Researchers from Shiv Nadar University in India have developed a novel ratiometric fluorescent probe that allows monitoring of mitochondrial esterase activity, which would be relevant for patients with lysosomal acid lipase deficiency (LAL-D).

According to the researchers, the newly developed esterase-specific fluorescent probe, named PM-OAc, offers several advantages over other esterase probes. For instance, it accumulates within the mitochondria and it has a dual-channel signal with large Stokes shifts.

“Although good progress has been made in monitoring esterase activity using small molecular fluorescent probes, a few drawbacks are limited to efficient probe development. For example, a turn-on response may lead to inaccurate
measurement due to pseudo-signal,” the researchers explained in Chemistry-A European Journal. “Contrary, ratiometric fluorescent probe can minimize errors due to the ratio of dual channel signals.”

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Moreover, PM-OAc binds to the catalytic site of esterases and can distinguish between live and dead cells.

Read more about LAL-D etiology

Mechanistically, the researchers showed that active esterases catalyze the conversion of PM-OAc to PM-O, inducing a shift in the emission wavelength of more than 140 nm (from 500 to 647 nm in alkaline pH).

PM-OAc showed good selectivity toward esterases in the presence of common biological species, including ions, reactive oxygen species, amino acids, ATP, adenosine 5′-diphosphate, and proteins. The detection limit of PM-OAc was 2.41×10-5 U/mL.

PM-OAc is based on a pentacyclic pyridinium derivative and exhibits ratiometric behavior based on intramolecular charge transfer.

Esterases are enzymes involved in the metabolism of esters. Esterase dysfunction has been linked to several conditions, including Wolman disease—a type of LAL-D.


Yadav R, Munan S, Kardam V, Dubey KD, Samanta A. Esterase specific fluorescent probe: mechanistic understanding using QM/MM calculation and cell states discrimination. Chemistry. Published online April 4, 2023. doi:10.1002/chem.202300244