The transition from the optical detection of individual molecules to the imaging of a (cellular) structure will be explained, together with a new definition of optical resolution. Further we will discuss how this methodology can be extended toward three dimensions as well as towards the microsecond timescale. I will highlight its potential in the study of the microdomain organization of the plasma membrane. We used stochastic superresolution imaging and single-molecule microscopy to study the partitioning of the signaling protein HRas in mouse fibroblast. By statistical analysis of the surface distribution of the proteins with 35 nm positional accuracy and tens of ms time resolution we were able to identify domains of increased HRas occupancy in the inner leaflet of the plasma membrane that have a size of ~100 nm.

Thomas Schmidt received a PhD in physics on the topic of “Spectroscopic Investigations of Energy- Transfer in NaNO ₂ :KNO ₂ ” from the University of Düsseldorf, Germany, in 1988. Subsequently he was postdoc at Leiden University, The Netherlands, where he further pursued high-resolution spectroscopy to learn about the glassy state of inorganic and biological material at low temperature. In 1993 he moved to the University of Linz, Austria, where he built up a group that developed single-molecule microscopy at room temperature. In 1999 he was appointed as full professor in Physics of Life Processes at the Leiden Institute of Physics, Leiden University, The Netherlands. Since, his group further developed single-molecule techniques for research in cell biology. His current research interests range from biomimetics to initial steps in cellular signaling, and cell mechanics. He mostly utilizes high-resolution, high-sensitivity optical techniques that permit to follow cellular processes one molecule at a time.