Laurdan as fluorescent probe to determinate the critical micelle temperature of polymers from Pluronic®-coated fluid phase liposomes

Future-generation liposomes for efficient drug-delivery systems may utilize multifunctional polymer coatings for stabilization and in order to take advantage of conferred properties such as stealth characteristics. In this scenario, understanding the dynamics of polymers coating liposomes versus polymers self-assembly as micelles is a critical issue. This paper describes a methodology to determinate the boundary between the presence of only liposomes and the coexistence of liposomes and micelles in mixed Pluronic®/fluid-phase lipid system, using Laurdan as a fluorescent probe. The temperature-mediated transition at the boundary region results in changes to the generalized polarization function of Laurdan, mainly due to the partition of Laurdan into micelles and increased exposure of the Laurdan probe to water at the liposome interfaces. The new methodology showed to be more sensitive than DLS and allows monitoring of the different organizations of polymers in polymer/lipid mixtures via a simple experimental technique. This new methodology should facilitate the development of smart-polymer-coated liposomes for drug delivery. Furthermore, its principle may be applied to the study of micelle–cell-membrane interactions in such applications.