Coumarin derivatives such as 7-O-Amino-4-methylumbelliferone have been shown to be useful in a simple spectroscopic assay for aldehydes in biologically relevant media.⁽¹⁾ Condensation of this compound with aldehydes (e.g., formaldehyde) forms aldimines that are susceptible to elimination with Lewis bases such as bovine serum albumin (BSA), forming blue-fluorescent 4-methylumbelliferone (4-MU). The excitation and emission maxima for 4-MU are the same at pH 7.0 (water) and pH 10.3 (0.15 M glycine buffer).⁽²⁾ Maximum fluorescence was observed at 445 nm when excited at 365 nm, and the fluorescence intensity is 100 times as intense at pH 10.3 than at pH 7.0.
5 mg = 26.2 micromoles; 25 mg = 131 micromoles.

Ref:

1. Salahuddin, S.; Renaudet, O.; Reymond, J.-L. Org. Biomol. Chem. 2004, 2, 1471-1475.
2. Strachan, R.; Wood, J.; Hirschmann, R. J. Org. Chem. 1962, 27, 1074-1075.