Microscopy DOI: 10.1002/anie.201204688 The Invention of Immersion Ultramicroscopy in 1912— The Birth of Nanotechnology?** Timo Mappes,* Norbert Jahr, Andrea Csaki, Nadine Vogler, Jürgen Popp, and Wolfgang Fritzsche history of science · nanoparticles · nanotechnology · ultramicroscopy 1. Introduction 2012 marks the centenary of the invention of one of the most remarkable techniques in nanoscience, one which has opened a new window to the study of colloidal solutions. This invention—the immersion ultramicroscope—may be said to mark the moment when modern nanotechnology began. Colored glass of the Roman times has fascinated histor- ians for a long time. One of the most prominent examples is the Lycurgus Cup, which dates back to the 4th century A.D., and nowadays is on display at the British Museum. [1] While this vessel appears pale-green in reflected light, its glass changes color when illuminated by transmitted light and appears translucent and bright-red. [2] This effect is caused by nanoparticles of a colloidal silver–gold alloy embedded in the glass matrix. [3] No description has survived from Roman times to tell how the glass workshops were able to make this material containing colloidal metal. More than 1300 years after this cup had been crafted, numerous publications in the 17th century appeared describing the preparation of colloidal gold. The most frequently cited report, though not the first, was published by Andreas Cassius in 1685. [4, 5] It would take another two centuries before Michael Faraday (1791–1867) speculated about the size of these finely distributed gold particles. In his “Bakerian Lecture : Experimental Relations of Gold (and Other Metals) to Light” in 1857 Faraday demon- strated the results of his work on what he called “gold sols”. [6] He attributed the color of his gold solutions to the size of the metal particles. Faraday used a projection microscope to demonstrate how the reduction of gold in “exceeding fine particles” resulted in a ruby-red-colored fluid. Using a micro- scope, he demonstrated a transformation of the fluids color to blue by mixing salt with his gold sol. While he could not explain the reason for the color alteration, he considered this effect to be an indication that “a mere variation in the size of its particles gave rise to a variety of resultant colours”. Although he had no clue about the real size of the particles causing this coloring, he suspected the waves of light to be “large compared to the dimensions of the particles”. Today, one of the microscope slides that he used for the experiments carried out during his lecture is kept at the Whipple Museum of the History of Science, University of Cambridge. [7] It took nearly another half a century before the chemist Richard Zsigmondy (1865–1929) and the physicist Henry Siedentopf (1872–1940) determined the size of colloidal gold by introducing a novel microscopical method. Interesting enough, Zsigmondy did not know about Faradays work until he had successfully created colloidal gold by the reduction of gold chloride with formaldehyde in a weakly alkaline solution. After Zsigmondy had access to Faradays work, he followed the Englishmans approach on using phosphorus as a reducing agent. By applying his experimental experience with formaldehyde and gold but using phosphorus as a re- ducing agent, Zsigmondy generated even finer gold particles. These fine particles were later used by Theodor Svedberg for his diffusion experiments. [8] But how was Zsigmondy able to determine the size or mass of his colloids? At the beginning of the 20th century, several approaches emerged to push the resolution limit of microscopes. Most of them were based on the theoretical work of Hermann von Helmholtz and Ernst Abbes theories on resolution. Consequently, microscope objectives with (very) high numer- ical apertures were introduced, or alternatively shorter wave- lengths, reaching into the deep ultraviolet, were used for microscopy. This resulted in the use of immersion oils with high refractive indices, such as 1-bromonaphthalene, for objectives having numerical apertures of 1.60, [9] as well as the introduction of monochromatic objectives for UV mi- croscopy at a wavelength of 275 nm. [10] Zsigmondy and [*] Priv.-Doz.Dr.-Ing. T. Mappes Institute of Microstructure Technology Karlsruhe Institute of Technology (KIT) 76128 Karlsruhe (Germany) E-mail: timo.mappes@kit.edu Homepage: www.biophotonic-systems.com Dipl.-Ing. N. Jahr, Dr. A. Csaki, Dr. N. Vogler, Prof.Dr. J. Popp, Priv.-Doz. Dr. W. Fritzsche Institute of Photonic Technology P.O. Box 100 239, 07702 Jena (Germany) [**] T.M. thanks Dr. Olaf Medenbach (Witten, Germany) for donating the illustrated immersion ultramicroscope to http://www. musoptin.com and Volker Vyskocil (Nettetal, Germany) for helping to locate and purchase the equipment for slit ultramicroscopy from the laboratories of the former Dynamit-Nobel AG in Troisdorf (Germany). Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/anie.201204688. . Angewandte Essays 11208  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2012, 51, 11208 – 11212