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[red-sensitive PMT stuff deleted]
> Also, has anyone ever substituted a PMT for the FCS photodiode in BD
> flow cytometers. We are trying to resolve and sort bacteria that are
> less than .2 microns. We can do it now but if a PMT will resolve these
> populations better then I would be interested in putting some extra time
> into making this work.
Placing a PMT in the forward scatter path would probably not help
you, because photon sensitivity is not the problem. There's actually a
lot of light coming down the FSC path, even when there is no particle in the
stream. Stream-to-air interfaces, liquid-to-glass interfaces, edges in a
square flow cell, or minor imperfections in a cuvette can all scatter light,
which gets around the beam stop and into your detector. If you put an
oscilloscope on the FSC channel, you will find that the signals are
actually measured against a large DC offset.
> Glenn
> MIT Flow Cytometry Core Facility
- John Ladasky
(just another flow cytometry hack at Stanford)
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