Cyclic voltammetry (CV) and square wave voltammetry (SWV) experiments were performed with an Autolab potentiostat PGSTAT204 (Metrohm Autolab B.V., Netherlands) controlled by the Nova software (version 2.1.5). The following parameters were used for SWV: step: 0.005 V, modulation amplitude 0.05 V, and frequency 25 Hz. CV measurements were performed at different scan rates and at least 3 scans were recorded. The acquisition of voltammetric curves was repeated at least 5 times for each aqueous solution. All measurements were performed in a three-electrode system with an Ag|AgCl|(3M) NaCl reference electrode, platinum wire as a counter electrode, and a glassy carbon disk electrode (GCE, Ø 3 mm, Mineral, Poland) as a working electrode. Before each measurement the GCE was polished on a Buehler polishing cloth to a mirror-like surface, using ethanol and 0.05 μm alumina powder (Al2O3). Then the GCE was rinsed and sonicated in ethanol and air-dried. Next, a 0.1 μL droplet of the organic phase was deposited on the active electrode surface. The modified GCE was immersed in the aqueous solution, where the counter and reference electrodes also were positioned (Fig. , SI). The organic droplet does not completely cover the surface of the glassy carbon electrode; thus, a three-phase junction is formed along the circumference of the droplet after immersion into the aqueous phase.