Constructing droplet interface bilayers from the contact of aqueous droplets in oil

We describe a protocol for forming an artificial lipid bilayer by contacting nanoliter aqueous droplets in an oil solution in the presence of phospholipids. A lipid monolayer forms at each oil-water interface, and when two such monolayers touch, a bilayer is created. Droplet interface bilayers (DIBs) are a simple way to generate stable bilayers suitable for single-channel electrophysiology and optical imaging from a wide variety of preparations, ranging from purified proteins to reconstituted eukaryotic cell membrane fragments. Examples include purified proteins from the a-hemolysin pore from Staphylococcus aureus, the anthrax toxin pore and the 1.2-MDa mouse mechanosensitive channel MmPiezo1. Ion channels and ionotropic receptors can also be reconstituted from membrane fragments without further purification. We describe two approaches for forming DIBs. In one approach, a lipid bilayer is created between two aqueous droplets submerged in oil. In the other approach, a membrane is formed between an aqueous droplet and an agarose hydrogel, which allows imaging in addition to electrical recordings. The protocol takes <30 min, including droplet generation, monolayer assembly and bilayer formation. In addition to the main protocol, we also describe the preparation of Ag/AgCl electrodes and sample preparation.