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Detecting single atoms of calcium and iron in biological structures by electron energy‐loss spectrum‐imaging
Author(s) -
Leapman R. D.
Publication year - 2003
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1046/j.1365-2818.2003.01173.x
Subject(s) - scanning transmission electron microscopy , atom (system on chip) , electron energy loss spectroscopy , electron , chemistry , detector , spectrometer , transmission electron microscopy , microscope , atomic physics , molecular physics , materials science , analytical chemistry (journal) , optics , nanotechnology , physics , quantum mechanics , computer science , embedded system , chromatography
Summary 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 ∼10 : 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 ∼5 : 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.