Toward Compositional Contrast by Cryo-STEM

ConspectusElectron microscopy (EM) is the most versatile tool for study of matter at scales ranging from subatomic to visible. The high vacuum environment and charged irradiation require careful stabilization many specimens interest. Biological samples are particularly sensitive due their composition light elements suspended in an aqueous medium. Early investigators developed techniques embedding staining with heavy metal salts contrast enhancement. Indeed, Nobel Prize 1974 recognized Claude, de Duve, Palade establishment field cell biology, largely developments separation preservation cellular components electron microscopy. A decade later, cryogenic fixation was introduced. Vitrification water avoids need dehydration provides ideal matrix which organic macromolecules suspended; specimen represents a native state, suddenly frozen time temperatures below ?150 °C. low temperature maintains vapor pressure microscope, amorphous nature medium diffraction crystalline ice. Such extremely delicate, however, cryo-EM imaging race information face ongoing damage by irradiation. Through this journey, enhanced resolution scale membranes molecules recently atoms. Cryo-EM pioneers, Dubochet, Frank, Henderson, were awarded 2017 structure determination biological macromolecules.A relatively untapped feature its composition. Nothing added nothing removed. Analytical spectroscopies based on energy loss or X-ray emission can be applied, but very small interaction cross sections conflict weak exposures required preserve sample integrity. To what extent we interpret quantitatively pixel intensities images themselves? Conventional cryo-transmission (TEM) limited respect, strong dependence transfer defocus absence spatial frequencies.Inspiration comes different modality cryo-tomography, using soft X-rays. Contrast depends difference atomic absorption between carbon oxygen region spectrum core level ionization energies, so-called window. Three dimensional (3D) reconstruction map local coefficient. quantitative enables visualization materials without stain measurement concentration quantitatively. We asked, aspects might transferred cryo-electron microscopy?Compositional accessible scanning transmission EM (STEM) via incoherent elastic scattering, number Z. STEM regarded as energy, angle performed weakly convergent beam. When coherent effects absent, that is, materials, dark signal measures flux scattered integrated over detector area. Learning these signals will open new dimension cryo-EM. This Account describes our efforts so far introduce tomography specimens. conclude some thoughts further developments.