BIOLOGICAL APPLICATIONS OF A COMPUTER CONTROLLED ANALYTICAL ELECTRON MICROSCOPE

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Electron energy loss spectra have been obtained by means of a Gatan parallel detector system consisting of Post-spectrometer Quadrupole lenses, a YAG scintillator, fiber-optic coupling, a photodiode array and associated electronics. The detector quantum efficiency was measured and found to be close to unity, giving approximately a 1000-fold improvement over the conventional serial recording of spectra. An energy resolution of about 1.5 eV was achieved at 100 keV beam energy. Spectra with good counting statistics could be recorded in 100 milliseconds, thus allowing real-time EELS to be performed. Preliminary data have been obtained from some fluorine analogs of neurotransmitters, indicating that such compounds might be detectable at biologically meaningful concentrations with an integration time of 1 second. It has also been possible to monitor radiation damage and mass loss in real-time by observing the decay of nitrogen, oxygen and fluorine core edges in organic molecules.