Aggregation-Induced Excimer Emission-Controlled Ratiometric Fluorescence Assay for Determining Critical Micelle Concentration of Surfactants

The critical micelle concentration (CMC) is a key physicochemical parameter that defines the onset of micelle formation in surfactant solutions. The determination of the CMC is essential for understanding surfactant behavior in various chemical, biological, and industrial applications. This study introduces a ratiometric fluorescence assay that exploits the distinct monomer-excimer emission behavior of pyrene-butyldipicolylamine (<b>Py-DPA</b>) to determine the CMC of various surfactants. <b>Py-DPA</b> forms self-assembled nanoaggregates in a buffered solution and exhibits strong aggregation-induced excimer emission. As the concentration of surfactant increases and micelle formation occurs, the dissolution of <b>Py-DPA</b> nanoaggregates induces a distinct fluorescence transition from excimer to monomer emission, providing a reliable indicator of micellization. The ratiometric fluorescence changes in excimer-monomer emission of <b>Py-DPA</b> enable the determination of the CMC for various surfactants, including cationic, anionic, nonionic, and zwitterionic types, demonstrating the versatility and applicability of the assay. Furthermore, the robustness and applicability of the assay are demonstrated under various conditions including variations in pH, ionic strength, and temperature.