A dust grain showing the nanofoam inside or a diatom with the individual mathematical designs inside is obviously noticeable. A group led by CFEL scientists Saa Bajt and Henry Chapman was able to image these structures without damaging them by using high-energy X-rays from the PETRA III synchrotron light source at DESY.
With little to no damage to the sample, their new method produces high-resolution X-ray images of dried biological material that has not been frozen, coated, or otherwise altered before. This technique, which is also used to scan luggage at airports, can produce images of the material with a resolution of one nanometer.
The unique method enables imaging to be carried out at less than one percent of the specimen’s X-ray damage threshold by making use of high-energy X-rays that are intensely focused through a collection of novel diffractive lenses. The outcomes, which uncover this technique as a promising device for more splendid cutting-edge light sources, for example, the arranged update project PETRA IV, have been distributed in the diary Light: Applications and Science.
“We used Compton scattering and discovered that the amount of energy deposited into a sample per number of photons detected is lower than with these other methods.”
Chapman, who is a leading scientist at DESY,
There are many different ways that X-ray light interacts with biological material, most of which are determined by the light’s energy and intensity. X-ray imaging of biological samples is constrained by radiation damage, which can range from minor structural changes to complete degradation.
At low energies, the sample’s atoms primarily absorb the X-rays, which cause their electrons to absorb the energy and escape from the atoms, causing damage to the sample. Pictures utilizing these low-energy X-beams in this way map out the example’s assimilation of the radiation. X-ray photons “bounce” off of the material like billiard balls without depositing their energy in a process known as elastic scattering at higher energies, where absorption is less likely.
Strategies like crystallography or ptychography utilize this communication. However, absorption can still occur, resulting in damage to the sample. There is, however, a third interaction: Compton scattering, in which the target material absorbs only a small amount of the X-ray energy. Because it requires even higher X-ray energies where there haven’t been any high-resolution lenses before, Compton scattering has been largely overlooked as a viable method of X-ray microscopy.
Chapman, who is a leading scientist at DESY, a professor at Universität Hamburg, and the inventor of various X-ray techniques at synchrotrons and free-electron lasers, states, “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.”
The sample’s low dose made it difficult to develop lenses that would be suitable. All materials are exposed to high-energy X-rays, which are barely bent or refracted for focusing. Multilayer Laue lenses, a new type of refractive lens, were developed under the direction of Bajt, who is a group leader at CFEL. These new optics involve north of 7300 nanometer-dainty substituting layers of silicon carbide and tungsten carbide that the group used to develop a holographic optical component that was sufficiently thick to productively concentrate the X-beam bar.
The team imaged a variety of biological materials by detecting Compton scattering data as the sample passed through the focused beam with this lens system and the PETRA III beamline P07 at DESY. In this mode of scanning microscopy, a very bright source is needed, and the brighter the source, the better the image resolution.
PETRA III is one of the synchrotron radiation offices overall that is brilliant enough at high X-beam energies to have the option to secure pictures this way in a sensible time. With the PETRA IV facility, which is planned, the technique could reach its full potential.
A cyanobacterium, a diatom, and even a pollen grain taken right outside the lab—”a very local specimen,” Bajt chuckles—were used as samples by the team to test the method. Each sample had a resolution of 70 nanometers.
In addition, Compton X-ray microscopy achieved the same resolution with a 2000 times lower X-ray dose when compared to images obtained from a pollen sample that were comparable using a conventional coherent-scattering imaging method at an energy of 17 keV. “We could not see any trace of where the beam had come into contact with them when we re-examined the specimens using a light microscope after the experiment,” she explains, indicating that no radiation damage was left behind.
Chapman asserts, “These results could even be better.” Because the sample emits X-rays in all directions, an ideal spherical detector would be used for this kind of experiment. In a way, it’s a piece like a molecule’s physical science impact try, where you want to gather information every which way.”
Chapman also noted that, in comparison to the other images, the one of the cyanobacteria has relatively few features. However, the data indicate that up to a resolution of 10 nm, without damage, individual organelles and even three-dimensional structures would become visible at a brightness higher than that of the planned PETRA IV upgrade. According to Bajt, the only limitation of this method was not the method itself but rather the source, specifically its brightness.
The method could then be used to complement cryo-electron microscopy and super-resolution optical microscopy by imaging whole unsectioned cells or tissue with a brighter source. It could also be used to track nanoparticles within a cell, such as by directly observing drug delivery. This method is ideal for non-biological applications as well due to the characteristics of Compton scattering, such as investigating the mechanics of battery charging and discharging.
According to Bajt, “there is much to explore going forward” due to the fact that “nothing like this technique has been in the literature yet.”
More information: Tang Li et al, Dose-efficient scanning Compton X-ray microscopy, Light: Science & Applications (2023). DOI: 10.1038/s41377-023-01176-5
