Detecting single atoms of calcium and iron in biological structures by electron energy-loss spectrum-imaging

被引:57
作者
Leapman, RD [1 ]
机构
[1] NIH, Div Bioengn & Phys Sci, ORS, Bethesda, MD 20892 USA
来源
JOURNAL OF MICROSCOPY-OXFORD | 2003年 / 210卷
关键词
calcium; detection limits; electron energy-loss spectroscopy; iron; macromolecular assembly; scanning transmission electron microscope; spectrum-imaging;
D O I
10.1046/j.1365-2818.2003.01173.x
中图分类号
TH742 [显微镜];
学科分类号
摘要
As techniques for electron energy-loss spectroscopy (EELS) reach a higher degree of optimization, experimental detection limits for analysing biological structures are approaching values predicted by the physics of the electron scattering. Theory indicates that it should be possible to detect a single atom of certain elements like calcium and iron contained in a macromolecular assembly using a finely focused probe in the scanning transmission electron microscope (STEM). To test this prediction, EELS elemental maps have been recorded with the spectrum-imaging technique in a VG Microscopes HB501 STEM coupled to a Gatan Enfina spectrometer, which is equipped with an efficient charge-coupled device (CCD) array detector. By recording spectrum-images of haemoglobin adsorbed onto a thin carbon film, it is shown that the four heme groups in a single molecule can be detected with a signal-to-noise ratio of similar to10:1. Other measurements demonstrate that calcium adsorbed onto a thin carbon film can be imaged at single atom sensitivity with a signal-to-noise ratio of similar to5:1. Despite radiation damage due to the necessarily high electron dose, it is anticipated that mapping single atoms of metals and other bound elements will find useful applications in characterizing large protein assemblies.
引用
收藏
页码:5 / 15
页数:11
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