Dispensing Single Drops as Electrochemical Reactors

Abstract

A strategy is proposed to generate single microdrops with femtoliter to microliter volumes as a liquid reactor and to guide them towards a reactive surface within a viscous carrier liquid. Reactions of the drop content with the surface are exemplified by exhaustive electrolysis of the reactor content, making use of an ion-conducting pathway through the carrier liquid. The mechanisms by which the redox-active species from the aqueous drop reach the electrode surface were established by a combination of time-lapse microscopy of the drop shape, chronoamperometric recording of the single drop electrolysis, and modelling of the reaction-transport problem, showing that partitioning over the liquid-liquid interface must be a key step in this mechanism. The possibilities of reagent delivery and external triggering of a reaction are expanded by the possibility for controlled addition of further dissolved reactants to the liquid microreactor.