Three-dimensional nanoparticle tracking and simultaneously membrane profiling during endocytosis of living cells

By utilizing a wide-field optical profiling technique and a bright-field particle-tracking algorithm, we record the tracks of gold nanoparticles as well as the topography of cell membranes during the endocytosis processes. The motion of 60 nm gold particles relative to the membrane is directly visualized without fluorescence labeling. The positioning accuracy of gold nanoparticles in three dimensions is nearly 20 nm. On the basis of the simultaneous particle tracks and membrane topography, we estimate the internalization efficiency of transferrin-coated gold nanoparticles on fibroblasts.