PULSE Institute, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, USA.
Nat Commun. 2012;3:1276. doi: 10.1038/ncomms2288.
Diffractive imaging with free-electron lasers allows structure determination from ensembles of weakly scattering identical nanoparticles. The ultra-short, ultra-bright X-ray pulses provide snapshots of the randomly oriented particles frozen in time, and terminate before the onset of structural damage. As signal strength diminishes for small particles, the synthesis of a three-dimensional diffraction volume requires simultaneous involvement of all data. Here we report the first application of a three-dimensional spatial frequency correlation analysis to carry out this synthesis from noisy single-particle femtosecond X-ray diffraction patterns of nearly identical samples in random and unknown orientations, collected at the Linac Coherent Light Source. Our demonstration uses unsupported test particles created via aerosol self-assembly, and composed of two polystyrene spheres of equal diameter. The correlation analysis avoids the need for orientation determination entirely. This method may be applied to the structural determination of biological macromolecules in solution.
利用自由电子激光的衍射成像,可以从大量弱散射的相同纳米粒子中确定结构。超短、超亮的 X 射线脉冲可以捕捉到随机取向的粒子在时间上被冻结的瞬间,并且在结构损坏发生之前就停止了。由于小颗粒的信号强度减弱,因此需要同时涉及所有数据来合成三维衍射体积。在这里,我们首次应用三维空间频率相关分析,从在 Linac Coherent Light Source 上收集的、以随机和未知方向存在的几乎相同的、未经支撑的气溶胶自组装测试粒子的单个飞秒 X 射线衍射图样中进行这种合成,这些测试粒子由两个相同直径的聚苯乙烯球组成。相关分析完全避免了确定取向的需要。该方法可应用于溶液中生物大分子的结构测定。