Applied_Biophysics_ECIS_Real_Time_Cell_Growth_Monitoring__Cell_Proliferation

ECIS measurements can be used to monitor cell proliferation, and experiments can be designed to determine how various changes in cell and culture conditions affect the rates at which the cell monolayer approaches confluence. To accomplish these studies, arrays are inoculated with a low cell density providing room for the dividing cell population. As the cell number increases, the amount of electrode area covered with the spread cells grows accordingly, causing the electrode impedance to rise. These impedance changes can be related to the relative cell proliferation rates or, more accurately, the rate at which the substrate becomes occupied with spread cells. More quantitative measurements can be obtained by observing the changes in capacitance measured at high AC frequencies. Dr. Joachim Wegener has modelled how ECIS impedance measurements respond to different degrees of fractional substrate coverage by spread cells. These calculations were carried out using the properties of MDCK type II cells and demonstrate that the capacitance measured at 40K Hz varies in a linear fashion with the fractional cell coverage (Wegener, et al 2000). Although this calculation was only carried out for the MDCK line, in general this correlation is valid for most lines and primary cell cultures. With this relationship, the percentage of the electrode area covered as a function of time can be easily followed.
	Calculated resistance (A) and capacitance (B) values of ECIS electrodes as a function of fractional coverage of the surface with adherent cells. Electrode parameters were modelled for three different frequencies: (...) 400 Hz, (- - -) 4 kHz, (___) 40 kHz. For a better comparison both quantities are normalized to the corresponding values of a cell-free electrode.
It is important to note that the ECIS approach measures the area blocked by the spread cells and not the number of cells directly. Nevertheless, this approach can yield useful proliferation-related data that, if required, can later be validated by experiments employing direct cell counting procedures. The appeal of the ECIS measurement is that it is fully automated and requires minimal manipulations. Once cells are added to the electrode arrays the incubator door remain closed, and data may be gathered for up to days if required. For these assays, we recommend the use of the 8W10E arrays, since theses follow the substratum coverage of ten individual electrodes. These are located at different sires on the well bottom and provide a more statistically relevant measurement of the overall condition of the culture.