Cellular impedance biosensors for drug screening and toxin detection

Biophysical phenotyping of single-cell based on impedance and application for individualized precision medicine

Single-cell biophysical characterization based on impedance measurement is an advantageous approach due to its label-free, high-efficiency, cost-effective and real-time capability. Biophysical phenotyping can yield timely and rich information on physiological and pathological state of cells for disease diagnosis, drug screening, precision medicine, etc. However, precise measurement on single-cell impedance is challenging, particularly hard to figure out the detailed biophysical parameters of single cell due to coupling and complexity of impedance model. Here, we propose an analytic determination method to decode single-cell electrophysiological parameters (including cell-substrate interface capacitance, cell membrane capacitance, cell membrane conductivity, and cytoplasm conductivity) from the impedances measured at optimized frequencies by using analytic solution rather than spectrum fitting. With this simple and fast analytic solution method, the physiological parameters of single cell in natural adhesion state can be accurately determined in real time. We validate this cell parameter determination method in monitoring the change of cell adhesion under hydraulic effects and exploring electrophysiological differences among MCF-7, HeLa, Huh7, and MDA-MB-231 cell lines. Particularly, we apply the approach to optimize tumor treating fields (TTFields) therapy, realizing individualized precision medicine. Our work provides an accurate and efficient approach for characterizing single-cell biophysical properties with real-time, in-situ, label-free, and less invasive advantages.

Electrochemical and Electrical Biosensors for Wearable and Implantable Electronics Based on Conducting Polymers and Carbon-Based Materials

Bioelectronic devices are designed to translate biological information into electrical signals and vice versa, thereby bridging the gap between the living biological world and electronic systems. Among different types of bioelectronics devices, wearable and implantable biosensors are particularly important as they offer access to the physiological and biochemical activities of tissues and organs, which is significant in diagnosing and researching various medical conditions. Organic conducting and semiconducting materials, including conducting polymers (CPs) and graphene and carbon nanotubes (CNTs), are some of the most promising candidates for wearable and implantable biosensors. Their unique electrical, electrochemical, and mechanical properties bring new possibilities to bioelectronics that could not be realized by utilizing metals- or silicon-based analogues. The use of organic- and carbon-based conductors in the development of wearable and implantable biosensors has emerged as a rapidly growing research field, with remarkable progress being made in recent years. The use of such materials addresses the issue of mismatched properties between biological tissues and electronic devices, as well as the improvement in the accuracy and fidelity of the transferred information. In this review, we highlight the most recent advances in this field and provide insights into organic and carbon-based (semi)conducting materials' properties and relate these to their applications in wearable/implantable biosensors. We also provide a perspective on the promising potential and exciting future developments of wearable/implantable biosensors.

Investigation of geometry-dependent sensing characteristics of microfluidic for single-cell 3D localization

Flow cytometry-based measurement techniques have been widely used for single-cell characterizations, such as impedance, size, and dielectric properties. However, in the measurement process, the reliability of the output measurement signal directly affects the ability of the microsystem to judge the characteristics of single cells. Here, we designed a multiple nonparallel electrode structure for single-cell 3D localization. The performance of the structures was studied by analyzing the changes in electric field strength and the output differential current. The effects of microchannel height, sensing electrode distance, electrode inclination angle, and electrode width on output signals are investigated by analyzing the current change and electric field strength of single cells passing from the center of the microchannel. The numerical simulation results indicate that, when the microchannel height is 20 µm, the distance of the sensing electrodes is 100 µm, the inclination angle is 30°, the electrode width is 20 µm, and the optimal signal quality can be obtained. Reducing the height of the flow channel and shortening the sensing electrode spacing can significantly improve the signal amplitude. When the channel height is 20 µm, the signal intensity increases by 80% than that of 30 µm. The signal intensity of induced current with the sensing electrode spacing of 100 µm is 42% higher than that with the spacing of 120 µm. We analyzed the presence of multiple independent cells and adherent cells in the detection area and demonstrated through simulation that the signal changes caused by multi-cells can be superimposed by multiple single-cell signals. The induced current signal intensity of the same volume of cells with an ellipticity of 1 is 49% lower than that of cells with an ellipticity of 4. Based on the numerical investigation, we expect that the optimal geometry structure design will aid in the development of better performance signal cell impedance cytometry microsystems.

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.

Evaluating the efficacy and cardiotoxicity of EGFR-TKI AC0010 with a novel multifunctional biosensor

Non-small cell lung cancer (NSCLC) is a leading cause of cancer mortality worldwide. Although epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have dramatically improved the life expectancy of patients with NSCLC, concerns about TKI-induced cardiotoxicities have increased. AC0010, a novel third-generation TKI, was developed to overcome drug resistance induced by EGFR-T790M mutation. However, the cardiotoxicity of AC0010 remains unclear. To evaluate the efficacy and cardiotoxicity of AC0010, we designed a novel multifunctional biosensor by integrating microelectrodes (MEs) and interdigital electrodes (IDEs) to comprehensively evaluate cell viability, electrophysiological activity, and morphological changes (beating of cardiomyocytes). The multifunctional biosensor can monitor AC0010-induced NSCLC inhibition and cardiotoxicity in a quantitative, label-free, noninvasive, and real-time manner. AC0010 was found to significantly inhibit NCI-H1975 (EGFR-L858R/T790M mutation), while weak inhibition was found for A549 (wild-type EGFR). Negligible inhibition was found in the viabilities of HFF-1 (normal fibroblasts) and cardiomyocytes. With the multifunctional biosensor, we found that 10 μM AC0010 significantly affected the extracellular field potential (EFP) and mechanical beating of cardiomyocytes. The amplitude of EFP continuously decreased after AC0010 treatment, while the interval decreased first and then increased. We analyzed the change in the systole time (ST) and diastole time (DT) within a beating interval and found that the DT and DT/beating interval rate decreased within 1 h after AC0010 treatment. This result probably indicated that the relaxation of cardiomyocytes was insufficient, which may further aggravate the dysfunction. Here, we found that AC0010 significantly inhibited EGFR-mutant NSCLC cells and impaired cardiomyocyte function at low concentrations (10 μM). This is the first study in which the risk of AC0010-induced cardiotoxicity was evaluated. In addition, novel multifunctional biosensors can comprehensively evaluate the antitumor efficacy and cardiotoxicity of drugs and candidate compounds.

PEDOT:PSS-Based Bioelectrodes for Multifunctional Drug Release and Electric Cell-Substrate Impedance Sensing

Electric cell-substrate impedance sensing (ECIS) is an innovative approach for the label-free and real-time detection of cell morphology, growth, and apoptosis, thereby playing an essential role as both a viable alternative and valuable complement to conventional biochemical/pharmaceutical analysis in the field of diagnostics. Constant improvements are naturally sought to further improve the effective range and reliability of this technology. In this study, we developed poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conducting polymer (CP)-based bioelectrodes integrated into homemade ECIS cell-culture chamber slides for the simultaneous drug release and real-time biosensing of cancer cell viability under drug treatment. The CP comprised tailored PEDOT:PSS, poly(ethylene oxide) (PEO), and (3-glycidyloxypropyl)trimethoxysilane (GOPS) capable of encapsulating antitumor chemotherapeutic agents such as doxorubicin (DOX), docetaxel (DTX), and a DOX/DTX combination. This device can reliably monitor impedance signal changes correlated with cell viability on chips generated by cell adhesion onto a predetermined CP-based working electrode while simultaneously exhibiting excellent properties for both drug encapsulation and on-demand release from another CP-based counter electrode under electrical stimulation (ES) operation. Cyclic voltammetry curves and surface profile data of different CP-based coatings (without or with drugs) were used to analyze the changes in charge capacity and thickness, respectively, thereby further revealing the correlation between their drug-releasing performance under ES operation (determined using ultraviolet-visible (UV-vis) spectroscopy). Finally, antitumor drug screening tests (DOX, DTX, and DOX/DTX combination) were performed on MCF-7 and HeLa cells using our developed CP-based ECIS chip system to monitor the impedance signal changes and their related cell viability results.

A review of bio-impedance devices

Bio-impedance measurement analysis primarily refers to a safe and a non-invasive technique to analyze the electrical changes in living tissues on the application of low-value alternating current. It finds applications both in the biomedical and the agricultural fields. This paper concisely reviews the origin and measurement approaches for concepts and fundamentals of bio-impedance followed by a critical review on bio-impedance portable devices with main emphasis on the embedded system approach which is in demand due to its miniature size and present lifestyle preference of monitoring health in real time. The paper also provides a comprehensive review of various bio-impedance circuits with emphasis on the measurement and calibration techniques.

Life in an optical fiber: Monitoring of cell cultures with microcavity in-line Mach-Zehnder interferometer

Monitoring cell adhesion and growth are crucial for various applications involving drug screening, cytotoxicity, and cytocompatibility studies. However, acquiring accurate information about the growing state and responsiveness to a treatment of a cell system in a real-time and label-free manner is still a challenge. This work presents the first research on direct, real-time, and label-free adherent cell culture monitoring using a microcavity in-line Mach-Zehnder interferometer (μIMZI) fabricated in an optical fiber. The sensing solution based on μIMZI offers a great advantage over many other monitoring concepts tracking the changes taking place on the microcavity's bottom surface and within its volume, thus offering a greater penetration depth. In this study, we verified performance of the approach using a non-cancer bone marrow stromal cell line HS-5. The results demonstrate that the changes of the acquired signal are closely related to the different states of cells' adhesion, proliferation, morphology, and variation of mass. Thus, this label-free, real-time μIMZI-based monitoring technique gives a great promise to the analysis or monitoring of relevant new treatments in future scientific, as well as clinical applications.

Biosensors to Monitor Cell Activity in 3D Hydrogel-Based Tissue Models

Three-dimensional (3D) culture models have gained relevant interest in tissue engineering and drug discovery owing to their suitability to reproduce in vitro some key aspects of human tissues and to provide predictive information for in vivo tests. In this context, the use of hydrogels as artificial extracellular matrices is of paramount relevance, since they allow closer recapitulation of (patho)physiological features of human tissues. However, most of the analyses aimed at characterizing these models are based on time-consuming and endpoint assays, which can provide only static and limited data on cellular behavior. On the other hand, biosensing systems could be adopted to measure on-line cellular activity, as currently performed in bi-dimensional, i.e., monolayer, cell culture systems; however, their translation and integration within 3D hydrogel-based systems is not straight forward, due to the geometry and materials properties of these advanced cell culturing approaches. Therefore, researchers have adopted different strategies, through the development of biochemical, electrochemical and optical sensors, but challenges still remain in employing these devices. In this review, after examining recent advances in adapting existing biosensors from traditional cell monolayers to polymeric 3D cells cultures, we will focus on novel designs and outcomes of a range of biosensors specifically developed to provide real-time analysis of hydrogel-based cultures.

Evaluating Membrane Electrical Properties of SMMC7721 Cells with TiO₂ NPs Applications to Cytotoxicity by Dielectric Spectroscopy

Titanium dioxide nanoparticles (TiO₂ NPs) represent one of the most frequently applied nanomaterials in numerous areas of daily life. Recent studies show that TiO₂ exposure increases the occupational risk of liver injury and inflammation, and even liver cancer to the workers of factories handling these NPs. However, the potential risks and biophysical effects of TiO₂ on hepatic cells need extensive evaluation. To this end, we explored the electrophysiological changes in the human liver cancer cell line SMMC7721 following exposure to TiO₂ NPs. TiO₂ NPs decreased the first (Δε₁) and second dielectric relaxation intensity (Δε₂) of the SMMC7721 cells by 6.62% and 0.86% respectively, and significantly increased the first characteristic frequency (f_c1, 4.82%) and the first Cole-Cole parameter (β₁, 1.24%). The double spherical-shell model showed that TiO₂ NPs significantly lowered the permittivity of unit-membrane and capacitance, as well as the conductivity of extracellular fluid, cytoplasm, and nuclear contents compared to the untreated control. Conclusively, this study revealed that TiO₂ NPs induce cytotoxic effects by disrupting the permeability and electrical conductivity of unit membranes. Further, we report that dielectric spectrum combined with model parameter analysis can evaluate the bioelectrical effects of TiO₂ NPs on human liver cancer cells.

Human Organs-on-Chips: A Review of the State-of-the-Art, Current Prospects, and Future Challenges

New emerging technologies, remarkably miniaturized 3D organ models and microfluidics, enable simulation of the real in vitro microenvironment ex vivo more closely. There are many fascinating features of innovative organ-on-a-chip (OOC) technology, including the possibility of integrating semipermeable and/or stretchable membranes, creating continuous perfusion of fluids into microchannels and chambers (while maintaining laminar flow regime), embedding microdevices like microsensors, microstimulators, micro heaters, or different cell lines, along with other 3D cell culture technologies. OOC systems are designed to imitate the structure and function of human organs, ranging from breathing lungs to beating hearts. This technology is expected to be able to revolutionize cell biology studies, personalized precision medicine, drug development process, and cancer diagnosis/treatment. OOC systems can significantly reduce the cost associated with tedious drug development processes and the risk of adverse drug reactions in the body, which makes drug screening more effective. The review mainly focus on presenting an overview of the several previously developed OOC systems accompanied by subjects relevant to pharmacy-, cancer-, and placenta-on-a-chip. The challenging issues and opportunities related to these systems are discussed, along with a future perspective for this technology.

Recent Advances in Electrical Impedance Sensing Technology for Single-Cell Analysis

Cellular heterogeneity is of significance in cell-based assays for life science, biomedicine and clinical diagnostics. Electrical impedance sensing technology has become a powerful tool, allowing for rapid, non-invasive, and label-free acquisition of electrical parameters of single cells. These electrical parameters, i.e., equivalent cell resistance, membrane capacitance and cytoplasm conductivity, are closely related to cellular biophysical properties and dynamic activities, such as size, morphology, membrane intactness, growth state, and proliferation. This review summarizes basic principles, analytical models and design concepts of single-cell impedance sensing devices, including impedance flow cytometry (IFC) to detect flow-through single cells and electrical impedance spectroscopy (EIS) to monitor immobilized single cells. Then, recent advances of both electrical impedance sensing systems applied in cell recognition, cell counting, viability detection, phenotypic assay, cell screening, and other cell detection are presented. Finally, prospects of impedance sensing technology in single-cell analysis are discussed.

Measurement methods of single cell drug response

In the last decades, a wide multitude of research activity has been focused on the development of new drugs, and devoted to overcome the challenges of high cost and low efficiency in drug evaluation. The measurement of drug response at the single cell level is a quicker, more direct and more accurate way to reflect drug efficacy, which can shorten the drug development period and reduce research costs. Therefore, the single cell drug response (SCDR) measurement technology has aroused extensive attention from researchers, and has become a hot topic in the fields of drug research and cell biology. Recent years have seen the emergence of various SCDR measurement technologies that feature different working principles and different levels of measurement performance. To better examine, compare and summarize the characteristics and functions of these technologies, we select signal-to-noise ratio, throughput, content, invasion, and device complexity as the criteria to evaluate them from the drug efficacy perspective. This review aims to highlight sixteen kinds of SCDR measurement technologies, including patch-clamp technique, live-cell interferometry, capillary electrophoresis, secondary ion mass spectrometry, and more, and report widespread representative examples of SCDR measurement the recent approaches for over the past forty years. Based on their reaction principles, these technologies are classified into four categories: electrical, optical, electrochemical, and mass spectrometry, and a detailed comparison is made between them. After in-depth understanding of these technologies, it is expected to improve or integrate these technologies to propose better SCDR measurement strategies, and explore methods in new drug development and screening, as well as disease diagnosis and treatment.

A multidimensional biosensor system to guide LUAD individualized treatment

Lung cancer, mainly non-small cell lung cancer (NSCLC), has been a global health problem, leading to maximum cancer death. Across adenocarcinoma patients, significant genetic and phenotypic heterogeneity was identified as responsible for individual cancer drug resistance, driving an urgent need for individualized treatment. High expectation has been set on individualized treatment for better responses and extended survival. There are pressing needs for and significant advantages of testing dosages and drugs directly on patient-specific cancer cells for preclinical drug testing and personalized drug selection. Monitoring the drug response based on patient-derived cells (PDCs) is a step toward effective drug development and individualized treatment. Despite the dependence on optical labels, optical equipment, and other complex manual operation, we here report a multidimensional biosensor system to guide adenocarcinoma individualized treatment by integrating 2D and 3D PDC models and cellular impedance biosensors. The cellular impedance biosensors were applied to quantitate drug response in 2D and 3D environments. Compared with 2D plate culture, 3D cultured cells were found to show higher resistance to anti-cancer drugs. Cell-cell, cell-ECM, and mechanical interactions in the 3D environment led to stronger drug resistance. The in vivo results demonstrated the reliability of the multidimensional biosensor system. Cellular impedance biosensors allow a fast, non-invasive, and quantitative manner for preselected drug screening in individualized treatment. Considering the potential for good distinguishment of different anti-cancer drugs, our newly developed strategy may contribute to drug response prediction in individualized treatment and new drug development.

Evaluation of Cancer Cell Lines by Four-Point Probe Technique, by Impedance Measurements in Various Frequencies

Cell-based biosensors appear to be an attractive tool for the rapid, simple, and cheap monitoring of chemotherapy effects at a very early stage. In this study, electrochemical measurements using a four-point probe method were evaluated for suspensions of four cancer cell lines of different tissue origins: SK-N-SH, HeLa, MCF-7 and MDA-MB-231, all for two different population densities: 50 K and 100 K cells/500 μL. The anticancer agent doxorubicin was applied for each cell type in order to investigate whether the proposed technique was able to determine specific differences in cell responses before and after drug treatment. The proposed methodology can offer valuable insight into the frequency-dependent bioelectrical responses of various cellular systems using a low frequency range and without necessitating lengthy cell culture treatment. The further development of this biosensor assembly with the integration of specially designed cell/electronic interfaces can lead to novel diagnostic biosensors and therapeutic bioelectronics.

Environmental Toxicology Assays Using Organ-on-Chip

Adverse effects of environmental toxicants to human health have traditionally been assayed using in vitro assays. Organ-on-chip (OOC) is a new platform that can bridge the gaps between in vitro assays (or 3D cell culture) and animal tests. Microenvironments, physical and biochemical stimuli, and adequate sensing and biosensing systems can be integrated into OOC devices to better recapitulate the in vivo tissue and organ behavior and metabolism. While OOCs have extensively been studied for drug toxicity screening, their implementation in environmental toxicology assays is minimal and has limitations. In this review, recent attempts of environmental toxicology assays using OOCs, including multiple-organs-on-chip, are summarized and compared with OOC-based drug toxicity screening. Requirements for further improvements are identified and potential solutions are suggested.

Aluminium Oxide Thin-Film Based In Vitro Cell-Substrate Sensing Device for Monitoring Proliferation of Myoblast Cells

We demonstrate cell-substrate interaction on aluminium oxide thin-film in metal-insulator-metal structure followed by the change in dielectric characteristics of Al₂O₃ as a function of progression of cellular growth. The theoretical calculation of the fabricated biosensor reveals that the changes in the intrinsic elemental parameters are mainly attributed to the cell-induced behavioural changes.

High throughput transepithelial electrical resistance (TEER) measurements on perfused membrane-free epithelia

Assessment of epithelial barrier function is critically important for studying healthy and diseased biological models. Here we introduce an instrument that measures transepithelial electrical resistance (TEER) of perfused epithelial tubes in the microfluidic OrganoPlate platform. The tubules are grown in microfluidic channels directly against an extracellular matrix, obviating the need for artificial filter membranes. We present TEER measurements on Caco-2 intestinal and renal proximal tubule epithelium. Forty tubules on one single plate were interrogated in less than a minute. We show that TEER measurement is significantly more sensitive than a fluorescent reporter leakage assay in response to staurosporine. We demonstrate a 40-channel time-lapse data acquisition over a 25 hour time period under flow conditions. We furthermore observed a 50% reduction in Caco-2 TEER values following exposure to a cocktail of inflammatory cytokines. To our best knowledge, this is the first instrument of its kind that allows routine TEER studies in perfused organ-on-a-chip systems without interference by artificial filter membranes. We believe the apparatus will contribute to accelerating routine adoption of perfused organ-on-a-chip systems in academic research and in industrial drug development.

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.

Potential of Drug Efficacy Evaluation in Lung and Kidney Cancer Models Using Organ-on-a-Chip Technology

Organ-on-a-chip (OoC) is an exponential technology with the potential to revolutionize disease, toxicology research, and drug discovery. Recent advances in OoC could be utilized for drug screening in disease models to evaluate the efficacy of new therapies and support new tools for the understanding of disease mechanisms. Rigorous validation of this technology is required to determine whether OoC models may represent human-relevant physiology and predict clinical outcomes in target disease models. Achievements in the OoC field could reveal exciting new avenues for drug development and discovery. This review attempts to highlight the benefits of OoC as per our understanding of the cellular and molecular pathways in lung and kidney cancer models, and discusses the challenges in evaluating drug efficacy.

Impedance-based Real-time Monitoring of Neural Stem Cell Differentiation

We present here the first impedance-based characterization of the differentiation process of two human mesencephalic fetal neural stem lines. The two dopaminergic neural stem cell lines used in this study, Lund human mesencephalic (LUHMES) and human ventral mesencephalic (hVM1 Bcl-X_L), have been developed for the study of Parkinsonian pathogenesis and its treatment using cell replacement therapy. We show that if only relying on impedance magnitude analysis, which is by far the most usual approach in, e.g., cytotoxicity evaluation and drug screening applications, one may not be able to distinguish whether the neural stem cells in a population are proliferating or differentiating. However, the presented results highlight that equivalent circuit analysis can provide detailed information on cellular behavior, e.g. simultaneous changes in cell morphology, cell-cell contacts, and cell adhesion during formation of neural projections, which are the fundamental behavioral differences between proliferating and differentiating neural stem cells. Moreover, our work also demonstrates the sensitivity of impedance-based monitoring with capability to provide information on changes in cellular behavior in relation to proliferation and differentiation. For both of the studied cell lines, in already two days (one day after induction of differentiation) equivalent circuit analysis was able to show distinction between proliferation and differentiation conditions, which is significantly earlier than by microscopic imaging. This study demonstrates the potential of impedance-based monitoring as a technique of choice in the study of stem cell behavior, laying the foundation for screening assays to characterize stem cell lines and testing the efficacy epigenetic control.

Label-Free Bioelectrochemical Methods for Evaluation of Anticancer Drug Effects at a Molecular Level

Cancer is a multifactorial family of diseases that is still a leading cause of death worldwide. More than 100 different types of cancer affecting over 60 human organs are known. Chemotherapy plays a central role for treating cancer. The development of new anticancer drugs or new uses for existing drugs is an exciting and increasing research area. This is particularly important since drug resistance and side effects can limit the efficacy of the chemotherapy. Thus, there is a need for multiplexed, cost-effective, rapid, and novel screening methods that can help to elucidate the mechanism of the action of anticancer drugs and the identification of novel drug candidates. This review focuses on different label-free bioelectrochemical approaches, in particular, impedance-based methods, the solid supported membranes technique, and the DNA-based electrochemical sensor, that can be used to evaluate the effects of anticancer drugs on nucleic acids, membrane transporters, and living cells. Some relevant examples of anticancer drug interactions are presented which demonstrate the usefulness of such methods for the characterization of the mechanism of action of anticancer drugs that are targeted against various biomolecules.

Marine Toxins Detection by Biosensors Based on Aptamers

Marine toxins cause great harm to human health through seafood, therefore, it is urgent to exploit new marine toxins detection methods with the merits of high sensitivity and specificity, low detection limit, convenience, and high efficiency. Aptasensors have emerged to replace classical detection methods for marine toxins detection. The rapid development of molecular biological approaches, sequencing technology, material science, electronics and chemical science boost the preparation and application of aptasensors. Taken together, the aptamer-based biosensors would be the best candidate for detection of the marine toxins with the merits of high sensitivity and specificity, convenience, time-saving, relatively low cost, extremely low detection limit, and high throughput, which have reduced the detection limit of marine toxins from nM to fM. This article reviews the detection of marine toxins by aptamer-based biosensors, as well as the selection approach for the systematic evolution of ligands by exponential enrichment (SELEX), the aptamer sequences. Moreover, the newest aptasensors and the future prospective are also discussed, which would provide thereotical basis for the future development of marine toxins detection by aptasensors.

A Microfluidic Device Integrating Impedance Flow Cytometry and Electric Impedance Spectroscopy for High-Efficiency Single-Cell Electrical Property Measurement

Single-cell impedance measurement is a label-free, noninvasive method for characterizing the electrical properties of single cells. At present, though widely used for impedance measurement, electric impedance flow cytometry (IFC) and electric impedance spectroscopy (EIS) are used alone for most microfluidic chips. In this paper, we present a microfluidic device combining the IFC and EIS techniques for single-cell electrical property measurement. The device uses hydrodynamic constriction to passively trap single cells and uses coplanar electrodes to obtain the impedance spectrum of the trapped cell via EIS and discrete impedance data points of the passing cells via IFC. Through experiment, we verified the individual functionality of IFC and EIS respectively, by revealing through IFC the impedance magnitude difference and quantifying through EIS the area-specific membrane capacitance and cytoplasm conductivity of the three types of cancer cells. We also demonstrated the complementarity of IFC and EIS, which holds for a wide range of the flow rate. We envision that the strategy of combining IFC and EIS provides a new thought in the efforts to enhancing the efficiency of electrical property measurement for single cells.

Bioelectrical Analysis of Various Cancer Cell Types Immobilized in 3D Matrix and Cultured in 3D-Printed Well

Cancer cell lines are important tools for anticancer drug research and assessment. Impedance measurements can provide valuable information about cell viability in real time. This work presents the proof-of-concept development of a bioelectrical, impedance-based analysis technique applied to four adherent mammalian cancer cells lines immobilized in a three-dimensional (3D) calcium alginate hydrogel matrix, thus mimicking in vivo tissue conditions. Cells were treated with cytostatic agent5-fluoruracil (5-FU). The cell lines used in this study were SK-N-SH, HEK293, HeLa, and MCF-7. For each cell culture, three cell population densities were chosen (50,000, 100,000, and 200,000 cells/100 μL). The aim of this study was the extraction of mean impedance values at various frequencies for the assessment of the different behavior of various cancer cells when 5-FU was applied. For comparison purposes, impedance measurements were implemented on untreated immobilized cell lines. The results demonstrated not only the dependence of each cell line impedance value on the frequency, but also the relation of the impedance level to the cell population density for every individual cell line. By establishing a cell line-specific bioelectrical behavior, it is possible to obtain a unique fingerprint for each cancer cell line reaction to a selected anticancer agent.

Single molecule protein patterning using hole mask colloidal lithography

The ability to manipulate single protein molecules on a surface is useful for interfacing biology with many types of devices in optics, catalysis, bioengineering, and biosensing. Control of distance, orientation, and activity at the single molecule level will allow for the production of on-chip devices with increased biological activity. Cost effective methodologies for single molecule protein patterning with tunable pattern density and scalable coverage area remain a challenge. Herein, Hole Mask Colloidal Lithography is presented as a bench-top colloidal lithography technique that enables a glass coverslip to be patterned with functional streptavidin protein onto patches from 15-200 nm in diameter with variable pitch. Atomic force microscopy (AFM) was used to characterize the size of the patterned features on the glass surface. Additionally, single-molecule fluorescence microscopy was used to demonstrate the tunable pattern density, measure binding controls, and confirm patterned single molecules of functional streptavidin.

Use of an Insulation Layer on the Connection Tracks of a Biosensor with Coplanar Electrodes to Increase the Normalized Impedance Variation

New technologies, such as biosensors and lab-on-a-chip, are reducing time consumption and costs for the detection and characterization of biological cells. One challenge is to detect and characterize cells and bacteria one by one or at a very low concentration. In this case, measurements have very low variations that can be difficult to detect. In this article, the use of an insulation layer on the connection tracks of a biosensor with coplanar electrodes is proposed to improve a biosensor previously developed. The impedance spectroscopy technique was used to analyze the influence of the insulation layer on the cutoff frequencies and on the normalized impedance variation. This solution does not induce changes in the cutoff frequencies, though it permits improving the normalized impedance variations, compared to the same biosensor without the insulation layer.

Evaluation of Lipid Accumulation Using Electrical Impedance Measurement under Three-Dimensional Culture Condition

The degeneration of adipocyte has been reported to cause obesity, metabolic syndrome, and other diseases. To treat these diseases, an effective in vitro evaluation and drug-screening system for adipocyte culture is required. The objective of this study is to establish an in vitro three-dimensional cell culture system to enable the monitoring of lipid accumulation by measuring electrical impedance, and to determine the relationship between the impedance and lipid accumulation of adipocytes cultured three dimensionally. Consequently, pre-adipocytes, 3T3-L1 cells, were cultured and differentiated to the adipocytes in our culture system, and the electrical impedance of the three-dimensional adipocyte culture at a high frequency was related to the lipid accumulation of the adipocytes. In conclusion, the lipid accumulation of adipocytes could be evaluated in real time by monitoring the electrical impedance during in vitro culture.

Influence of Electrode Connection Tracks on Biological Cell Measurements by Impedance Spectroscopy

The limit of detection of a biological sensor is an important parameter because, when it is optimized, it allows the detection of a reduced number of biological cells and the reduction of the detection time. This parameter can be improved upon with a reduction in electrode size, but the rate of detection is similarly reduced as well. To avoid this problem, we propose a sensor matrix composed of 20 × 20 µm² coplanar square electrodes with a standard clean room manufacturing process. However, it was observed that the exposition of electrode connection tracks to the solution reduces the normalized impedance variation. In this pursuit, we propose in this paper an analysis of electrode connection tracks on the normalized impedance variation and cutoff frequencies to biological cell measurements by impedance spectroscopy. The experimental results were obtained using the E4990A Keysight impedance analyser (Keysight Technologies, Santa Rosa, CA, USA) with a frequency band ranging from 100 Hz to 12 MHz, thus allowing for good measurement accuracy. Therefore, it was found that, for the measurements between the electrodes with 9 µm of connection tracks in contact with the solution, the normalized impedance variation was from 3.7% to 4.2% for different measurements, while, for the electrodes with 40 µm of connection tracks in contact with the solution, the normalized impedance variation was from 1.8% to 2.1% for different measurements.

High-Density Electrical Recording and Impedance Imaging With a Multi-Modal CMOS Multi-Electrode Array Chip

Multi-electrode arrays, both active or passive, emerged as ideal technologies to unveil intricated electrophysiological dynamics of cells and tissues. Active MEAs, designed using complementary metal oxide semiconductor technology (CMOS), stand over passive devices thanks to the possibility of achieving single-cell resolution, the reduced electrode size, the reduced crosstalk and the higher functionality and portability. Nevertheless, most of the reported CMOS MEA systems mainly rely on a single operational modality, which strongly hampers the applicability range of a single device. This can be a limiting factor considering that most biological and electrophysiological dynamics are often based on the synergy of multiple and complex mechanisms acting from different angles on the same phenomena. Here, we designed a CMOS MEA chip with 16,384 titanium nitride electrodes, 6 independent operational modalities and 1,024 parallel recording channels for neuro-electrophysiological studies. Sixteen independent active areas are patterned on the chip surface forming a 4 × 4 matrix, each one including 1,024 electrodes. Electrodes of four different sizes are present on the chip surface, ranging from 2.5 × 3.5 μm² up to 11 × 11.0 μm², with 15 μm pitch. In this paper, we exploited the impedance monitoring and voltage recording modalities not only to monitor the growth and development of primary rat hippocampal neurons, but also to assess their electrophysiological activity over time showing a mean spike amplitude of 144.8 ± 84.6 μV. Fixed frequency (1 kHz) and high sampling rate (30 kHz) impedance measurements were used to evaluate the cellular adhesion and growth on the chip surface. Thanks to the high-density configuration of the electrodes, as well as their dimension and pitch, the chip can appreciate the evolutions of the cell culture morphology starting from the moment of the seeding up to mature culture conditions. The measurements were confirmed by fluorescent staining. The effect of the different electrode sizes on the spike amplitudes and noise were also discussed. The multi-modality of the presented CMOS MEA allows for the simultaneous assessment of different physiological properties of the cultured neurons. Therefore, it can pave the way both to answer complex fundamental neuroscience questions as well as to aid the current drug-development paradigm.

Impedance Study of Dopamine Effects after Application on 2D and 3D Neuroblastoma Cell Cultures Developed on a 3D-Printed Well

In this work, the assessment of the interactions of a bioactive substance applied to immobilized cells in either a two-dimensional (2D) or three-dimensional (3D) arrangement mimicking in vivo tissue conditions is presented. In particular, dopamine (DA) was selected as a stimulant for the implementation of an impedance analysis with a specific type of neural cells (murine neuroblastoma). The aim of this study was the extraction of calibration curves at various frequencies with different known dopamine concentrations for the description of the behavior of dopamine applied to 2D and 3D cell cultures. The results present the evaluation of the mean impedance value for each immobilization technique in each frequency. The differential responses showed the importance of the impedance when frequency is applied in both 2D and 3D immobilization cases. More specifically, in 2D immobilization matrix impedance shows higher values in comparison with the 3D cell culture. Additionally, in the 3D case, the impedance decreases with increasing concentration, while in the 2D case, an opposite behavior was observed.

Assessing the Potential Deployment of Biosensors for Point-of-Care Diagnostics in Developing Countries: Technological, Economic and Regulatory Aspects

Infectious diseases and antimicrobial resistance are major burdens in developing countries, where very specific conditions impede the deployment of established medical infrastructures. Since biosensing devices are nowadays very common in developed countries, particularly in the field of diagnostics, they are at a stage of maturity at which other potential outcomes can be explored, especially on their possibilities for multiplexing and automation to reduce the time-to-results. However, the translation is far from being trivial. In order to understand the factors and barriers that can facilitate or hinder the application of biosensors in resource-limited settings, we analyze the context from several angles. First, the technology of the devices themselves has to be rethought to take into account the specific needs and the available means of these countries. For this, we describe the partition of a biosensor into its functional shells, which define the information flow from the analyte to the end-user, and by following this partition we assess the strengths and weaknesses of biosensing devices in view of their specific technological development and challenging deployment in low-resource environments. Then, we discuss the problem of cost reduction by pointing out transversal factors, such as throughput and cost of mistreatment, that need to be re-considered when analyzing the cost-effectiveness of biosensing devices. Beyond the technical landscape, the compliance with regulations is also a major aspect that is described with its link to the validation of the devices and to the acceptance from the local medical personnel. Finally, to learn from a successful case, we analyze a breakthrough inexpensive biosensor that is showing high potential with respect to many of the described aspects. We conclude by mentioning both some transversal benefits of deploying biosensors in developing countries, and the key factors that can drive such applications.

Bionic 3D spheroids biosensor chips for high-throughput and dynamic drug screening

To perform the drug screening, planar cultured cell models are commonly applied to test efficacy and toxicity of drugs. However, planar cultured cells are different from the human 3D organs or tissues in vivo. To simulate the human 3D organs or tissues, 3D spheroids are developed by culturing a small aggregate of cells which reside around the extracellular matrix and interact with other cells in liquid media. Here we apply lung carcinoma cell lines to engineer the 3D lung cancer spheroid-based biosensor using the interdigitated electrodes for drug efficacy evaluation. The results show 3D spheroid had higher drug resistance than the planar cell model. The anticarcinogen inhibition on different 3D lung cancer spheroid models (A549, H1299, H460) can be quantitatively evaluated by electric impedance sensing. Besides, we delivered combination of anticarcinogens treatments to A549 spheroids which is commonly used in clinic treatment, and found the synergistic effect of cisplatin plus etoposide had higher drug response. To simultaneously test the drug efficacy and side effects on multi-organ model with circulatory system, a connected multiwell interdigitated electrode arraywas applied to culture different organoid spheroids. Overall, the organization of 3D cancer spheroids-based biosensor, which has higher predictive value for drug discovery and personalized medicine screening, is expected to be well applied in the area of pharmacy and clinical medicine.

Applications of Bioimpedance Measurement Techniques in Tissue Engineering

Rapid development in the field of tissue engineering necessitates implementation of monitoring methods for evaluation of the viability and characteristics of the cell cultures in a real-time, non-invasive and non-destructive manner. Current monitoring techniques are mainly histological and require labeling and involve destructive tests to characterize cell cultures. Bioimpedance measurement technique which benefits from measurement of electrical properties of the biological tissues, offers a non-invasive, label-free and real-time solution for monitoring tissue engineered constructs. This review outlines the fundamentals of bioimpedance, as well as electrical properties of the biological tissues, different types of cell culture constructs and possible electrode configuration set ups for performing bioimpedance measurements on these cell cultures. In addition, various bioimpedance measurement techniques and their applications in the field of tissue engineering are discussed.

Real-Time Bioimpedance Sensing of Antifibrotic Drug Action in Primary Human Cells

Fibrotic diseases are among the most serious health issues with severe burdens due to their chronic nature and a large number of patients suffering from the debilitating effects and long-term sequelae. Collagenase treatment is a nonsurgical option but has limited results. To date, there is no potent noninvasive solution for fibrosis. Part of the reason for this is the lack of appropriate in vitro live cell screening tools to assess the efficacy of new therapeutical agents. Here, we demonstrate the utility of a cell-based electrochemical impedance biosensor platform to screen the efficacy of potential antifibrotic compounds. The platform employs a label-free and noninvasive strategy to detect the progression of fibrosis and the potency of the antifibrotic molecules in real-time. The fundamental principle that governs this novel system is that dynamic changes in cell shape and adhesion during fibrosis can be measured accurately by monitoring the changes in the impedance. This is achieved by growing the cells on a transparent interdigitated indium tin oxide (ITO) electrodes. It was demonstrated by monitoring the efficacy of a model antifibrotic compound, PXS64, on cells collected from patients with Dupuytren's contracture. We confirmed the validity of the developed biochemical impedance biosensor as an tool for in vitro screening of antifibrotic compounds and provided quantitative information on subcellular influences of the examined chemical molecules using correlative microscopy analyses that monitor the average cell area, cell morphology, and the amount and directionality of the deposited extracellular matrix protein collagen and measurement of cytosolic Ca²⁺ changes.

Study of small-cell lung cancer cell-based sensor and its applications in chemotherapy effects rapid evaluation for anticancer drugs

Small cell lung cancer (SCLC) is a smoking-related cancer disease. Despite improvement in clinical survival, SCLC outcome remains extremely poor. Cisplatin (DDP) is the first-line chemotherapy drug for SCLC, but the choice of second-line chemotherapy drugs is not clear. In this paper, a SCLC cell-based sensor was proposed, and its applications in chemotherapy effects rapid evaluation for anticancer drugs were investigated. SCLC cell lines lung adenocarcinoma cell (LTEP-P) and DDP-resistant lung adenocarcinoma cell (LTEP-P/DDP-1.0) are cultured on carbon screen-printed electrode (CSPE) to fabricate integrated cell-based sensor. Several chemotherapy anticancer drugs, including cisplatin, ifosmamide, gemcitabine, paclitaxel, docetaxel, vinorelbine, etoposide, camptothecin, and topotecan, are selected as experimental chemicals. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) tests are conducted to evaluate chemotherapy drug effects on LTEP-P and LTEP-P/DDP-1.0 cell lines. Electrical cell-substrate impedance sensing (ECIS) responses to anti-tumor chemicals are measured and processed by double-layered cascaded stochastic resonance (DCSR). Cisplatin solutions in different concentrations measurement results demonstrate that LTEP-P cell-based sensor presents quantitative analysis abilities for cisplatin and topotecan. Cisplatin and its mixtures can also be discriminated. Results demonstrate that LTEP-P cell-based sensor sensitively evaluates chemotherapy drugs' apoptosis function to SCLC cells. LTEP-P/DDP-1.0 cell-based sensor responses demonstrate that gemcitabine, vinorelbine, and camptothecin are ideal second-line drugs for clinical post-cisplatin therapy than other drugs according to MTT test results. This work provides a novel way for SCLC second-line clinical chemotherapy drug screening.

On Chip Bioelectric Impedance Spectroscopy Reveals the Effect of P-Glycoprotein Efflux Pumps on the Paracellular Impedance of Tight Junctions at the Blood-Brain Barrier

Bioelectric impedance spectroscopy was used to elucidate the influence of P-gp efflux pumps on the kinetics of tight junction down-regulation in confluent monolayers of Madine Darby Canine Kidney Epithelial Cells (MDCK) following administration of phenylarsine oxide (PAO), a molecule that inhibits protein tyrosine phosphatases (PTP) and induces matrix metalloproteinase activity. Matrix metalloproteinases (MMPs) and phosphatase inhibitors induce modification of occludin tight junction proteins critical for the proper function of the blood-brain barrier. The addition of PAO to MDCKII cell lines resulted in a dramatic decrease in monolayer resistance. In contrast, MDCKII-MDR1 cells transfected with the MDR1 gene treated with PAO showed an initial decrease in monolayer resistance followed by a partial recovery and subsequent decrease. This resistance decay reversal was suppressed with the addition of the P-glycoprotein (P-gp) pump inhibitor elacridar, and is attributed to PAO efflux. These results illustrate impedance spectroscopy can be used to characterize the competing kinetics of efflux and down-regulation of tight junctions. In addition, the resistance decay reversal effect can be used to evaluate P-gp pump inhibitor efficacy.

Cell suspension concentration monitoring by using a miniaturized serial high frequency SAWR sensor

In this paper, a miniaturized cell suspension concentration monitoring method was investigated. The sensing unit was a carbon screen-printed electrode (CSPE) in serial with a 433MHz vacuum-packaged surface acoustic wave resonator (SAWR). SAWR provided a stable and high operating frequency, which helps to keep the stability and sensitivity of the monitoring system. Living cells suspensions in different concentrations were prepared and dropcast on CSPE. Frequency responses of the sensor were recorded. Cell quantity variation within the same culture media volume changed the dielectric properties of CSPE and finally affected the SAWR frequency. SAWR frequency declined with the decrease of cell concentration. The proposed sensor provided high sensitivity and remarkable stability for the cell suspensions.

Single Cell Electrical Characterization Techniques

Electrical properties of living cells have been proven to play significant roles in understanding of various biological activities including disease progression both at the cellular and molecular levels. Since two decades ago, many researchers have developed tools to analyze the cell’s electrical states especially in single cell analysis (SCA). In depth analysis and more fully described activities of cell differentiation and cancer can only be accomplished with single cell analysis. This growing interest was supported by the emergence of various microfluidic techniques to fulfill high precisions screening, reduced equipment cost and low analysis time for characterization of the single cell’s electrical properties, as compared to classical bulky technique. This paper presents a historical review of single cell electrical properties analysis development from classical techniques to recent advances in microfluidic techniques. Technical details of the different microfluidic techniques are highlighted, and the advantages and limitations of various microfluidic devices are discussed.

Non-Faradaic electrical impedimetric investigation of the interfacial effects of neuronal cell growth and differentiation on silicon nanowire transistors

Silicon nanowire field-effect transistor (SiNW FET) devices have been interfaced with cells; however, their application for noninvasive, real-time monitoring of interfacial effects during cell growth and differentiation on SiNW has not been fully explored. Here, we cultured rat adrenal pheochromocytoma (PC12) cells, a type of neural progenitor cell, directly on SiNW FET devices to monitor cell adhesion during growth and morphological changes during neuronal differentiation for a period of 5-7 d. Monitoring was performed by measuring the non-Faradaic electrical impedance of the cell-SiNW FET system using a precision LCR meter. Our SiNW FET devices exhibited changes in impedance parameters during cell growth and differentiation because of the negatively charged cell membrane, seal resistance, and membrane capacitance at the cell/SiNW interface. It was observed that during both PC12 cell growth and neuronal differentiation, the impedance magnitude increased and the phase shifted to more negative values. However, impedance changes during cell growth already plateaued 3 d after seeding, while impedance changes continued until the last observation day during differentiation. Our results also indicate that the frequency shift to above 40 kHz after growth factor induction resulted from a larger coverage of cell membrane on the SiNWs due to distinctive morphological changes according to vinculin staining. Encapsulation of PC12 cells in a hydrogel scaffold resulted in a lack of trend in impedance parameters and confirmed that impedance changes were due to the cells. Moreover, cytolysis of the differentiated PC12 cells led to significant changes in impedance parameters. Equivalent electrical circuits were used to analyze the changes in impedance values during cell growth and differentiation. The technique employed in this study can provide a platform for performing investigations of growth-factor-induced progenitor cell differentiation.