Researchers from the East China University of Science and Technology in Shanghai have developed a new phenazine-based near-infrared fluorescent probe to detect intracellular carboxylesterases, the enzymes involved in the pathophysiology of Wolman disease—a type of lysosomal acid lipase deficiency (LAL-D).

The newly developed probe, named DBPpys, could selectively detect carboxylesterases with a low detection limit and a large Stokes shift in vitro.

The ability of DBPpys to selectively detect carboxylesterases was maintained even with varying temperatures and pH conditions, as well as in the presence of different interfering substances, including inorganic salts, reactive oxygen species, certain amino acids, adenosine 50-diphosphate, adenosine 50-triphosphate, and proteins.

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“These results provide a strategy for the development of additional near-infrared fluorescent probes for carboxylesterase activity monitoring and a potential tool for in vivo fluorescence imaging,” the study’s authors wrote in Molecules.

Read more about LAL-D etiology

By using DBPpys, the researchers were able to determine the activity of endogenous carboxylesterases in HeLa cells by analyzing the magnitude of fluorescence intensity.

Moreover, they showed that DBPpys had low cytotoxicity to HeLa cells and could potentially be used to assess the health status of cells.

Overall, these results suggest that the DBPpys probe may be suitable for application in biological systems.

In addition, the researchers demonstrated that DBPpys could be converted into DBPpy by carboxylesterase in HeLa cells. DBPpy localized in lipid droplets in HeLa cells and showed potential as imaging tool to localize these storage organelles within cells.

Previous studies have found an abnormal expression of carboxylesterase in Wolman disease and other disorders. Wolman disease is caused by loss-of-function mutations in the LIPA gene, resulting in the near-complete absence (<1%) of lysosomal acid lipase activity.


Li C, Li S, Li X, et al. A turn-on lipid droplet-targeted near-infrared fluorescent probe with a large stokes shift for detection of intracellular carboxylesterases and cell viability imaging. Molecules. 2023;28(5). doi:10.3390/molecules28052317