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On the Possibility of a Phosphorescence Microscope Albert Szent-Györgyi Institute for Muscle Research, Marine Biological Laboratory, Woods Hole, Massachusetts. Received 29 July 1964. Fluorescent emission, owing to the short lifetime of singlet excitation, appears on visual observation as simultaneous with light absorption. Triplet excitation, at a low temperature, may have a long lifetime and the corresponding phosphorescent light emission may appear to the observer as an independent afterglow. The parameters favoring or disfavoring singlet and triplet exci- tation are different, and so the phosphorescent light emission can give information about interesting properties and reactions. To quote an example, Steele and the author have found earlier 1 that the long-lived phosphorescent light emission of nucleic acid can be quenched by carcinogens and mutagens. The quenching was found dependent on the length of the molecule suggesting the existence of delocalized triplet states. These experiments should be repeated before their result is accepted, but, all the same, they suggest that the microscopic examination of tissues in phosphores- cent light may be very rewarding. A phosphorescent microscope would be very easy to build. The only difference, as compared to usual light microscopes, would be that the condenser and object slide would have to be of quartz, and uv light would have to be used for illumination. Visible light would not interfere. In addition, the microscope should have built in two rotating disks, rotated on the same axis, one of the disks being between the object and the light source, and one between the object and the observer. The disks should have holes located in such a way that while the disk below the object admits light, the disk above the object obstructs it. The two disks would thus alter- nately cut out the illuminating and the observed light, a principle on which all phosphoroscopes are built. In addition, the micro- scope would have to be provided with an equipment for the cooling of the object to liquid air temperatures. The author has approached several firms for the building of such an instrument without success, this not being a good business proposition. All the same, a phosphorescent micro- scope might give valuable information about interesting and subtle properties and reactions, as carcinogenesis and muta- genesis. This research was supported by a grant from the National Institutes of Health. Reference 1. R. H. Steele and A. Szent-Györgyi, Proc. Natl. Acad. Sci. U.S. 43, 487 (1957). January 1965 / Vol. 4, No. 1 / APPLIED OPTICS 137
