Time Course Measurements
The impedance can be sampled as often as several times per sec to as slowly as desired. Each impedance reading is plotted as a point, in Ohms or nanofarads (C), verses time. The total acquisition time is user controlled and can range from a fraction of an hour to several days. The following plot is a measurement of cells attaching and spreading in two different wells of an array. Curve #4 are BCS cells and curve #5 are NRK cells. The electrode in each well was sampled at a few second intervals for 15 hours.
Following inoculation at time zero, impedance increases during as the cells attach to the electrode and begin spreading. The impedance continues to increase until the cells reach confluence at 2 hours for the BCS cells and 10 hours for the NRK cells. The small fluctuations in the curves are due to micromotion from the constant movement of the monolayer of cells on the electrode.
With the wounding option, an elevated voltage is applied to the electrode for several seconds. The cells on the electrode are killed, presumably from severe electroporation. Notice in the plot that the impedance falls back from its peak value at cells confluence to that of an open electrode because the cells no longer offer a resistance to the current flow.
The time and intensity of the elevated voltage can be user controlled and reduced so the cells can also be electroporated without cell death.