Bovine serum albumin (BSA) is a common endocytic cargo, which typically ends up being degraded by proteases in the lysosome. Our Self-Quenched BODIPY FL Conjugate of BSA (Green) is a derivative of BSA. The BSA here is heavily labelled with fluorescence dye BODIPY FL. The high local concentration of the fluorophore on BSA causes prominent self-quenching of the dye conjugate. Proteolysis of the BSA releases peptide fragments that carry the fluorophores, thereby relieving the dye from self-quenching (de-quenching). Monitoring of the de-quenched fluorophore provides a reliable assay to monitor lysosome function, the lysosome cargo degradation, or assess proteolytic activity in vitro. This could be assayed using flow cytometry, fluorescence micr