Recent Advances in Monitoring Cell Behavior Using Cell-Based Impedance Spectroscopy

A CMOS-integrated terahertz near-field sensor based on an ultra-strongly coupled meta-atom

Recently, plasmonic-based sensors operating in the terahertz frequency range have emerged as perspective tools for rapid and efficient label-free biosensing applications. In this work, we present a fully electronic approach allowing us to achieve state-of-the-art sensitivity by utilizing a near-field-coupled electronic sensor. We demonstrate that the proposed concept enables the efficient implementation and probing of a so-called ultra-strongly coupled sub-wavelength meta-atom as well as a single resonant circuit, allowing to limit the volume of material under test down to a few picoliter range. The sensor has been monolithically integrated into a cost-efficient silicon-based CMOS technology. Our findings are supported by both numerical and analytical models and validated through experiments. They lay the groundwork for near-future developments, outlining the perspectives for a terahertz microfluidic lab-on-chip dielectric spectroscopy sensor.

Sensing of gene expression in live cells using electrical impedance spectroscopy and DNA-functionalized gold nanoparticles

A novel electrical impedance spectroscopy-based method for non-destructive sensing of gene expression in living cells is presented. The approach used takes advantage of the robustness and responsiveness of electrical impedance spectroscopy and the highly specific and selective nature of DNA hybridization. The technique uses electrical impedance spectroscopy and gold nanoparticles functionalized with single-stranded DNA complementary to an mRNA of interest to provide reliable, real-time, and quantifiable data on gene expression in live cells. The system was validated by demonstrating specific detection of the uidA mRNA, which codes for the β-glucuronidase (GUS) enzyme, in Solanum lycopersicum MsK8 cells. Gold nanoparticles were functionalized with single-stranded DNA oligonucleotides consisting of either a sequence complementary to uidA mRNA or an arbitrary sequence. The DNA-functionalized gold nanoparticles were mixed with cell suspensions, allowing the gold nanoparticles to penetrate into the cells. The impedance spectra of suspensions of cells with gold nanoparticles inserted within them were then studied. In suspensions of uidA-expressing cells and gold nanoparticles functionalized with the complementary single-stranded DNA oligonucleotide, the impedance magnitude in the frequency range of interest was significantly higher (146 %) in comparison to all other controls. Due to its highly selective nature, the methodology has the potential to be used as a precision agricultural sensing system for accurate and real-time detection of markers of stress, viral infection, disease, and normal physiological activities.

Recent advances in electrochemical cell-based biosensors for food analysis: Strategies for sensor construction

Owing to their advantages such as great specificity, sensitivity, rapidity, and possibility of noninvasive and real-time monitoring, electrochemical cell-based biosensors (ECBBs) have been a powerful tool for food analysis encompassing the areas of nutrition, flavor, and safety. Notably, the distinctive biological relevance of ECBBs enables them to mimic physiological environments and reflect cellular behaviors, leading to valuable insights into the biological function of target components in food. Compared with previous reviews, this review fills the current gap in the narrative of ECBB construction strategies. The review commences by providing an overview of the materials and configuration of ECBBs, including cell types, cell immobilization strategies, electrode modification materials, and electrochemical sensing types. Subsequently, a detailed discussion is presented on the fabrication strategies of ECBBs in food analysis applications, which are categorized based on distinct signal sources. Lastly, we summarize the merits, drawbacks, and application scope of these diverse strategies, and discuss the current challenges and future perspectives of ECBBs. Consequently, this review provides guidance for the design of ECBBs with specific functions and promotes the application of ECBBs in food analysis.

A review of electrochemical impedance as a tool for examining cell biology and subcellular mechanisms: merits, limits, and future prospects

Herein the development of cellular impedance biosensors, electrochemical impedance spectroscopy, and the general principles and terms associated with the cell-electrode interface is reviewed. This family of techniques provides quantitative and sensitive information into cell responses to stimuli in real-time with high temporal resolution. The applications of cell-based impedance biosensors as a readout in cell biology is illustrated with a diverse range of examples. The current state of the field, its limitations, the possible available solutions, and the potential benefits of developing biosensors are discussed.

A biologically validated mathematical model for decoding epithelial apical, basolateral, and paracellular electrical properties

Epithelial tissues form selective barriers to ions, nutrients, waste products, and infectious agents throughout the body. Damage to these barriers is associated with conditions such as celiac disease, cystic fibrosis, diabetes, and age-related macular degeneration. Conventional electrophysiology measurements like transepithelial resistance can quantify epithelial tissue maturity and barrier integrity but are limited in differentiating between apical, basolateral, and paracellular transport pathways. To overcome this limitation, a combination of mathematical modeling, stem cell biology, and cell physiology led to the development of 3 P-EIS, a novel mathematical model and measurement technique. 3 P-EIS employs an intracellular pipette and extracellular electrochemical impedance spectroscopy to accurately measure membrane-specific properties of epithelia, without the constraints of prior models. 3 P-EIS was validated using electronic circuit models of epithelia with known resistances and capacitances, confirming a median error of 19% (interquartile range: 14%-26%) for paracellular and transcellular resistances and capacitances (n = 5). Patient stem cell-derived retinal pigment epithelium tissues were measured using 3 P-EIS, successfully isolating the cellular responses to adenosine triphosphate. 3 P-EIS enhances quality control in epithelial cell therapies and has extensive applicability in drug testing and disease modeling, marking a significant advance in epithelial physiology.NEW & NOTEWORTHY This interdisciplinary paper integrates mathematics, biology, and physiology to measure epithelial tissue's apical, basolateral, and paracellular transport pathways. A key advancement is the inclusion of intracellular voltage recordings using a sharp pipette, enabling precise quantification of relative impedance changes between apical and basolateral membranes. This enhanced electrochemical impedance spectroscopy technique offers insights into epithelial transport dynamics, advancing disease understanding, drug interactions, and cell therapies. Its broad applicability contributes significantly to epithelial physiology research.

Fabrication of ITO microelectrodes and electrode arrays using a low-cost CO2 laser plotter

Good electronic (Rs = ∼5 Ω sq-1) and optical properties (transmittance: >83%) make indium tin oxide (ITO) an attractive electrode substrate. Despite the commercial availability of high-quality ITO and some low-cost methods for direct deposition being in use by now, the definition of patterns is still a concern. Putting their popularity and extensive use aside, the manufacturing of ITO electrodes so far lacks a rapid, highly reproducible, flexible, cost-effective, easy patterning process that could surpass difficult, time-consuming techniques such as lithography. Herein, we present a low-cost method based on CO2 laser irradiation for preparing ITO microelectrodes and electrode arrays. Electrodes of different sizes and shapes were examined to identify the performance of the proposed methods. Direct ablation of the ITO layer was optimized for rectangular electrodes of 25, 50, and 100 μm in width, while laser cutting of scotch tape stencils and subsequent wet etching were used to create circular electrodes with a diameter of 1.75 mm. A multielectrode array system consisting 8 of these circular electrodes was fabricated on a (25 × 25) mm2 plate, characterized electrochemically through cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM), and as an example application used for monitoring the anchoring behavior of HeLa and HepG2 cell cultures through cell-based electrochemical impedance spectroscopy. Together, the direct ablation method and preparation of laser cut stencils form a complete toolbox, which allows for low-cost and fast fabrication of ITO electrodes for a wide variety of applications. To demonstrate the general availability of the method, we have also prepared a batch of electrodes using a laser plotter in a local printing shop, achieving high intra-workshop reproducibility.

Mammalian Cell-Growth Monitoring Based on an Impedimetric Sensor and Image Processing within a Microfluidic Platform

In recent years, advancements in microfluidic and sensor technologies have led to the development of new methods for monitoring cell growth both in macro- and micro-systems. In this paper, a microfluidic (MF) platform with a microbioreactor and integrated impedimetric sensor is proposed for cell growth monitoring during the cell cultivation process in a scaled-down simulator. The impedimetric sensor with an interdigitated electrode (IDE) design was realized with inkjet printing and integrated into the custom-made MF platform, i.e., the scaled-down simulator. The proposed method, which was integrated into a simple and rapid fabrication MF system, presents an excellent candidate for the scaled-down analyses of cell growths that can be of use in, e.g., optimization of the cultivated meat bioprocess. When applied to MRC-5 cells as a model of adherent mammalian cells, the proposed sensor was able to precisely detect all phases of cell growth (the lag, exponential, stationary, and dying phases) during a 96-h cultivation period with limited available nutrients. By combining the impedimetric approach with image processing, the platform enables the real-time monitoring of biomasses and advanced control of cell growth progress in microbioreactors and scaled-down simulator systems.

Design and Modeling of a Device Combining Single-Cell Exposure to a Uniform Electrical Field and Simultaneous Characterization via Bioimpedance Spectroscopy

Previous studies have demonstrated the electropermeabilization of cell membranes exposed to an electric field with moderate intensity (<2 V/cm) and a frequency of <100 MHz. Bioimpedance spectroscopy (BIS) is an electrical characterization technique that can be useful in studying this phenomenon because it is already used for electroporation. In this paper, we report a device designed to perform BIS on single cells and expose them to an electric field simultaneously. It also allows cells to be monitored by visualization through a transparent exposure electrode. This device is based on a lab-on-a-chip (LOC) with a microfluidic cell-trapping system and microelectrodes for BIS characterization. We present numerical simulations that support the design of the LOC. We also describe the fabrication of the LOC and the first electrical characterization of its measurement bandwidth. This first test, performed on reference medium with a conductivity in the same order than human cells, confirms that the measurement capabilities of our device are suitable for electrical cells characterization.

A CMOS Multi-Electrode Array for Four-Electrode Bioimpedance Measurements

This work demonstrates how a multi-electrode array (MEA) dedicated to four-electrode bioimpedance measurements can be implemented on a complementary metal-oxide-semiconductor (CMOS) chip. As a proof of concept, an 8 × 8 pixel array along with dedicated amplifiers was designed and fabricated in the TSMC 180 nm process. Each pixel in the array contains a circular current carrying (CC) electrode that can act as a current source or sink. In order to measure a differential voltage between the pixels, each CC electrode is surrounded by a ring shaped pick up (PU) electrode. The differential voltages can be measured by an on-board instrumentation amplifier, while the currents can be measured with an on-bard transimpedance amplifier. Openings in the passivation layer exposed the aluminum top metal layer, and a metal stack of zinc, nickel and gold was deposited in an electroless plating process. The chips were then wire bonded to a ceramic package and prepared for wet experiments by encapsulating the bonding wires and pads in the photoresist SU-8. Measurements in liquids with different conductivities were performed to demonstrate the functionality of the chip.

Construction of a biocompatible MWCNTs-chitosan composite interface and its application to impedance cytosensing of osteoblastic MC3T3-E1 cells

In this work a carboxylated MWCNTs-chitosan composite sol-gel material was developed via one-step electrodeposition on a glassy carbon electrode as the cytosensing interface of a novel impedance cytosensor. SEM verified the formation of a three-dimensional hierarchical and porous microstructure favorable for the adhesion and spreading of osteoblastic MC3T3-E1 cells. By correlating impedance measurements with fluorescence microscopic characterization results, the cytosensor was demonstrated to have the ability to determine the MC3T3-E1 cell concentration ranging from 5 × 103 to 5 × 108 cell per mL with a detection limit of 1.8 × 103 cell per mL. The impedance cytosensor also enabled monitoring of the cell behavior regarding the processes of cell attachment, spreading, and proliferation in a label-free and quantitative manner. By taking advantage of this cytosensing method, investigating the effect of the C-terminal pentapeptide of osteogenic growth peptide (OGP(10-14)) on MC3T3-E1 cells was accomplished, demonstrating the potential for the application of OGP(10-14) in bone repair and regeneration. Therefore, this work afforded a convenient impedimetric strategy for osteoblastic cell counting and response monitoring that would be useful in evaluating the interactions between osteoblastic cells and specified drugs.

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.

Syngas Fermentation to Acetate and Ethanol with Adaptative Electroactive Carboxydotrophs in Single Chambered Microbial Electrochemical System

Microbial electrosynthesis system (MES; single-chambered) was fabricated and evaluated with carbon cloth/graphite as a working/counter electrode employing an enriched microbiome. Continuous syngas sparging (at working electrode; WE) enabled the growth of endo electrogenic bacteria by availing the inorganic carbon source. Applied potential (−0.5 V) on the working electrode facilitated the reduction in syngas, leading to the synthesis of fatty acids and alcohols. The higher acetic acid titer of 3.8 g/L and ethanol concentration of 0.2 g/L was observed at an active microbial metabolic state, evidencing the shift in metabolism from acetogenic to solventogenesis. Voltammograms evidenced distinct redox species with low charge transfer resistance (Rct; Nyquist impedance). Reductive catalytic current (−0.02 mA) enabled the charge transfer efficiency of the cathodes favoring syngas conversion to products. The surface morphology of carbon cloth and system-designed conditions favored the growth of electrochemically active consortia. Metagenomic analysis revealed the enrichment of phylum/class with Actinobacteria, Firmicutes/Clostridia and Bacilli, which accounts for the syngas fermentation through suitable gene loci.

Advanced Materials and Sensors for Microphysiological Systems: Focus on Electronic and Electrooptical Interfaces

Advanced in vitro cell culture systems or microphysiological systems (MPSs), including microfluidic organ-on-a-chip (OoC), are breakthrough technologies in biomedicine. These systems recapitulate features of human tissues outside of the body. They are increasingly being used to study the functionality of different organs for applications such as drug evolutions, disease modeling, and precision medicine. Currently, developers and endpoint users of these in vitro models promote how they can replace animal models or even be a better ethically neutral and humanized alternative to study pathology, physiology, and pharmacology. Although reported models show a remarkable physiological structure and function compared to the conventional 2D cell culture, they are almost exclusively based on standard passive polymers or glass with none or minimal real-time stimuli and readout capacity. The next technology leap in reproducing in vivo-like functionality and real-time monitoring of tissue function could be realized with advanced functional materials and devices. This review describes the currently reported electronic and optical advanced materials for sensing and stimulation of MPS models. In addition, an overview of multi-sensing for Body-on-Chip platforms is given. Finally, one gives the perspective on how advanced functional materials could be integrated into in vitro systems to precisely mimic human physiology.

Organic Bioelectronics for In Vitro Systems

Bioelectronics have made strides in improving clinical diagnostics and precision medicine. The potential of bioelectronics for bidirectional interfacing with biology through continuous, label-free monitoring on one side and precise control of biological activity on the other has extended their application scope to in vitro systems. The advent of microfluidics and the considerable advances in reliability and complexity of in vitro models promise to eventually significantly reduce or replace animal studies, currently the gold standard in drug discovery and toxicology testing. Bioelectronics are anticipated to play a major role in this transition offering a much needed technology to push forward the drug discovery paradigm. Organic electronic materials, notably conjugated polymers, having demonstrated technological maturity in fields such as solar cells and light emitting diodes given their outstanding characteristics and versatility in processing, are the obvious route forward for bioelectronics due to their biomimetic nature, among other merits. This review highlights the advances in conjugated polymers for interfacing with biological tissue in vitro, aiming ultimately to develop next generation in vitro systems. We showcase in vitro interfacing across multiple length scales, involving biological models of varying complexity, from cell components to complex 3D cell cultures. The state of the art, the possibilities, and the challenges of conjugated polymers toward clinical translation of in vitro systems are also discussed throughout.

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.

Editorial for the Special Issue on Micro and Nano Devices for Cell Analysis

In recent years, miniaturized systems (micro- and nano-devices) called a lab-on-a-chip or micro-total analysis system (µ-TAS) have received attention as new systems for chemical and biochemical analyses [...].

An easy-fabricated and disposable polymer-film microfluidic impedance cytometer for cell sensing

We report here an easy-fabricated and disposable polymer-film microfluidic impedance cytometer (PMIC) integrated with inertial focusing and parallel facing electrodes for cell sensing. The cells are first focused in an asymmetric serpentine channel, and then their impedance signals are measured when passing through the electrode region. The proposed PMIC device is the first impedance cytometer that is fabricated into a flexible sheet (with a thickness of 0.45 mm) by using the materials of commonly-available ITO-coated polymer films and double-sided adhesive tapes, the whole fabrication process is shortened from traditional 3-4 days to less than 5 min by using UV laser cutting. To verify the feasibility of our device for cell sensing, we explore the focusing behaviors of three differently sized particles and two types of tumor cells, and analyze their impedance signals. The results show that our device is capable of obtaining impedance information on numbers, diameters, and longitudinal positions of cells. We envision that our PMIC device is promising in label-free cell sensing owning to the advantages of low cost, small footprint, and simple fabrication.

Microfluidic impedance cytometry for single-cell sensing: Review on electrode configurations

Single-cell analysis has gained considerable attention for disease diagnosis, drug screening, and differentiation monitoring. Compared to the well-established flow cytometry, which uses fluorescent-labeled antibodies, microfluidic impedance cytometry (MIC) offers a simple, label-free, and noninvasive method for counting, classifying, and monitoring cells. Superior features including a small footprint, low reagent consumption, and ease of use have also been reported. The MIC device detects changes in the impedance signal caused by cells passing through the sensing/electric field zone, which can extract information regarding the size, shape, and dielectric properties of these cells. According to recent studies, electrode configuration has a remarkable effect on detection accuracy, sensitivity, and throughput. With the improvement in microfabrication technology, various electrode configurations have been reported for improving detection accuracy and throughput. However, the various electrode configurations of MIC devices have not been reviewed. In this review, the theoretical background of the impedance technique for single-cell analysis is introduced. Then, two-dimensional, three-dimensional, and liquid electrode configurations are discussed separately; their sensing mechanisms, fabrication processes, advantages, disadvantages, and applications are also described in detail. Finally, the current limitations and future perspectives of these electrode configurations are summarized. The main aim of this review is to offer a guide for researchers on the ongoing advancement in electrode configuration designs.

Cultivating Multidisciplinarity: Manufacturing and Sensing Challenges in Cultured Meat Production

Meat cultivation via cellular agriculture holds great promise as a method for future food production. In theory, it is an ideal way of meat production, humane to the animals and sustainable for the environment, while keeping the same taste and nutritional values as traditional meat and having additional benefits such as controlled fat content and absence of antibiotics and hormones used in the traditional meat industry. However, in practice, there is still a number of challenges, such as those associated with the upscale of cultured meat (CM). CM food safety monitoring is a necessary factor when envisioning both the regulatory compliance and consumer acceptance. To achieve this, a multidisciplinary approach is necessary. This includes extensive development of the sensitive and specific analytical devices i.e., sensors to enable reliable food safety monitoring throughout the whole future food supply chain. In addition, advanced monitoring options can help in the further optimization of the meat cultivation which may reduce the currently still high costs of production. This review presents an overview of the sensor monitoring options for the most relevant parameters of importance for meat cultivation. Examples of the various types of sensors that can potentially be used in CM production are provided and the options for their integration into bioreactors, as well as suggestions on further improvements and more advanced integration approaches. In favor of the multidisciplinary approach, we also include an overview of the bioreactor types, scaffolding options as well as imaging techniques relevant for CM research. Furthermore, we briefly present the current status of the CM research and related regulation, societal aspects and challenges to its upscaling and commercialization.

Quantitative Evaluation of Burn Injuries Based on Electrical Impedance Spectroscopy of Blood with a Seven-Parameter Equivalent Circuit

A quantitative and rapid burn injury detection method has been proposed based on the electrical impedance spectroscopy (EIS) of blood with a seven-parameter equivalent circuit. The degree of burn injury is estimated from the electrical impedance characteristics of blood with different volume proportions of red blood cells (RBCs) and heated red blood cells (HRBCs). A quantitative relationship between the volume portion H_HCT of HRBCs and the electrical impedance characteristics of blood has been demonstrated. A seven -parameter equivalent circuit is employed to quantify the relationship from the perspective of electricity. Additionally, the traditional Hanai equation has been modified to verify the experimental results. Results show that the imaginary part of impedance Z_Imt under the characteristic frequency (f_c) has a linear relationship with H_HCT which could be described by Z_Imt = −2.56H_HCT − 2.01 with a correlation coefficient of 0.96. Moreover, the relationship between the plasma resistance R_p and H_HCT is obtained as R_p = −7.2H_HCT + 3.91 with a correlation coefficient of 0.96 from the seven -parameter equivalent circuit. This study shows the feasibility of EIS in the quantitative detection of burn injury by the quantitative parameters Z_Imt and R_p, which might be meaningful for the follow-up clinical treatment for burn injury.

Tracking of Glycans Structure and Metallomics Profiles in BRAF Mutated Melanoma Cells Treated with Vemurafenib

Nearly half of patients with advanced and metastatic melanomas harbor a BRAF mutation. Vemurafenib (VEM), a BRAF inhibitor, is used to treat such patients, however, responses to VEM are very short-lived due to intrinsic, adaptive and/or acquired resistance. In this context, we present the action of the B-Raf serine-threonine protein kinase inhibitor (vemurafenib) on the glycans structure and metallomics profiles in melanoma cells without (MeWo) and with (G-361) BRAF mutations. The studies were performed using α1-acid glycoprotein (AGP), a well-known acute-phase protein, and concanavalin A (Con A), which served as the model receptor. The detection of changes in the structure of glycans can be successfully carried out based on the frequency shifts and the charge transfer resistance after interaction of AGP with Con A in different VEM treatments using QCM-D and EIS measurements. These changes were also proved based on the cell ultrastructure examined by TEM and SEM. The LA-ICP-MS studies provided details on the metallomics profile in melanoma cells treated with and without VEM. The studies evidence that vemurafenib modifies the glycans structures and metallomics profile in melanoma cells harboring BRAF mutation that can be further implied in the resistance phenomenon. Therefore, our data opens a new avenue for further studies in the short-term addressing novel targets that hopefully can be used to improve the therapeutic regiment in advanced melanoma patients. The innovating potential of this study is fully credible and has a real impact on the global patient society suffering from advanced and metastatic melanomas.