The device enables a second drop to be mixed in a first drop deposited on an electrically insulating layer of an analysis support, in a viscous liquid environment and to mix the resulting drop. The device comprises at least one injector forming the second drop above the first drop. After formation of the second drop, a voltage impulse is applied between a first electrode, arranged under the electrically insulating layer of the analysis support, underneath the first drop, and a second electrode arranged near the outlet orifice of the injector. The voltage impulse fosters the coalescence phenomenon between the two drops, while preventing risks of contamination of the injector by the reagent of the first drop.