Aliphatic Chain-Derived Fluorescein Aggregates for Surfactants Discrimination and CMC Determination.

Surfactants are widely used across diverse industries. Critical micelle concentration (CMC) is a key parameter governing their performance. While various established methods exist for characterizing CMC, there remains an urgent need for more sensitive, visually detectable, and versatile detection technologies to keep pace with the rapid advancement of novel surfactants. Herein, we report the development of a fluorescent probe SP-18, which synthesized by introducing a long alkyl chain into a low-toxicity fluorescein dye. By incorporating a hydrophobic n-octadecyl chain into the water-soluble fluorescein dye, the probe aggregates in aqueous media, leading to fluorescence quenching. Upon the addition of surfactants, (including anionic surfactant SDS, cationic surfactant DTAB, zwitterionic surfactant SB3-12, and nonionic surfactant Triton X-100), the probe inserts into the micelles that form. This leads to dissociation of fluorescent aggregates and triggers a fluorescence “turn-on” response. Specifically, SP-18 exhibits distinct spectral shifts (e.g., a blue-shifted emission and unique absorption changes) for SDS, enabling its selective identification among the four surfactant types. This work provides the probe SP-18 as a dual-function tool for robust CMC determination and specific surfactant identification.