The ECIS technique can monitor the viability

The ECIS technique can monitor the viability of cell by measuring electric signals from the ci-1033 exposed to toxic substances [8–11]. The ECIS sensor uses alternating-current (AC) with a wide frequencies (from 100Hz to 64kHz) to measure the impedance of in vitro cells seeded on the sensor. The measured impedance values provide real-time information on cell membrane capacitance, cytoplasm conductivity, and cell behavior related to attachment, growth, metastasis, motility, and viability [12–20]. The existence of membrane potential is a distinguishing feature between living and apoptotic cells [21]. When cells attach and spread on the surface of planar electrodes of ECIS sensors after seeding, they behave essentially like insulating particles that impede the unrestricted current flow from the electrode into the bulk of the electrolyte and thereby the impedance between electrodes gradually increase [22]. When the cells form a monolayer, the impedance has stable values over a period of time. When the cells are apoptotic as a result of exposure to toxicants the cells lose their dielectric properties, and the measured impedance values of cell membrane decrease. Any change in cell–cell interaction or cell–substrate interaction due to alterations in metabolism, chemical, biological or physical stimuli will cause the current pathways through and around the cell to change, leading to a corresponding increase or decrease in impedance [23]. Thus, impedance spectroscopy of cells activity is a versatile and sensitive way to detect the response of the cells to a variety of toxic agents and pharmaceutical drugs [22,24–34]. Although ECIS is a very promising method for toxicity sensing, this technique has not been frequently used for testing the drinking water toxicity [10,11,23]. The primary goal of this paper is to improve the responsiveness of the ECIS-based sensor to a wide range of toxicants in water. In order to select the appropriate cell lines for toxicity experiments, two different adherent cell lines were used such as: BAEC and RFPEC. Many toxicants end up in the bloodstream independent of their primary route of exposure such as respiratory tract, skin, eyes, gastrointestinal tract, etc and cause injury [35]. Vascular endothelial cells have direct contact with blood and line the circulatory system of the entire human body, from the heart to the smallest capillaries [36]. In this work, endothelial cells were chosen for toxicity experiments as they mimic the human body’s response to toxicants. For toxicity testing using ECIS technique, ideal cell types are cells that rapidly form a monolayer and provide high impedance values. The high impedance values are important for precise monitoring of the cell viability. When the cells are apoptotic they lose their dielectric properties, the cells monolayer tend to detach from the sensing electrodes causing their impedance values to decrease to zero. In this research BAECs was chosen as the preferential cell type for water toxicity testing because they form strong intercellular junctions, firmly attach to the substrate and are able to form a uniform monolayer with high impedance values for at least 30days [37]. In previous work, label-free ECIS and acoustic cell-based sensors had been successfully developed [7]. While successfully detecting toxicants, the BAECs tested required a long response time, thus making it unsuitable for field use. In an attempt to speed up the cell’s response to toxicants, in this work two different types of cultureware were employed. The PDMS culturewares were (i) simple open wells and (ii) enclosed culture chambers with perfusion microchannels. When both media and toxicants were pipetted in the open wells, it is expected that turbulent flow will disrupt the uniformity of the cell monolayer. This paper introduces the usage of microfluidic perfusion barriers inside the cell culture chambers to minimize disruption. It is expected that the perfusion barriers minimizes fluid shear stress and is able to maintain the integrity of the cell monolayer for as long as possible. This hypothesis is supported by finite element modeling results. Experimentally, various toxicants such as: nicotine, phenol, ammonia and aldicarb were tested with commercially available ECIS sensors. Merging the advantages of label-free ECIS multiparametric cellular sensing with microfluidic technology can improve long-term cell maintenance and cytotoxicity sensing capabilities for field use.