Fluorescent Nanotubes to Illuminate the Inner Workings of Laboratory Mice

Stanford researchers have developed an improved imaging method using fluorescent carbon nanotubes that create color images centimeters beneath the skin with far more clarity than conventional dyes provide. For a creature the size of a mouse, a few centimeters makes a great difference. The results were published in Proceedings of the National Academy of Sciences.

"We have already used similar carbon nanotubes to deliver drugs to treat cancer in laboratory testing in mice, but you would like to know where your delivery went, right?" said Hongjie Dai, a professor of chemistry. "With the fluorescent nanotubes, we can do drug delivery and imaging simultaneously - in real time - to evaluate the accuracy of a drug in hitting its target."

Researchers inject the single-walled carbon nanotubes into a mouse and then watch as the tubes are delivered to internal organs by the bloodstream. The nanotubes fluoresce brightly in response to the light of a laser directed at the mouse, while a camera attuned to the nanotubes' near-infrared wavelengths records the images. By attaching the nanotubes to a medication, researchers can see how the drug is progressing through the mouse's body. The key to the nanotubes' usefulness is that they shine in a different portion of the near-infrared spectrum than most dyes.

Biological tissues - whether mouse or human - naturally fluoresce at wavelengths below 900 nanometers, which is in the same range as the available biocompatible organic fluorescent dyes. That results in undesirable background fluorescence, which muddles the images when dyes are used.

But the nanotubes used by Dai's group fluoresce at wavelengths between 1,000 and 1,400 nanometers. At those wavelengths there is barely any natural tissue fluorescence, so background "noise" is minimal.
The nanotubes usefulness is further boosted because tissue scatters less light in the longer wavelength region of the near-infrared, reducing image smearing as light moves or travels through the body.

By selecting single-walled carbon nanotubes with different diameters and other properties, Dai and his team can fine-tune the wavelength at which the nanotubes fluoresce.
The nanotubes can be seen immediately upon injection into the bloodstream of mice.

http://news.stanford.edu

Authors:
Louis Bergeron

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Keywords: Carbon Nanotubes Fluorescence Fluorescent Carbon Nanotubes Hongjie Dai Nanotechnology Stanford University

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