Fig. 1.

Imaging single molecules. (A) Illustration of single-molecule imaging. A diffraction-limited pumping region (green) illuminates a sample such as a cell containing fluorescent labels. For single-molecule imaging, only one molecule should be emitting (red) within a diffraction-limited pumping volume. (B) Example of wide-field epifluorescence imaging of single fluorescently labelled transmembrane proteins on a cell surface. Frame: 12× 12 μm. (C) Wide-field fluorescence image of a bacterial cell (red) containing a single protein fusion between the bacterial actin protein MreB and EYFP. Rendered in three dimensions with the z-axis as brightness, a single molecule looks like a mountain. A total of 100 ms acquisition time, bar: 0.5 μm. [Adapted and reproduced by permission from (Moerner, 2007); copyright the National Academy of Sciences.]