Vortex microscope sees more than ever before
In a first for imaging, new microscope captures details, 3D motion of molecules in liquid

Date:
February 17, 2022
Source:
Washington University in St. Louis
Summary:
A new imaging technology uses polarized 'optical vortices' to
provide a detailed, dynamic view of molecules in motion.



FULL STORY ========================================================================== Understanding the nitty gritty of how molecules interact with each other
in the real, messy, dynamic environment of a living body is a challenge
that must be overcome in order to understand a host of diseases, such
as Alzheimer's.


========================================================================== Until now, researchers could capture the motion of a single molecule,
and they could capture its rotation -- how it tumbles as it bumps into surrounding molecules -- but only by compromising 3D resolution.

Now, the lab of Matthew Lew, assistant professor of electrical and
systems engineering at the McKelvey School of Engineering at Washington University in St. Louis, has developed an imaging method that provides an unprecedented look at a molecule as it spins and rolls through liquid, providing the most comprehensive picture yet of molecular dynamics
collected using optical microscopes.

The research was published in a special issue of the Journal of
Physical Chemistry B. The Feb. 17, 2022, Festschrift is dedicated to
Nobel laureate William E. (W.E.) Moerner, an imaging pioneer, Washington University alumnus and mentor to more than 100 students over the years, including Lew.

Moerner was the first person to observe optical signatures of a single molecule; previously, researchers weren't sure it was even possible to
measure such signals.

Now Lew's lab is the first to be able to visualize the orientation and direction of a molecule's rotational movement -- how it spins and wobbles
- - while it's in a liquid system.



==========================================================================
The new imaging technology, called a vortex microscope, relies on a
particular type of light: a polarized optical vortex.

"You can bend the light in a certain way so that the photons are spinning
along their path," Lew said. Instead of a straight "beam of light,"
this optical vortex is shaped more like a corkscrew. It's created by
shining light through a helical-shaped lens, the top of which is uneven, sloping downward into a spiral.

The microscope also splits the light into two different directions of polarization, providing insight into the direction of the wobble of
nano-sized light sources, the molecules in the sample.

For their experiments, Lew and first author Tianben Ding, then
a postdoctoral researcher in Lew's lab, looked at amyloid beta
fibers. Clumps of these proteins, found in the brain, are associated
with Alzheimer's disease. The team added fluorescent tracer molecules
to the fibers.

The tracers' job was to probe the surfaces of the amyloid beta
fibers. Each time a tracer bumped into a fiber, it emitted a light.



==========================================================================
The light carried information about its interaction with the fiber. After
it passed through the lens, that information was translated by an
algorithm developed by Lew's team.

An optical vortex is not a "point" of light, but it's spread out in more
of a donut shape. Based on the donut's properties -- is it stretched
out along a certain axis, or darker in some places? -- the algorithm
can infer seven distinct properties of the tracer molecule, including
its position and direction.

Because the team used a polarized optical vortex, they also can determine
the direction of the wobble, a novel ability of the vortex microscope.

The ways in which the molecule interacts with the fiber can, in turn,
help paint a picture of the fiber's motion and topology.

Putting it all together, the vortex microscope offers a detailed look
into how the surfaces of these amyloid beta fibers interact with each
other -- how they bounce off each other or attach -- and how their
surfaces affect whether or not they begin to aggregate.

"This is the first time we can measure these very detailed dynamics of
how molecules move and rotate inside liquid systems," Lew said.

========================================================================== Story Source: Materials provided by
Washington_University_in_St._Louis. Original written by Brandie
Jefferson. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Tianben Ding, Matthew D. Lew. Single-Molecule Localization
Microscopy of
3D Orientation and Anisotropic Wobble Using a Polarized Vortex
Point Spread Function. The Journal of Physical Chemistry B, 2021;
125 (46): 12718 DOI: 10.1021/acs.jpcb.1c08073 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220217141309.htm

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