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 advantage of the Linear relationship between the mass of a thin sample and the scattered fraction of the incident electrons, Mass determination by electron scattering was first performed by scanning transmission electron microscopy (STEM), collecting the elastically scattered electrons by an annular dark-field detector, In the energy-filtering transmission electron microscope (EFTEM), the dark-held images formed by inelastically scattered electrons are recorded with a highly Linear and sensitive slow-scan CCD camera, A calibration factor relating the collected fi action of scattered electrons to the mass of a sample can be determined by using a particle of known molecular mass as a reference standard, Processing of the digital dark-held images obtained by the slow-scan CCD camera allows the mass of thin particles, the mass per length of filaments, or the mass per area of planar samples to be determined, To validate this approach, a number of typical biological samples were evaluated in the EFTEM and the results obtained were compared with those from STEM, The data presented demonstrate that an EFTEM equipped with a high-performance slow-scan CCD camera is an effective electron optical device for mass determination of biomolecular assemblies with an accuracy and reproducibility comparable to that achieved by STEM. (C) 1997 Academic Press.