Herein, we report a novel fluorescent 'light-up' probe useful for carboxylesterase assay that is based on a tetraphenylethylene derivative containing carboxylic ester groups. The specific cleavage of the carboxylic ester bonds by carboxylesterase results in the generation of a relatively hydrophobic moiety that self-assembles into supramolecular microfibers, thus giving rise to 'turn-on' fluorescent signals. A high sensitivity towards carboxylesterase was achieved with a detection limit as low as 29 p M, which is much lower than the corresponding assays based on other fluorescent approaches. [ABSTRACT FROM AUTHOR]