then submerged in an aqueous electrolyte to create an interface between the two liquid phases. In this system, the organic drop does not cover the whole surface of the working electrode, so around the circumference of the drop, a three-phase junction is formed, where the two liquid phases and the solid electrode all meet. No electrolyte is added to the organic phase, which is one of the advantages of the TPE system. The electrochemical oxidation or reduction of a lipophilic redox probe in the organic phase is only possible when both the organic and aqueous phases are in contact with the active surface of the electrode (Fig. in SI). When the redox molecule in the organic phase undergoes a redox reaction (say, an oxidation), the additional charge generated in this phase has to be compensated by the transfer of an ion across the liquid-liquid interface. This can be either an ion from the aqueous phase to the organic phase Red org + An aq -→ Ox org + + An org - or the expulsion of the charged redox probe from the organic to the aqueous solution Red org + An aq -→ Ox aq + + An aq -