MASS DETERMINATION BY INELASTIC ELECTRON-SCATTERING IN AN ENERGY-FILTERING TRANSMISSION ELECTRON-MICROSCOPE WITH SLOW-SCAN CCD-CAMERA

One method of determining the mass of biomolecular assemblies takes ad vantage of the Linear relationship between the mass of a thin sample a nd the scattered fraction of the incident electrons, Mass determinatio n by electron scattering was first performed by scanning transmission electron microscopy (STEM), collecting the elastically scattered elect rons by an annular dark-field detector, In the energy-filtering transm ission electron microscope (EFTEM), the dark-held images formed by ine lastically scattered electrons are recorded with a highly Linear and s ensitive slow-scan CCD camera, A calibration factor relating the colle cted fi action of scattered electrons to the mass of a sample can be d etermined by using a particle of known molecular mass as a reference s tandard, Processing of the digital dark-held images obtained by the sl ow-scan CCD camera allows the mass of thin particles, the mass per len gth of filaments, or the mass per area of planar samples to be determi ned, To validate this approach, a number of typical biological samples were evaluated in the EFTEM and the results obtained were compared wi th those from STEM, The data presented demonstrate that an EFTEM equip ped with a high-performance slow-scan CCD camera is an effective elect ron optical device for mass determination of biomolecular assemblies w ith an accuracy and reproducibility comparable to that achieved by STE M. (C) 1997 Academic Press.