Vision molecules change shape inside nanotubes

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17 July 2007 NanoTechWeb
Vision molecules change shape inside nanotubes

Belle Dumé

High-resolution images of shape changes in retinal molecules – important for vision – may help us to understand how we see, report researchers in Japan. Using a transmission electron microscope (TEM), Kazu Suenaga and colleagues at the National Institute of Advanced Industrial Science and Technology (AIST) imaged a single retinal molecule by attaching it to a carbon-60 molecule trapped inside a carbon nanotube. The work might also eventually lead to devices that mimic eyes, says the team.

When retinal molecules are stimulated by light, they change shape – going from being bent (cis) to straight (trans). This shape change triggers a cascade of biochemical reactions that ultimately results in an electrical impulse being sent along the optic nerve, so allowing us to see.

To investigate this mechanism, Suenaga and colleagues began by attaching a single retinal molecule to a carbon fullerene molecule so that they could put the hybrid Ret-C60 into a single-walled carbon nanotube. In this way, the nanotube acts as a "sample holder".

A scheme of the molecules in the experiment. The cis and trans retinal chromophores attached to the C60 fullerenes inside nanotubes are shown. (Credit: K Suenaga)

Next, the researchers equipped a high-resolution TEM with an aberration corrector, which allows for a higher spatial resolution without the need to increase the microscope's accelerating voltage above 120 kV. This moderate voltage, and the fact that the sample is protected inside a nanotube, ensures that the biomolecules are not damaged by the electron beam in the microscope

The researchers achieved a resolution of 0.14 nm, which is the same as the distance between two carbon molecules. This meant they were able to see the C–C bonds in the retinal molecule changing shape from cis to trans.

"The dynamic behaviour of retinal is responsible for vision," explained Suenanga. "Our experiment therefore allows us to observe how we see with our eyes at the molecular level. People say that human eyes are one of the most efficient detectors. If we can correctly modify the retinal molecules at the single-molecule level, we may be able to fabricate a device that mimics eyes."

Since the samples are not damaged in the microscope, the team says that its technique could be used to visualize other molecules, not just retinal. "For example, to investigate molecular recognition events such as protein folding or steric hindrance," said Suenaga.

The researchers reported their work in Nature Nanotechnology.


Story posted: 17th July 2007
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