Assessment of Cytotoxicity by Analysis of Impedance Fluctuations

Abstract

Electric cell-substrate impedance sensing (ECIS) has been used to monitor cell behavior in tissue culture and has proven to be very sensitive to cell morphological changes and cell motility. In this method, cells are cultured on small gold electrodes carrying weak AC signals. The impedance of these electrodes changes dramatically when cells attach and spread on their surface, because the cell membranes restrict the current flow. In addition, cell motion may reveal itself as a fluctuation in the measured impedance, which is always associated with living cells and persists even when the cells grow into a confluent layer. The impedance fluctuation is attributed to incessant changes in the size of the cell-substrate space as cells persistently rearrange their cell-substrate adhesion sites. The magnitude of this sort of vertical motion detected by ECIS is of the order of nanometers and referred to as micromotion. Here, we applied ECIS to evaluate dose-dependent responses of NIH 3T3 cells exposed to cytochalasin B, cadmium chloride, and H-7 dihydrochloride, a protein kinase C inhibitor. To detect the alternation of cell micromotion in response to cytotoxic challenge, time-series impedance fluctuations of cell-covered electrodes were monitored and the values of power spectrum, variance, and variance of the increment were calculated to verify the difference. While a dose-dependent relationship for each chemical was generally observed from the overall resistance of the cell monolayer, the analysis of impedance fluctuations distinguished cytochalasin B, cadmium chloride, and H-7 dihydrochloride levels as low as 0.1, 10, and 1 micromole respectively. The analytical methods used in this study can serve as a model approach for ECIS and other electrochemical impedance biosensors to investigate various aspects of cellular responses to toxins in general.