Light-induced transformation of vesicles to micelles and vesicle-gels to sols†
Vesicles are self-assembled nanocontainers that are used for the controlled release of cosmetics, drugs, and proteins. Researchers have been seeking to create photoresponsive vesicles that could enable the triggered release of encapsulated molecules with accurate spatial resolution. While several photoresponsive vesicle formulations have been reported, these systems are rather complex as they rely on special light-sensitive amphiphiles that require synthesis. In this study, we report a new class of photoresponsive vesicles based on two inexpensive and commercially available amphiphiles. Specifically, we employ p-octyloxydiphenyliodonium hexafluoroantimonate (ODPI), a cationic amphiphile that finds use as a photoinitiator, and a common anionic surfactant, sodium dodecylbenzenesulfonate (SDBS). Mixtures of ODPI and SDBS form “catanionic” vesicles at certain molar ratios due to ionic interactions between the cationic and anionic headgroups. When irradiated with ultraviolet (UV) light, ODPI loses its charge and, in turn, the vesicles are converted into micelles due to the loss of ionic interactions. In addition, a mixture of these photoresponsive vesicles and a hydrophobically modified biopolymer gives a photoresponsive vesicle-gel. The vesicle-gel is formed because hydrophobes on the polymer insert into vesicle bilayers and thus induce a three-dimensional network of vesicles connected by polymer chains. Upon UV irradiation, the network is disrupted because of the conversion of vesicles to micelles, with the polymer hydrophobes getting sequestered within the micelles. As a result, the gel is converted to a sol, which manifests as a 40 000-fold light-induced drop in sample viscosity.