Background:

5(6)-Carboxyfluorescein contains a carboxylic acid that can be used to react with primary amines via carbodiimide activation of the carboxylic acid; cell-impermeant 5,6-FAM can also be used as a nonfixable polar tracer to investigate fusion, lysis and gap-junctional communication and to detect changes in cell or liposome volume.

[1]. Babcock DF. Examination of the intracellular ionic environment and of ionophore action by null point measurements employing the fluorescein chromophore. J Biol Chem. 1983 May 25;258(10):6380-9. [2]. Bonizzoni M, et al. PAMAM dendrimer-induced aggregation of 5(6)-carboxyfluorescein. J Org Chem. 2012 Feb 3;77(3):1258-66.