Exosomes are small membrane vesicles secreted by cells and enriched with plenty of proteins. Considering their significant roles in different physical activities and potential value for diagnostic drug delivery, researchers have put great efforts in in vitro tracking and content analysis of exosomes. Recently, the emergence of different kinds of super-resolution microscopy provides powerful tools for exosome study. Here, we demonstrate the application of single-molecule localization based super-resolution imaging technique in the imaging and tracking of cancer-derived exosomes. In the experiment, first, cancer-derived exosomes are extracted from the culture media of tumor cells. Then the exosome membrane receptors are labeled with photoswitchable probes, which allow super-resolution imaging of these membrane receptors via photoactivated localization microscopy (PALM) or stochastic optical reconstruction microscopy (STORM). By using human breast cancer cell-derived exosomes, we demonstrated simultaneous dual-color PALM/STORM imaging of two kinds of membrane receptors on the exosome membrane. Moreover, the successful labeling and imaging of exosomes make it possible to observe the interaction between cancer-derived exosomes and normal cells. Meanwhile, we realized the colocalization of cancer-derived exosomes and lysosomes in recipient cells with PALM/STORM imaging. Since exosomes play a vital role in intercellular communications, we anticipate that the presented PALM/STORM-based imaging and tracking of exosomes holds a great potential in the investigation of the mechanism of exosome-mediated cancer metastasis.
Keywords: PALM/STORM; exosomes; intracellular tracking; membrane receptors; super-resolution imaging.