New sensor detects ever smaller nanoparticles
Novel optical resonator can track the movement of nanoparticles in space


Date:
November 11, 2021
Source:
Karlsruher Institut fu"r Technologie (KIT)
Summary:
Nanoparticles are omnipresent in our environment: Viruses in ambient
air, proteins in the body, as building blocks of new materials for
electronics, or in surface coatings. Visualizing these smallest
particles is a problem: They are so small that they can hardly be
seen under an optical microscope. Researchers have now developed
a sensor that not only detects nanoparticles, but also determines
their condition and tracks their movements in space.



FULL STORY ========================================================================== Conventional microscopes produce enlarged images of small structures or
objects with the help of light. Nanoparticles, however, are so small that
they hardly absorb or scatter light and, hence, remain invisible. Optical resonators increase the interaction between light and nanoparticles:
They capture light in smallest space by reflecting it thousands of
times between two mirrors. In case a nanoparticle is located in the
captured light field, it interacts thousands of times with the light
such that the change in light intensity can be measured. "The light
field has various intensities at different points in space. This allows conclusions to be drawn with respect to the position of the nanoparticle
in the three-dimensional space," says Dr. Larissa Kohler from KIT's Physikalisches Institut.


========================================================================== Resonator Makes Movements of Nanoparticles Visible And not only that:
"If a nanoparticle is located in water, it collides with water molecules
that move in arbitrary directions due to thermal energy. These collisions
cause the nanoparticle to move randomly. This Brownian motion can now
also be detected," the experts adds. "So far, it has been impossible for
an optical resonator to trackthe motion of a nanoparticle in space. It
was only possible to state whether or not the particle is located in the
light field," Kohler explains. In the novel fiber-based Fabry-Pe'rot
resonator, highly reflecting mirrors are located on the ends of glass
fibers. It allows us to derive the hydrodynamic radius of the particle,
that is the thickness of the water surrounding the particle, from its three-dimensional movement. This is important, because this thickness
changes the properties of the nanoparticle.

"As a result of the hydrate shell, it is possible to detect nanoparticles
that would have been too small without it," Kohler says. Moreover, the
hydrate shell around proteins or other biological nanoparticles might
have an impact on biological processes.

Sensor Provides Insight into Biological Processes A potential
application of the resonator may be the detection of three-
dimensional motion with high temporal resolution and characterization
of optical properties of biological nanoparticles, such as
proteins, DNA origami, or viruses. In this way, the sensor might
provide insights into not yet understood biological processes. (mex) ========================================================================== Story Source: Materials provided by
Karlsruher_Institut_fu"r_Technologie_(KIT). Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Larissa Kohler, Matthias Mader, Christian Kern, Martin Wegener,
David
Hunger. Tracking Brownian motion in three dimensions and
characterization of individual nanoparticles using a fiber-based
high-finesse microcavity.

Nature Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-26719-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211111130248.htm

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