Throw away the highlighter, this Gizmodo link has an interesting clip on how to make glow-in-the-dark printer ink. The inter-titles could do with a spell-check ("seringes"???) but it looks like a fun idea.

This link also carries the clip but has more details on the glow-in-the-dark powder as well as an ingenious covert printing idea for the spy-minded. The powder's made by Glow Inc., who also make glow-in-the-dark paints -- at up to US$500 a gallon!