Tabletop x-ray laser TOOLS AND TECHNIQUES
A team of physicists has produced the first ultrafast tabletop laser that emits a beam of x-rays, which could help in the design and optimization of the nextgeneration of electronics and energy storage devices. They presented a real beam of photons with sufficient intensity for use as an effective tabletop x-ray light
source, despite only a small fraction of the laser light being converted into x-rays. Although many have tried to develop x-ray lasers at a reasonable size, they tended to need huge amounts of power, making them overly expensive and impractical. However, this study, by a team from the University of Colorado Boulder along with international colleagues, reported in the journal Science [Popmintchev et al., Science (2012) doi: 10.1126/ science.1218497], produced a tabletop device comprising of an x-ray tube that provides a bright beam of directed x-rays. The device efficiently combines over 5000 low-energy mid-infrared laser photons to generate each highenergy x-ray photon. It forces every atom in a multiatmosphere pressure gas to emit the x-rays. Although it was previously expected that the wavelength of light generated through such a process
would be limitied to a few dozen times shorter than the wavelength of visible light, this research has proved otherwise. The laser-like x-ray beam produces a beam of light with a wavelength over a 5000 times shorter, with the team still not having determined what the physical limit of the process might be. With x-ray wavelengths being 1000 times shorter than visible light and able to penetrate materials, the device could lead to innovative uses based on improved control of nanotechnology, particularly as imaging resolution is directly tied to wavelength – as x-rays have such a short wavelength they are effective in studies of very small objects. One possible application for the new device is in types of x-ray spectroscopy that benefit from very short light pulses; techniques which help explain how materials behave on very short timescales. The next step is to use this new type of light source in fundamental studies of material dynamics, as well as in x-ray imaging.
Bacterial chainmail exposed BIOMATERIALS The structure of a protective protein coat that The imaging process involved a combination of x-ray gives important clues as to how the remarkable feat of surrounds many bacteria has been unveiled by a team crystallography and electron microscopy (EM). A key self-assembly is achieved,” Howorka says. of international scientists. The findings could have step was the use of small antibodies – called nanobodies The subject of this study was the harmless soil bacterium potential uses in disease treatment and the development – to stabilise and crystallise single s-layer proteins so Geobacillus stearothermophilus, but the team expects of vaccines and novel nanomaterials. they could be x-rayed. “To look at the whole s-layer, we their combination technique to work on a range of The existence of a bacterial protein coat, called an used EM and fitted the structure of the s-layer protein different bacteria such as the superbug Clostridium s-layer, has been known for some time – but little determined by x-ray crystallography into the projection difficile and Bacillus anthraci, the bacterium responsible concerning its structure or function has been reported. maps obtained from the EM,” explains Han Remaut, for anthrax. “This provides a real opportunity to find “This is the first time that a bacterial s-layer protein team leader at the Flanders Institute for Biotechnology chinks in the bacterial armour that would allow precise has been fully characterised at atomic resolution,” – VIB in Belgium. “The atomistic picture of the lattice targeting of antibiotics against these challenging team member Stefan Howorka from pathogens,” says Howorka. University College London, UK, told An in depth knowledge of the self Materials Today. assembly process means that the s-layer The imaging work, published in Nature could also be exploited as a vaccine [Baranova, E., et al., Nature (2012) doi: carrier in the future. “Peptide sequences 10.1038/nature11155], shows that the from pathogens could be inserted coating is designed like a miniature into the protein lattice to generate a suit of armour. “The coat is composed powerful vaccine. As it is known that of identical protein units which hook presenting immunogenic peptide at high together like a chainmail,” says Howorka. density can boost the immune response,” “This remarkably optimised layer not Howorka explains. “Additionally, the only provides a tough but flexible coat porous protein lattice could be applied of armour to protect the bacterium, but as an isoporous membrane for high-end is also permeable allowing nutrients and filtration applications.” The protective coating of a simple soil bacterium resembles chainmail. Courtesy of Han Remaut. other substances to diffuse in or out.” Nina Notman
JULY-AUGUST 2012 | VOLUME 15 | NUMBER 7-8