Electrical cell impedance spectral mesoscopic model applied to experimental data of variable size microelectrodes

We apply the electric cell-substrate impedance sensing (ECIS) technique to monolayers of Madin-Darby canine kidney type II cells cultured on microelectrodes of different sizes. We analyze the effect of the microelectrode radius on the parameters provided by existing ECIS models. The cellular properties inferred from the models should be invariant to the change in the microelectrode radius used for the measurements, since these properties are inherent to the type of cells studied. The current standard model, the Giaever-Keese (GK) model, derived from electrical balances of a single cell extended to infinity by suitable boundary conditions, assumes an infinite microelectrode. The model is fitted to experimental data acquired with a large-radius microelectrode, which can be considered infinite for practical purposes. We compute the impedance of the other cell-covered microelectrodes from the parameters obtained with the GK model, resulting in values strongly discrepant with the experimental data for small microelectrodes. We repeat the process with the mean field (MF) model, an alternative model that depends on the microelectrode radius but not on the cell radius. In this paper we introduce the mesoscopic model, an analytical model that simultaneously includes the properties of an individual cell and the sizes of the microelectrode and the insulator (region between the microelectrode and the ground). The impedances calculated with the mesoscopic model are in excellent agreement with experimental data. Finally, the mesoscopic model reduces to the MF model when the insulator goes to infinity and to the GK model when it goes to zero.

Optimization, fabrication, and characterization of four electrode-based sensors for blood impedance measurement

In this work, an optimized, non-invasive four electrode-based impedimetric sensors have been designed, fabricated, and characterized for measuring the impedance of a biological cell. The impedimetric sensors having four mono-polar electrodes were fabricated utilizing the photolithography technique with gold as the electrode material. Furthermore, the impedance of the electrolyte/electrode interface was simulated by optimizing different parameters, including applied voltage, PBS thickness, and diameter, using COMSOL Multiphysics software for a frequency range of 100 Hz to 1 MHz. Next, the impedance of the fabricated device was measured experimentally using the electrochemical impedance spectroscopy (EIS) technique. Then, the COMSOL data was equated with the impedance obtained from the fabricated devices to realize the feasibility and error percentage (RSE < 5%) of the sensor. The equivalent circuit model for the measured impedance data of PBS was obtained utilizing the ZsimpWin software. Besides, the mathematical relations between the impedance, phase angle and the area of the electrode were interpreted for the fabricated impedimetric sensors. Later on, a real blood sample was also characterized to demonstrate the feasibility and the validity of the proposed technique and the fabricated devices in cell diagnosis.

Four electrode-based impedimetric biosensors for evaluating cytotoxicity of tamoxifen on cervical cancer cells

In the current study, novel four electrode-based impedimetric biosensors have been fabricated using photolithography techniques and utilized to evaluate the cytotoxicity of tamoxifen on cervical cancer cell lines. The cell impedance was measured employing the electric cell-substrate impedance sensing (ECIS) method over the frequency range of 100 Hz to 1 MHz. The results obtained from impedimetric biosensors indicate that tamoxifen caused a significant reduction in the number of HeLa cells on the electrode surfaces in a dose-dependent manner. Next, the impedance values recorded by the fabricated biosensors have been compared with the results obtained from the different conventional techniques such as 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), live-dead cell assay, and flow cytometric analysis to estimate the cytotoxicity of tamoxifen. The impedimetric cytotoxicity of tamoxifen over the growth and proliferation of HeLa cells correlates well with the traditional methods. In addition, the IC50 values obtained from impedimetric data and MTT assay are comparable, signifying that the ECIS technique can be an alternative method to assess the cytotoxicity of different novel drugs. The working principle of the biosensor has been examined by scanning electron microscopy, indicating the detachment of cells from gold surfaces in a dose-dependent manner, signifying the decrease in impedance at higher drug doses.

Real-Time Analysis of the Stability of Oil-In-Water Pickering Emulsion by Electrochemical Impedance Spectroscopy

In this paper, electrical impedance spectroscopy (EIS) was applied to investigate the stability of oil-in-water (O/W) Pickering emulsions prepared with negatively charged silica nanoparticles in combination with a trace amount of redox switchable fluorescent molecules, ferrocene azine (FcA). Electrical impedance values of emulsions obtained at different emulsification speeds were estimated according to the frequency response data with frequencies ranging from 1 MHz to 1 Hz. The equivalent circuit model of toluene-in-water emulsion was established by the resistor (R_O/W) and capacitor (C_O/W) in parallel connection. Nyquist diagrams for the emulsions prepared by toluene and water were characterized by the formation of one semi-circle. The droplet size distribution is one of the important factors that affect the stability of the emulsion, except for the volume fraction of water and oil, the size of stabilizing particles, etc. The average particle size of the emulsion droplets decreased as the emulsification speed increased, indicating the higher stability of the emulsion. It was found that the fitted impedance value R_O/W of the emulsion decreased with decreasing particle size prepared at different emulsification speeds and storage time by performing real-time EIS detection techniques. The results suggested that EIS could be used to characterize the stability of a toluene-in-water emulsion stabilized by FcA modified silica nanoparticles. Moreover, based on the good electrochemical activity of the FcA molecule, the stability of the Pickering emulsion can be modulated by adding oxidant and reductant and detected by EIS in real-time.

AC and DC Differential Bridge Structure Suitable for Electrochemical Interfacial Capacitance Biosensing Applications

This paper presents a capacitive differential bridge structure with both AC and DC excitation and balancing capability for low cost electrode-solution interfacial capacitance biosensing applications. The proposed series RC balancing structure offers higher sensitivity, lower susceptibility to common-mode interferences, and drift control. To evaluate the bridge performance in practice, possible effects of initial bridge imbalance due to component mismatches are investigated considering the required resolution of the balancing networks, sensitivity, and linearity. This evaluation is also a guideline to designing the balancing networks, balancing algorithm and the proceeding readout interface circuitry. The proposed series RC bridge structure is implemented along with a custom single frequency real-time amplification/filtering readout board with real-time data acquisition and sine fitting. The main specifications for the implemented structure are 8-bit detection resolution if the total expected fractional capacitance change at the interface is roughly 1%. The characterization and measurement results show the effectiveness of the proposed structure in achieving the design target. The implemented structure successfully achieves distinct detection levels for tiny total capacitance change at the electrode-solution interface, utilizing Microcystin-(Leucine-Arginine) toxin dilutions as a proof of concept.

Cell Line Classification Using Electric Cell-Substrate Impedance Sensing (ECIS)

We present new methods for cell line classification using multivariate time series bioimpedance data obtained from electric cell-substrate impedance sensing (ECIS) technology. The ECIS technology, which monitors the attachment and spreading of mammalian cells in real time through the collection of electrical impedance data, has historically been used to study one cell line at a time. However, we show that if applied to data from multiple cell lines, ECIS can be used to classify unknown or potentially mislabeled cells, factors which have previously been associated with the reproducibility crisis in the biological literature. We assess a range of approaches to this new problem, testing different classification methods and deriving a dictionary of 29 features to characterize ECIS data. Most notably, our analysis enriches the current field by making use of simultaneous multi-frequency ECIS data, where previous studies have focused on only one frequency; using classification methods to distinguish multiple cell lines, rather than simple statistical tests that compare only two cell lines; and assessing a range of features derived from ECIS data based on their classification performance. In classification tests on fifteen mammalian cell lines, we obtain very high out-of-sample predictive accuracy. These preliminary findings provide a baseline for future large-scale studies in this field.

Bioimpedance Analysis of Epithelial Monolayers after Exposure to Nanosecond Pulsed Electric Fields

Exposures to pulsed electric fields (PEFs) are known to affect cell membranes and consequently also cell-cell interactions as well as associated characteristics. Bioimpedance analysis offers direct and non-invasive insights into structural and functional changes of cell membranes and extracellular matrices through a rigorous evaluation of electrical parameters. Accordingly, the multi-frequency impedance of confluent monolayers of rat liver epithelial WB-F344 cells was monitored in situ before and after exposure to nanosecond PEFs (nsPEFs). The results were fitted by two Cole models in series to obtain the Cole parameters for the monolayer. For an interpretation of the results, dielectric parameters, were correlated with changes of the TJ protein zonula occludens (ZO-1) and the paracellular permeability of the monolayer Cole parameters in general change as a function of pulse number and time. The findings demonstrate that impedance analysis is an effective method to monitor changes of TJs cell-cell contacts and paracellular permeability and relate them to exposure parameters.

Electrical cell-substrate impedance sensing with field-effect transistors is able to unravel cellular adhesion and detachment processes on a single cell level

We introduce a novel technique of impedimetric sensing of cellular adhesion, which might have the potential to supplement the well-known technique of Electrical Cell-substrate Impedance Sensing (ECIS) in cell culture assays. In contrast to the already commercialized ECIS method, we are using ion-sensitive field-effect transistor (ISFET) devices. The standard gold microelectrode size in ECIS is in the range of 100-250 μm in diameter. Reason for this limitation is that when downscaling the sensing electrodes, their effective impedance governed by the metal-liquid interface impedance is becoming very large and hence the currents to be measured are becoming very small reaching the limit of standard instrumentation. This is the main reason why typical assays with ECIS are focusing on applications like cell-cell junctions in confluent cultures. Single cell resolution is barely reachable with these systems. Here we use impedance spectroscopy with ISFET devices having gate dimensions of only 16 × 2 μm(2), which is enabling a real single cell resolution. We introduce an electrically equivalent circuit model, explain the measured effects upon single cell detachment, and present different cellular detachment scenarios. Our approach might supplement the field of ECIS with an alternative tool opening up a route for novel cell-substrate impedance sensing assays with so far unreachable lateral resolution.