Derek Sant'Angelo writes: >I have an ambitious postdoc who would like to analyze the protein content >of exosomes by FACS. He tells me that exosomes range in size from 50 - 100 >nM. > >Has anyone ever done this? or know if it is possible to do FACS analysis on >"cells" this small? > >We have access to a FacScan, a FacScalibur, a FacsVantage and a MoFlo - any >thoughts on which machine might be best for this analysis? You could do this if you could get enough of a fluorescent protein stain on the exosomes. They are too small for scatter triggering on commercial instruments, but, if you could covalently label them with a few thousand molecules of an efficient dye (see the Molecular Probes catalog), you should get enough signal to trigger on fluorescence in a FACScan or Calibur (the bigger machines are probably less sensitive). You'd probably have to dialyze or ultracentrifuge to remove unreacted dye, and it might not be easy to distinguish exosomes from other proteinaceous particles. A high-sensitivity, slow-flow instrument (lab-built versions exist) might be able to do better. -Howard
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