Bock, H., Geisler, C., Wurm, C. A., von Middendorff, C., Jakobs, S., Schonle, A., Egner, A., Hell, S. W. and Eggeling, C.
Two-color far-field fluorescence nanoscopy based on photoswitchable emitters. Applied Physics B 88: 161-165 (2007).

We demonstrate two-color far-field fluorescence microscopy with nanoscale spatial resolution based on the photoswitching of individual fluorescent markers. By enabling, recording, and disabling the emission of the reversibly switchable fluorescent protein rsFastLime and of the organic fluorophore cyanine5, we recorded two-color nanoscale images inside whole cells. The position of individual emitters was determined with a typical accuracy of 20 nm, which largely constitutes the lateral resolution of the system. Photoswitching in two-color colocalization experiments represents a major step towards the application of far-field fluorescence nanoscopy to the study of (biological) samples on the macromolecular level.