Iowa State University and Ames Laboratory researchers, left to right, Sanjeevi Sivasankar, Chi-Fu Yen and Hui Li have invented microscope technology to study single biological molecules. Photo by Bob Elbert. |
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blending optical and atomic force microscope technologies, Iowa State
University and Ames Laboratory researchers have found a way to complete
3D measurements of single biological molecules with unprecedented
accuracy and precision.
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
U.S. Department of Energy’s Ames Laboratory.
Details
of the technology were recently published by the journal Nano Letters.
Co-authors of the study are 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.
The
project was supported by lab startup funds from Iowa State University
and a $120,075 grant from the Grow Iowa Values Fund, a state economic
development program.
Sivasankar’s
research program has two objectives: to learn how biological cells
adhere to each other and to develop new tools to study those cells.
That’s why the new microscope technology – called standing wave axial nanometry (SWAN) – was developed in Sivasankar’s lab.
Here’s
how the technology works: 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.
The
paper reports that measurements of a molecule’s height are accurate to
less than a nanometer. It also reports that measurements can be taken
again and again to a precision of 3.7 nm.
Sivasankar’s
research team used fluorescent nanospheres and single strands of DNA to
calibrate, test and prove their new instrument.
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.
“We
hope to use this technology to move that research forward,” he said.
“And in doing that, we’ll continue to invent new technologies.”
Fluorescence Axial Localization with Nanometer Accuracy and Precision
