September 28, 2001

Novel applications of technology

Jill D. Pasteris, Ph.D., has broken new ground through her studies using the laser Raman microprobe

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(From left) Research scientists Brigitte Wopenka, Ph.D., and John Freeman, Ph.D., work with Professor Jill D. Pasteris, Ph.D., all in earth and planetary sciences in Arts & Sciences, to load a sample for analysis by the laser Raman microprobe in Pasteris' McDonnell Hall laboratory.

By Tony Fitzpatrick

Jill Dill Pasteris, Ph.D., professor of earth and planetary sciences in Arts & Sciences, began her geology career studying rocks from the Earth's mantle and today is making fascinating discoveries about bone, teeth and minerals on the sea floor. She has traversed this less-traveled road thanks to a vehicle that has brought her prominence across disciplines and nations as well.

The vehicle is a spectroscopic instrument called the laser Raman microprobe. It yokes a powerful microscope and an equally potent laser, allowing Pasteris and her colleagues to analyze minerals and other particles in the micrometer range --that's one-millionth of a meter.

As a young geologist, Pasteris learned to appreciate the power of microscopy from her professors at Bryn Mawr College and from a legendary master, Paul Ramdohr of the University of Heidelberg, Germany. Thanks to a 1974 Fulbright Fellowship, she spent a year working with him. That was between finishing her bachelor's degree at Bryn Mawr and enrolling in the doctoral program in geology at Yale University.

"At Heidelberg, I looked at all sorts of ore deposit rocks under the microscope," said Pasteris in her third-floor McDonnell Hall office. "Dr. Ramdohr suggested I get more specific in my interest, and I chose South African kimberlites."

Kimberlites are rocks from which diamonds are recovered. They are found deep in the Earth's mantle, some 100 to120 miles below the Earth's surface. Pasteris studied kimberlites and noticed tiny, micrometer-sized packets of fluid known as fluid inclusions trapped within some of the minerals.

"I asked: Wouldn't these fluids be guides to help us understand what's going on and how the diamonds are stabilized?" Pasteris said. "You might think of cracking open the minerals and extracting the fluids, but this leads to contamination. The laser Raman microprobe, however, lets you take a laser beam and drop it right on the inclusion you're looking at. It's remarkable. You don't have to mess up the sample."

Pasteris came to Washington University in 1980. Within three years, with help from the University, the National Science Foundation, Monsanto Co. and others, she bought a laser Raman microprobe, the first one in the country to be deployed in a geology department. Since then, she has purchased two others that have greater capabilities.

Initially, Pasteris used the Raman microprobe to analyze those minute fluid inclusions in rocks from the mantle that had first captured her interest. She and her colleagues then broadened their studies to various chemical reactions among melts, fluids and rocks. For instance, they used Raman spectroscopy to try to understand the 1991 eruption of Mt. Pinatubo in the Philippines.

In the mid-1990s, Pasteris and her group, which includes earth and planetary sciences research scientists Brigitte Wopenka, Ph.D., and John Freeman, Ph.D., wizards with the Raman microprobe, began their travels down yet a different road. They were approached by Harry Brandon, D.Sc., research assistant professor of plastic surgery who also is a mechanical engineer. He asked if she and her group could apply the laser Raman microprobe to analyze minerals in human tissue. Not just any tissue, but tissue that had been adjacent to silicone breast implants.

The Pasteris family (clockwise from left); Jill, Arthur, and fraternal twins Jessica and Jennifer.

The project came about because of claims by a pathologist that the polymer silicone had degraded in the body to form a crystalline silica material that, as Pasteris explained, a geologist would call quartz. The pathologist believed that this was one of many problems that made the women feel ill.

"When Harry suggested collaborating, I thought that it sounded a lot like what we do with rocks," Pasteris said. "In either rock or tissue, we can analyze minerals. We thought it could work."

The kind of microscopy that the pathologist used was not as detailed or definitive as that of the laser Raman microprobe.

"Essentially," Pasteris explained, "all he could provide was an inference from his optical observations. In contrast, the Raman microprobe could provide definitive spectra of microparticles no more than a couple of micrometers in diameter that would be a fingerprint of the minerals."

Brandon's collaborator, V. Leroy Young, M.D., the William G. Hamm Professor of Plastic Surgery, provided samples of breast tissue both from women with and without silicone breast implants.

"We found various particles in both types of tissue," Pasteris said. "One thing we realized is that it's essentially impossible for silicone to spontaneously convert to quartz. The most common thing we found in both types of tissue was calcite --that's what Tums are made of, and clamshells, too. There was no evidence of different kinds of solids in implants versus the control group. But we did find evidence that some silicone did indeed leak into the tissue."

The Pasteris group's study began fours years ago and is concluded now, but "it launched us into researching biominerals," Pasteris said.

Pasteris and her group now collaborate with Matthew J. Silva, Ph.D., assistant professor of orthopaedic surgery, on the material properties of bone.

"We have a great collaboration with Matt, as we have had with Harry and Leroy," Pasteris said. "Matt's background is in mechanical engineering, and he wanted to know more about the mineral composition of bone and what it is that makes bone so very strong yet very flexible."

Bone is dominated by apatite, a calcium phosphate mineral occurring in crystalline grains on the order of tens of nanometers (billionths of a meter) in size. The grains are bound by ordered networks of collagen fibers, protein that comprises between 20 and 30 percent by weight of bone. Pasteris and her collaborators are making inroads into understanding the intricately complex relationship between the mineral grains, collagen fibers and mineral-collagen interfaces that give bone its extraordinary mechanical properties.

"We're fascinated by how all of this comes together," Pasteris said. "While bone is dominated by minerals, it's not frequently looked at the way a geological product would be. It's a wonderfully bioengineered material."

One of the fascinations of bone is the nano-size of the apatite crystals. Some process in the body prevents the apatite crystals from becoming larger. It's already been shown that if the apatite crystals can be chemically changed, bone strength changes, a principle that might someday lead to a therapy for osteoporosis and other bone diseases.

"The fact that the crystals grow no larger suggests that there's a reason for this and makes me wonder how the body keeps them from growing larger," Pasteris said. "These are the kinds of questions that mineralogists can address."

Raman spectroscopy is a vehicle that most recently has led Pasteris and her group to the sea floor. They have collaborated with biologists at the Monterey Bay Aquarium Research Institute (MBARI) in California to analyze the kind of sulfur that unusual bacteria oxidize on the ocean floor. With oceanographer Peter Brewer of MBARI, Pasteris and her colleagues now are testing a fiber-optic, portable Raman spectrometer that MBARI will place inside its remotely operated vehicle on the sea floor at several kilometers depth.

The scientists want to examine clathrate hydrates, which are ice-like solids that trap gas molecules such as greenhouse gases methane and carbon dioxide. Understanding how these solids encapsulate the greenhouse gases could lead to the safe storing of unwanted greenhouse gases on the sea floor.

Pasteris has been honored many times for her teaching, including the 1995 Emerson Electric Excellence in Teaching Award and the 1995 Faculty Teaching Award presented by the University's Council of Students of Arts & Sciences. She regularly teaches the undergraduate courses "Earth Materials" and "Resources of the Earth," plus the graduate course "Environmental Mineralogy."

"I try to tell my students that there is power in learning the fundamentals because they are launching pads," Pasteris said. "We see a lot of our research taking advantage of the fundamental things we've learned."

"Jill Pasteris is a superb researcher and teacher," said Raymond E. Arvidson, Ph.D., the James S. McDonnell Distinguished University Professor and chair of earth and planetary sciences. "She is involved in a wide array of studies using the Raman spectrometers in her lab as the focus. She consistently receives great comments from students in her courses as someone who cares about teaching and cares about students, in addition to being someone who excels in explaining difficult concepts in ways that are understandable."

Pasteris and her husband, Arthur, have two daughters, Jennifer and Jessica, fraternal twins and sophomores at Ladue Horton Watkins High School. Her daughters tend toward sports and the arts more than sciences, unlike their mother, who caught the geology bug at an early age.