Dynamic label-free imaging of lipid nanodomains

Significance Cell membranes are thought to partition into small (10–100 nm) and transient (<100 ms) lipid platforms or “rafts” to control signaling and trafficking across the membrane. The difficulty in observing such species has made “lipid rafts” a contentious topic. Indirect evidence for their existence has been available for decades, but it has not been possible to reveal their dynamics directly. By exploiting the differences in light scattering from different lipid phases, we achieve dynamic imaging of lipid nanodomains. We observe nanodomain formation, destruction, and coalescence—behaviors previously hypothesized but never observed, yet are critical to their proposed function. Lipid rafts are submicron proteolipid domains thought to be responsible for membrane trafficking and signaling. Their small size and transient nature put an understanding of their dynamics beyond the reach of existing techniques, leading to much contention as to their exact role. Here, we exploit the differences in light scattering from lipid bilayer phases to achieve dynamic imaging of nanoscopic lipid domains without any labels. Using phase-separated droplet interface bilayers we resolve the diffusion of domains as small as 50 nm in radius and observe nanodomain formation, destruction, and dynamic coalescence with a domain lifetime of 220 ± 60 ms. Domain dynamics on this timescale suggests an important role in modulating membrane protein function.