In research detailed in the current issue of Science magazine, a team of Rice University chemists led by fullerene discoverer and Nobel laureate Richard Smalley describes the first observations of fluorescence in carbon nanotubes. Fluorescence occurs when a substance absorbs one wavelength of light and emits a different wavelength in response. The Rice experiments, conducted by Smalley's group and the photophysics research team of chemist R. Bruce Weisman, found that nanotubes absorbed and gave off light in the near-infrared spectrum, which could prove useful in biomedical and nanoelectronics applications.
"Some of the most sophisticated biomedical tests today -- such as MRI exams -- cannot be performed in a doctor's office because the equipment too large and too expensive to operate," said Smalley, University Professor at Rice. "Because nothing in the human body fluoresces in the near-infrared spectrum, and human tissue is fairly transparent at that spectrum, one can envision a test apparatus based on this technology that would be as inexpensive and simple to use as ultrasound."
Optical biosensors based on nanotubes could also be targeted to seek out specific targets within the body, such as tumor cells or inflamed tissues. Targeting would be achieved by wrapping the tubes with a protein that would bind only to the target cells. Since nanotubes fluoresce with a single wavelength of light, and different diameter nanotubes give off different wavelengths, it may be possible to tailor different sizes of tubes to seek specific targets, and thus diagnose multiple maladies in a single test using a cocktail of nanotubes.