Electron Microscopes Reveal The Hitherto Unseen

Press, Volume CIX, Issue 32178, 23 December 1969, Page 6

Electron Microscopes Reveal The Hitherto Unseen

rt v

WALTER SULLIVAN

Will we ever be able to look into the very heart of things—to see for ourselves the basic architecture of living tissue, of metal alloys, of plastics? This question has been raised by recent French completion of an electron microscope twice as powerful as any previously existing and with 10 times the power of any in operation a few years ago. A visit to the French instrument, at the Laboratory of Electronic Optics at Toulouse, and its sister microscope at the same centre (now in second place in relative power) shows the extent to which efforts to see the very small have become “big science.” The new multi-million-dol-lar instrument (not including its accelerator) weighs 22 tons and stands 10ft tall. What a contrast to the desktop instrument with which Anton van Leeuwenhoek, three centuries ago, opened up the wonderful world of microscopic life forms! Seeing Atoms Interviews with a number of those in this country, France and Britain pressing forward in the development of high-voltage electron microscopes has reverted a wide feeling that before long it may be possible, for example, to see individual

atoms and “read” the genetic message in a strand of DNA (deoxyribonucleic acid) much as an experienced teletype operator can read the words punched into perforated type by his machine. It is DNA that carries, from one generation of cell*—or people—to the next the blueprints that control the structure and function of an individual. Already electron microscopes are providing stereo images showing, in three dimensions, the complex interweaving of DNA strands in chromosomes that package the genetic material during cell division. In another laboratory such an instrument is enabling an extremely patient researcher, slicing through hundreds of consecutive section* of the optic nerve, to construct a large, table-top model, showing as never before the detailed structure of the communications system that enables us to see. Crystal Structure A recent visit to the Cavendish Laboratory at Cambridge University found a specialist from Britain's National Steel Company working with a powerful electron microscope to explore the crystal structure of various steels. He explained that steels with a high carbon content make knife blades that stay sharp the longest—but they rust Stainless steel blades remain bright but get dull. It Is from studying, under extremely high magnification, bow the various alloys form dislocated crystal structures

that the steel men hope to find a way to combine the advantages of sharpness and stainlessness. The reason that efforts to see the ultra-small are being carried out with electron microscopes is that ordinary microscopes cannot “see” anything smaller than the wavelengths of light used for the observation. When a beam of electrons Is accelerated to high energy, the electrons move in a wavelike manner with wavelengths thousands of times shorter than that typical of visible light Electron Beam The design of an electron microscope is analogous to that of an optical microscope, but instead of using glass lenses to focus the light magnetic lenses are placed In the path of the electron beam. The giant French microscope at Toulouse has six such lenses, the largest weighing two tons. Its 100-odd Cock-croft-Walton accelerators are designed to produce an electron beam of 3 million volts, which requires a tension across the system of 3.5 million volts.

The other instrument at Toulouse develops 1.5 million volts. None outside France were believed to achieve substantially more than one million volts, although the Soviet group headed by Dr Nikolai Popov told in August of plans for a 3-million-volt instrument Miilion-volt microscopes are now being sold by Japan and Britain and one is being used in this county by United States Steel.

Specialists point out that the level of voltage is not a direct measure of efficiency in studying the very small. One difficulty is that a very high voltage beam acts on specimens with subtle shading, much as a very bright light wipes out the contrast in a photographic transparency. Voltage Rate Thus many believe that the microscopes that are finally able to distinguish individual atoms will have voltages of about 200,000, rather than several millions. The DNA code may be read with voltages as low as 10,000. These, however, are still in the highvoltage category. The chief advantage of extremely high voltages is that such beams can penetrate relatively thick specimens. For weaker electron microscopes the specimen must be sliced so thin that the researcher often wonders whether the slicing or etching process has not distorted the specimen. The super-powerful beams, like those at Toulouse, can penetrate specimens 25 times thicker than standard electron microscopes. For this reaseon they are particularly applicable to metal samples and to the study of living tissue. One of the dreams of microbiologists is to watch the life processes of bacteria under the very high magnification of an electron microscope. Gaston Dupouy and his colleagues at Toulouse have implanted bacteria in a capsule whose internal temperature and humidity are

kept friendly to the organism while it is exposed to the electron beam.

At Harvard University, Dr Keith K. Porter is studying the fine structure of rods in the retina. Others are focusing on details of the “synapses" where nerve ends Ing meet and communication with one another in mysterious ways. At the University of Chicago, Albert Crewe is building a scanning electron microscope of 100,000 volts as a prelude to construction of one that, he hopes, can see individual atoms. A scanning microscope sweeps a very narrow electron beam back and forth across the specimen, revealing its surface features rather than ite Internal structure.

And what will atoms look like?. Dr Frants Perrier at Toulouse points out that we will see atoms only In terms of what the electrona "tell us.” Atoms will not look like solid objects, such as those that we see in terms of their effect upon visible light. When that stage is reached, according to Dr Humberto Fermandez-Moran, professor in the biophysics department at the University of Chicago, it may become possible "not only to predict, but also to design lite at the molecular level. "Scientists will have a power," he continued, "more awesome than any ever imagined. In turn, they will have the grave responsibility of using this power wisely.” —New York Times News Service copyright.