Used as a fluorescent probe in biological and biochemical assays to detect esterase enzyme activity. The compound is cell-permeable and non-fluorescent in its intact form. Once inside cells, esterases cleave the butyrate groups, releasing fluorescein, which is highly fluorescent and trapped within the cell. This fluorescence allows for the visualization and quantification of cellular esterase activity, making it useful in cell viability assays, flow cytometry, and fluorescence microscopy. Also employed in environmental and industrial applications to trace fluid flow and detect leaks due to its strong fluorescent signal in aqueous environments.