Understanding the interaction between synthetic nanostructures and living cells is of crucial importance for the development of nanotechnology-based intracellular delivery systems. Fluorescence microscopy is one of the most widespread tools owing to its ability to image multiple colors in native conditions. However, due to the limited resolution, it is unsuitable to address individual diffraction-limited objects. Here we introduce a combination of super-resolution microscopy and single-molecule data analysis to unveil the behavior of nanoparticles during their entry into mammalian cells. Two-color Stochastic Optical Reconstruction Microscopy (STORM) addresses the size and positioning of nanoparticles inside cells and probes their interaction with the cellular machineries at nanoscale resolution. Moreover, we develop image analysis tools to extract quantitative information about internalized particles from STORM images. To demonstrate the potential of our methodology, we extract previously inaccessible information by the direct visualization of the nanoparticle uptake mechanism and the intracellular tracking of nanoparticulate model antigens by dendritic cells. Finally, a direct comparison between STORM, confocal microscopy, and electron microscopy is presented, showing that STORM can provide novel and complementary information on nanoparticle cellular uptake.
Keywords: STORM; cellular uptake; delivery; nanoparticles; super resolution imaging.