I’ve experimented with various types of edible and non-edible liquids that fluoresce under UV light:

• Vitamin B6 - edible
• Tonic water (or simply quinine) - edible; good for cocktails
• Dissolved highlighter in isopropyl alcohol (yellow is the brightest) - NOT edible

Here’s a fun shot of draining a highlighter! You could do this a lot more quickly by taking out the wick inside the pen, but this looks much cooler, and isn’t that what’s truly important…?

https://www.instagram.com/reel/CU_71zzD-Eo/