Timo Mappes

Early precursors of fluorescence cytometry: foundation of cell theory and fluorescence microscopy

Timo Mappes1,2
Fluorescence based cytometry is eventually based on (1) understanding of cells, and (2) the principle of fluorescence. The foundation of both topics is closely connected with the site of Jena.
The cell theory was formulated in 1839 by Theodor Schwann (1810-1882) and Matthias Jakob Schleiden (1804-1881). Schleiden performed the major part of his research in Jena, closely collaborating with the microscope makers of his time. The developments in optics enabled him to microscopically see and characterize the cellular structures and eventually to postulate: (A) All living organisms are composed of one or more cells, and (B) the cell is the most basic unit of life.  
Pushing the resolution in microscopy has been a major driver of development since establishing the Abbe equation: d = λ / 2 NA. Reducing the wavelength into the deep Ultraviolet and thus improving the resolution, August Köhler (1866-1948) and Moritz von Rohr (1868-1940) designed dedicated optics. In 1903 the team presented a microscope’s beam path designed entirely for 275 nm, enabling wide-field immersion microscope-photography with magnifications up to 2500x. While doing so they were the first to observe autofluorescence in the microscopic sample.
 
1 Stiftung Deutsches Optisches Museum, Carl-Zeiss-Platz 12, 07743 Jena, Germany
2 Friedrich-Schiller-Universität Jena, Fürstengraben 1, 07745 Jena, Germany