Coherent brightfield (COBRI) microscopy for ultrahigh-speed single- particle tracking on lipid bilayer membranes

Following the journey of a single molecule is a powerful tool for studying the structures and functions of biological membranes. To resolve the interplays between individual membrane molecules and their nano-associations, membrane dynamics needs to be measured at the nanoscale with high temporal resolution. Here, we demonstrate ultrahigh-speed coherent brightfield (COBRI) microscopy for capturing diffusive motion of single lipid molecules in model membranes labeled by single 40 nm gold nanoparticles with a spatial precision of 3.6 nm and a temporal resolution of 2.56 microseconds (corresponding to a frame rate of 390 kHz) under an illumination intensity of 15 mu W/mu m(2) . Our method is readily applicable to the future study of plasma membrane of live cells where the transient confinements in membrane nanodomains could be investigated with unprecedented clarity.