New tool to measure single biological molecules developed

Researchers from Iowa State University and Ames Laboratory in the US have blended optical and atomic force microscope technologies to develop complete 3-Dimensional measurements of single biological molecules.

The new microscope technology is called standing wave axial nanometry (SWAN).

Existing technologies allow researchers to measure single molecules on the x and y axes of a 2-D plane. The new technology allows researchers to make height measurements (the z axis) down to the nanometer- just a billionth of a meter- without custom optics or special surfaces for the samples.

"This is a completely new type of measurement that can be used to determine the z position of molecules," said Sanjeevi Sivasankar, an Iowa State assistant professor of physics and astronomy and an associate of the US Department of Energy's Ames Laboratory.

The study published in the journal Nano Letters was co-authored by Sivasankar; Hui Li, an Iowa State post-doctoral research associate in physics and astronomy and an associate of the Ames Laboratory; and Chi-Fu Yen, an Iowa State doctoral student in electrical and computer engineering and a student associate of the Ames Laboratory.

Researchers attach a commercial atomic force microscope to a single molecule fluorescence microscope. The tip of the atomic force microscope is positioned over a focused laser beam, creating a standing wave pattern.

A molecule that has been treated to emit light is placed within the standing wave. As the tip of the atomic force microscope moves up and down, the fluorescence emitted by the molecule fluctuates in a way that corresponds to its distance from the surface. That distance can be compared to a marker on the surface and measured.

"We can detect the height of the molecule with nanometer accuracy and precision," Sivasankar said in a statement.