Microenvironment Sensitive Probe for Ratiometric sensing of Vesicle to Micelle Transition

Interconversion of Micelles and Vesicles is central to nanomedicine; however, the phenomenon is challenging to monitor in real time. We report an amphiphilic pyrene–vinyl pyridine fluorophore, P3-2, as a ratiometric probe for vesicle-to-micelle transitions. In lipid vesicles, P3-2 remains largely monomeric, whereas in micelles it forms emissive aggregates, producing a large red shift (>100 nm). A coexistence of monomeric and aggregated states was observed in aqueous medium, which results in further discrimination among micelle, vesicle, and non-surfactant environments. Detergent-induced vesicle solubilization was also observed, with the emission ratio (I565/I432) of the probe directly reflecting bilayer disruption, confirming its capability of detecting vesicle to micelle transition in real time. Additives such as Urea, NaCl, Cholesterol, and PEG also modulated its response. The differential behaviours of P3-2 in different microenvironments stem from the probe’s intramolecular charge-transfer character (ICT) and aggregation-induced emission (AIE). Collectively, P3-2 provides a simple, fast, and reliable optical tool for real-time monitoring of nano-aggregation transitions, opening up possibilities of new opportunities in the optimization of lipid-based drug delivery systems and probing membrane dynamics.