A ratiometric fluorescent probe for mitochondrial esterase specific detection in living cells

Monitoring esterase activities in living cells are beneficial to predict the metabolism of various esters and evaluate the efficacy of therapeutic prodrugs. Up to now, subcellular esterase in cytoplasm/lysosome has been evaluated by fluorescence technology. However, accurate and reliable mitochondrial esterase detection remains a challenge, due to the lack of organelle specificity. Here, we demonstrate a mitochondrial directed esterase probe (Naph-Ester) which allows for the quantitative detection of mitochondrial esterase, as well as monitoring esterase content change in real time. Naph-Ester manifests remarkably ratiometric and red-shifted (about 127 nm) fluorescence in the presence of esterase. Benefiting from the ratiometric property, high specificity and low cytotoxicity, Naph-Ester provides reliable detection of mitochondrial esterase in living cells. Notably, its internalization path was identified to be energy dependent endocytosis, avoiding from hydrolysis by cytostromatic esterase. Overall, the present work demonstrates an effective esterase probe which can be applied as a reliable tool to monitor mitochondrial esterase.