How can I detect a specific molecule on a surface?
Simple UV spectroscopy is not an option. 

You won't find anything at all above 254 nm - probably just a a weak band in the 220 nm range. Indolizidines are pretty dead in UV.

Derivatisation towards a fluorescent compound would require clevage of a $\ce{C-N}$ bond, formally a dealkylation of the tertiary bridgehead amine.

I have no idea if a reagent like 2-naphthyl chloroformate, which does form fluorescent carbamates upon heating with tertiary amines will work here and honestly, I wouldn't bother to try.

As pointed out in Martin's comment, GC/MS after washing/extraction probably is the way to go.