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Hey, Ian!

ian gibbins wrote:

> Martin's explanation seems pretty likely, but occasionally we have seen 
> emission from Cy5 down to green wavelengths, especially when the dye is 
> in very high concentrations (eg in a dye-filled neuron). I seem to 
> remember that there was some discussion on the list about this sort of 
> phenomenon a while back??

In the mid-90's, when Cy5 first came out, there were problems with it 
being contaminated with a green fluorophore.  When notified, the 
manufacturers seemed to have cleaned it pretty quickly.  In any case, I 
haven't seen much of that problem for a while but then I haven't been 
looking for it.

I've also seen cases where a shorter-wavelength dye, when present in 
high concentrations, can form what I presume are non-covalently bound 
dimers (--imagine fluorophore molecules stacking one atop the other) 
that have different (red-shifted) excitation-emission spectra than the 
native dye.  Thus a pure fluorophore in a sufficiently high 
concentration can sometimes appear to be a mixture.  However, I've only 
seen cases where it's a red-shift, not a green-shift.

Good luck!

Martin
-- 
Martin Wessendorf, Ph.D.                   office: (612) 626-0145
Assoc Prof, Dept Neuroscience                 lab: (612) 624-2991
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