4-Methylumbelliferyl β-D-N,N'-diacetylchitobioside (4-μU-(GlcNAc)2) is a fluorogenic substrate for chitinases and chitobiosidases. 4-μU-(GlcNAc)2 is cleaved by chitinases and chitobiosidases to release the fluorescent moiety 4-μU. 4-μU fluorescence is pH-dependent with excitation maxima of 320 and 360 nm at low (1.97-6.72) and high pH (7.12-10.3), respectively, and an emission maximum ranging from 445 to 455 nm, increasing as pH decreases.