Sudan dyes don't bind to the lipids via chemical binding but are dissolved in lipids (eg. neutral fats seen in emboly). So you need at least a small amount of fats, where the dye can be dispersed (fatdroplets).

For my understanding the double-layer of liposomes can be compared to the cytomembran, which is not stained by Sudan.

I refer to Sudan III or Sudan IV as fat-stain.

Dear Gudrun,

Sudan dyes is fluorescent ?