A universal strategy for the sensitive investigation of cell responses to external stimuli, in particular nanosecond pulsed electric fields (nsPEFs), was developed based on electrical impedance spectroscopy (EIS) in combination with a multi-peak analysis for the distribution of relaxation times (DRT). The DRT method provides high resolution for the identification of different polarization processes without a priori assumptions, as they are needed by more conventional approaches, such as an evaluation by equivalent circuit models. Accordingly, the physical properties of cells and their changes due to external stimuli can be uncovered and visualized and dispersion mechanisms introduced by Schwan et al. clearly identified. These are in particular relaxation processes at about 100 kHz that are associated with cell membrane characteristics and dominating respective changes of the distribution function for epithelial cell monolayers after exposure. A relatively moderate evolution at about 10 kHz may represent the polarization of extracellular matrices. Relaxation processes at around 1 MHz were suggested to be associated with intracellular changes. Conversely, the distribution of relaxation times can aid the optimization of the experimental design with respect to intended responses by an external stimulus.
Keywords: Distribution of relaxation times; Electrical impedance spectroscopy; Gaussian functions; Multi-peak analysis; Nanosecond pulsed electric fields.
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