Reproducibility of ECIS measurements
Reproducibility of data is, of course, an essential quality of any analytical measurement. All ECIS instruments can perform concurrent measurements on up to 96 individual culture wells providing an opportunity to see typical spread of cell data. When using 8W1E arrays, the active area being monitored is 250 micrometers in diameter or an area of about 5 x 10-4 cm2 . If one is dealing with a confluent layer of cells of cell density 2 x 105 cells per cm2, then only 100 cells are being monitored. In spite of this relatively small number, the ECIS response is very uniform. Consider the data shown below where six individual wells are inoculated with a monodisperse suspension of BS-C-1 cells. As these cells attach and spread the resistive portion of the impedance at 4000 Hz increases with a spread in the data of only about 10%.
Another informative example involves the ECIS automated wound-healing assay. In this case 4 confluent layers of cells in individual wells are wounded at the first arrow; once these heal, they are again wounded. Notice the high reproducibility of the data from well to well. The black trace is the control that was not wounded but simply shows the normal level of fluctuations due to cell movements.
These examples are with one active electrode per well. We also have an 8W10E array that has 10 small electrodes spaced over the bottom of the well. This arrangement allows for 10 times as many cells to be monitored (1000 cells for the example above) and results in even better reproducibility.
Note, the ECIS software includes a program that will convert any ECIS data file to an ASCII text file that can be manipulated by other programs such as Excel.