PURPOSE: Mid- and far-infrared (energies below 1 eV) microprobes using synchrotron radiation are being used to address problems such as:

• Chemistry in biological tissues
• Chemical identification and molecular conformation
• Environmental biodegradation
• Mineral phases in geological and astronomical specimens
• Electronic properties of novel materials
• Forensic studies

HOW THE TECHNIQUE WORKS: Infrared synchrotron radiation is focused through, or reflected from, a small spot on the specimen and then analyzed using a spectrometer. Tuning to characteristic vibrational frequencies serves as a sensitive fingerprint for molecular species. Images of the various species are built up by raster scanning the specimen through the small illuminated spot.

UNIQUENESS: Infrared radiation from a synchrotron is more intense than that from a conventional laboratory source. Even so, the radiation dose is mild and nondestructive, permitting the study of fragile specimens and even live biological systems.

EXAMPLES:

Misfolded Protein Structure in Alzheimer’s Disease
Biodegradation of Organic Contaminants Catalyzed by Humic Acid
In Situ Prion Protein Structural Changes in Mad Cow Disease and Scrapie

Visible-light, UV, and IR images of Alzheimer’s diseased brain tissue.

Alzheimer’s disease is characterized by the death of nerve cells in particular regions of the brain. The brain shrinks as gaps develop in the temporal lobe and hippocampus, which are responsible for storing and retrieving new information. This in turn affects a patient’s ability to remember, speak, think, and make decisions. It is not known what causes nerve cells to die but there are characteristic appearances of the brain after death. In particular, “tangles” and “plaques” made from protein fragments are observed under the microscope in damaged areas of brain. A combination of ultraviolet and infrared light is being used to study the structure of the proteins involved in the formation of plaques and tangles in the brain. Fluorescence microscopy is used to identify the plaques and tangles, and infrared imaging is used to determine their structures within brain tissue. At the same time, infrared imaging is also used to study the health of the nerve cells surrounding the plaques and tangles in the brain tissue. Understanding the structures of the plaques and tangles in Alzheimer’s-diseased brain tissue may help to develop ways of preventing them from forming, thus preventing progression of the disease. In addition, identification of plaques and tangles in other organs may provide a biopsy method for early diagnosis of Alzheimer’s disease in the future.

L.M. Miller, P. Dumas, N. Jamin, J.-L. Teillaud, J. Miklossy, and L. Forro, “Combining IR spectroscopy with fluorescence imaging in a single microscope: Biomedical applications using a synchrotron infrared source,” Rev. Sci. Instr. 73, 1357 (2002).

Contour diagram from infrared mapping showing the distribution of Mycobacterium sp. JLS bacteria on a mineral surface.

Contaminants in the environment come in many forms, one of which is that of the toxic organic (carbon-based) chemicals known as polycyclic aromatic hydrocarbons (PAHs). These include more than 100 different chemicals resulting from incomplete burning of coal, oil, gas, garbage, and other organic substances like tobacco or grilled meat. Converting PAHs into nontoxic chemicals removes the hazard, but learning how to do this in an efficient and cost-effective way remains to be accomplished. Remarkably, since bacteria are feared by many people as infectious germs, some species of these microorganisms may provide a solution by, in effect, ingesting the PAHs and during digestion converting them into a less toxic chemical, a process known as biodegradation. Researchers have made use of an infrared technique to show that the speed of biodegradation can be dramatically increased (almost a hundred times) by adding a soil-derived organic (humic) acid along with the bacteria to a PAH spot on a mineral surface. This finding will influence the development of environmental cleanup strategies based on biodegradation.

H.-Y Holman, K. Nieman, D.L. Sorensen, C.D. Miller, M.C. Martin, T. Borch, W.R. McKinney, and R.C. Sims, “Catalysis of PAH biodegradation by humic acid shown in synchrotron infrared studies,” Environ. Sci. Technol. 36, 1276 (2002).

Left: Light microscope image of an immunostained prion-infected cell. Right: Infrared image of the Amide I absorption maximum, which shows the misfolded prion protein located in or near the cell membrane of the infected cell.

Transmissible spongiform encephalopathies, such as scrapie, mad cow disease, and Creutzfeldt-Jakob disease, are a group of fatal neurodegenerative disorders characterized by the conversion of the normal prion protein (PrP) into misfolded aggregates (PrP^Sc). The mechanism behind this structural conversion is unclear. To analyze the disease-related protein structural changes directly in the tissue environment, scientists have examined the protein structure within the dorsal root ganglia in scrapie-infected Syrian hamsters. Using synchrotron-based infrared microscopic imaging, individual neurons are scanned for the distribution of protein structure based on the infrared absorption of the protein backbone mode. The high brilliance of the synchrotron infrared light source permitted subcellular spatial resolution. The scientists observed regions of increased structural change in and/or around scrapie-affected cells. No evidence of these structural changes is observed in normal neurons. Comparison of the infrared images with PrP^Sc immunostaining of the same tissue demonstrated that the altered regions correspond to the misfolded structure of PrP^Sc.

J. Kneipp, L.M. Miller, M. Joncic, M. Kittel, P. Lasch, M. Beekes, and D. Naumann, “In situ identification of protein structural changes in prion-infected tissue,” Biochim. Biophys. Acta. 1639, 152 (2003).