Rémy Bois, Sabina Scarabino, Valérie Ravaine, Neso Sojic

Langmuir, 2017, DOI: 10.1021/acs.langmuir.7b01585

We describe a method to confine electrochemiluminescence (ECL) at the oil-water interface of emulsion droplets which are stabilized by luminophore-grafted microgels. These hydrogel nanoparticles incorporating covalently-bound  as the luminophore are irreversibly adsorbed at the interface of micrometric oil droplets dispersed in a continuous aqueous phase. We study the electrochemical and ECL properties of this multiscale system, composed of a collection of droplets in close contact in the presence of two types of model coreactants. ECL emission is observed upon oxidation of the coreactant and of the luminophore. ECL imaging confirms that light is emitted at the surface of oil droplets. Interestingly, light emission is observed more than 100-µm far from the electrode. It is possibly due to the interconnection between redox-active microgels making an entangled 2D-network at the dodecane/water interface and/or to some optical effects related to the light propagation and refraction at the different interfaces in this multiphasic system. Confining ECL in such an inhomogeneous medium should find promising applications in the study of compartmentalized systems, interfacial phenomena, sensors and analysis of single oil droplets.