Fluorinated organic molecules have considerable potential as tracers in bio logical systems, since a number of fluorinated analogs demonstrate biological activity similar to that of the parent molecule1. To date, however, the subcellular localization of fluorine has been hampered by the relatively low sensitivity of conventional X-ray microanalysis systems to fluorine. Electron energy-loss spectroscopy, in contrast, is a very efficient method for detecting light elements. We have capitalized on the high sensitivity of this technique to fluorine to identify and localize fluorinated serotonin at a subcellular level in human platelets.Intact human platelets were incubated with 10-5 M concentrations of either serotonin (5HT) or 4,6 difluoroserotonin (DF5HT)2 for 30 minutes at 37°C. Following the incubation period, air-dried whole mounts3 were prepared on 200 mesh copper grids coated with collodion and carbon. Individual platelets were examined at 80 kv in the STEM mode (10 nm spot size), utilizing a Jeol 100B microscope equipped with a field emission gun, a scanning attachment, an electron spectrometer, and a Kevex analysis recording system.
