Dual microscopy method studies single biological molecules

Pairing atomic force microscopy (AFM) and optical microscopy, researchers have developed a way to complete 3D measurements of single biological molecules with unprecedented accuracy and precision.

Iowa State University and Ames Laboratory researchers Sanjeevi Sivasankar, Chi-Fu Yen, and Hui Li have invented a microscopy method—standing wave axial nanometry (SWAN)—to study single biological molecules
Iowa State University and Ames Laboratory researchers Sanjeevi Sivasankar, Chi-Fu Yen, and Hui Li have invented a microscopy method—standing wave axial nanometry (SWAN)—to study single biological molecules

Pairing atomic force microscopy (AFM) and optical microscopy, researchers in the Ames Laboratory at Iowa State University (Ames, IA) have developed a way to complete 3D measurements of single biological molecules with unprecedented accuracy and precision. The new method enables height measurements (the z axis) down to the nanometer without custom optics or special surfaces for the samples.

The research program, led by Sanjeevi Sivasankar, an assistant professor of physics and astronomy and an associate of the U.S. Department of Energy’s Ames Laboratory, aims to learn how biological cells adhere to each other and to develop new tools to study those cells.

The researchers' method—standing wave axial nanometry (SWAN)—entails attaching 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.

Iowa State University and Ames Laboratory researchers Sanjeevi Sivasankar, Chi-Fu Yen, and Hui Li have invented a microscopy method—standing wave axial nanometry (SWAN)—to study single biological moleculesIowa State University and Ames Laboratory researchers Sanjeevi Sivasankar, Chi-Fu Yen, and Hui Li have invented a microscopy method—standing wave axial nanometry (SWAN)—to study single biological molecules
Iowa State University and Ames Laboratory researchers Sanjeevi Sivasankar, Chi-Fu Yen, and Hui Li have invented a microscopy method—standing wave axial nanometry (SWAN)—to study single biological molecules. (Image courtesy of Bob Elbert)

The research team, using fluorescent nanospheres and single strands of DNA to test their instrument, reported measurements of a molecule’s height accurate to <1 nm in their paper. They also report that measurements can be taken again and again to a precision of 3.7 nm.

Users who could benefit from the technology include medical researchers who need high-resolution data from microscopes. Sivasankar thinks the technology has commercial potential and is confident it will advance his own work in single-molecule biophysics.

Details of the technology have been published in Nano Letters; for more information, please visit http://pubs.acs.org/doi/abs/10.1021/nl301542c.

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