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The Dayside : Electron microscopy is beautiful

By: Charles Day
13 March 2015
Last month Josh Redlich of Sterling Publishing kindly sent me a copy of a new coffee-table book whose title hints at its gorgeous contents—Science Is Beautiful: The Human Body Under the Microscope (Batsford, 2015). Written by Colin Slater, the book consists of high-resolution, close-up images of the cells, organelles, and other tiny components that make up our bodies. Thanks to the deft and extensive use of false color, the images, which come from labs around the world, are captivating.

This scanning electron micrograph image of organelles in two liver cells appears on page 31 of Science Is Beautiful. CREDIT: Sterling Publishing

The book may interest physicists for at least two reasons. First, some of the technologies used to create the images, such as electron microscopy, confocal microscopy, and x-ray radiography, were invented and developed by physicists. And as last year’s Nobel Prize in Chemistry evinced, physicists continue to invent new technologies for observing biological systems.

The second source of potential interest lies in what the images depict. Just as physicists continue work on new biophysical techniques—imaging and nonimaging—they also continue to apply their knowledge of physics to understand biological systems.

More personally, some of the images brought back memories of the biophysical research that I covered when I was a regular contributor to Physics Today‘s Search and Discovery department. For example, page 96 features a scanning electron micrograph of cochlear hair cells, whose resonant wobbling mediates our ability to detect sound. For the magazine’s June 2010 issue, I wrote a news story about an ingenious experiment conducted by Pascal Martin of the Curie Institute and his collaborators. By yoking a hair cell to a virtual, computer-controlled clone, Martin’s team demonstrated that the elastic membrane on which the hairs sit lowers the detection threshold. And it does so by coupling the hairs’ vibrations and averaging out their stochastic fluctuations.

Scanning electron microscope image of the Penicillin fungus. CREDIT: Sterling Publishing

Page 24 features a scanning electron micrograph of cultured neurons caught as they extend their dendritic arbors. (Dendrites sprout from a neuron’s cell body, the soma, to form a tree-like network that gathers information from other nerve cells.) For Physics Today‘s October 2000 issue, I wrote about an experiment that answered a pressing question about dendrites: How is it that signals that travel along dendrites of different lengths arrive at the soma with equal strength even though dendrites, lacking insulation, behave like leaky pipes? Summarizing the experiment, I wrote:

Apparently, nature has either (a) built a system with ineffectual components or (b) provided a method for boosting signals. The answer is b. In last month’s Nature Neuroscience, Jeff Magee (Louisiana State University) and Erik Cook (Baylor College of Medicine) confirm that many signals arrive at the soma with the same strength regardless of how far away in the dendritic arbor the signals originate. They also found out how nature pulls off this trick: Rather than being topped up along the way with a system of repeaters (analogous to the devices used in long-distance optical and electric cables), the signals actually start out stronger.

Besides nostalgia, the electron micrographs in Science Is Beautiful evoked another reaction: They made me wonder who first imaged a biological specimen with electrons. Thanks to the power of the interwebs, the answer was easy to discover.

In 1933, two years after they had built the world’s first electron microscope, physicist Enrst Ruska and engineer Max Knoll demonstrated that the resolution obtained from an electron microscope could exceed that from a light microscope. Among the pioneers who sought to extend and apply the improved resolution was Ladislaus Marton of the Free University of Brussels.

Transmission electron microscope image of a T4 bacteriophage in the process of injecting its viral DNA into its host, an Escherichia coli bacterium. CREDIT: Sterling Publishing

For a chapter of the book The Beginnings of Electron Microscopy (World Scientific, 1985) Charles Süsskind recounted Marton’s contributions to electron microscopy. As Süsskind tells it, Marton had concluded that biological objects offered the richest field of application for the new imaging technique. But would delicate biological specimens survive bombardment by high-energy electrons for long enough to form an image?

Perhaps because the first images that Ruska and Knoll took were of tungsten wires and other refractory objects, it was widely believed that biological samples would “burn to a cinder.” Marton shared that misgiving, but he strove instead to make biological samples more robust. He impregnated them with osmium, which has a high melting point, mounted them on stages that had conducted heat efficiently, and sliced them thin.

On 4 April 1934 Marton turned on his homemade electron microscope and made an image of a 15-μm-thick section of a leaf from Drosera intermedia, an insectivorous herb known commonly as the spoonleaf sundew. Two months later, Nature published his brief accountof making the first-ever electron microscope image of a biological sample.

Scanning electron microscope image of bone marrow stem cells in the process of developing into various types of blood cells. CREDIT: Sterling Publishing

Ironically, having worked hard to forestall damage to his sample, Marton discovered that his worries were based on the mistaken assumption that the source of contrast in transmission electron images is absorption. In fact, in the relatively thick samples that Marton used, scattering, which is less damaging than absorption, predominates. That realization emboldened Marton and others to further pursue the biological applications of electron microscopy.

Marton emigrated to the US in 1938 with his wife and scientific collaborator, Claire. He continued to make advances in electron microscopy—first at the RCA Research Laboratories and the University of Pennsylvania, where he held joint appointments, and then later at the National Bureau of Standards, where he founded and led the lab’s electron physics division.

For more about Marton, read the obituary that his NBS colleague Howland Fowler wrote forPhysics Today‘s May 1979 issue.

Source: Scitation

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This entry was posted on March 13, 2015 by in Biology, Physics, Sci-Media, Tech News and tagged , , , .

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