Feasibility of Tracking Multiple Single-Cell Properties with Impedance Spectroscopy

Identification and Drug Screening of Single Cells from Human Tumors on Semiconductor Chip for Cancer Precision Medicine

Drug screening of primary tumor cells directly assesses the drug efficacy on specific tumors, promoting personalized cancer treatment. The application of a microfluidic platform has realized drug screening using a limited amount of biopsy samples for cancer precision medicine. However, all the techniques face an inevitable issue of not all the primary tumor cells being cancer cells. Here, a system is introduced that integrates single-cell identification and drug screening on one semiconductor chip so that both drug efficacy on cancer cells and drug toxicity on noncancerous cells can be obtained simultaneously. An integrated circuit is built on the semiconductor chip for single-cell electric impedance sensing (IC-ECIS) of ultra-weak signals for distinguishing cancer cells from noncancerous cells without affecting cell vitality. Single-cell identification is validated using breast, lung, and liver cell lines as well as liver cancer specimens from clinical patients. The accuracy on commercial cell lines is ≈80%, and the diagnostic results of tumor tissues are consistent with clinical pathology results. Drug screening is run on the same chip after single cell identification for dual evaluation of drug efficacy and toxicity in both breast cancer models and clinical liver cancer patients. The on-chip drug screening is confirmed with off-chip counterpart experiments in breast cell lines. The effectiveness or ineffectiveness of a drug screened on the IC-ECIS chip demonstrated consistency in the presence or absence of specific mutations in the drug-related genes determined via exome sequencing of individual liver tumors, validating the method for precision medicine.

High-accuracy gastric cancer cell viability evaluation based on multi-impedance spectrum characteristics

The increasing attention to precision medicine is widely paid to greatly rise the cure rate of cancer. Improving the stability and accuracy of cancer cell viability evaluation is one of the keys for precision medicine, as excess dosage of anti-cancer drugs not only kills the cancer cells, but also does harm to normal cells. Electrochemical impedance sensing (EIS) method is well known as a label-free, non-invasive approach for real-time, online monitoring of cell viability. However, the existing EIS methods using single-frequency impedances cannot reflect the comprehensive information of cellular impedance spectroscopy (CIS), ultimately leading to a poor stability and low accuracy of cancer cell viability evaluation. In this paper, we proposed a multi-frequency approach for improving the stability and accuracy of cancer cell viability evaluation based on multi-physical properties of CIS, including cell adhesion state and cell membrane capacitance. The results show that the mean relative error of multi-frequency method is reduced by 50% compared with single-frequency method, while the maximum relative error of the former is 7∼fold smaller than that of the latter. The accuracy of cancer cell viability evaluation is up to 99.6%.

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.

Gradient-based impedance synthesis for breast and lung cancer cell screening deploying planar and nano-structured electrodes

World Health Organization articulated 9.8 million casualties globally in 2018 due to cancer. Cancer, as the world's second most fatal disease, can be recuperated well if diagnosed at an early stage. In this work, a gradient-based impedance synthesis of normal and cancerous cells of breast and lungs, is demonstrated numerically for early-stage cancer detection. Low-voltage single-cell level examination is employed for indomitable diagnosis. MCF-7 and MCF-10A are utilized as breast cancer and breast normal cells, respectively; likewise, SK-MES and NL-20 are utilized as lung cancer and lung normal cell. Pre-examination numerical setup validity ensured with multiple test regimes. Micro-scaled planar and nano-structured electrodes are employed individually to witness the effect of the electrode's structure during electrical impedance examination of cancer and non-cancer cell. Frequency range, at which differential impedance effect is found detectable, for breast and lung cancer cell pairs is determined to be 10⁷ Hz and 10⁸ Hz, respectively. By surpassing the conventional impedance spectroscopy with tedious data fitting formalities, the gradient synthesis technique for cancer detection is introduced. The gradient synthesis for cancer detection is found independent of electrode shape effect. Gradient for breast cancer cell is found to be 2 times greater than the normal breast cell while for lung cancer cell it is found to be 1.5 times greater than the normal lung cell. Our results suggest that as the frequency of applied electrical stimulus increases, impedance of cancerous cell falls at the rate almost double than its counterpart normal cell. This work provides a theoretical basis for further experimental exploration of gradient-based impedance synthesis in cancer therapy and serves as a design tool for performance optimization. Figure 1 (a) Represents electrical Impedance analysis of breast normal cell MCF-10A and breast cancer cell MCF-7 using micro-scaled planar and nano-structured electrodes. (b) Gradient impedance synthesis performed, for breast normal cell (MCF-10A) and breast cancer cell (MCF-7) likewise for lungs normal cell (NL-20) and lungs cancer cell (SK-MES), which assures clear differential effect for cancer screening. Surpassing the conventional and tedious data fitting impedance spectroscopies, a novel gradient-based impedance spectroscopy for early cancer detection is introduced. It clearly detects cancer without any data fitting formalities to find parameter of identification. Planar and nano structure electrodes are used to witness the impact of electrode shape on cell impedance. Breast normal MCF-10A and cancer cell MCF-7 as well as lungs normal NL-20 and cancer cell SK-MES are examined to reflect the efficacy of our work. Single cell level examination is performed for authenticated results.

How to Choose a Proper Theoretical Analysis Model Based on Cell Adhesion and Nonadhesion Impedance Measurement

The accurate equivalent circuit model contributes to the better fitting of required cell characteristics, such as cell impedance, cell adhesion area, and cell-electrode distance. However, so many theoretical models on specific modules make it difficult for new researchers to understand the whole model of electrode system physically. Besides, the accurate theoretical model and the simplified calculations obviously contradict each other; therefore, it is confusing for many researchers to choose the proper theoretical model to calculate the specific parameters required. In this review, we first discuss the problems and suggestions of electrode system design for cell adhesion-based measurement in terms of parasitic capacitance, detection range of cell number, electric field distribution, and interelectrode distance. The design of electrode system for cell nonadhesion measurement was analyzed in terms of microchannel size and electrode position. Then, we discuss the advantages and disadvantages of various equivalent circuit models according to different requirements of researchers, and simultaneously provide a corresponding theoretical model for researchers. Various factors influencing electric impedance spectroscopy (EIS) such as the parasitic capacitance between microelectrodes, the changes of cell adhesion area and cell-electrode distance, the electrode geometry, and the surface conductivity of electrode were quantitatively analyzed to contribute to better understanding of the equivalent models. Finally, we gave advice to optimize the theoretical models further and perspectives on building uniform principles of theoretical model optimization in the future.

Evaluating cell viability heterogeneity based on information fusion of multiple adhesion strengths

Cell viability evaluation is significantly meaningful for cellular assays. Some cells with weak viability are easily killed in the detection of anticancer drugs, while others with strong viability survive and proliferate, ultimately leading to the treatment failure or the inaccuracy of biological assays. Accurately evaluating cell viability heterogeneity still remains difficult. This article proposed a multiphysical property information fusion method for evaluating cell viability heterogeneity based on polynomial regression in a single-channel integrated microfluidic chip. In this method, adhesion strengths τ_N , that are defined as the magnitude of shear stress needed to detach (100 - N) % of cell population, were extracted as the independent variables of polynomial regression model by calculating the nonlinear fitting of the impedance-response curves for shear stress (cell detachment assay). Besides, by calculating the nonlinear fitting of the drug dose-response curves for cancer cells (IC₅₀ assay), the half-maximal inhibitory concentration (IC₅₀ ) was extracted as the dependent variables of polynomial regression model. The results show that the mean relative error of our fusion method averagely reduces by 6.04% and 62.79% compared with the multiple linear regression method and the cell counting method. Moreover, a simplified theoretical model used to describe the quantitative relationship between cell viability and its adhesion strengths was built to provide a theoretical basis for our fusion method.

Bioimpedance Spectroscopy: Basics and Applications

In this review, we aim to introduce the reader to the technique of electrical impedance spectroscopy (EIS) with a focus on its biological, biomaterials, and medical applications. We explain the theoretical and experimental aspects of the EIS with the details essential for biological studies, i.e., interaction of metal electrodes with biological matter and liquids, strategies of measurement rate increasing, noise reduction in bio-EIS experiments, etc. We also give various examples of successful bio-EIS practical implementations in science and technology, from whole-body health monitoring and sensors for vision prosthetic care to single living cell examination platforms, virus disease research, biomolecules detection, and implementation of novel biomaterials. The present review can be used as a bio-EIS tutorial for students as well as a handbook for scientists and engineers because of the extensive references covering the contemporary research papers in the field.

Classification of the mechanism of toxicity as applied to human cell line ECV304

The objective of this study was to identify the pattern of cytotoxicity testing of the human cell line ECV304 using three techniques of an ensemble learning algorithm (bagging, boosting and stacking). The study of cell morphology of ECV304 cell line was conducted using impedimetric measurement. Three types of toxins were applied to the ECV304 cell line namely 1 mM hydrogen peroxide (H₂O₂), 5% dimethyl sulfoxide and 10 μg Saponin. The measurement was conducted using electrodes and lock-in amplifier to detect impedance changes during cytotoxicity testing within a frequency range 200 and 830 kHz. The results were analysed, processed and extracted using detrended fluctuation analysis to obtain characteristics and features of the cells when exposed to the each of the toxins. Three ensemble algorithms applied showed slightly different results on the performance for classifying the data set from the feature extraction that was performed. However, the results show that the cell reaction to the toxins could be classified.

Simulation and Experiment for Electrode Coverage Evaluation by Electrochemical Impedance Spectroscopy Using Parallel Facing Electrodes

A parallel facing electrode (PFE) structure for adherent cell monitoring by electrochemical impedance spectroscopy (EIS) was developed, and its characteristics were investigated by both computer simulation and experiment. The PFE model consists of two facing gold electrode strips separated by 40 μm, and the area of its intersection is 500 × 500 μm. Computer simulation of EIS with adherent cells showed a distinct difference in solution resistance for different cell coverage, which was confirmed by experimental results using latex beads suspension. A well-defined relationship between solution resistance and cell coverage in our PFE is promising for quantitative evaluation of cell density, morphology and fatality.

A non-contact impedimetric biosensing system for classification of toxins associated with cytotoxicity testing

We report on a novel impedance spectroscopy measurement and data analysis technique for cytotoxicity testing. The technique combines non-contact measurement with real-time impedance data analysis based on the toxin dose dependency of the outputs, making it suitable for high throughput screening. A multi-electrode array was designed and fabricated such that a standard well plate could be positioned above the electrodes, negating the requirement for bespoke culture wells with integrated electrodes. For cytotoxicity testing, endothelial cells, type ECV304, within the wells were exposed to various concentrations of 3 toxins, dimethyl sulphoxide, cadmium chloride and saponin, which exhibit different modes of action on cells. Impedance spectra were recorded every 30 min over a 24 h period. From the spectra 'toxin maps' were produced which presented the correlation between impedance output and dose of toxin versus frequency and time. The results demonstrated characteristic toxin maps for each toxin and significantly differences between the three toxins studied. Using complementary measurement methods, we showed that these differences in toxin maps related to morphological and physiological changes in the cells due to the differing mode of action of each toxin.

An Evaluation Approach of Cell Viability Based on Cell Detachment Assay in a Single-Channel Integrated Microfluidic Chip

Due to the heterogeneity of cancer cell populations, the traditional evaluation approach of cell viability based on the cell counting assay is quite inaccurate for the dose-response test of anticancer drugs, cell toxicology assays, and other biochemical stimulations. In this paper, an evaluation approach of cell viability based on the cell detachment assay in a single-channel integrated microfluidic chip is proposed to improve the accuracy of cell viability assessment. The electrodes are coated by fibronectin for specific cell adhesion, and it is biologically significant to study the cell detachment assay in vitro. The maximum number of cells that can be detected by this sensor is about 10⁵ cells (overgrowing), while the minimum is about 100 cells. This method is calibrated with the half-maximal inhibitory concentration assay, and the results show that the cell viability calculated by adhesion strength is more accurate than that evaluated using the cell counting assay. Meanwhile, the shear rate is transformed into shear stress for the comparability among the results in other papers. The most sensitive frequency is also determined as 1 kHz according to normalized impedance. Besides, the impedance of cell adhesion affected by different shear stresses is monitored to study the optimized plan for long-term culture of cells in the integrated microfluidic chip prepared for the cell detachment assay. Adhesion strength τ₂₅, which is the magnitude of shear stress needed to detach 75% of cell population, is introduced to describe the cell adhesion forces. It is calculated and normalized based on the cell detachment assay to evaluate cell viability. The relative errors of the cell detachment method compared with those of the cell counting method decrease by 0.637 (0% FBS), 0.586 (0.5% FBS), and 0.342 (2% FBS).

On Modeling Diversity in Electrical Cellular Response: Data-Driven Approach

Electrical properties of biological cells and tissues possess valuable information that enabled numerous applications in biomedical engineering. The common foundation behind them is a numerical model that can predict electrical response of a single cell or a network of cells. We analyzed the past empirical observations to propose the first statistical model that accurately mimics biological diversity among animal cells, yeast cells, and bacteria. Based on membrane elasticity and cell migration mechanisms, we introduce a more realistic three-dimensional geometry generation procedure that captures membrane protrusions and retractions in adherent cells. Together, they form a model of diverse electrical response across multiple cell types. We experimentally verified the model with electrical impedance spectroscopy of a single human cervical carcinoma (HeLa) cell on a microelectrode array. The work is of particular relevance to medical diagnostic and therapeutic applications that involve exposure to electric and magnetic fields.

Electrical Impedance Characterization of Erythrocyte Response to Cyclic Hypoxia in Sickle Cell Disease

Cell sickling is the process in which intracellular polymerization of deoxygenated sickle hemoglobin (HbS) leads to distorted, rigid cells, resulting in abnormal blood rheology and painful vaso-occlusion. Current methods for detection of this process mainly rely on optical microscopy of cellular morphology and measurements of cell deformability and blood rheology. As electrical impedance of cells is a sensitive indicator of changes in cellular structure and biophysical characteristics, it can be a promising marker for characterization of abnormal blood rheology and a means more convenient than optics to be integrated into point-of-care devices. In this work, a microfluidics-based electrical impedance sensor has been developed for characterizing the dynamic cell sickling-unsickling processes in sickle blood. The sensor is capable of measuring the continuous variation in the sickle cell suspension due to cyclic hypoxia-induced intracellular HbS polymerization and depolymerization. Simultaneous microscopic imaging of cell morphological change shows the reliability and repeatability of the electrical impedance-based measurements of cell sickling and unsickling processes. Strong correlation is found between the electrical impedance measurement and patients' hematological parameters such as levels of HbS and fetal hemoglobin. The combination of electrical impedance measurement and on-chip hypoxia control provides a promising method for rapid assessment of the dynamic processes of cell sickling and unsickling in patients with sickle cell disease.