14 DAY TRIAL // The age when experts will be able to observe and understand the interactions that take place between nanotubes and molecules at a very small level is not as far off as some have feared, an innovation from experts at the Sandia National Laboratories in the US shows. The team has managed to produce a special type of nanotubes, which is able to detect radiation in the full visible light spectrum. This could allow investigators to peer deep inside molecules and to understand how they react and transform to light, or when subjected to a number of other modifying factors.
The SNL scientists again turned to nature for the creation of their light-detecting nanotube, more specifically to the human eye. When light falls on our retinas, it initiates a number of cascade processes, which trigger chemical and electrical impulses that eventually are turned into the electricity that flows to our brain. Improving on this concept, the American experts equipped their nanotubes, which were in the 1 to 10 nm range, with cromophores. When struck by light, these formations undergo a slight chemical shift, and thus modify a threshold on a transistor made entirely from a single-walled carbon nanotube.
“In our eyes, the neuron is in front of the retinal molecule, so the light has to transmit through the neuron to hit the molecule. We placed the nanotube transistor behind the molecule – a more efficient design,” Xinjian Zhou, an SNL researcher who has been part of the team that created the new devices, explains. Their study, entitled “Color Detection Using Chromophore-Nanotube Hybrid Devices,” is published in a recent edition of the scientific journal Nano Letters.
The construction of the device itself was very difficult, especially the part where they had to create a transistor from a carbon nanotube. After depositing the structure on a silicon wafer, the team used a process called photolithography to define intricate electric paths and circuits on the tube. Basically, this means that they used light to etch the desired patterns, in such a manner that the carbon nanotube would act precisely like its standard counterparts.
Other researchers had to synthesize chromophore molecules that would respond to the red, green, and orange light “bands” in the visible spectrum. This was essential to the success of the project, as earlier attempts of creating light-sensitive nanotubes only succeeded in identifying a narrow wavelength of light, and only at laser-intensity.