A turn-on fluorescence probe based on aggregation-induced emission for leucine aminopeptidase in living cells and tumor tissue.

Abnormally-expressed leucine aminopeptidase (LAP) is associated with diverse physiological and pathological disorders; hence developing a highly selective and sensitive detection system for LAP is of great significance. Herein, a fluorescent light-up system with aggregation-induced emission (AIE) characteristic, (DPA-TPE-Leu) has been developed for detecting LAP, in which the recognition unit l-leucine amide group also acts as the hydrophilic moiety. Upon LAP-triggered enzymatic reaction, l-leucine amide moiety is cleaved from the probe molecule, resulting in the formation and aggregation of the hydrophobic reaction product (DPE-TPE-OH) with AIE effect and thus giving out the turn-on green fluorescence. The system features excellent photostability, large Stokes shift (194 nm), good water solubility, high sensitivity with the detection limit of 0.16 U L, favorable specificity and low cytotoxicity. It has been effectively utilized in fluorescent imaging of endogenous LAP in living cells, and also successfully applied for fluorescent imaging of HepG2 xenograft tumor. Such a fluorescent assay could provide a convenient and sensitive method for detecting LAP activity and might aid in the auxiliary diagnosis of hepatocellular carcinoma and related pathological analysis in biopsy.