E-Mail IMAGE: Confocal fluorescence images of glass surfaces coated with the cyanine dyes Alexa Fluor 647 (a) and CF660C (b) and with carborhodamine dye ATTO647N (c) after light excitation at 568 nanometres... view more Credit: Team Markus Sauer / University of Wuerzburg The latest developments in fluorescence microscopy make it possible to image individual molecules in cells or molecular complexes with a spatial resolution of up to 20 nanometres. However, under certain circumstances, an effect occurs that falsifies the results: the laser light used can cause very reactive oxygen molecules to form in the sample. These can then damage the fluorescent dyes used to such an extent that they no longer fluoresce. Among microscopy experts, this effect is known as photobleaching.