Biological specimens imaged with X-rays without damage
Groundbreaking technique using a new kind of focusing lens overcomes
previous X-ray imaging limitations

Date:
May 30, 2023
Source:
Deutsches Elektronen-Synchrotron DESY
Summary:
Scientists have managed to image delicate biological structures
without damaging them. Their new technique generates high resolution
X-ray images of dried biological material that has not been frozen,
coated, or otherwise altered beforehand -- all with little to no
damage to the sample. This method, which is also used for airport
baggage scanning, can generate images of the material at nanometer
resolution.


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FULL STORY ==========================================================================
A pollen grain showing the nanofoam within or a diatom with the individual geometric structures inside clearly visible: Using high-energy X-rays
from the PETRA III synchrotron light source at DESY, a team led by
CFEL scientists Sasa Bajt and Henry Chapman has managed to image these structures without damaging them. Their new technique generates high
resolution X-ray images of dried biological material that has not been
frozen, coated, or otherwise altered beforehand -- all with little to
no damage to the sample. This method, which is also used for airport
baggage scanning, can generate images of the material at nanometre
resolution. Using high energy X-rays that are intensely focussed through
a set of novel diffractive lenses, the special technique allows imaging
to be performed at less than 1% of the X-ray damage threshold of the
specimen.

The results, which reveal this method as a promising tool for brighter
next- generation light sources such as the planned upgrade project PETRA
IV, have been published in the journal Light: Science & Applications.

X-ray light interacts with biological material in a variety of ways,
mostly depending on the energy and intensity of the light. At the same
time, radiation damage, such as small structural changes up to complete degradation of the sample, is the limiting factor during X-ray imaging of biological samples. At low energies, the X-rays are primarily absorbed
by the atoms in the sample, whose electrons take on the energy, causing
them to spring out of the atoms and cause damage to the sample. Images
using these low-energy X-rays thus map out the sample's absorption
of the radiation. At higher energies, absorption is less likely, and
a process called elastic scattering occurs, where the X-ray photons
"bounce" off of the matter like billiard balls without depositing their
energy. Techniques such as crystallography or ptychography use this interaction. Nevertheless, absorption can still occur, meaning damage
to the sample happens anyway. But there is a third interaction: Compton scattering, where the X-rays leave only a tiny amount of their energy
in the target material. Compton scattering had been largely ignored as a
viable method of X- ray microscopy, since it requires even higher X-ray energies where until now no suitable high-resolution lenses existed.

"We used Compton scattering and we figured out that the amount of energy deposited into a sample per number of photons that you can detect is
lower than using these other methods," says Chapman, who is a leading
scientist at DESY, a professor at Universita"t Hamburg, and inventor of different X-ray techniques at synchrotrons and free-electron lasers.

The advantage of low dose in the sample posed a challenge for making
suitable lenses. High-energy X-rays pass through all materials and
are hardly refracted, or bent, as needed for focussing. Bajt, who is a
group leader at CFEL, led efforts to develop a new kind of refractive
lens, called multilayer Laue lenses. These new optics comprise over
7300 nanometre-thin alternating layers of silicon carbide and tungsten
carbide that the team used to construct a holographic optical element
that was thick enough to efficiently focus the X- ray beam.

Using this lens system and the PETRA III beamline P07 at DESY, the team
imaged a variety of biological materials by detecting Compton scattering
data as the sample was passed through the focused beam. This mode of
scanning microscopy requires a very bright source -- the brighter,
the better -- which is focused to a spot that defines the image
resolution. PETRA III is one of the synchrotron radiation facilities
worldwide which is bright enough at high X-ray energies to be able to
acquire images this way in a reasonable time. The technique could reach
its full potential with the planned PETRA IV facility.

To test the method, the team used a cyanobacterium, a diatom, and even a
pollen grain collected directly outside the lab ("a very local specimen,"
Bajt laughs) as their samples, and achieved a resolution of 70 nanometres
for each.

Moreover, when compared with images obtained from a similar pollen sample
using a conventional coherent-scattering imaging method at an energy
of 17 keV, Compton X-ray microscopy achieved a similar resolution with
2000 times lower X- ray dose. "When we re-examined the specimens using
a light microscope after the experiment, we could not see any trace of
where the beam had come in contact with them," she explains -- meaning
no radiation damage was left behind.

"These results could even be better," Chapman says. "Ideally, an
experiment like this would use a spherical detector, because the X-rays
coming out of the sample go in every direction from the sample. In that
way, it's a bit like a particle physics collision experiment, where you
need to collect data in all directions." Additionally, Chapman pointed
out that the image of the cyanobacteria is relatively featureless as
compared to the others. However, the data indicate that at a higher
brightness, such as that of the planned PETRA IV upgrade, individual
organelles and even structures in three dimensions would become visible
-- up to a resolution of 10 nm without damage being a problem. "Really,
the only limitation of this technique was not the nature of the technique itself but rather the source, namely its brightness," says Bajt.

With a brighter source, the method could then be used for imaging whole unsectioned cells or tissue, complementing cryo-electron microscopy and
super- resolution optical microscopy, or for tracking nanoparticles within
a cell, such as for directly observing drug delivery. The characteristics
of Compton scattering makes this method ideal for non-biological uses as
well, such as examining the mechanics of battery charging and discharging.

"There hasn't been anything like this technique in the literature yet,"
says Bajt, "so there is much to explore going forward." The experiment involved researchers from DESY, CFEL, the Hamburg Centre for Ultrafast
Imaging excellence cluster (CUI) of the Universita"t Hamburg, and Lund University in Sweden.

DESY is one of the world's leading particle accelerator centres and investigates the structure and function of matter -- from the interaction
of tiny elementary particles and the behaviour of novel nanomaterials and
vital biomolecules to the great mysteries of the universe. The particle accelerators and detectors that DESY develops and builds at its locations
in Hamburg and Zeuthen are unique research tools. They generate the most intense X-ray radiation in the world, accelerate particles to record
energies and open up new windows onto the universe. DESY is a member of
the Helmholtz Association, Germany's largest scientific association, and receives its funding from the German Federal Ministry of Education and
Research (BMBF) (90 per cent) and the German federal states of Hamburg
and Brandenburg (10 per cent).

* RELATED_TOPICS
o Plants_&_Animals
# Extreme_Survival # Developmental_Biology # Biology #
Biotechnology
o Matter_&_Energy
# Physics # Optics # Detectors # Medical_Technology
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========================================================================== Journal Reference:
1. Tang Li, J. Lukas Dresselhaus, Nikolay Ivanov, Mauro Prasciolu,
Holger
Fleckenstein, Oleksandr Yefanov, Wenhui Zhang, David Pennicard,
Ann- Christin Dippel, Olof Gutowski, Pablo Villanueva-Perez,
Henry N. Chapman, Sasa Bajt. Dose-efficient scanning Compton
X-ray microscopy. Light: Science & Applications, 2023; 12 (1)
DOI: 10.1038/s41377-023-01176-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230530124743.htm

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