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.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.