Resazurin has a blue to purple color (at pH > 6.5) . It can be irreversibly reduced to the pink-colored and highly fluorescent resorufin (7-Hydroxy-3H-phenoxazin-3-one).

Surprisingly, 300ul of water based mixture containing 0.067mM resazruin, 50mM bicine pH9 was prepared in a transparent 96-well plate, after 24h at room temperature with light, it turns to pink and has fluorescence. PS: Resazurin is suggested to be protected from light.

Anyone can explain that?

Thanks!