Tracking Single Molecules in Living Cells and Whole Organisms With Carbon Nanotubes

Despite rapid improvements of fluorescent probes, observing individual proteins in living cells or whole organisms remains virtually impossible because of probe instability and autofluorescence of cells. Novel nanomaterials open up approaches that can overcome these problems. Single-­walled carbon nanotubes (SWNTs) exhibit highly stable, near-­infrared luminescence. Here we specifically target SWNTs to kinesin-­1 motor proteins expressed in COS-­7 cells as well as in C. elegans neurons. The combination of photostability and high signal-­to-­noise ratio makes it possible to accurately track individual motors traversing the entire cell. Remarkably, we distinguish the motor’s motion along its microtubule (MT) track from the track’s underlying random non-­thermal fluctuations. Visualizing intracellular single-­molecule dynamics within whole living organisms will be extremely powerful to explore the molecular basis of fundamental biological processes, including intracellular transport, in situ.