Photomodulation of vesicle dynamics using fluorescent photoswitchable amphiphiles

Modulating membrane permeability and morphology remains a central challenge in the design of responsive colloidal and self-assembled systems. Here, we present a strategy that integrates fluorescently labelled, photoswitchable amphiphiles into lipid vesicles to enable real-time visualization of dynamic membrane behavior and light-triggered cargo release. A novel amphiphilic molecule based on an azobenzene core was synthesized and functionalized with the fluorophore Nile red. This compound was incorporated into giant and large unilamellar vesicles (GUVs and LUVs) composed primarily of POPC (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine) lipids. The response of the vesicles to alternating UV and visible light was characterized using confocal microscopy, fluorescence spectroscopy, and molecular dynamics simulations. Upon irradiation, vesicles exhibited reversible morphological transformations including budding, swelling, and prolate deformation. Fluorescence imaging confirmed efficient incorporation of the amphiphiles into lipid membranes, and the solvatochromic behavior of Nile red enabled distinction between lipid domains. Simulations revealed that Z-isomerization induces asymmetric expansion of the outer membrane leaflet, increasing surface tension and bending modulus, key drivers of the observed shape changes. Furthermore, cargo release assays with LUVs demonstrated controlled, reversible light-induced permeability. The temporal mismatch between morphological response and ROS (reactive oxygen species) generation, along with the reversibility of the effects, supports a non-oxidative, photomechanical mechanism. Based on these findings, fluorescent photoswitchable amphiphiles can be considered as powerful tools for both functional membrane engineering and the study of the relationship between molecular-level interactions, polarity, and macroscale membrane behavior.