Padraig
We have used Cy-labeled ligands extensively.  They are extremely bright
but do bleach rather quickly in aqueous media.  Apparently, if you mount
in something like methyl salicylate, there's less of a problem.  The
fluorescence signal may be bright enough to get away with using the 568
nm line to excite (about 11% of max absorbtion), in which case bleaching
is reduced substantially.
Jackson immunoreasearch sells many Cy5-labeled reagents, and you can
label anything they don't sell using reactive dye kits available from
Amersham/BDS.
Feel free contact me for more information.
 
Peter Sargent
UCSF
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