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  • Biomolecules Show Their True Colors
Oct 2011
DURHAM, N.C., Oct. 28, 2011 — After years of black-and-white and false-color 3-D molecular imaging, events beneath the surface of the skin can now be viewed in their true colors. A novel method detects and shows, for example, the vivid shades of red of hemoglobin as it is carried by blood vessels.

Using the technique, developed at Duke University, other molecules also can be visualized, including dyes introduced to illuminate a multitude of biomechanisms. The developers believe the true-color imaging method could have significant implications for clinics and basic science labs by providing new perspectives of basic biological functions.

To achieve a colorful view below the skin, the Duke researchers created a modified form of optical coherence tomography (OCT), which uses optical “echoes” to reconstruct the structure underneath a tissue’s surface.

“While with conventional OCT we are able to see structures such as blood vessels and even capillaries, the main drawback is that it doesn’t provide some basic functional information, including absorption, which also gives the true color of the structures,” said Francisco Robles, graduate student in the laboratory of Adam Wax of Duke’s Pratt School of Engineering.

Using a modified form of optical coherence tomography, Duke researchers devised a way to image cellular reactions beneath the skin’s surface in true color. (Image: Adam Wax)

“We expect that this new technique will have several important applications, such as visualizing tumor-development processes, like angiogenesis and oxygen deprivation,” Wax said. “It also could help in detecting diseases of the eye, especially those that impact the tiny vessels of the eye. It may have effectiveness in monitoring the delivery and effectiveness of drugs.”

To achieve this ability to see true colors, Robles and his colleagues Christy Wilson and Gerald Grant developed a novel method for collecting and interpreting the information provided by the OCT procedure to simultaneously include information regarding the wavelengths reflected by the target tissues.

“Each point on the three-dimensional image that we collect contains a great deal of useful information that we can use to reconstruct what’s happening at the molecular level,” Robles said. “The data not only helps create three-dimensional images, but it also contains important spectral information.”

Blood, or more specifically the hemoglobin being carried by red blood cells, provides the absorption that makes the process work. In a sense, the hemoglobin, which carries oxygen, acts as a contrast agent because of its absorption properties, which give blood its red color. Many disorders can be characterized by the levels of blood oxygen, a characteristic that can be detected in true shades of red by the new technique.

“The level of hemoglobin in tissue is very important,” Robles said. “The additional information we can collect enables us to see subtle shifts in hemoglobin levels as well as changes in how the hemoglobin is being distributed in local tissues.”

The Duke team tested the new system in mice. When conventional OCT was employed, certain structures — such as muscle and vessels — could be observed. However, these images were black and white and couldn’t reveal information about the tissue function.

“With the new system, we observed a wealth of information we couldn’t before,” Robles said. “The muscle layer at the surface was relatively colorless because of low hemoglobin levels. However, as the light continued through the blood vessels below, a red shift in color was clear. To our knowledge, these are the first micron-scale cross-sectional images of living tissue in true color.”

Robles’ research has been published online by Nature Photonics.

The proprietary rights to the OCT technology are owned by Oncoscope Inc., a Durham-based company founded in 2006 by Wax and based on the Duke technology. Wax, who still has a financial interest in the company, was a highlighted speaker in Photonics Media’s October 2011 webinar, “The Future of Optics: Two Perspectives”.

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