Hi Ewald,

My lab has been using PerCP-Cy5.5 for many years and you do not typically require a stabilizer when using this dye combination. Pe-Cy5.5 is quite unstable, but PerCP-Cy5.5 is typically resistant to a lot of things, including PFA fixation and/or saponin permeablization. Can you be a bit more specific what renders it unstable in your protocol? 

Hi Dominic,

I am more interested to find out if there is an additive that helps to keep the tandem-labelled antibodies stable for a longer time (increases long-term storage time). Anyway thank you for your suggestion.

Most cheaply available proteins should work just fine (e.g. Casein, ovalbumin)

I'd be tempted to investigate a hydrophobic-hydrophilic block copolymers.

I've wanted to investigate the potential of such materials for stabilizing proteins in solution for some time, as the hydrophobic section should bind proteins at their hydrophobic sites, and the hydrophilic sections should stabilize the solution, and sterically hinder any degradation pathways.

Something like a PEG with a hydrophobic end group should be capable of doing the trick. I think the size and nature of the end group will be the key.