Microfluidic emulsion separation—simultaneous separation and sensing by multilayernanofilm structures

Abstract

Emulsion separation is of high relevance for filtration applications, liquid–liquid-partitioning ofbiomolecules like proteins and recovery of products from droplet microreactors. Selectiveinteraction of various components of an emulsion with substrates is used to designmicrofluidic flow chambers for efficient separation of emulsions into their individualcomponents. Our lab-on-a-chip device consists of an emulsion separation cell with anintegrated silicon sensor chip, the latter allowing the detection of liquid motion via thefield-effect signal. Thus, within our lab-on-a-chip device, emulsions can be separated whilethe separation process is monitored simultaneously. For emulsion separation a surfaceenergy step gradient, namely a sharp interface between the hydrophobic and hydrophilicparts of the separation chamber, is used. The key component of the lab-on-a-chip systemis a multilayer and multifunctional nanofilm structure which not only providesthe surface energy step gradient for emulsion separation but also constitutes thefunctional parts of the field-effect transistors. The proof-of-principle was performedusing a model emulsion consisting of immiscible aqueous and organic solventcomponents. Droplet coalescence was identified as a key aspect influencing theseparation process, with quite different effects during separation on open surfaces ascompared to slit geometry. For a detailed description of this observation, an analyticalmodel was derived and lattice Boltzmann computer simulations were performed.By use of grazing incidence small angle x-ray scattering (GISAXS) interfacialnanostructures during gold nanoparticle deposition in a flow field were probedto demonstrate the potential of GISAXS for in situ investigations during flow.