Other researchers have demonstrated nanotubes that can detect light of specific wavelengths, including ultraviolet light, but never the entire visible spectrum of light. “This is a significant milestone,” says George Grüner, a professor of physics and head of the Nano-Biophysics Group at the University of California, Los Angeles, who was not involved in the Sandia work.

 

The light sensor inside a digital camera–known as a charge-coupled device–converts light into an electrical signal because as photons bombard silicon, they create electron holes in the material. In contrast, carbon-nanotube light sensors work in a similar way to biological eyes. The nanotubes are decorated with three kinds of chromophores–molecules that change shape in response to a particular wavelength of light. This change in shape results in a change in the chromophores’ orientations with respect to the nanotube that, in turn, changes the electrical conductivity of the nanotube in a way that can be measured to deduce the color and intensity of the light. The Sandia researchers used three different types of chromophores, which respond to either red, green, or blue bands of the visible-light spectrum.