Fluorinated oil-surfactant mixtures with the density of water: artificial cells for synthetic biology

Abstract

Water-in-oil emulsions provide matrices for compartments that have many uses in diversity science. However, hydrophobic species are frequently incompatible with biological systems. For this reason, fluorinated matrices are often sought, since fluorinated species are neither hydrophilic nor hydrophobic; they therefore do not interact with most biomolecules. However, most fluorinated oils have densities much higher than the density of water (1 g/ml). Consequently, water droplets float in fluorinated oils, aggregating near their surfaces. This facilitates droplet-droplet collision and fusion, exposing droplets to air interfaces and making their manipulation difficult. Here, we report the synthesis, characterization, and use of fluorinated polysiloxane oils that have densities close to the density of water. These, with a non-ionic fluorosilicone surfactant, produce thermostable water-in-oil emulsions that neither float nor sink. We show how droplets in these emulsions can host many biological processes, including PCR, DNA origami, rolling circle amplification (RCA), and Taqman ® assays. Further, oil-diffusible reagents can initiate reactions within the droplets. The droplets can also be used with unnatural DNA emerging from synthetic biology, including DNA built from artificially expanded genetic information systems (AEGIS) with six nucleotide "letters".