Tiny ruler to measure macromolecular movement

June 17, 2011

The 3-D plasmon ruler is constructed from five gold nanorods in which one nanorod (red) is placed perpendicular between two pairs of parallel nanorods (yellow and green).

Paul Alivisatos of the Lawrence Berkeley National Laboratory and colleagues have designed a first-of-its-kind ruler capable of measuring the configuration and movement of macromolecules, such as DNA.

The researchers constructed an “H”-shaped device out of five gold nanorods, the length and position of each of which could be controlled. They then looked for changes in spectra associated with plasmon coupling — the tendency for waves of free electrons associated with metallic nanoparticles to interact with each other.

As a molecule pushes or pulls pieces of the device, plasmons in the rods interact in distinct ways. By measuring the light scattered by the plasmon interactions, the researchers were able to deduce how the ruler, and anything attached to it, moves, in three dimensions.

The researchers say the rulers could be used to study protein folding and how DNA molecules interact with enzymes.

Na Liu, Mario Hentschel, Thomas Weiss, A. Paul Alivisatos, and Harald Giessen. Three-Dimensional Plasmon Rulers, Science 17 June 2011: 1407-1410. [DOI:10.1126/science.1199958]