New X-ray imaging technique: a breakthrough in structural research
For the first time, a team of international scientists has used a new X-ray imaging technique called flash diffractive imaging. It is hoped that in the future, the technique will revolutionise structure research by enabling researchers to obtain nanometre resolution images of viruses, cells and even proteins. The study, which was partly funded by the EU's Sixth Framework Programme, is published in the latest online edition of the journal Nature Physics. Until now, X-ray imaging experiments have been hampered by the fact that the very radiation used to create the image destroys the sample. 'However, there is a way to circumvent the problem,' said Prof Janos Hajdu of Uppsala University, one of the authors of the study. 'Take the image faster than the relevant damage processes.' Theories predicted that a single diffraction pattern could be recorded from a large macromolecule, virus or cell by firing an extremely short, very bright X-ray pulse. 'There were two big questions however,' commented Prof Hajdu. 'Can an interpretable image be recorded from a single free-electron laser pulse before the sample is turned into a plasma by the X-rays? And does the diffraction pattern really carry structural information about the object before the object is destroyed?' Computer simulations had suggested that a near-atomic resolution structure could be achieved by well-thought out choice of pulse length and intensity of X-ray length before the sample is destroyed. To test their theory, the researchers used the soft X-ray free-electron laser FLASH at DESY - the German Electron Synchrotron. 'As the only soft X-ray laser providing extremely bright coherent pulses of just 25 femtoseconds duration, FLASH is the world's first radiation source to permit this and other proof-of-principle experiments,' said Prof Jochen Schneider, DESY's Research Director. 'Due to pioneering efforts at DESY, FLASH is also the first user facility in this area that is available to a broad scientific community.' In their experiment, the researchers directed an intense free-electron laser pulse with a wavelength of 32 nm and a duration of just 25 femtoseconds at their sample, a three micrometre wide picture of two stick people walking beneath a sun, which had been cut into a thin membrane with an ion beam. The energy of the laser quickly heated the sample to around 60,000 Kelvin, causing it to vaporise, but before the sample was destroyed, the scientists were able to record a diffraction pattern. Computer algorithms successfully translated this pattern back into the original image. The resolution of the image obtained in this experiment, which used soft X-rays, was 62nm, but the researchers are already looking at the potential of 'hard' X-rays which have a much shorter wavelength. In the paper they note that the same experiment carried out using a hard-X-ray free electron laser operating at a wavelength of 15nm would yield a resolution just 0.3nm. The scientists also note that the technique will enable them to study the structure of more proteins than is currently possible as it does not require the crystallisation of the sample; many biomolecules resist crystallisation. 'The entire collaboration is very excited by these results,' commented Prof. Hajdu. 'Flash imaging has implications for studying molecular structures in biology in a whole new way. A scientific community is forming to achieve these goals by combining biology with atomic, plasma and astrophysics for the first time.' However, the scientists will have to wait awhile before they can test their new technique on hard X-rays, as the facilities which will produce these are still being built. The Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center in the US is due to become operational in 2009. Meanwhile construction is due to start in Hamburg next year on the European X-ray Free Electron Laser (XFEL). The facility, which is due to become operational in 2013 was highlighted in the recently published European Roadmap for Research Infrastructures.
Countries
Germany, Sweden, United States