- The Washington Times - Wednesday, October 12, 2005

Scott Whittaker magnifies unseen worlds. Small details become a big deal when they are seen through a scanning electron microscope.

Mr. Whittaker, the scanning electron microscopy lab manager at the Smithsonian National Museum of Natural History, brings items into focus, aiding the many researchers who need increased visualization for their work.

“We are a visual species,” Mr. Whittaker says. “Inevitably, one of the first questions we will ask is what something looks like.”

The field of microscopy has come a long way since 17th-century pioneers such as Anton van Leeuwenhoek and Robert Hooke first peered at cells. Today, scanning electron microscopy is used in a number of fields, with artists and scientists alike benefiting from the technology.

The scanning electron microscopes at the National Museum of Natural History can magnify external structures on objects up to 150,000 times, Mr. Whittaker says.

“Nowadays, we can see such things as flagella and cilia on the outside of the cell,” he says. “We can see the three-dimensional details on single-celled organisms, such as dinoflagellates, which are crucial to distinguish between species.”

A botanist studying a tree can walk into the forest and adequately describe its morphological characteristics, he says. With the scanning electron microscope, much smaller organisms, even those that can’t be seen with the naked eye, can be magnified for study.

A scanning electron microscope works by creating a cloud of electrons similar to how an incandescent light bulb creates light, he says. In this case, a thin wire filament is heated to make a cloud of electrons, he adds.

The cloud of electrons is accelerated toward the item to be viewed. The cloud is condensed into a beam and focused with a series of electromagnetic lenses onto the item. The electrons generate a signal, which is displayed onto a computer screen.

In contrast to the scanning electron microscope, under an optical microscope, which uses light and glass lenses with about 1,000 times magnification, only a small portion of the organism is in focus at any one time, he says.

When studying an organism such as the dinoflagellates that cause red tide, the scanning electron microscope enhances the overall information collected, says Maria Faust, research scientist in the department of botany at the museum.

For instance, she can distinguish the cell wall structure and numerous other structures that are present on the surface of an organism, all useful in descriptive taxonomy, in which the museum specializes.

The research at the Smithsonian is used by countless other researchers around the world in their own studies on morphology, toxicity or ecology and by professionals doing applied science, Ms. Faust says.

“Without the SEM, you couldn’t identify all the details of any kind of organism,” Ms. Faust says. “You have to describe the organisms to name them.”

Examining viruses, fungi, insects, mites and nematodes under the scanning electron microscope makes the country’s crops safer, says Eric Erbe, research scientist in electron microscopy at the Henry A. Wallace Beltsville Agricultural Research Center, which is part of the Agricultural Resource Service in the U.S. Department of Agriculture.

Because hundreds of pests invade crops, Mr. Erbe says his department studies healthy plants and learns how to grow them more effectively.

“We look at the host plant to see how it looks in the healthy and infected state,” Mr. Erbe says. “We look at the pest to see structurally what it looks like, to give individual researchers information.”

Scanning electron microscopes even can identify how works of art were made, says Blythe McCarthy, conservation scientist at the Freer Gallery of Art and the Arthur M. Sackler Gallery in Southwest. She holds a doctorate in material science and engineering.

“We have a scientist who looks at tool marks on jade,” Ms. McCarthy says. “We’re also looking at tool marks on silver.”

Using an energy dispersive spectrometer, a feature of some scanning electron microscopes, researchers can determine what element is present in a tiny sample from a work of art, says Barbara Berrie, senior conservation scientist at the National Gallery of Art in Northwest. She holds a doctorate in chemistry.

In her department, the scanning electron microscope is used to analyze and investigate works of art, mostly for preservation purposes.

For instance, the procedure can clarify whether a black substance is charcoal or bone black, a pigment made from burned bones. Also, faded pigments in some paintings can be identified, such as Geranium Lake, a red color distinguished by the presence of bromine, she says.

“Sometimes, we can see scraps of paint that are invisible to the naked eye,” Ms. Berrie says. “When it’s very old, very weathered material, it’s hard to see through optical microscopy.”

Three-dimensional chemical imaging is a goal for future scanning electron microscopes, says John Henry Scott, physicist at the National Institute of Standards and Technology in Gaithersburg. He holds a doctorate in physics.

One of the organization’s missions is to anticipate the next generation of measurement needs, he says. For instance, semiconductor manufacturers, which make computer chips, are facing difficulties because the pieces are becoming smaller and smaller without a way to measure them.

Right now, three-dimensional chemical imaging is being tested in the transmission electron microscope, a cousin of the scanning electron microscope that has the ability of atomic resolution, he says. Eventually, Mr. Scott says, he hopes the scanning electron microscope also will have that capability.

“When you give people the ability to see objects, the research and development increase rapidly,” Mr. Scott says. “Look at how long it took biology to grow until the invention of the optical microscope. Then, there was an explosion in the field of biology.”

LOAD COMMENTS ()

 

Click to Read More

Click to Hide