Which fluorescent substrate should I use for B-galactosidase system for microscopy?

For beta-galactosidase, two commonly used fluorescent substrates are FDG (fluorescein di-beta-D galactopyranoside) and MUG (4-methylumbelliferone beta-D-galactopyranoside). Beta-galactosidase hydrolyzes the substrates, which are initially colorless, and in doing so creates a product that fluoresces.