Where is it heading? Single-particle tracking of single-walled carbon nanotubes.

Single-particle tracking of individual single-walled carbon nanotubes (SWNTs) using their near-infrared band gap fluorescence is a powerful tool for understanding how these Brownian rods diffuse and interact with various molecular force potentials, including living systems. Pioneered by the Weisman laboratory at Rice University, the method is one of the only available to study single SWNT molecules in solution over extended periods since SWNTs have no apparent irreversible photobleaching threshold at moderate fluence and no intrinsic blinking mechanism. Recent progress by Tsyboulski et al. shows how real-time measurement of rotational and transitional diffusivities can provide information about rod length and mechanical properties. Recently, Jin et al. used single-particle tracking to map the trajectories of SWNTs as they are incorporated into and expelled from NIH-3T3 cells in real time. The technique has provided the first evidence of nanoparticle exocytosis in this case and demonstrates an expulsion rate that closely matches the endocytosis rate. The ability to track and to analyze single molecules in this way may lead to new technologies that utilize as their platform a single, freely diffusing nanotube.