Assuming the Poly-Prep Slides are clean, it is doubtful that dipping the slides into ethanol or other solvents will decrease the artifact you are seeing. Poly-Prep slides have been noted to have blue fluorescence in the UV range. There are reference articles that mention blue fluorescence of L-Lysine in the UV range. The full PDF can be downloaded at the URL provided below. In house experience with the polymer matches that of the monomer.
https://www.sciencedirect.com/science/article/pii/S1386142522008666