Figure legends
Figure 1. (a) Vertical electrodes to measure the capacitance of cells in a hydrogel with vertical resolution. (b) Real-time capacitance of hydrogels seeded with different cell concentrations. (c) Fluorescent optical images of hydrogels containing different cell densities. (scale bar: 100 μm). Reproduced with permission.(S.-M. Lee et al., 2016) Copyright 2015, Elsevier B.V.
Figure 2. (a) Horizontal electrodes for measuring cells in hydrogel using the hanging-drop technique. (b) Correlation between cell number and impedance magnitude measured at discrete frequencies (500, 1000 and 5000 Hz). Reproduced with permission.(Lei et al., 2018) Copyright 2017, Elsevier B.V.
Figure 3. (a) Schematic of the parallel electrodes for the impedance biosensor. (b) Equivalent circuit of cells in 3D within the matrigel. (c) Measurement of cells in 3D culture using the parallel electrodes (3D ECMIS). Reproduced with permission.(Pan et al., 2019) Copyright 2018, Elsevier B.V.
Figure 4. (a) Schematic of the poly(3,4-ethylenedioxythiophene) xanthan gum (PEDOT:xanthan) electroactive scaffold used to host and monitor cells. (b) Impedance spectrum of the scaffold with no cells (blue), after cell growth within the scaffold over 7 days (red) and PEDOT:xanthan gum scaffold after 7 days of incubation (37 °C, 5% CO2) in culture media without cells (dashed lines). Reproduced with permission.(Del Agua et al., 2018) Copyright 2018, American Chemical Society. (c) Typical impedance spectrum of 2D cells grown on electrodes. Reproduced with permission.(Del Agua et al., 2018) Copyright 2015, Elsevier B.V.
Figure 5. Equivalent circuit and typical impedance spectrum of cells in 2D. Adapted with permission.(Benson et al., 2013) Copyright 2013, BioMed Central Ltd.
Figure 6. Parallel impedance electrodes to measure the maturity of a reconstructed human epidermis (RHE). (a) Detailed view of one measurement chamber with a RHE in a transwell insert and equivalent circuit. (b) Bode plots of impedance spectra from RHE at different time points. Reproduced with permission.(Groeber et al., 2015) Copyright Groeber et al., 2014.
Figure 7. (a) Radially distributed circular electrodes (adapted from (Yin et al., 2018)) (b) Rectangular electrodes at the boundary of the well were used to monitor spheroid and (c) reconstructed images for the spheroid samples in 2% Triton X-100 solution (1-2) and HG culture medium (3-4). Reproduced with permission.(Wu, Yang, et al., 2018; Wu, Zhou, et al., 2018) Copyright Wu et al., 2018.
Figure 8. The electrode design shows the placement of current injecting electrodes on parallel walls and the placement of voltage sensing electrodes on the bottom surface as well as the two parallel walls. Reproduced with permission.(E. J. Lee et al., 2014) Copyright Lee et al.; licensee BioMed Central Ltd. 2014.