Maigné Alan, Wolf Matthias
Molecular Cryo-Electron Microscopy Unit, Okinawa Institute of Science and Technology Graduate School, Okinawa Prefecture, Kunigami District, Onna, Tancha 191-1, 904-0495,Japan.
Microscopy (Oxf). 2018 Mar 1;67(suppl_1):i86-i97. doi: 10.1093/jmicro/dfx088.
Since the development of parallel electron energy loss spectroscopy (EELS), charge-coupled devices (CCDs) have been the default detectors for EELS. With the recent development of electron-counting direct-detection cameras, micrographs can be acquired under very low electron doses at significantly improved signal-to-noise ratio. In spectroscopy, in particular in combination with a monochromator, the signal can be extremely weak and the detection limit is principally defined by noise introduced by the detector. Here we report the use of an electron-counting direct-detection camera for EEL spectroscopy. We studied the oxygen K edge of amorphous ice and obtained a signal noise ratio up to 10 times higher than with a conventional CCD.We report the application of electron counting to record time-resolved EEL spectra of a biological protein embedded in amorphous ice, revealing chemical changes observed in situ while exposed by the electron beam. A change in the fine structure of nitrogen K and the carbon K edges were recorded during irradiation. A concentration of 3 at% nitrogen was detected with a total electron dose of only 1.7 e-/Å2, extending the boundaries of EELS signal detection at low electron doses.
自从并行电子能量损失谱（EELS）发展以来，电荷耦合器件（CCD）一直是EELS的默认探测器。随着电子计数直接探测相机的最新发展，可以在非常低的电子剂量下以显著提高的信噪比获取显微照片。在光谱学中，特别是与单色仪结合使用时，信号可能极其微弱，检测限主要由探测器引入的噪声决定。在此，我们报告了将电子计数直接探测相机用于EEL光谱学的情况。我们研究了非晶冰的氧K边，获得的信噪比比传统CCD高出多达10倍。我们报告了应用电子计数来记录嵌入非晶冰中的生物蛋白质的时间分辨EEL光谱，揭示了在电子束照射时原位观察到的化学变化。在辐照过程中记录了氮K和碳K边精细结构的变化。仅用1.7 e-/Å2的总电子剂量就检测到了3 at%的氮浓度，扩展了低电子剂量下EELS信号检测的边界。
