Arrays are oxygen plasma etched the day they are shipped from Applied BioPhysics. This step sterilizes the arrays and also cleans the gold resulting in clean, pristine electrodes. Over time, small molecules in the atmosphere adsorb to the gold surfaces resulting in increased electrode impedance and resistance - lower capacitance. When exposed to tissue culture medium these molecules slowly desorb, and the impedance values can eventually return to those associated with clean electrodes. To assure this takes place in a timely manner, we strongly recommend that researchers take measures to clean the gold before cell inoculation.

Our preferred way to accomplish this is with the amino acid cysteine. The cysteine forms a covalent linkage with the gold electrode surface, likely displacing any small unwanted molecules that have adsorbed to the gold surface over time. This treatment cleans and modifies the electrode surfaces enhancing experimental repeatability with minimum variation between ECIS wells.

To accomplish this, the well should be flooded with a 10 mM sterile solution of L-cysteine in distilled water. The solution can easily be prepared in your laboratory and filter sterilized or purchased from AppliedBioPhysics (Electrode-stabilizing solution). After exposure to the cysteine and thorough rinsing, the wells are ready for inoculation with cells. The time for the cysteine exposure depends upon the history of the array: for relatively newly etched arrays often the reaction is completed in only a few minutes, but to be certain the reaction has gone to completion, an hour-long exposure is recommended for all arrays.                

If you plan to coat the electrodes with an ECM or other protein, this can be accomplished either before or after the cysteine treatment. We occasionally see subtle differences in the behavior of cells depending upon the order of these electrode treatments. This is not entirely unexpected as in one case the protein interacts with the gold and in the other with the cysteine layer (both are hydrophilic in nature and ready for protein adsorption).

An alternative way to clean the electrodes uses the ECIS electrical stabilization method. This feature is built into the ECIS software, and more information can be found in the ECIS Manual.