Single Nanotubes Display Steady, Narrow Emissions

Reporting in the Sept. 4 issue of Science, researchers at the University of Rochester in New York and at Universität Siegen in Germany describe their identification of constant, narrow-linewidth fluorescence from individual single-walled carbon nanotubes. The phenomenon may have uses in the development of single-photon emitters for quantum cryptography or of single-molecule sensors for biological applications.

Using single-molecule fluorescence spectroscopy, the researchers excited individual 200- to 300-nm-long nanotubes at room temperature with 632.8-nm light from a HeNe laser. At excitation powers of less than 70 kW/cm², the nanotubes produced near-IR signals with a linewidth of 23 meV that did not fluctuate on time scales of 40 ms to 100 s. In contrast, single quantum dots and most molecules display fluorescent responses that are intermittent or that blink.

Significantly, the spectra of nanotubes with identical structures differed, which the researchers suggest may be a response to their surroundings. This effect has potential for use in single-molecule studies, by monitoring the particular changes in a nanotube's emission as it comes in contact with a biological molecule.