Bulk Aggregation Based Fluorescence Turn‐On Sensors for Selective Detection of Progesterone in Aqueous Solution

Steroids are polycyclic compounds that share tetracyclic ring as core scaffold, and selective detection of a steroid is challenging owing to their structural similarities. The discovery of chemosensors that recognize progesterone by alteration of self‐aggregation state is described, and these show significant fluorescence turn‐on. A self‐aggregated 48‐membered dansyl library was screened against a series of metabolites in aqueous buffer and discovered two compounds (PG‐1, PG‐2) exhibited exceptional selectivity for progesterone. Following studies of aggregation properties of probes using dynamic light scattering and transmission electron microscopy supports progesterone recognition lead to the generation of bulk aggregates that induce fluorescence enhancement. Though many fluorescence sensing mechanisms have been proposed, a sensing mode based on the bulk aggregate formation of fluorophore has never been reported, and this may open a new avenue of chemosensor design. A fluorescent library based on the dansyl fluorophore were screened for various metabolites. Two probes (PG‐1, PG‐2) showed exceptional selectivity for progesterone, with more than 15‐fold fluorescence enhancement. The fluorescent enhancement was shown to be induced by bulk aggregation of progesterone together with PG‐1 and PG‐2.