LOW-ENERGY LOSS ELECTRON-MICROSCOPY OF CHROMOPHORES

A novel prism-mirror-prism imaging electron spectrometer with 1 eV ene rgy resolution for a transmission electron microscope permits imaging with spectral energies corresponding to light-optical colour absorptio ns. The instrument selects the molecular orbital excitations of natura l chromophores or of specific dyes normally used in biological light m icroscopy for delineation and chemical identification, bur images them with electron microscopic detail. Heavy atom contrast agents customar ily used in electron microscopy are not required. The first results ex ploit the intrinsic red colour of hematin molecules to demonstrate the potential of the technique and address its spatial resolution. Glycos aminoglycans in cartilage stained with Alcian blue are selectively dep icted in situ by means of the electron-induced molecular absorption of this chromophore. Thus, with the use of specific colours the direct o r indirect analysis of local chemistry by electron microscopy is possi ble, and can be carried out with a depiction of spatial detail as smal l as 16 Angstrom, or at least 100-fold finer than observed by light mi croscopy. (C) 1998 Elsevier Science Ltd. All rights reserved.