We have shown that electron energy loss spectroscopic imaging (EELS) in the scanning transmission electron microscope (STEM) can provide single atom sensitivity for elements such as calcium and iron bound to proteins adsorbed onto thin carbon films. A spectrum-imaging system incorporating a 100x1340 pixel CCD detector enables collection of parallel EELS data at each image pixel. Advantages of this new system are (i) the low noise level that provides higher analytical sensitivity, (ii) the short read-out time of around 10 ms, which provides faster acquisition, (iii) the two-dimensional array of square pixels, which allows exact correction for channel gain variations, and (iv) the improved point-spread function of the optical coupling of the detector array to the scintillator. Compensation for specimen drift is achieved in real-time by cross-correlating annular dark-field images recorded at the end of each scan line. Using ferritin molecules as a reference structure, iron maps have been obtained from individual hemoglobin molecules showing detection of four iron atoms per molecule. By absorbing a very low salt concentration onto a carbon support film, it is feasible to image single atoms of calcium using this system. Possible future applications include the characterization of individual macromolecules that contain bound atoms of specific elements.

National Institute of Health (NIH)
Office of The Director, National Institutes of Health (OD)
Intramural Research (Z01)
Project #
Application #
Study Section
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Office of the Director, NIH
United States
Zip Code
Zhang, Peijun; Land, William; Lee, Stanton et al. (2005) Electron tomography of degenerating neurons in mice with abnormal regulation of iron metabolism. J Struct Biol 150:144-53
Berra, Lorenzo; De Marchi, Lorenzo; Yu, Zu-Xi et al. (2004) Endotracheal tubes coated with antiseptics decrease bacterial colonization of the ventilator circuits, lungs, and endotracheal tube. Anesthesiology 100:1446-56
Tuli, Richard; Nandi, Sumon; Li, Wan-Ju et al. (2004) Human mesenchymal progenitor cell-based tissue engineering of a single-unit osteochondral construct. Tissue Eng 10:1169-79
Goping, Gertrud; Pollard, Harvey B; Srivastava, Meera et al. (2003) Mapping protein expression in mouse pancreatic islets by immunolabeling and electron energy loss spectrum-imaging. Microsc Res Tech 61:448-56
Leapman, R D (2003) Detecting single atoms of calcium and iron in biological structures by electron energy-loss spectrum-imaging. J Microsc 210:5-15
Hongpaisan, J; Pivovarova, N B; Colegrove, S L et al. (2001) Multiple modes of calcium-induced calcium release in sympathetic neurons II: a [Ca2+](i)- and location-dependent transition from endoplasmic reticulum Ca accumulation to net Ca release. J Gen Physiol 118:101-12
Leapman, R D; Rizzo, N W (1999) Towards single atom analysis of biological structures. Ultramicroscopy 78:251-68