Electrowetting is an electrocapillary phenomenon that was identified initially by Lippmann , who demonstrated that the position of the mercury meniscus in a capillary can be controlled by applying an external voltage. Nowadays, the term electrowetting is generally referred to any situation where the application of voltage induces shape variations of a liquid/liquid or liquid/gas interface . Experiments are normally performed with a dielectric layer between the electrode and the solution (Electrowetting on Dielectric, EWOD) in order to prevent degradation of both the substrate and the electrolyte (i.e., electrolysis). In this case, the applied potential difference charges both sides of the dielectric layer so that the capacitance of the system is set by the thickness of the dielectric layer and large voltages are needed to induce changes in surface energy and hence wetting. An alternative strategy that tackles the high energy demands of EWOD is the use of ultra-smooth conductive substrates which, together with an accurate tuning of the underlying physicochemical processes, allows electrowetting experiments to be performed without the need of the dielectric layer . This approach is referred to as electrowetting on conductors (EWOC) .