Revealing rotational modes of functionalized gold nanorods on live cell membranes.

A full understanding of cell mechanics requires knowledge of both translational and rotational dynamics. The single particle orientation and rotational tracking (SPORT) technique is combined here with correlation analysis to identify the fundamental rotational modes: in-plane rotation and out-of-plane tilting, as well as other more complex rotational patterns, from the vast image data captured at a temporal resolution of 5 ms for single gold nanorod probes in live cell imaging experiments. The unique capabilities of visualizing and understanding rotational motions of functional nanoparticles on live cell membranes allow correlation of the rotational and translational dynamics in unprecedented detail and provide new insights into complex membrane processes. Particles with functionalized surfaces, which interact with the membrane in fundamentally different ways, can exhibit distinct rotational modes and are, for the first time, directly visualized, and these show the early events for membrane approach and attachment.