Effect of surfactants on carryover liquid volume in immiscible phase magnetic bead separation

Abstract

This manuscript describes the transport of beads across an interface of two immiscible liquids, an aqueous phase and an oil phase, through a microfluidic channel and across another interface into an elution reservoir. This technique can be used for isolating molecules that bind to the beads from the surrounding aqueous material, i.e separation of particular biomolecules from a sample. However, the interface allows a small volume of aqueous liquid to be carried over along with the beads. Carryover liquid from sample to elution reservoir may be detrimental in downstream applications like polymerase chain reactions. Here we quantify carryover volume in relation to different surfactant and protein doped sample liquids. Our data suggest that the carryover volume increases rapidly with an increase in the oil-liquid interfacial tension (γ) up to a critical interfacial tension, γ>∼20dynes/cm, at which point the carryover volumes remain roughly constant. Our experiments also show that lower values of γ produce more numerous smaller bead clusters while higher γ allows movement of fewer large bead clusters. Lastly, we identify two modes of liquid carryover, interstitial and enveloping, and the conditions under which either occur. We discuss our results in comparison to literature studies.