Toxicity studies using mammalian cells and impedance spectroscopy method

Effective Capacitance from Equivalent Electrical Circuit as a Tool for Monitoring Non-Adherent Cell Suspensions at Low Frequencies

Analyzing the electrical double layer (EDL) in electrical impedance spectroscopy (EIS) measurement at low frequencies remains a challenging task for sensing purposes. In this work, we propose two approaches to deal with the EDL in measuring impedance for particles and non-adherent cells in an electrolytic suspension. The first approach is a simple procedure to compute a normalized electrical impedance spectrum named dispersed medium index (DMi). The second is the EIS modeling through an equivalent electric circuit based on the so-called effective capacitance (Cef), which unifies the EDL phenomena. Firstly, as an experiment under controlled conditions, we examine polymer particles of 6, 15, and 48 μm in diameter suspended in a 0.9% sodium chloride solution. Subsequently, we used K-562 cells and leukocytes suspended in a culture medium (RPMI-1640 supplemented) for a biological assay. As the main result, the DMi is a function of the particle concentration. In addition, it shows a tendency with the particle size; regardless, it is limited to a volume fraction of 0.03 × 10-4 to 58 × 10-4. The DMi is not significantly different between K-562 cells and leukocytes for most concentrations. On the other hand, the Cef exhibits high applicability to retrieve a function that describes the concentration for each particle size, the K-562 cells, and leukocytes. The Cef also shows a tendency with the particle size without limitation within the range tested, and it allows distinction between the K-562 and leukocytes in the 25 cells/µL to 400 cells/µL range. We achieved a simple method for determining an Cef by unifying the parameters of an equivalent electrical circuit from data obtained with a conventional potentiostat. This simple approach is affordable for characterizing the population of non-adherent cells suspended in a cell culture medium.

An impedimetric assay for the identification of abnormal mitochondrial dynamics in living cells

Mitochondrial dynamics (fission and fusion) plays an important role in cell functions. Disruption in mitochondrial dynamics has been associated with diseases such as neurobiological disorders and cardiovascular diseases. Analysis of mitochondrial fission/fusion has been mostly achieved through direct visualization of the fission/fusion events in live-cell imaging of fluorescently labeled mitochondria. In this study, we demonstrated a label-free, non-invasive Electrical Impedance Spectroscopy (EIS) approach to analyze mitochondrial dynamics in a genetically modified human neuroblastoma SH-SY5Y cell line with no huntingtin protein expression. Huntingtin protein has been shown to regulate mitochondria dynamics. We performed EIS studies on normal SH-SY5Y cells and two independent clones of huntingtin-null cells. The impedance data was used to determine the suspension conductivity and further cytoplasmic conductivity and relate to the abnormal mitochondrial dynamics. For instance, the cytoplasm conductivity value was increased by 11% from huntingtin-null cells to normal cells. Results of this study demonstrated that EIS is sensitive to characterize the abnormal mitochondrial dynamics that can be difficult to quantify by the conventional microscopic method.

Current research progress of mammalian cell-based biosensors on the detection of foodborne pathogens and toxins

Foodborne diseases caused by pathogens and toxins are a serious threat to food safety and human health; thus, they are major concern to society. Existing conventional foodborne pathogen or toxin detection methods, including microbiological assay, nucleic acid-based assays, immunological assays, and instrumental analytical method, are time-consuming, labor-intensive and expensive. Because of the fast response and high sensitivity, cell-based biosensors are promising novel tools for food safety risk assessment and monitoring. This review focuses on the properties of mammalian cell-based biosensors and applications in the detection of foodborne pathogens (bacteria and viruses) and toxins (bacterial toxins, mycotoxins and marine toxins). We discuss mammalian cell adhesion and how it is involved in the establishment of 3D cell culture models for mammalian cell-based biosensors, as well as evaluate their limitations for commercialization and further development prospects.

MEMS biosensor for monitoring water toxicity based on quartz crystal microbalance

This paper presents the use of a commercial quartz crystal microbalance (QCM) to investigate live-cell activity in water-based toxic solutions. The QCM used in this research has a resonant frequency of 10 MHz and consists of an AT-cut quartz crystal with gold electrodes on both sides. This QCM was transformed into a functional biosensor by integrating with polydimethylsiloxane culturing chambers. Rainbow trout gill epithelial cells were cultured on the resonators as a sensorial layer. The fluctuation of the resonant frequency, due to the change of cell morphology and adhesion, is an indicator of water toxicity. The shift in the resonant frequency provides information about the viability of the cells after exposure to toxicants. The toxicity result shows distinct responses after exposing cells to 0.526 μM of pentachlorophenol (PCP) solution, which is the Military Exposure Guidelines concentration. This research demonstrated that the QCM is sensitive to a low concentration of PCP and no further modification of the QCM surface was required.

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

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

A Multidisciplinary Approach Toward High Throughput Label-Free Cytotoxicity Monitoring of Superparamagnetic Iron Oxide Nanoparticles

Abstract: This paper focuses on cytotoxicity examination of superparamagnetic iron oxide nanoparticles (SPIONs) using different methods, including impedance spectroscopy. Recent advances of SPIONs for clinical and research applications have triggered the need to understand their effects in cells. Despite the great advances in adapting various biological and chemical methods to assess in-vitro toxicity of SPIONs, less attention has been paid on the development of a high throughput label-free screening platform to study the interaction between the cells and nanoparticles including SPIONs. In this paper, we have taken the first step toward this goal by proposing a label-free impedimetric method for monitoring living cells treated with SPIONs. We demonstrate the effect of SPIONs on the adhesion, growth, proliferation, and viability of neuroblastoma 2A (N2a) cells using impedance spectroscopy as a label-free method, along with other standard microscopic and cell viability testing methods as control methods. Our results have shown a decreased viability of the cells as the concentration of SPIONs increases with percentages of 59%, 47%, and 40% for 100 µg/mL (C4), 200 µg/mL (C5), 300 µg/mL (C6), respectively. Although all SPIONs concentrations have allowed the growth of cells within 72 hours, C4, C5, and C6 showed slower growth compared to the control (C1). The growth and proliferation of N2a cells are faster in the absence or low concentration of SPIONS. The percent coefficient of variation (% CV) was used to compare cell concentrations obtained by TBDE assay and a Scepter cell counter. Results also showed that the lower the SPIONs concentration, the lower the impedance is expected to be in the sensing electrodes without the cells. Meanwhile, the variation of surface area (∆S) was affected by the concentration of SPIONs. It was observed that the double layer capacitance was almost constant because of the higher attachment of cells, the lower surface area coated by SPIONs. In conclusion, impedance changes of electrodes exposed to the mixture of cells and SPIONs offer a wide dynamic range (>1 MΩ using Electric Cell-substrate Impedance electrodes) suitable for cytotoxicity studies. Based on impedance based, viability testing and microscopic methods' results, SPIONs concentrations higher than 100 ug/mL and 300 ug/mL cause minor and major effects, respectively. We propose that a high throughput impedance-based label-free platform provides great advantages for studying SPIONs in a cell-based context, opening a window of opportunity to design and test the next generation of SPIONs with reduced toxicity for biomedical or medical applications.

A Novel Mass-Producible Capacitive Sensor with Fully Symmetric 3D Structure and Microfluidics for Cells Detection

Affinity biosensors of interdigitated electrodes have been widely used in cell detection. This research presents a mass-producible and disposable three-dimensional (3D) structure capacitive sensor based on the integrated circuit package lead frames for cell concentration detection. The fully symmetric 3D interdigital electrode structure makes the sensor more homogeneous and sensitive. (3-Aminopropyl) triethoxysilane (APTES) and glutaraldehyde are immobilized onto gold-plated electrodes. By overlaying the microfluidic channels on top, the volume of the solution is kept constant to obtain repeatable measured capacitance values. Moreover, using the upgraded reading and writing functions and circular measurement of the E4980A Data Transfer Program, an automatic multigroup test system is developed. It is shown that the cell concentration and capacitance are inversely correlated, and the cell concentration range of 10³⁻10⁶ CFU∙mL-1 is achieved. In addition, the rate of capacitance change matches that of state-of-the-art biosensors reported. A program is developed to find the optimal voltage and frequency for linear fitting between the capacitance change and cell concentration. Future work will employ machine learning-based data analysis to drug resistance sensitivity test of cell lines and cell survival status.

Nano and Microsensors for Mammalian Cell Studies

This review presents several sensors with dimensions at the nano- and micro-scale used for biological applications. Two types of cantilever beams employed as highly sensitive temperature sensors with biological applications will be presented. One type of cantilever beam is fabricated from composite materials and is operated in the deflection mode. In order to achieve the high sensitivity required for detection of heat generated by a single mammalian cell, the cantilever beam temperature sensor presented in this review was microprocessed with a length at the microscale and a thickness in the nanoscale dimension. The second type of cantilever beam presented in this review was operated in the resonant frequency regime. The working principle of the vibrating cantilever beam temperature sensor is based on shifts in resonant frequency in response to temperature variations generated by mammalian cells. Besides the cantilever beam biosensors, two biosensors based on the electric cell-substrate impedance sensing (ECIS) used to monitor mammalian cells attachment and viability will be presented in this review. These ECIS sensors have dimensions at the microscale, with the gold films used for electrodes having thickness at the nanoscale. These micro/nano biosensors and their mammalian cell applications presented in the review demonstrates the diversity of the biosensor technology and applications.

Stretchable impedance sensor for mammalian cell proliferation measurements

This paper presents the fabrication and testing of a novel stretchable electric cell-substrate impedance sensing (ECIS) lab on a chip device. This is the first time that ECIS electrodes were fabricated on a stretchable polydimethylsiloxane (PDMS) substrate and ECIS measurements were performed on mammalian cells exposed to cyclic strain. The stretchable ECIS biosensors simulate in vitro the dynamic environment of organisms, such as pulsation, bending and stretching, which enables investigations on cell behavior that undergoes mechanical stimuli in biological tissue. Usually cell-based assays used in cell mechanobiology rely on endpoint cell tests, which provide a limited view on dynamic cellular mechanisms. The ECIS technique is a label-free, real-time and noninvasive method to monitor the cellular response to mechanical stimuli. Bovine aortic endothelial cells (BAECs) have been used in this research because the BAECs are exposed in vivo to cyclic physiologic elongation produced by blood circulation in the arteries. These innovative stretchable ECIS biosensors were used to analyze the proliferation of BAECs under different cyclic mechanical stimulations. The results of fluorescence based cell proliferation assays confirmed that the stretchable ECIS sensors were able to analyze in real-time the BAEC proliferation. The novel stretchable ECIS sensor has the ability to analyse cell proliferation, determine the cell number and density, and apply mechanical stimulation at the same time.

An Impedance-Based Mold Sensor with on-Chip Optical Reference

A new miniaturized sensor system with an internal optical reference for the detection of mold growth is presented. The sensor chip comprises a reaction chamber provided with a culture medium that promotes the growth of mold species from mold spores. The mold detection is performed by measuring impedance changes with integrated electrodes fabricated inside the reaction chamber. The impedance change in the culture medium is caused by shifts in the pH (i.e., from 5.5 to 8) as the mold grows. In order to determine the absolute pH value without the need for calibration, a methyl red indicator dye has been added to the culture medium. It changes the color of the medium as the pH passes specific values. This colorimetric principle now acts as a reference measurement. It also allows the sensitivity of the impedance sensor to be established in terms of impedance change per pH unit. Major mold species that are involved in the contamination of food, paper and indoor environments, like Fusarium oxysporum, Fusarium incarnatum, Eurotium amstelodami, Aspergillus penicillioides and Aspergillus restrictus, have been successfully analyzed on-chip.

Microfluidic Impedimetric Cell Regeneration Assay to Monitor the Enhanced Cytotoxic Effect of Nanomaterial Perfusion

In the last decade, the application of nanomaterials (NMs) in technical products and biomedicine has become a rapidly increasing market trend. As the safety and efficacy of NMs are of utmost importance, new methods are needed to study the dynamic interactions of NMs at the nano-biointerface. However, evaluation of NMs based on standard and static cell culture end-point detection methods does not provide information on the dynamics of living biological systems, which is crucial for the understanding of physiological responses. To bridge this technological gap, we here present a microfluidic cell culture system containing embedded impedance microsensors to continuously and non-invasively monitor the effects of NMs on adherent cells under varying flow conditions. As a model, the impact of silica NMs on the vitality and regenerative capacity of human lung cells after acute and chronic exposure scenarios was studied over an 18-h period following a four-hour NM treatment. Results of the study demonstrated that the developed system is applicable to reliably analyze the consequences of dynamic NM exposure to physiological cell barriers in both nanotoxicology and nanomedicine.