Carbon Nanotubes Fluoresce at Right Wave Length for Seeing Internal Organs

Images that would otherwise be murky are made clear by using fluorescent carbon nanotubes

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Carbon Nanotubes Fluoresce at Right Wave Length for Seeing Internal Organs

Researchers at Stanford University have discovered that fluorescent single-walled carbon nanotubes improve on the murky images provided by traditional dyes and deliver detailed and clear images of the internal organs of mice.

Interestingly, the idea of using fluorescent carbon nanotubes to illuminate the internal organs was partly inspired by the use of carbon nanotubes in drug delivery.

"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?" says Hongjie Dai, a Stanford chemistry professor. "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."

The technique, described this month in the journal Proceedings of the National Academy of Sciences, is able to produce such clear images because of the wavelength at which the carbon nanotubes operate.

The problem has been that both the biocompatible dyes used today and biological tissue fluoresce at the same wavelength of below 900 nanometers. This creates a background fluorescence that results in murky images.

But the carbon nanotubes fluoresce at between 1000 and 1400 nm, where the biological tissue is hardly emitting any fluorescence so that there is minimal background noise.

"The nanotubes fluoresce naturally, but they emit in a very oddball region," Dai says. "There are not many things—living or inert—that emit in this region, which is why it has not been explored very much for biological imaging."

While computer tomography and magnetic resonance imaging still rule the roost when it comes to imaging deep tissue, this should push the capabilities and application of fluorescence imaging, which is used mainly in research and requires far simpler machinery.

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The Ultimate Transistor Timeline

The transistor’s amazing evolution from point contacts to quantum tunnels

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A chart showing the timeline of when a transistor was invented and when it was commercialized.

Even as the initial sales receipts for the first transistors to hit the market were being tallied up in 1948, the next generation of transistors had already been invented (see “The First Transistor and How it Worked.”) Since then, engineers have reinvented the transistor over and over again, raiding condensed-matter physics for anything that might offer even the possibility of turning a small signal into a larger one.

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