Researchers demonstrate label-free super-resolution microscopy
Imaging method measures particle size and position with nanometer
precision

Date:
April 21, 2022
Source:
Optica
Summary:
Researchers describe a new measurement and imaging approach that can
resolve nanostructures smaller than the diffraction limit of light
without requiring any dyes or labels. The work is a modification
of laser scanning microscopy. It represents an important advance
toward a new and powerful microscopy method that could be used to
see the fine features of complex samples beyond what is possible
with conventional microscopes and techniques.



FULL STORY ========================================================================== Researchers have developed a new measurement and imaging approach that
can resolve nanostructures smaller than the diffraction limit of light
without requiring any dyes or labels. The work represents an important
advance toward a new and powerful microscopy method that could one day be
used to see the fine features of complex samples beyond what is possible
with conventional microscopes and techniques.


==========================================================================
The new method, described in Optica, is a modification of laser scanning microscopy, which uses a strongly focused laser beam to illuminate
a sample.

The researchers expanded on the technique by measuring not only
the brightness, or intensity, of the light after it interacts with a
specimen under study, but also detecting other parameters encoded in
the light field.

"Our approach could help extend the microscopy toolbox used to study nanostructures in a variety of samples," said research team leader
Peter Banzer from the University of Graz in Austria. "In comparison
to super-resolution techniques based on a similar scanning approach,
our method is fully non- invasive, meaning it doesn't require any
fluorescent molecules to be injected into a specimen before imaging."
The researchers show that they can measure the position and sizes of
gold nanoparticles with an accuracy of several nanometers, even when
multiple particles were touching.

"Our novel approach to laser-scanning microscopy could close the
gap between conventional microscopes with limited resolution and super-resolution techniques that require modification of the specimen
under study," said Banzer.

Capturing more from light In laser-scanning microscopy, a light beam is
scanned across the sample and the transmitted, reflected or scattered
light coming from the sample is measured.

Although most microscopy methods measure the intensity, or brightness, of
light coming from the sample, a great deal of information is also stored
in other characteristics of the light such as its phase, polarization
and the scattering angle. To capture this additional information,
the researchers examined the spatial resolution of the intensity and polarization information.

"The phase and polarization of light, together with its intensity,
vary spatially in a way that incorporates fine details about the sample
with which it interacts -- much like the shadow of an object tells us
something about the shape of the object itself," said Banzer. "However,
much of this information is ignored if only the overall light power is
measured after the interaction." They demonstrated the new approach
by using it to study simple samples containing metallic nanoparticles
of different sizes. They did this by scanning the area of interest and
then recording polarization and angle-resolved images of the transmitted
light. The measured data was evaluated using an algorithm that creates a
model of the particles that automatically adapts to resemble the measured
data as precisely as possible.

"Although the particles and their distances were much smaller than the resolution limit of many microscopes, our method was able to resolve
them," said Banzer. "In addition, and even more importantly, the algorithm
was able to provide other parameters about the sample such as the precise
size and position of the particles." The researchers are now working to
adapt the method so that it could be used with more complex samples. The functionality of the approach can also be expanded by tailoring the
structure of the light that interacts with the sample and incorporating artificial intelligence-based approaches into the image processing
steps. On the detection side, the authors, together with other experts,
are currently developing a special camera as part of a European project
called SuperPixels. This next-generation detection device will becapable
of resolving polarization and phase information in addition to intensity.

"Our study is another demonstration of the pivotal role that the structure
of light can play in the field of optics and light-based technologies,"
said Banzer. "Many intriguing applications and phenomena have been
demonstrated already, but there is more to come."

========================================================================== Story Source: Materials provided by Optica. Note: Content may be edited
for style and length.


========================================================================== Related Multimedia:
* Nanostructures_smaller_than_diffraction_limit_of_light ========================================================================== Journal Reference:
1. Jo"rg S. Eismann, Peter Banzer. Sub-diffraction-limit Fourier-plane
laser
scanning microscopy. Optica, 2022; 9 (5): 455 DOI:
10.1364/OPTICA.450712 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/04/220421100140.htm

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