Impedimetric monitoring of adherent animal cells relies on cell-covered goldfilm electrodes that serve as growth substrate and measuring electrode at a time. When the cells attach and spread on the electrode surface, the dielectric cell bodies increase the electrical impedance of the electrode, as the current is now forced to flow around or through the cells. The exact current pathway can be experimentally controlled by the AC frequency of the driving voltage that is used in the experiment.
The sketch below illustrates the principle of the measurement with a micrograph of a cell-covered electrode. The figure on the right demonstrates the richness in information when the complex impedance Z is measured as a function of frequency during attachment and spreading of cells upon the electrodes.
For most applications current flow around the cells is of of greater interest as the measured impedance holds information on cell-cell and cell-substrate contacts. Whenever the cells change their shape in response to a biological, chemical or physical stimulus, this cell repsonse is mirrored in a corresponding change in impedance. Thus, impedance readings basically provide a very sensitive measurement of cell shape changes with a resolution better than an optical microscope and a broad bioanalytical applicability.
Impedimetric monitoring is also referred to as electric cell-substrate impedance sensing or short ECIS which has been first described by Ivar Giaever and Charles R. Keese in 1984. More information can be found in our papers and in the corresponding WIKIPEDIA section.
Applications of ECIS in our lab inlcude: