Hachtel Jordan A, Huang Jingsong, Popovs Ilja, Jansone-Popova Santa, Keum Jong K, Jakowski Jacek, Lovejoy Tracy C, Dellby Niklas, Krivanek Ondrej L, Idrobo Juan Carlos
Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Computational Sciences and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Science. 2019 Feb 1;363(6426):525-528. doi: 10.1126/science.aav5845.
The identification of isotopic labels by conventional macroscopic techniques lacks spatial resolution and requires relatively large quantities of material for measurements. We recorded the vibrational spectra of an α amino acid, l-alanine, with damage-free "aloof" electron energy-loss spectroscopy in a scanning transmission electron microscope to directly resolve carbon-site-specific isotopic labels in real space with nanoscale spatial resolution. An isotopic red shift of 4.8 ± 0.4 milli-electron volts in C-O asymmetric stretching modes was observed for C-labeled l-alanine at the carboxylate carbon site, which was confirmed by macroscopic infrared spectroscopy and theoretical calculations. The accurate measurement of this shift opens the door to nondestructive, site-specific, spatially resolved identification of isotopically labeled molecules with the electron microscope.
用传统的宏观技术识别同位素标记缺乏空间分辨率，并且需要相对大量的材料用于测量。我们在扫描透射电子显微镜中使用无损的“远距”电子能量损失光谱记录了α氨基酸L-丙氨酸的振动光谱，以在真实空间中以纳米级空间分辨率直接分辨碳位点特异性同位素标记。在羧酸盐碳位点的C标记L-丙氨酸中，观察到C-O不对称拉伸模式下同位素红移为4.8±0.4毫电子伏特，这通过宏观红外光谱和理论计算得到了证实。这种位移的精确测量为用电子显微镜对同位素标记分子进行无损、位点特异性、空间分辨的识别打开了大门。
