli, The Monte Carlo Method for Semiconductor Device Simulation, Springer-Verlag, New York (1989) https://doi.org/10.1007/978-3-7091-6963-6. Google ScholarCrossref2. S. Selberherr, Analysis and Simulation of Semiconductor Devices, Springer-Verlag, New York (1984) https://doi.org/10.1007/978-3-7091-8752-4. Google ScholarCrossref3. M. P. Allen, D. J. Tildesley, Computer Simulation of Liquids, Oxford U. Press, New York (1987). Google Scholar4. T. Schlick, Molecular Modeling and Simulation, Springer-Verlag, New York (2002). Google ScholarCrossref© 2005 American Institute of Physics.

Potassium channels and vascular proliferation

Potassium channels are currently the focus of much attention because of their recently discovered role in the regulation of vascular smooth muscle growth. Dramatic alterations in the expression and activity of K + channels causing marked changes in the cell's electrical properties accompany enhanced growth of smooth muscle cells (SMCs). These findings indicate that alterations in K + channel function are important for SMC proliferation. However, the mechanisms by which changes in K + channel activity influence cellular growth pathways are poorly understood. The emergent electrical properties caused by modulation of K + channels are associated with marked differences in the spatial and temporal organization of Ca 2+ signaling. Thus, changes in K + channel function may represent a universal mechanism by which Ca 2+ signals are targeted towards activation of gene expression and cell growth. As enhanced growth of smooth muscle underlies many cardiovascular diseases and clinical pathologies, the identification of an important role for K + channels in SMC proliferation indicates a new source of therapeutic targets to regulate proliferative vascular disorders.