Sub-100 nm gold nanoparticle vesicles as a drug delivery carrier enabling rapid drug release upon light irradiation.

Previously, we reported gold nanoparticles coated with semifluorinated ligands self-assembled into gold nanoparticle vesicles (AuNVs) with a sub-100 nm diameter in tetrahydrofuran (THF). (1) Although this size is potentially useful for in vivo use, the biomedical applications of AuNVs were limited, as the vesicular structure collapsed in water. In this paper, we demonstrate that the AuNVs can be dispersed in water by cross-linking each gold nanoparticle with thiol-terminated PEG so that the cross-linked vesicles can work as a drug delivery carrier enabling light-triggered release. Rhodamine dyes or anticancer drugs were encapsulated within the cross-linked vesicles by heating to 62.5 °C. At this temperature, the gaps between nanoparticles open, as confirmed by a blue shift in the plasmon peak and the more efficient encapsulation than that observed at room temperature. The cross-linked AuNVs released encapsulated drugs upon short-term laser irradiation (5 min, 532 nm) by again opening the nanogaps between each nanoparticle in the vesicle. On the contrary, when heating the solution to 70 °C, the release speed of encapsulated dyes was much lower (more than 2 h) than that triggered by laser irradiation, indicating that cross-linked AuNVs are highly responsive to light. The vesicles were efficiently internalized into cells compared to discrete gold nanoparticles and released anticancer drugs upon laser irradiation in cells. These results indicate that cross-linked AuNVs, sub-100 nm in size, could be a new type of light-responsive drug delivery carrier applicable to the biomedical field.