Cell Impedance Measurements Research Articles

Predicting Long-Term Stability from Short-Term Measurement: Insights from Modeling Degradation in Perovskite Solar Cells during Voltage Scans and Impedance Spectroscopy.

A drift-diffusion model is used to investigate the effect of device degradation on current-voltage and impedance measurements of perovskite solar cells (PSCs). Modifications are made to the open-source drift-diffusion software IonMonger to model degradation via an increasing recombination rate during the course of characterization experiments. Impedance spectroscopy is shown to be a significantly more sensitive measure of degradation than current-voltage curves, reliably detecting a power conversion efficiency drop of as little as 0.06% over a 4 h measurement. Furthermore, we find that fast degradation occurring during impedance spectroscopy can induce loops lying above the axis in the Nyquist plot, the first time this experimentally observed phenomenon has been replicated in a physics-based model.

Effects of Arthrospira platensis on Human Umbilical Vein Endothelial Cells

Atherosclerosis is initiated by injury or damage to the vascular endothelial cell monolayer. Therefore, the early repair of the damaged vascular endothelium by a proliferation of neighbouring endothelial cells is important to prevent atherosclerosis and thrombotic events. Arthrospira platensis (AP) has been used as a dietary supplement, mainly due to its high content of vitamins, minerals, amino acids, and pigments such as chlorophylls, carotenoids, and phycocyanin, ingredients with antioxidant, anti-inflammatory, and anti-thrombotic properties. Therefore, in this prospective, placebo-controlled, data-driven, sample-size-estimated in vitro study, we tested whether an aqueous extract of AP at different concentrations (50, 100, and 200 µg/mL) had an effect on the different cellular parameters of human umbilical vein endothelial cells. Therefore, cell impedance measurement and cell proliferation were measured to investigate the monolayer formation. In addition, cell viability, integrity, and metabolism were analysed to evaluate singular cellular functions, especially the antithrombotic state. Furthermore, cell–cell and cell–substrate interactions were observed. The highest proliferation was achieved after the addition of 100 µg/mL. This was consistently confirmed by two independent optical experiments in cell cultures 48 h and 85 h after seeding and additionally by an indirect test. At this concentration, the activation or dysfunction of HUVECs was completely prevented, as confirmed by prostacyclin and interleukin-6 levels. In conclusion, in this study, AP induced a significant increase in HUVEC proliferation without inducing an inflammatory response but altered the hemostasiological balance in favour of prostacyclin over thromboxane, thereby creating an antithrombotic state. Thus, APE could be applied in the future as an accelerator of endothelial cell proliferation after, e.g., stent placement or atherosclerosis.

Impregnated LSM-YSZ electrodes with RuO2/SDC nanocomposites for solid oxide cells

La0.8Sr0.2MnO3-δ-Y0.16Zr0.84O2-δ (LSM-YSZ) composites have been widely used as the oxygen electrodes in solid oxide cells (SOCs), however, their poor activities for oxygen reduction and evolution reactions result in relatively low cell performance. A common method to promote electrocatalytic activities of LSM-YSZ composites is to tailor the microstructure by impregnation. In this study, nanocomposite catalysts are developed by one-pot infiltration, where nano scale particles of RuO2 and Ce0.8Sm0.2O2-δ (SDC) are highly dispersed to achieve a uniform distribution with reduced particle sizes. Impedance measurements of symmetrical oxygen electrode cells reveal that modifying LSM-YSZ electrodes with SDC and RuO2/SDC can substantially promote their activities for oxygen reduction reactions (ORR). The measured polarization resistances at 750°C in air are 2.23, 0.24 and 0.14 Ω cm2 for the blank, SDC and RuO2/SDC modified LSM-YSZ electrodes, respectively. Compared to pure SDC, RuO2/SDC composites show higher ORR promotion, which can be correlated with their more surface oxygen vacancies. Solid oxide cells with thin YSZ electrolytes, RuO2/SDC impregnated LSM-YSZ oxygen electrode substrates and thin fuel electrodes of La0.3Sr1.55Fe1.5Ni0.1Mo0.4O6 achieve a peak power density of 0.7 W cm−2 at 750°C in the fuel cell mode and a steam electrolysis current density of 2.31 A cm−2 at 1.3 V and 800°C in the electrolysis mode.

Calocedrus formosana Essential Oils Induce ROS-Mediated Autophagy and Apoptosis by Targeting SIRT1 in Colon Cancer Cells.

Colorectal cancer is the most common cancer that affects both sexes and has a poor prognosis due to aggressiveness and chemoresistance. Essential oils isolated from Calocedrus formosana (CF-EOs) have been shown to demonstrate anti-termite, antifungal, anti-mosquito, and anti-microbial activities. However, the anticancer effects of CF-EOs are not yet fully understood. Therefore, the present study aimed to explore the molecular mechanism underlying CF-EOs-mediated anti-proliferative activity in colon cancer cells. Here, cell impedance measurements showed that CF-EOs inhibit proliferation in colon cancer cells with wild-type or mutant p53. Flow cytometry revealed that CF-EOs at 20, 50 µg/mL significantly induced ROS generation and autophagy in both HCT116 p53-wt and HCT116 p53-null cell lines, whereas pretreatment with the ROS scavenger N-acetyl cysteine (NAC) markedly attenuated these changes. CF-EOs also induced apoptosis at 50 µg/mL in both lines, as determined by flow cytometry. Protein analysis showed that CF-EOs markedly induced apoptosis markers, including Trail, cleaved caspase-3, cleaved caspase-9, and cleaved PARP, as well as autophagy markers, such as the levels of ULK1, Atg5, Atg6, Atg7, and the conversion of LC3-I to LC3-II. CF-EOs were further found to inhibit the activity and expression of the NAD+-dependent deacetylase SIRT1 to increase the levels of acetylated p53 (Ac-p53) in p53-wt cells and acetylated c-Myc (Ac-c-Myc) in p53-null cells, ultimately inducing apoptosis in both lines. Interestingly, suppression of SIRT1 by CF-EOs enhanced the acetylation of ULK1, which in turn prompted ROS-dependent autophagy in colon cancer cells. The induction of apoptosis and autophagy by CF-EOs suggests that they may have potential as a promising new approach for treating cancer. Collectively, our results suggest that essential oils isolated from Calocedrus formosana act as a promising anticancer agent against colon cancer cells by targeting SIRT1 to induce ROS-mediated autophagy and apoptosis.

Boosting cytotoxicity of adoptive allogeneic NK cell therapy with an oncolytic adenovirus encoding a human vIL-2 cytokine for the treatment of human ovarian cancer

Despite good results in the treatment of hematological malignancies, Natural killer (NK) cells have shown limited effectiveness in solid tumors, such as ovarian cancer (OvCa). Here, we assessed the potential of an oncolytic adenovirus expressing a variant interleukin-2 (vIL-2) cytokine, Ad5/3-E2F-d24-vIL2 (vIL-2 virus), also known as TILT-452, to enhance NK cell therapy efficacy in human OvCa ex vivo. Human OvCa surgical specimens were processed into single-cell suspensions and NK cells were expanded from healthy blood donors. OvCa sample digests were co-cultured ex vivo with NK cells and vIL-2 virus and cancer cell killing potential assessed in real time through cell impedance measurement. Proposed therapeutic combination was evaluated in vivo with an OvCa patient-derived xenograft (PDX) in mice. Addition of vIL-2 virus significantly enhanced NK cell therapy killing potential in treated OvCa co-cultures. Similarly, vIL-2 virus in combination with NK cell therapy promoted the best in vivo OvCa tumor control. Mechanistically, vIL-2 virus induced higher percentages of granzyme B in NK cells, and CD8+ T cells, while T regulatory cell proportions remained comparable to NK cell monotherapy in vivo. Ad5/3-E2F-d24-vIL2 virus treatment represents a promising strategy to boost adoptive NK cell therapeutic effect in human OvCa.

Improving the cytotoxic response of tumor-infiltrating lymphocytes towards advanced stage ovarian cancer with an oncolytic adenovirus expressing a human vIL-2 cytokine

While the presence of tumor-infiltrating lymphocytes (TILs) associates with improved survival prognosis in ovarian cancer (OvCa) patients, TIL therapy benefit is limited. Here, we evaluated an oncolytic adenovirus coding for a human variant IL-2 (vIL-2) cytokine, Ad5/3-E2F-d24-vIL2 (vIL-2 virus), also known as TILT-452, as an immunotherapeutic strategy to enhance TIL responsiveness towards advanced stage OvCa tumors. Fragments of resected human OvCa tumors were processed into single-cell suspensions, and autologous TILs were expanded from said samples. OvCa tumor specimens were co-cultured with TILs plus vIL-2 virus, and cell killing was assessed in real time through cell impedance measurement. Combination therapy was further evaluated in vivo through a patient-derived xenograft (PDX) ovarian cancer murine model. The combination of vIL-2 virus plus TILs had best cancer cell killing ex vivo compared to TILs monotherapy. These results were supported by an in vivo experiment, where the best OvCa tumor control was obtained when vIL-2 virus was added to TIL therapy. Furthermore, the proposed therapy induced a highly cytotoxic phenotype demonstrated by increased granzyme B intensity in NK cells, CD4+ T, and CD8+ T cells in treated tumors. Our results demonstrate that Ad5/3-E2F-d24-vIL2 therapy consistently improved TILs therapy cytotoxicity in treated human OvCa tumors.

Perovskite-Based Materials As Alternative Fuel Electrodes for Solid Oxide Electrolysis Cells (SOECs)

Perovskites show high potential as alternative fuel electrodes in solid oxide electrolysis cells (SOECs) due to their high chemical stability, high conductivity, good catalytic activity and cost-effectiveness. In this work, four perovskites (strontium-iron-niobate double perovskite (SFN), strontium-iron-titanate (STF), lanthanum-strontium-titanate (LST), and lanthanum-strontium-iron-manganese (LSFM)) were examined as fuel electrode materials for SOECs. First, the chemical stability of the perovskites in a reducing atmosphere and the reactivity between the electrode and electrolyte material were analyzed. Besides featuring good chemical stability under reducing conditions, SFN double perovskite and LST exhibit the lowest interaction with the electrolyte (yttria-stabilized zirconia, 8YSZ) after thermal treatment. The results indicate a need for a barrier layer between the tested electrode materials and the YSZ electrolyte to achieve sufficient cell performance throughout its operation in the electrolysis mode. After thoroughly evaluating all preliminary tests, STF was chosen for the first subsequent electrochemical tests. Initial impedance measurements of symmetrical electrolyte-supported cells consisting of pure STF-based electrodes with and without a barrier layer between the electrodes and the electrolyte were conducted to obtain a base for further optimization. For the 5STF fuel electrode, the obtained EIS data confirm the conclusion from the reactivity experiments. Applying a barrier layer at the 5STF fuel electrode/ electrolyte interface is needed to reduce the cell´s ohmic and polarization resistances.

Targeting Glioblastoma-Associated Macrophages for Photodynamic Therapy Using AGuIX®-Design Nanoparticles.

Glioblastoma (GBM) is the most difficult brain cancer to treat, and photodynamic therapy (PDT) is emerging as a complementary approach to improve tumor eradication. Neuropilin-1 (NRP-1) protein expression plays a critical role in GBM progression and immune response. Moreover, various clinical databases highlight a relationship between NRP-1 and M2 macrophage infiltration. In order to induce a photodynamic effect, multifunctional AGuIX®-design nanoparticles were used in combination with a magnetic resonance imaging (MRI) contrast agent, as well as a porphyrin as the photosensitizer molecule and KDKPPR peptide ligand for targeting the NRP-1 receptor. The main objective of this study was to characterize the impact of macrophage NRP-1 protein expression on the uptake of functionalized AGuIX®-design nanoparticles in vitro and to describe the influence of GBM cell secretome post-PDT on the polarization of macrophages into M1 or M2 phenotypes. By using THP-1 human monocytes, successful polarization into the macrophage phenotypes was argued via specific morphological traits, discriminant nucleocytoplasmic ratio values, and different adhesion abilities based on real-time cell impedance measurements. In addition, macrophage polarization was confirmed via the transcript-level expression of TNFα, CXCL10, CD-80, CD-163, CD-206, and CCL22 markers. In relation to NRP-1 protein over-expression, we demonstrated a three-fold increase in functionalized nanoparticle uptake for the M2 macrophages compared to the M1 phenotype. The secretome of the post-PDT GBM cells led to nearly a three-fold increase in the over-expression of TNFα transcripts, confirming the polarization to the M1 phenotype. The in vivo relationship between post-PDT efficiency and the inflammatory effects points to the extensive involvement of macrophages in the tumor zone.

The Influence of Electrode Design on Detecting the Effects of Ferric Ammonium Citrate (FAC) on Pre-Osteoblast through Electrical Cell-Substrate Impedance Sensing (ECIS)

Detection sensitivity is a crucial factor in the application of ECIS sensors. For these biosensors, the electrode configuration has a direct impact on sensitivity, yet few studies on monopolar electrodes have been reported. In this study, ECIS sensor arrays, which have a series of working electrode configuration with a wide diameter range and different electrode number, were fabricated to monitor living osteoblast-like MC3T3-E1 cells. The experimental results revealed that when the electrode diameter was larger than 25 μm, electrodes with smaller diameter and number yielded higher impedance values and generated more impedance shift to cell status change. The membrane capacitance obtained by equivalent circuit fitting was at the same level. When the electrode diameter was even smaller, the results in detection of cell monolayer were opposite, and there was no distinct relationship between impedance and membrane capacitance shift to cell status change and electrode geometry. The proposed sensor chip, allowing for a sustained and stable detection of cellular impedance, provides the basis for the selection of the electrode configuration of monopolar electrodes. The test results of electrodes with a diameter of 25 μm and lower indicated the possibility of single cell impedance measurement, which can provide unique insight into the heterogeneous electrical behavior of cells, and, in this case, the electrode size should be close to the cell size.

Development of an Alternative Binder System for Lithium-Ion Battery Graphite Anodes - Correlation of Fast-Charging Capability with Ionic Pore Resistance and Pore Size Distribution

Binders can have a significant impact on the performance of lithium-ion batteries (LIBs), even though they constitute only a small portion of the battery electrodes. Among others, binders influence mechanical properties of the electrode, like adhesion and cohesion, as well as its electrochemical properties, which include the ionic and electronic conductivity.1 The most commonly used binder system for water-based graphite anodes is a combination of CMC and SBR. CMC ensures good rheological properties and is used as a thickening agent, whereas SBR provides an increased flexibility of the electrode.2–4 However, there are also disadvantages associated with the use of this binder system. CMC is very brittle and provides only a limited Li-ion conductivity, which is especially problematic for thick electrodes and high current densities.5, 6 In addition, CMC/SBR systems show poor electrical conductivity.7 Since fast-charging of LIBs is a key factor to ensure the economic success of battery electric vehicles, in this work a tailored binder system for water-based graphite anodes is developed by combining specific rheological, mechanical and electrochemical properties to enable an improvement in fast-charging capability. The fast-charging capability of the water-based graphite anodes prepared in this work is characterized in pouch cells using a NCM622 cathode. Since the fast-charging capability of anodes is closely related to the ionic resistance within the electrode`s porous structure, as well as its porosity and pore size distribution, electrochemical impedance measurements of symmetrical coin cells are performed to determine the ionic pore resistance. Hg-intrusion porosity measurements also provide information about the pore size distribution of the graphite anodes containing the used binder systems.It is shown that compared to the CMC/SBR binder system, a selective combination of different alternative binders for graphite anodes, based on their rheological, mechanical, as well as electrochemical properties, can improve the fast-charging capability of full cells at 4C (~ 10 mAh cm-2) in the constant-current step by more than 20% with regard to the theoretical capacity. In addition, a direct correlation between the ionic pore resistance and the pore size distribution of the graphite anodes containing the different binder systems with their fast-charging capability could be revealed.

A time-resolved fibrosis model – in vitro assessment of antifibrotic implant coatings

Abstract Wound healing after implant surgery represents a spontaneous repair process that, when disturbed, can lead to a pathological situation known as fibrosis, characterized by excessive proliferation, increased extracellular matrix deposition, and scarring of the tissue. Tissue-specific cell culture models simulating physiological or pathophysiological cell responses are valuable research tools in the field of fibrosis, among others. In such in vitro systems, endpoint measurements are typically used to assess cell viability and/or proliferation. However, this approach is usually time consuming, costly and often leads to the destruction of the sample. Additionally, these conventional in vitro systems provide only a single snapshot of the respective sample at the end of the experiment. Therefore, we aimed to evolve the fibrotic disease in vitro model established by Stahnke et al. To this end, we chose a time-resolved, non-invasive approach based on cell impedance measurements and bright-field microscopy that allows continuous monitoring of the cells. Such measurements can be directly conducted using the xCELLigence RTCA eSight system. This system was used to characterize the cellular responses of the fibrosarcoma cell line HT-1080 and primary fibroblasts isolated from the Tenon’s capsule of human donors to TGF-β1, a key cytokine involved in the pathogenesis of fibrosis. The data shows that compared to Tenon’s fibroblasts the response of HT-1080 cells to TGF- β1 is less pronounced and only detectable within a narrow time frame. Thus, HT-1080 do not appear to be a suitable cell culture model for the assessment of antifibrotic implant coatings.

Efficient Cell Impedance Measurement by Dielectrophoretic Cell Accumulation and Evaluation of Chondrogenic Phenotypes.

The quantitative and functional analyses of cells are important for cell-based therapies. In this study, to establish the quantitative cell analysis method, we propose an impedance measurement method supported by dielectrophoretic cell accumulation. An impedance measurement and dielectrophoresis device was constructed using opposing comb-shaped electrodes. Using dielectrophoresis, cells were accumulated to form chain-like aggregates on the electrodes to improve the measurement sensitivity of the electrical impedance device. To validate the proposed method, the electrical impedance and capacitance of primary and de-differentiated chondrocytes were measured. As a result, the impedance of the chondrocytes decreased with an increase in the passage number, whereas the capacitance increased. Therefore, the impedance measurement method proposed in this study has the potential to identify chondrocyte phenotypes.

Accelerated Stress Tests for Solid Oxide Cells via Artificial Aging of the Fuel Electrode

Solid Oxide Cells (SOCs) are under intensive development due to their great potential to meet the 2030 targets for decarbonization. One of their advantages is that they can work in reversible mode. However, in respect to durability, there are still some technical challenges. Although the quick development of experimental and modeling approaches gives insight into degradation mechanisms, an obligatory step that cannot be avoided is the performance of long-term tests. Taking into account the target for a commercial lifetime is 80,000 h, experiments lasting years are not acceptable for market needs. This work aims to develop accelerated stress tests (ASTs) for SOCs by the artificial aging of the fuel electrode via redox cycling, which follows the degradation processes of calendar aging (Ni coarsening and migration). However, it can cause irreversible damage by the formation of cracks at the interface anode/electrolyte. The advantages of the developed procedure are that it offers a mild level of oxidation, which can be governed and regulated by the direct impedance monitoring of the Ni network resistance changes during oxidation/reduction on a bare anode sample. Once the redox cycling conditions are fixed and the anode/electrolyte sample is checked for cracks, the procedure is introduced for the AST in full-cell configuration. The developed methodology is evaluated by a comparative analysis of current voltage and impedance measurements of pristine, artificially aged, and calendar-aged button cells, combined with microstructural characterization of their anodes. It can be applied in both fuel cell and electrolyzer mode. The results obtained in this study from the electrochemical tests show that the artificially aged experimental cell corresponds to at least 3500 h of nominal operation. The number of hours is much bigger in respect to the microstructural aging of the anode. Taking into consideration that the duration of the performed 20 redox cycles is about 50 to 60 working hours, the acceleration factor in respect to experimental timing is estimated to be higher than 60, without any damaging of the sample. This result shows that the selected approach is very promising for a large decrease in testing times for SOCs.

Development of a Matlab/Simulink Model for Monitoring Cell State-of-Health and State-of-Charge via Impedance of Lithium-Ion Battery Cells

Lithium-ion battery cells not only show different behaviors depending on degradation and charging states, but also overcharge and overdischarge of cells shorten battery life and cause safety problems, thus studies aiming to provide an accurate state of a cell are required. Measurements of battery cell impedance are used for cell SoH and SoC estimation techniques, but it generally takes a long time for a cell in each state to be prepared and cell voltage response is measured when charging and discharging under each condition. This study introduces an electrical equivalent circuit model of lithium-ion cells developed in the MATLAB/Simulink environment. Cell SoC, SoH, temperature, and C-rate are considered for more accurate cell impedance prediction, and the simulation results are verified with the measurement results. The developed model is suitable for use in cell SoC and SoH monitoring studies by successfully outputting cell impedance through real-time prediction of cell voltage during discharge.

COMPARISON OF THREE ANALYZERS FOR ASSESSING COMPLETE BLOOD COUNTS IN NONHUMAN PRIMATES.

Diagnostic hematology can prove challenging to the exotic animal practitioner presented with a nonhuman primate patient. Few point-of-care automated cell counters are calibrated for primate samples. Twenty-one samples from 17 nonhuman primates presented to an exotic animal practice were analyzed. Samples were run on both canine and feline settings on each of two veterinary point-of-care analyzers: one that assays by impedance technology, and one that assays by laser flow cytometry. Samples were also sent to a reference laboratory to be assayed on an analyzer that performs simultaneous impedance and laser measurements of blood cells and has been calibrated for use in nonhuman primates. Fourteen analytes were assessed for each sample on each machine. Manual hematocrits and total white blood cell counts were also performed on 16 of the samples. Statistical analysis indicated some variance between individual parameters, but overall correlation was acceptable.

Anemia Diagnostic System Based on Impedance Measurement of Red Blood Cells.

Anemia is a condition in which red blood cells or the hemoglobin in the blood is lower than in healthy people. Red blood cells transport and supply oxygen needed to various organs in the human body. Anemia is caused by hypoxemia due to the lack of red blood cells and causes other serious health problems, such as heart problems, pregnancy complications, severe fatigue, or death. There are many causes of anemia, and it can be diagnosed by measuring hematocrit or hemoglobin levels in the blood. Even though there are various diagnostic devices on the market, these devices are inconvenient because their systems are bulky, heavy, expensive, or inaccurate. This study proposed a new anemia diagnostic system based on the impedance measurement of red blood cells. The proposed system consists of a test strip that collects a blood sample from the finger and a hemoglobin meter that measures the impedance of the blood and converts it into the concentration of hemoglobin. The proposed test strip that does not contain enzymes or reagents was designed in accordance with class 1 approval by the Food and Drug Administration (FDA). The hemoglobin meter was designed to include a hardware block, an algorithm block and a calibration block through empirical work. We also compared it to reference impedance to prove the accuracy of the hemoglobin meter. The experimental results with human blood indicated the superiority of the anemia diagnostic system. As a result, the overall standard deviation of impedance measurements was less than 1%, and the coefficient of variance of the proposed system was 1.7%, which was better than that of other commercial systems.

A Method for Monitoring State-of-Charge of Lithium-Ion Cells Using Multi-Sine Signal Excitation

In this paper, a method for monitoring SoC of a lithium-ion battery cell through continuous impedance measurement during cell operation is introduced. A multi-sine signal is applied to the cell operating current, and the cell SoH and SoC can be simultaneously monitored via impedance at each frequency. Unlike existing studies in which cell impedance measurement is performed ex situ through EIS equipment, cell state estimation is performed in situ. The measured impedance takes into account cell temperature and cell SoH, enabling accurate SoC estimation. The measurement system configured for the experiment and considerations for the selection of measurement parameters are described, and the accuracy of cell SoC estimation is presented.

High-Energy Li-Ion Cells: Impact of Electrode Ageing on Second Life Viability

High energy cells embedding Nickel-rich and silicon-doped graphite are promoted because they allow electric vehicles to increase their range. We study the ageing of such cells, aiming to reuse them in a second life application. Assuming that second life depends on what they experienced during their first life, we submit 26 fresh cells to 6 different ageing protocols, before a less demanding second life ageing. We find that initial cycling at 0 °C and calendar ageing at 45 °C are leading to the shortest second life. We also find that this originates in the resistance of negative electrodes, thanks to symmetrical coin cell impedance measurements. Dismantling of the cells reveals that lithium plating induced pore clogging is responsible of the fast second life capacity fade. Thanks to differential voltage analysis measurements, we also show that this mechanism affects the positive electrode facing the clogged zones. Conversely, we could not show any correlation between the silicon phase degradation and second life longevity. In addition, the increase of the charge transfer resistance of positive electrodes protects the cells by preventing the spread of lithium plating. Diagnosis and sorting of aged cells must thus rely on resistance measurements.

Broadband electrical impedance as a novel characterization of oxidative stress in single L6 skeletal muscle cells

Oxidative stress (OS) is one of the leading causes of cytotoxicity and is linked to many human physio-pathological conditions. In particular, myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) induced by OS is debilitating to quality of life, while no clear biological markers have been identified for diagnostic measures. Recently, impedance measurements of peripheral blood cells of ME/CFS patients have been shown as a promising approach to diagnose the disease. Inspired by this study and aiming to interrogate muscle cells directly, we investigated if broadband measurements of single muscle cells could differentiate normal and oxidatively stressed cell populations. We first optimized a protocol through H2O2 treatment to introduce oxidative stress to cultured rat L6 skeletal muscle cells. The treated cells were further characterized through broadband impedance spectroscopy of single cells using a microfluidic lab-on-a-chip system. The resulting dielectric properties of cytoplasm permittivity and conductivity are electrically distinct from normally cultured cells. The reflection and transmission coefficients, ΔS11 and ΔS21, of the normal cells are tightly clustered and closely resemble those of the cell-free solution across the frequency range of 9 kHz to 9 GHz. On the other hand, dielectric properties of the oxidized cells have a wide distribution in the GHz range, deviating both in the positive and negative directions from the normally cultured cells. Simulation results guide our hypothesis that the dielectric differences could be linked to ion alterations, while calcium imaging directly supports the contribution of calcium flux to the observed deviation of S parameters. The unique electrical profile associated with oxidized cells in the GHz frequencies provide a framework for future development of technologies to diagnose oxidative-stress related diseases such as ME/CFS.

Design and 3D modeling investigation of a microfluidic electrode array for electrical impedance measurement of single yeast cells.

High-resolution microscopic imaging may cause intensive image processing and potential impact of light irradiation on yeast replicative lifespan (RLS). Electrical impedance spectroscopy (EIS) could be alternatively used to perform high-throughput and label-free yeast RLS assays. Prior to fabricating EIS-integrated microfluidic devices for yeast RLS determination, systematic modeling and theoretical investigation are crucial for device design and optimization. Here, we report three-dimensional (3D) finite-element modeling and simulations of EIS measurement in a microfluidic single yeast in situ impedance array (SYIIA), which is designed by patterning an electrode matrix underneath a cell-trapping array. SYIIA was instantiated and modeled as a 5×5 sensing array comprising 25 units for cell immobilization, culturing, and time-lapse EIS recording. Simulations of yeast growing and budding in a sensing unit demonstrated that EIS signals enable the characterization of cell growth and daughter-cell dissections. In the 5×5 sensing array, simulation results indicated that when monitoring a target cell, daughter dissections in its surrounding traps may induce variations of the recorded EIS signals, which could cause mistakes in identifying target daughter-cell dissections. To eliminate the mis-identifications, electrode array pitch was optimized. Therefore, the results could conduct the design and optimization of microfluidic electrode-array-integrated devices for high-throughput and accurate yeast RLS assays.