> ... Our Olympus confocal uses a Hamamatsu R928 PMT with a
> spectral response curve that suggests 30-50% detection at
> the Cy5 emission peak of 680 nm. ....
>
> Charles J. Butterick  (Chuck)
 
I do not think that any PMT with a quantum efficiency of 30-50% exists.
Your PMT (R928) has a QE of about 5% in the 700 nm (curve 552U in the
Hamamatsu brochure). You could improve the QE for Cy5-red by buying a
new tube. The R636-10 is also a side-on tube (28 mm), can be used in
the same socket/voltage-devider and has a QE of 14% at 700 nm (curve
650U).
 
We use an EMI tube (9828) for the detection of Cy5. We did not compare
it with other tubes yet, but it should have a QE of 10% for Cy5. We
bought an EMI because they are cheaper (less expensive) than comparable
Hamamatsu tubes.
 
Erik Manders
 
 
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            Erik Manders                |
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