Fig. 4

a Sensitivity field of the two-electrode system without a cell visualized in the x–y plane through the center of the electrodes, and b the normalized sensitivity along the horizontal position x at three different vertical positions y above the MEA base plate and electrodes. The normalized sensitivity (b) was calculated as the average over the volume of a cell at corresponding locations. Observe that here the color scale of sensitivity is between 0 and 1, as with a two electrode setup no negative values of S occur