Molecular Voyeurism: coming to a microscope near you

The development of atomic force microscope and scanning tunneling microscopes (STM) provide resolution that no other imaging technique can touch. These microscope techniques have progressed to the point that if an atom is dropped onto a specially prepared surface, called atomically flat, then the microscope will provide you with a picture of the atom—the proverbial red blob on a black background. The same is true of small molecules, where each atom is imaged and the molecular structure can be clearly seen. However, getting a picture out takes time, so a complete picture tends to be a time average of the molecule. What that really means is that researchers only get clear pictures of molecules that sit still.

In the Brevia section of Science, researchers are reporting imaging of the step-wise motion of a single molecule. To achieve this, the scientists fixed carbon nanotubes of various widths to a surface. They then deposited hydrocarbon molecules in the carbon nanotubes. This confines the molecules to motion in one dimension, which is important to keep the molecule within the field of view of the STM. They show that some hydrocarbons stick and no motion is observed, however, others moved slowly along the carbon nanotube (the movies are very blurry).

So is this a big advance in microscopy? No, but it is a nice demonstration of single molecule imaging. To put this in context, researchers in the nanotechnology area want to make small molecules that move in a controlled way along a surface. To do this, it will help to be able to observe how such motion works in one dimension—giving chemists more knowledge with which to choose functional groups from their catalog.