Hi, I am using ion-selective microelectrode to measure the extracellular concentration of a certain ion probe (in this case, tetramethyl ammonium, TMA+). The ISM is double-barreled, with one acting as a reference and the other the ion-sensing electrode. This double-barreled ISM is coupled to an iontophoretic electrode, which is used to iontophoretically inject the TMA ion probe. Then the ISM detects the release and diffusion of the iontophoresed TMA+.

In my experimental paradigm, whenever the nearby iontophoresis is turned on and off, there is a sudden jump in the field potential caused by the iontophoretic current, so that the reference detects a step-like increase of the field potential. This is expected, since local field potential is raised by the step iontophoretic current. However, sometimes the potential jump detected by the ion-sensing barrel is larger than that sensed by the reference barrel, such that the signal difference (ISM signal is supposed to subtract the field potential) still exhibits a jump. I am bothered by what cause the signal jump. Someone said is caused by capacitive coupling between iontophoretic electrode the ion-sensing electrode, but I do not think so, because capacitive coupling should behave transiently. The fact is that the differential ISM signals shows a step-like behavior that synchronized with the iontophoretic current. I guessed that this phenomenon is caused by cross coupling between the between iontophoretic electrode the ion-sensing electrode. But I do not know how to remove the cross coupling.

Does anyone have a better explanation as to why it happens how I can remove it?