Electrical Impedance Measurements of Biological Cells in Response to External Stimuli

Phenylalanine Regulates Milk Protein Synthesis via LAT1-mTOR Signaling Pathways in Bovine Mammary Epithelial Cells

Phenylalanine (Phe) is a potentially limiting amino acid for lactating cows. The mechanism by which Phe regulates milk protein synthesis remains unclear. The present study elucidates the mechanisms by which phenylalanine affects milk protein synthesis, amino acid utilization, and related signaling pathways in bovine mammary epithelial cells (BMECs). The BMECs were treated with five concentrations (0, 0.22, 0.44, 0.88, 1.76 mM, and serum free). Rapamycin inhibitors and RNA interference (RNAi) were used to inhibit the phosphorylation of the mammalian target of rapamycin (mTOR) signaling pathway and the expression of relevant amino acid transporters, respectively. The results showed that 4×Phe (0.88 mM) significantly increased (p < 0.05) both the mRNA and protein expression of α-casein (CSN1S1), β-casein (CSN2), and κ-casein (CSN3), as well as L-type amino acid transporter-1 (LAT1) mRNA expression. Protein expression and modification assays of mTOR-related proteins showed that 4×Phe could increase (p < 0.05) the expression of α-casein and eukaryotic initiation factor 4E-binding protein-1 (4EBP1) and tended to increase the expression of ribosomal protein S6 protein kinase (S6K1, p = 0.054). The general control nonderepressible 2 (GCN2) signaling pathway factor, eukaryotic initiation factor 2 (eIF2α), was downregulated by 4×Phe treatment (p < 0.05). The rapamycin inhibition test showed that Phe regulated casein synthesis via the mTOR signaling pathway. RNAi experiments showed that LAT1 mediated the entry of Phe into cells. Moreover, 4×Phe treatment tended to decrease (0.05 < p < 0.10) the consumption of valine, leucine, histidine, tyrosine, cysteine, alanine, asparagine, and serine in the medium. Collectively, phenylalanine enhanced α-casein synthesis by regulating the phosphorylation of 4EBP1 and eIF2α and promoting the formation of the mTOR-centered casein translation initiation complex.

Vertical Microfluidic Trapping System for Capturing and Simultaneous Electrochemical Detection of Cells

Electrochemical impedance spectroscopy (EIS) is a non-invasive and label-free method widely used for characterizing cell cultures and monitoring their structure, behavior, proliferation and viability. Microfluidic systems are often used in combination with EIS methods utilizing small dimensions, controllable physicochemical microenvironments and offering rapid real-time measurements. In this work, an electrode array capable of conducting EIS measurements was integrated into a multichannel microfluidic chip which is able to trap individual cells or cell populations in specially designed channels comparable to the size of cells. An application-specific printed circuit board (PCB) was designed for the implementation of the impedance measurement in order to facilitate connection with the device used for taking EIS spectra and for selecting the channels to be measured. The PCB was designed in consideration of the optical screening of trapped cells in parallel with the EIS measurements which allows the comparison of EIS data with optical signals. With continuous EIS measurement, the filling of channels with cell suspension can be followed. Yeast cells were trapped in the microfluidic system and EIS spectra were recorded considering each individual channel, which allows differentiating between the number of trapped cells.

Label-free, non-contact determination of resting membrane potential using dielectrophoresis

Measurement of cellular resting membrane potential (RMP) is important in understanding ion channels and their role in regulation of cell function across a wide range of cell types. However, methods available for the measurement of RMP (including patch clamp, microelectrodes, and potential-sensitive fluorophores) are expensive, slow, open to operator bias, and often result in cell destruction. We present non-contact, label-free membrane potential estimation which uses dielectrophoresis to determine the cytoplasm conductivity slope as a function of medium conductivity. By comparing this to patch clamp data available in the literature, we have demonstratet the accuracy of this approach using seven different cell types, including primary suspension cells (red blood cells, platelets), cultured suspension cells (THP-1), primary adherent cells (chondrocytes, human umbilical mesenchymal stem cells), and adherent (HeLa) and suspension (Jurkat) cancer cell lines. Analysis of the effect of ion channel inhibitors suggests the effects of pharmaceutical agents (TEA on HeLa; DMSO and neuraminidase on red blood cells) can also be measured. Comparison with published values of membrane potential suggest that the differences between our estimates and values recorded by patch clamp are accurate to within published margins of error. The method is low-cost, non-destructive, operator-independent and label-free, and has previously been shown to allow cells to be recovered after measurement.

Microfluidic characterization of single-cell biophysical properties and the applications in cancer diagnosis

Single-cell biophysical properties play a crucial role in regulating cellular physiological states and functions, demonstrating significant potential in the fields of life sciences and clinical diagnostics. Therefore, over the last few decades, researchers have developed various detection tools to explore the relationship between the biophysical changes of biological cells and human diseases. With the rapid advancement of modern microfabrication technology, microfluidic devices have quickly emerged as a promising platform for single-cell analysis offering advantages including high-throughput, exceptional precision, and ease of manipulation. Consequently, this paper provides an overview of the recent advances in microfluidic analysis and detection systems for single-cell biophysical properties and their applications in the field of cancer. The working principles and latest research progress of single-cell biophysical property detection are first analyzed, highlighting the significance of electrical and mechanical properties. The development of data acquisition and processing methods for real-time, high-throughput, and practical applications are then discussed. Furthermore, the differences in biophysical properties between tumor and normal cells are outlined, illustrating the potential for utilizing single-cell biophysical properties for tumor cell identification, classification, and drug response assessment. Lastly, we summarize the limitations of existing microfluidic analysis and detection systems in single-cell biophysical properties, while also pointing out the prospects and future directions of their applications in cancer diagnosis and treatment.

Polarization of disk electrodes in high-conductivity electrolyte solutions

We investigate the polarization of disk electrodes immersed in an electrolyte solution and subjected to a small external AC voltage over a wide range of frequencies. A mathematical model is developed based on the Debye-Falkenhagen approximation to the coupled Poisson-Nernst-Planck equations. Analytical techniques are used for predicting the spatial distribution of the electric potential and the complex impedance of the system. Scales for impedance and frequency are identified, which lead to a self-similar behavior for a range of frequencies. Experiments are conducted with gold electrodes of sizes in the range 100-350 μm immersed in a high-conductivity KCl solution over five orders of magnitude in frequency. A collapse of data on impedance magnitude and phase angle onto universal curves is observed with scalings motivated by the mathematical model. A direct comparison with the approximate analytical formula for impedance is made without any fitting parameters, and a good agreement is found for the range of frequencies where the analytical model is valid.

Phenotypic Characterization of 2D and 3D Prostate Cancer Cell Systems Using Electrical Impedance Spectroscopy

Prostate cancer is the second leading cause of death in men. A challenge in treating prostate cancer is overcoming cell plasticity, which links cell phenotype changes and chemoresistance. In this work, a microfluidic device coupled with electrical impedance spectroscopy (EIS), an electrode-based cell characterization technique, was used to study the electrical characteristics of phenotype changes for (1) prostate cancer cell lines (PC3, DU145, and LNCaP cells), (2) cells grown in 2D monolayer and 3D suspension cell culture conditions, and (3) cells in the presence (or absence) of the anti-cancer drug nigericin. To validate observations of phenotypic change, we measured the gene expression of two epithelial markers, E-cadherin (CDH1) and Tight Junction Protein 1 (ZO-1). Our results showed that PC3, DU145, and LNCaP cells were discernible with EIS. Secondly, moderate phenotype changes based on differences in cell culture conditions were detected with EIS and supported by the gene expression of CDH1. Lastly, we showed that EIS can detect chemoresistant-related cell phenotypes with nigericin drug treatment. EIS is a promising label-free tool for detecting cell phenotype changes associated with chemoresistance. Further development will enable the detection and characterization of many other types of cancer cells.

Optimization design of interdigitated microelectrodes with an insulation layer on the connection tracks to enhance efficiency of assessment of the cell viability

BACKGROUND

Microelectrical Impedance Spectroscopy (µEIS) is a tiny device that utilizes fluid as a working medium in combination with biological cells to extract various electrical parameters. Dielectric parameters of biological cells are essential parameters that can be extracted using µEIS. µEIS has many advantages, such as portability, disposable sensors, and high-precision results.

RESULTS

The paper compares different configurations of interdigitated microelectrodes with and without a passivation layer on the cell contact tracks. The influence of the number of electrodes on the enhancement of the extracted impedance for different types of cells was provided and discussed. Different types of cells are experimentally tested, such as viable and non-viable MCF7, along with different buffer solutions. This study confirms the importance of µEIS for in vivo and in vitro applications. An essential application of µEIS is to differentiate between the cells' sizes based on the measured capacitance, which is indirectly related to the cells' size. The extracted statistical values reveal the capability and sensitivity of the system to distinguish between two clusters of cells based on viability and size.

CONCLUSION

A completely portable and easy-to-use system, including different sensor configurations, was designed, fabricated, and experimentally tested. The system was used to extract the dielectric parameters of the Microbeads and MCF7 cells immersed in different buffer solutions. The high sensitivity of the readout circuit, which enables it to extract the difference between the viable and non-viable cells, was provided and discussed. The proposed system can extract and differentiate between different types of cells based on cells' sizes; two other polystyrene microbeads with different sizes are tested. Contamination that may happen was avoided using a Microfluidic chamber. The study shows a good match between the experiment and simulation results. The study also shows the optimum number of interdigitated electrodes that can be used to extract the variation in the dielectric parameters of the cells without leakage current or parasitic capacitance.

Changes in Electrical Capacitance of Cell Membrane Reflect Drug Partitioning-Induced Alterations in Lipid Bilayer

The plasma membrane is a lipid bilayer that establishes the outer boundary of a living cell. The composition of the lipid bilayer influences the membrane's biophysical properties, including fluidity, thickness, permeability, phase behavior, charge, elasticity, and formation of flat sheet or curved structures. Changes in the biophysical properties of the membrane can be occasioned when new entities, such as drug molecules, are partitioned in the bilayer. Therefore, assessing drugs for their effect on the biophysical properties of the lipid bilayer of a cell membrane is critical to understanding specific and non-specific drug action. Previously, we reported a non-invasive technique for real-time characterization of cellular dielectric properties, such as membrane capacitance and cytoplasmic conductivity. In this study, we discuss the potential application of the technique in assessing the biophysical properties of the cell membrane in response to interaction with amiodarone compared to aspirin/acetylsalicylic acid and glucose. Amiodarone is a potent drug used to treat cardiac arrhythmia, but it also exerts various non-specific effects. Compared to aspirin and glucose, we measured a rapid and higher magnitude increase in membrane capacitance on cells under amiodarone treatment. Increased membrane capacitance induced by aspirin and glucose quickly returned to baseline in 15 s, while amiodarone-induced increased capacitance sustained and decreased slowly, approaching baseline or another asymptotic limit in ~2.5 h. Because amiodarone has a strong lipid partitioning property, we reason that drug partitioning alters the lipid bilayer context and subsequently reduces bilayer thickness, leading to an increase in the electrical capacitance of the cell membrane. The presented microfluidic system promises a new approach to assess drug-membrane interactions and delineate specific and non-specific actions of the drug on cells.

Impedance-Based Neutralizing Antibody Detection Biosensor with Application in SARS-CoV-2 Infection

Although safe and efficacious coronavirus disease-2019 (COVID-19) vaccines are available, real protective immunity is revealed by the serum COVID-19 neutralizing antibody (NAb) concentration. NAbs deactivate the virus by attaching to the viral receptor-binding domain (RBD), which interacts with angiotensin-converting enzyme 2 (ACE2) on the human cell. This paper introduces inexpensive, rapid, sensitive, and quantifiable impedance-based immunosensors to evaluate the NAb. The sensor limit of detection is experimentally determined in different buffer dilutions using bovine IgG-anti-bovine IgG interaction. The dominance of AC electrokinetic transport and molecular diffusion in the sensor is investigated using scaling analysis and numerical simulations. The results demonstrated that the sensor detection mechanism is mainly based on the diffusion of the biomolecules onto the electrode surface. After evaluating the sensor working principles, viral RBD buffers, including different NAb concentrations, are applied to the sensor, immobilized with the human ACE2 (hACE2). Results demonstrate that the sensor is capable of NAb detection in the analytical measuring interval between 45 ng/mL and 185 ng/mL. Since the present sensor provides fast test results with lower costs, it can be used to assess the NAb in people's blood serum before receiving further COVID vaccine doses.

A comparison of conventional and advanced electroanalytical methods to detect SARS-CoV-2 virus: A concise review

Respiratory viruses are a serious threat to human wellbeing that can cause pandemic disease. As a result, it is critical to identify virus in a timely, sensitive, and precise manner. The present novel coronavirus-2019 (COVID-19) disease outbreak has increased these concerns. The research of developing various methods for COVID-19 virus identification is one of the most rapidly growing research areas. This review article compares and addresses recent improvements in conventional and advanced electroanalytical approaches for detecting COVID-19 virus. The popular conventional methods such as polymerase chain reaction (PCR), loop mediated isothermal amplification (LAMP), serology test, and computed tomography (CT) scan with artificial intelligence require specialized equipment, hours of processing, and specially trained staff. Many researchers, on the other hand, focused on the invention and expansion of electrochemical and/or bio sensors to detect SARS-CoV-2, demonstrating that they could show a significant role in COVID-19 disease control. We attempted to meticulously summarize recent advancements, compare conventional and electroanalytical approaches, and ultimately discuss future prospective in the field. We hope that this review will be helpful to researchers who are interested in this interdisciplinary field and desire to develop more innovative virus detection methods.

Electrical characterization of tumor-derived exosomes by conductive atomic force microscopy

The physical properties of tumor-derived exosomes have gained much attention because they are helpful to better understand the exosomes in biomedicine. In this study, the conductive atomic force microscopy (C-AFM) was employed to perform the electrical characterizations of exosomes, and it obtained the topography and current images of samples simultaneously. The exosomes were absorbed onto the mica substrates coated with a gold film of 20 nm thick for obtaining the current images of samples by C-AFM in air. The results showed that the single exosomes had the weak conductivity. Furthermore, the currents on exosomes were measured at different bias voltages and pH conditions. It illustrated that the conductivity of exosomes was affected by external factors such as bias voltages and solutions with different pH values. In addition, the electrical responses of low and high metastatic potential cell-derived exosomes were also compared under different voltages and pH conditions. This work is important for better understanding the physical properties of tumor-derived exosomes and promoting the clinical applications of tumor-derived exosomes.

Effects of nanostructuration on the electrochemical performance of metallic bioelectrodes

The use of metallic nanostructures in the fabrication of bioelectrodes (e.g., neural implants) is gaining attention nowadays. Nanostructures provide increased surface area that might benefit the performance of bioelectrodes. However, there is a need for comprehensive studies that assess electrochemical performance of nanostructured surfaces in physiological and relevant working conditions. Here, we introduce a versatile scalable fabrication method based on magnetron sputtering to develop analogous metallic nanocolumnar structures (NCs) and thin films (TFs) from Ti, Au, and Pt. We show that NCs contribute significantly to reduce the impedance of metallic surfaces. Charge storage capacity of Pt NCs is remarkably higher than that of Pt TFs and that of the other metals in both morphologies. Circuit simulations of the electrode/electrolyte interface show that the signal delivered in voltage-controlled systems is less filtered when nanocolumns are used. In a current-controlled system, simulation shows that NCs provide safer stimulation conditions compared to TFs. We have assessed the durability of NCs and TFs for potential use in vivo by reactive accelerated aging test, mimicking one-year in vivo implantation. Although each metal/morphology reveals a unique response to aging, NCs show overall more stable electrochemical properties compared to TFs in spite of their porous structure.

A Microfluidic Dielectric Spectroscopy System for Characterization of Biological Cells in Physiological Media

Dielectric spectroscopy (DS) is a promising cell screening method that can be used for diagnostic and drug discovery purposes. The primary challenge of using DS in physiological buffers is the electrode polarization (EP) that overwhelms the impedance signal within a large frequency range. These effects further amplify with the miniaturization of the measurement electrodes. In this study, we present a microfluidic system and the associated equivalent circuit models for real-time measurements of cell membrane capacitance and cytoplasm resistance in physiological buffers with 10 s increments. The current device captures several hundreds of biological cells in individual microwells through gravitational settling and measures the system's impedance using microelectrodes covered with dendritic gold nanostructures. Using PC-3 cells (a highly metastatic prostate cancer cell line) suspended in cell growth media (CGM), we demonstrate stable measurements of cell membrane capacitance and cytoplasm resistance in the device for over 15 min. We also describe a consistent application of the equivalent circuit model, starting from the reference measurements used to determine the system parameters. The circuit model is tested using devices with varying dimensions, and the obtained cell parameters between different devices are nearly identical. Further analyses of the impedance data have shown that accurate cell membrane capacitance and cytoplasm resistance can be extracted using a limited number of measurements in the 5 MHz to 10 MHz range. This will potentially reduce the timescale required for real-time DS measurements below 1 s. Overall, the new microfluidic device can be used for the dielectric characterization of biological cells in physiological buffers for various cell screening applications.

Advance of microfluidic constriction channel system of measuring single-cell cortical tension/specific capacitance of membrane and conductivity of cytoplasm

This paper reported a microfluidic platform which realized the characterization of inherent single-cell biomechanical and bioelectrical parameters simultaneously. Individual cells traveled through a constriction channel with deformation images and impedance variations captured and processed into cortical tension T_c , specific membrane capacitance C_sm , and cytoplasmic conductivity σ_cy based on an equivalent biophysical model. These properties of thousands of individual cells of K562, Jurkat, HL-60, HL-60 treated with paraformaldehyde (PA)/cytochalasin D (CD)/concanavalin A (ConA), granulocytes of Donor 1, Donor 2, and Donor 3 were quantified for the first time. Leveraging T_c , C_sm , and σ_cy , (1) high accuracies of classifying wild-type and processed HL-60 cells (e.g., 93.5% of PA treated vs. CD treated HL-60 cells) were realized, revealing the effectiveness of using these three biophysical parameters in cell-type classification; (2) low accuracies of classifying normal granulocytes from three donors (e.g., 56.4% of Donor 1 vs. 2), indicating comparable parameters for normal granulocytes. In conclusion, this platform can characterize single-cell T_c , C_sm , and σ_cy concurrently and quantify multiple parameters in single-cell analysis.

Dynamically controlled dielectrophoresis using resonant tuning

Electrically polarizable micro- and nanoparticles and droplets can be trapped using the gradient electric field of electrodes. But the spatial profile of the resultant dielectrophoretic force is fixed once the electrode structure is defined. To change the force profile, entire complex lab-on-a-chip systems must be re-fabricated with modified electrode structures. To overcome this problem, we propose an approach for the dynamic control of the spatial profile of the dielectrophoretic force by interfacing the trap electrodes with a resistor and an inductor to form a resonant resistor-inductor-capacitor (RLC) circuit. Using a dielectrophoretically trapped water droplet suspended in silicone oil, we show that the resonator amplitude, detuning, and linewidth can be continuously varied by changing the supply voltage, supply frequency, and the circuit resistance to obtain the desired trap depth, range, and stiffness. We show that by proper tuning of the resonator, the trap range can be extended without increasing the supply voltage, thus preventing sensitive samples from exposure to high electric fields at the stable trapping position. Such unprecedented dynamic control of dielectrophoretic forces opens avenues for the tunable active manipulation of sensitive biological and biochemical specimen in droplet microfluidic devices used for single-cell and biochemical reaction analysis.

Dielectrophoresis: Developments and applications from 2010 to 2020

The 20th century has seen tremendous innovation of dielectrophoresis (DEP) technologies, with applications being developed in areas ranging from industrial processing to micro- and nanoscale biotechnology. From 2010 to present day, there have been 981 publications about DEP. Of over 2600 DEP patents held by the United States Patent and Trademark Office, 106 were filed in 2019 alone. This review focuses on DEP-based technologies and application developments between 2010 and 2020, with an aim to highlight the progress and to identify potential areas for future research. A major trend over the last 10 years has been the use of DEP techniques for biological and clinical applications. It has been used in various forms on a diverse array of biologically derived molecules and particles to manipulate and study them including proteins, exosomes, bacteria, yeast, stem cells, cancer cells, and blood cells. DEP has also been used to manipulate nano- and micron-sized particles in order to fabricate different structures. The next 10 years are likely to see the increase in DEP-related patent applications begin to result in a greater level of technology commercialization. Also during this time, innovations in DEP technology will likely be leveraged to continue the existing trend to further biological and medical-focused applications as well as applications in microfabrication. As a tool leveraged by engineering and imaginative scientific design, DEP offers unique capabilities to manipulate small particles in precise ways that can help solve problems and enable scientific inquiry that cannot be addressed using conventional methods.

A hybrid Genetic Algorithm and Levenberg-Marquardt (GA-LM) method for cell suspension measurement with electrical impedance spectroscopy

A hybrid Genetic Algorithm (GA) and Levenberg-Marquardt (GA-LM) method is proposed for cell suspension measurement with electrical impedance spectroscopy. This algorithm combines the GA with global search ability and Levenberg-Marquardt (LM) algorithm with local search ability, which has the advantages of high accuracy and high robustness. First, GA-LM is compared with GA and LM algorithm separately by ideal simulation. Second, Gaussian noise is added to the ideal simulation data. The anti-noise ability of the GA-LM is discussed. Finally, experiments are conducted to verify the practicability of the proposed GA-LM method. In the experiment, GA-LM is used to fit the impedance spectrum of yeast suspensions with different volume fractions and active states. The results show that the GA-LM algorithm can converge to the real value that is set in the simulation under ideal numerical simulation conditions. In the simulation within 2% noise level, the mean relative error of the parameter solution is less than 4%, and the root mean square error of the fitting is less than 0.4. This method also performs well in fitting of the experimental data. In addition, the electric double layer resistance and cell membrane capacitance are selected as the main indicators for the identification of yeast suspension concentration and activity, respectively.

Dielectrophoretic Manipulation of Cancer Cells and Their Electrical Characterization

Electromanipulation and electrical characterization of cancerous cells is becoming a topic of high interest as the results reported to date demonstrate a good differentiation among various types of cells from an electrical viewpoint. Dielectrophoresis and broadband dielectric spectroscopy are complementary tools for sorting, identification, and characterization of malignant cells and were successfully used on both primary tumor cells and culture cells as well. However, the literature is presenting a plethora of studies with respect to electrical evaluation of these type of cells, and this review is reporting a collection of information regarding the functioning principles of different types of dielectrophoresis setups, theory of cancer cell polarization, and electrical investigation (including here the polarization mechanisms). The interpretation of electrical characteristics against frequency is discussed with respect to interfacial/Maxwell-Wagner polarization and the parasitic influence of electrode polarization. Moreover, the electrical equivalent circuits specific to biological cells polarizations are discussed for a good understanding of the cells' morphology influence. The review also focuses on advantages of specific low-conductivity buffers employed currently for improving the efficiency of dielectrophoresis and provides a set of synthesized data from the literature highlighting clear differentiation between the crossover frequencies of different cancerous cells.

Electrical Impedance Spectroscopy for Monitoring Chemoresistance of Cancer Cells

Electrical impedance spectroscopy (EIS) is an electrokinetic method that allows for the characterization of intrinsic dielectric properties of cells. EIS has emerged in the last decade as a promising method for the characterization of cancerous cells, providing information on inductance, capacitance, and impedance of cells. The individual cell behavior can be quantified using its characteristic phase angle, amplitude, and frequency measurements obtained by fitting the input frequency-dependent cellular response to a resistor-capacitor circuit model. These electrical properties will provide important information about unique biomarkers related to the behavior of these cancerous cells, especially monitoring their chemoresistivity and sensitivity to chemotherapeutics. There are currently few methods to assess drug resistant cancer cells, and therefore it is difficult to identify and eliminate drug-resistant cancer cells found in static and metastatic tumors. Establishing techniques for the real-time monitoring of changes in cancer cell phenotypes is, therefore, important for understanding cancer cell dynamics and their plastic properties. EIS can be used to monitor these changes. In this review, we will cover the theory behind EIS, other impedance techniques, and how EIS can be used to monitor cell behavior and phenotype changes within cancerous cells.

Microfabricated electrochemical sensing devices

Electrochemistry provides possibilities to realize smart microdevices of the next generation with high functionalities. Electrodes, which constitute major components of electrochemical devices, can be formed by various microfabrication techniques, and integration of the same (or different) components for that purpose is not difficult. Merging this technique with microfluidics can further expand the areas of application of the resultant devices. To augment the development of next generation devices, it will be beneficial to review recent technological trends in this field and clarify the directions required for moving forward. Even when limiting the discussion to electrochemical microdevices, a variety of useful techniques should be considered. Therefore, in this review, we attempted to provide an overview of all relevant techniques in this context in the hope that it can provide useful comprehensive information.

Personalized Drug Efficacy Monitoring Chip

Cancer drug resistance mechanisms such as tumor heterogeneity and adaptable feedback loops are prevalent issues facing cancer therapy development. Drug resistance can be unique to a cancer type and, most importantly, to each individual cancer patient. Consequently, testing different dosages and therapeutics directly on each individual patient sample (i.e., tumor and cancer cells) has compelling advantages compared to large scale in vitro drug testing and is a step toward personalized drug selection and effective treatment development. Recently, microfluidic-based chemo-sensitivity assays on patient biopsies have been proposed. Despite their novelty, these platforms usually rely on optical labels, optical equipment, or complex microfabricated channel geometries and structures. In this work, we proposed a novel lab on a chip platform capable of real-time and continuous screening of drug efficacy on (cancer) cell subpopulations without the need of labels or bulky readout optical equipment. In this platform, several label-free and rapid techniques have been implemented for the precise capturing of cells of interest in parallel with the real-time measurement and characterization of the effectiveness of candidate therapeutic agents. To demonstrate the utility of the platform, the effect of an apoptotic inducer, topoisomerase I inhibitor, 7-ethyl-10-hydrocamptothecin (SN38) on human colorectal carcinoma cancer cells (HCT 116) was used as a study model. Additionally, electrical results were optically verified to examine the continuous measurements of the biological mechanisms, specifically, apoptosis and necrosis, during therapeutic agent characterizations. The proposed device is a versatile platform which can also be easily redesigned for the automated and arrayed analysis of cell-drug interaction down to the single cell level. Our platform is another step toward enabling the personalized screening of drug efficacy on individual patients' samples that potentially leads to a better understanding of drug resistance and the optimization of patients' treatments.

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.

Quantification of Cell Death Using an Impedance-Based Microfluidic Device

Dielectric spectroscopy is a nondestructive method to characterize dielectric properties by measuring impedance data over a frequency spectrum. This method has been widely used for various applications such as counting, sizing, and monitoring biological cells and particles. Recently, utilization of this method has been suggested in various stages of the drug discovery process due to low sample consumption and fast analysis time. In this study, we used a previously developed microfluidic system to confine single PC-3 cells in microwells using dielectrophoretic forces and perform the impedance measurements. PC-3 cells are treated with 100 μM Enzalutamide drug, and their impedance response is recorded until the cells are totally dead as predicted with viability tests. Four different approaches are used to analyze the impedance spectrum. Equivalent circuit modeling is used to extract the cell electrical properties as a function of time. Principal component analysis (PCA) is used to quantify cellular response to drug as a function of time. Single frequency measurements are conducted to observe how the cells respond over time. Finally, opacity ratio is defined as an additional quantification method. This device is capable of quantitatively measuring drug effects on biological cells and detecting cell death. The results show that the proposed microfluidic system has the potential to be used in early stages of the drug discovery process.

A Multichannel FRA-Based Impedance Spectrometry Analyzer Based on a Low-Cost Multicore Microcontroller

Impedance spectrometry (IS) is a characterization technique in which a voltage or current signal is applied to a sample under test to measure its electrical behavior over a determined frequency range, obtaining its complex characteristic impedance. Frequency Response Analyzer (FRA) is an IS technique based on Phase Sensitive Detection (PSD) to extract the real and imaginary response of the sample at each input signal, which presents advantages compared to FFT-based (Fast Fourier Transform) algorithms in terms of complexity and speed. Parallelization of this technique has proven pivotal in multi-sample characterization, reducing the instrumentation size and speeding up analysis processes in, e.g., biotechnological or chemical applications. This work presents a multichannel FRA-based IS system developed on a low-cost multicore microcontroller platform which both generates the required excitation signals and acquires and processes the output sensor data with a minimum number of external passive components, providing accurate impedance measurements. With a suitable configuration, the use of this multicore solution allows characterizing several impedance samples in parallel, reducing the measurement time. In addition, the proposed architecture is easily scalable.