MSGID: 1:317/3 6476cd8d   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    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   
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   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).   
      
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   Story Source: Materials provided by   
   Deutsches_Elektronen-Synchrotron_DESY. Note: Content may be edited for   
   style and length.   
      
      
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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   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/05/230530124743.htm   
      
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