Laser Photolysis of Dye-Sensitized Nanocapsules Occurs via a Photothermal Pathway

Light-addressable nanocapsules offer a powerful method for delivering spatiotemporally precise signals to-cells. Thus far, the mechanism involved in the photolysis of nanocapsules has been opaque. This paper presents experimental evidence that rules out a photochemical pathway in favor of a photothermal mechanism in the fir-red photolysis of dye-sensitized, lipid-vesicle based nanocapsules. Photolysis efficiency was unaffected by the presence of radical inhibitors, and mass spectrometry measurements confirmed that the photolytic process did not produce dye radicals. Measurements of dye quantum yield in the lipid membrane showed an inverse correlation between quantum yield of the dye and photolysis efficiency of the vesicle. The result is consistent with the notion that a decrease in quantum yield translates into more vibrational relaxation and thermal motion of the dye molecules in the membrane and thus more efficient photothermal disruption of the vesicle. Furthermore, we observed that the decrease in quantum yield and increase in photolysis efficiency was caused by the formation of raftlike domains that clustered the dye molecules into concentrated regions. On the basis of this information, we were able to design new nanocapsules using ternary mixtures of lipid and cholesterol that promoted the formation of raft domains and dye clustering. These nanocapsules showed improved photolysis efficiency over the best results we obtained previously.