Biomimetic membrane in a microfluidic chip for the electrical and optical monitoring of biological reactions.

Biological membranes separate distinct inner and outer compartments through the organization of fluid lipids into two-dimensional bilayers. The specific lipid composition varies across different membrane types. Model membranes play a crucial role in replicating certain features of biological membranes. They provide invaluable insights to decipher reactions at biological membranes in physicochemical cues. In this Protocol, we present a comprehensive procedure for creating a biomimetic membrane that encompasses key characteristics of biological membranes. Each leaflet of this horizontal and large (~10,000 µm²) membrane is obtained from a separate set of liposomes, allowing control of the lipid distribution between the two bilayer leaflets. Suspended in a vertical conduit separating two controllable horizontal microfluidic channels, this membrane can be used for the reconstitution of chemical or molecular reactions in close proximity to the membrane on the desired leaflet. The microfluidic chip containing the two channels separated by the vertical conduit is made of poly(dimethylsiloxane) and is fabricated from resin molds. Initially, oil is trapped in the conduit. Liposome solutions are pushed in each channel and spread on the trapped oil-buffer interface, forming a separate leaflet facing each channel. As oil is absorbed by poly(dimethylsiloxane), the two leaflets assemble and form a bilayer. We outline four applications of this biomimetic membrane microfluidic setup, incorporating optical microscopy and/or electrical readouts (patch-clamp amplifiers): single-particle and global diffusion, membrane fusion and channel formation. The entire protocol, covering chip fabrication, membrane formation and various measurements, can be completed within 2-3 d.