Microscopy Pioneers Pioneers in Optics: Robert Day Allen
Michael W. Davidson National High Magnetic Field Laboratory , Florida State University , Tallahassee , FL 32306
davidson@magnet.fsu.edu
Robert Day Allen (1927-1986)
Robert Day Allen was a renowned microscopist, as well as a prominent researcher of cell motility processes, and a co-developer of video-enhanced contrast (VEC) microscopy, which is a modifi cation of the traditional form of diff erential interference contrast (DIC) microscopy. He also served as a professor at Dartmouth College and the Marine Biological Laboratory (MBL) in Wood’s Hole, Massachusetts, publish- ing numerous scientifi c works during his lifetime. Some of his most important scientifi c contributions were made together with his wife and fellow scientist Nina Strömgren Allen.
In the midst of teaching a short summer optical microscopy course at the Marine Biological Laboratory, the Allens, who were both faculty members at Dartmouth, made a surprise discovery. When Nina Strömgren Allen and Jeff
Travis attached a video camera and television to a microscope in order to enable Robert Allen to present a preparation to the entire class for simultaneous viewing, they discovered that sub-resolution structures could be imaged with video diff erential contrast that are not ordinarily observed with the resolutions available using a conventional light microscope. Although an electron microscope is able to display even smaller objects, the preparations must be fi xed. T e video microscopy technique that the Allens devel- oped is capable of imaging specimens that are alive and mobile. DIC is also an excellent mechanism for rendering contrast in transparent specimens. It is a beam-shearing interference system in which the reference beam is sheared by a minuscule amount, generally somewhat less than the diameter of an Airy disk. T e technique produces a monochromatic shadow-cast image that eff ectively displays the gradient of optical paths for both high and low spatial frequencies present in the specimen. T ose regions of the specimen where the optical paths increase along a reference direction appear brighter (or darker), whereas regions where the path diff erences decrease appear in reverse contrast. As the gradient of optical path diff erence grows steeper, image contrast is dramatically increased. Along with Georges Nomarski and George B. David, Robert Day Allen assisted the Carl Zeiss Optical Company in developing a Nomarski diff erential interference microscope for transmitted light applications. In a hallmark paper published in Zeitschriſt für wissenschaſt liche Mikroskopie und mikroskopische
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Nina Strömgren Allen, a co-developer of VIC microscopy with Robert Day Allen, her husband.
Technik , Allen and his colleagues defi ned the basic principles of the DIC technique and the interpretation of images. Robert Allen worked with Nina Strömgren Allen to modify the camera and microscope confi guration in a manner that allowed for maximum resolution, contrast, and magnifi cation. T e pair and Shinya Inoué, who was a resident scientist at MBL and an invited lecturer in the Allens’s microscopy course, described the new method at a meeting of the American Society for Cell Biology. T en in 1982, the Allens advanced their work by capturing video images digitally and then used a frame memory to analyze and quantify images. On October 25, 1983, the couple received a United States patent for their development of Allen Video Enhanced light microscopy. Video microscopy, alone and coupled to diff erential interference contrast optical systems, is now commonly used in laboratories around the world and has proved especially useful in the study of cell biology. For example, the technique enabled the real-time observation of microtubules, with which Allen was directly involved, and ultimately led to the detection of the motor molecule kinesin. In addition, Allen was able to visualize objects that were below the limit of resolution of the light microscope and were normally observed only with an electron microscope. In 1986, Allen died from cancer. T e Robert Day Allen
Fellowship, off ered through the Marine Biological Laboratory, was created in his memory and is awarded annually to a young researcher dedicated to the study of cellular motility and anatomy.
doi: 10.1017/S1551929515000218
www.microscopy-today.com • 2015 May
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