Event Abstract

High-throughput impedance-based cell adhesion and migration assay with single-cell resolution using CMOS microelectrode array

  • 1 Interuniversity Microelectronics Centre (IMEC), Belgium
  • 2 Faculty of Sciences, KU Leuven, Belgium
  • 3 Delft University of Technology, Netherlands

Cell culture heterogeneity is a topic that recently gathered a lot of attention and triggered the development of novel single-cell analysis techniques (Tellez-Gabriel et al., 2016). Current techniques are often performed on cell populations, possibly averaging out relevant biological variability (Altschuler and Wu, 2010). Studying small subpopulations in a large ensemble of cells requires a technique that allows for single cell resolution with reasonable throughput. Single-cell electrical impedance spectroscopy (EIS) measurements can provide a way to classify cell types based on their unique impedance profiles. Whole-cell patch clamping has been the gold standard for decades to determine electrical cell parameters, but this technique has in recent years been complemented by microelectrode array (MEA) technology. Advantages of this technology include high-throughput screening, non-invasiveness and facile sample handling. Moreover, cell properties that cannot be studied with patch clamping (such as adhesion strength, cell motility and morphological change) can be inferred from the electrical parameters measured with MEAs. We have developed a novel CMOS MEA, which features both fixed-frequency impedance monitoring and electrical impedance spectroscopy, aiming to provide a flexible platform for impedance-based bioassay development (Lopez et al., 2018). This device contains more than 16k microelectrodes of various sizes for EIS. Impedance monitoring mode measures real-time impedance at fixed frequencies (1kHz, 10kHz) with 1024 parallel recording channels. In electrical impedance spectroscopy mode, impedance is measured at 16 frequencies from 10 Hz to 1 MHz with 64 parallel current DACs. To establish the ground truth for the on-chip impedance circuitry, we first developed an equivalent electrical model in physiological medium of the TiN electrodes with areas ranging from approximately 10 µm2 to 100 µm2. In order to do so, we used a passive variant of the CMOS chip with identical back end of line processing, connected to an off-chip potentiostat. The electrodes were electrically modeled by a constant phase element in parallel with a charge transfer resistance. Electrode size demands a trade-off between low electrode impedance and high spatial resolution. Even the smallest electrode size of 2.5 x 3.5 µm2 showed sufficiently small impedance of 1 MΩ at 1 kHz. Other electrode sizes measured at 1 kHz were 4.5 x 4.5 µm2 (700 kΩ), 6.5 x 7 µm2 (400 kΩ) and 11 x 11 µm2 (100 kΩ). Next, impedance spectra of HeLa cells cultued on-chip were measured to evaluate the resistance through the gap between cell and electrode, also called sealing resistance. These values ranged between 10 kΩ and 1 MΩ, showing large variability between individual electrodes, which depended on electrode size but also on cellular membrane coverage of the electrode. Confocal microscopy images of the HeLa cells on the chip confirmed a correlation between this electrode coverage and the measured impedance values. In future experiments, single cell impedance will be used in monitoring melanoma cell lines on-chip. The melanoma cell line is a model for cell heterogeneity, being either an ‘invasive’ or a ‘proliferative’ phenotype. In this way, single cell information, phenotype identification and switching can be studied.

References

Altschuler, S. J., and Wu, L. F. (2010). Cellular Heterogeneity: Do Differences Make a Difference? Cell 141, 559–563. doi:10.1016/j.cell.2010.04.033.
Lopez, C. M., Chun, H. S., Berti, L., Wang, S., Bulcke, C. Van Den, Weijers, J.-W., et al. (2018). A 16384-Electrode 1024-Channel Multimodal CMOS MEA for High-Throughput Intracellular Action Potential Measurements and Impedance Spectroscopy in Drug- Screening Applications. in 2018 International Solid-State Circuits Conference (IEEE), 4–6. doi:10.1109/ISSCC.2018.8310385.
Tellez-Gabriel, M., Ory, B., Lamoureux, F., Heymann, M. F., and Heymann, D. (2016). Tumour heterogeneity: The key advantages of single-cell analysis. Int. J. Mol. Sci. 17. doi:10.3390/ijms17122142.

Keywords: electrical impedance spectroscopy, microelectrode array, Single-Cell Analysis, cell migration, Cell Adhesion, HeLa, Melanoma

Conference: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays, Reutlingen, Germany, 4 Jul - 6 Jul, 2018.

Presentation Type: Oral Presentation

Topic: Assay development

Citation: Van Den Bulcke C, Sekeri M, Lagae L and Braeken D (2019). High-throughput impedance-based cell adhesion and migration assay with single-cell resolution using CMOS microelectrode array. Conference Abstract: MEA Meeting 2018 | 11th International Meeting on Substrate Integrated Microelectrode Arrays. doi: 10.3389/conf.fncel.2018.38.00103

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Received: 18 Mar 2018; Published Online: 17 Jan 2019.

* Correspondence: Mr. Carl Van Den Bulcke, Interuniversity Microelectronics Centre (IMEC), Leuven, Belgium, carl.vandenbulcke@imec.be