Near infrared to ultraviolet upconversion nanocomposite for controlling the permittivity of polyspiropyran shell

Near infrared to ultraviolet (NIR-to-UV) up-conversion nanocomposites, composed of an upconversion nanoparticle (UCNP) core and a transformable polyspiropyran shell, were prepared by distillation precipitation polymerization and the template method. The polyspiropyran shell can undergo reversible hydrophoblic-hydrophilic transformations through the switching of UV and visible light and by variation of pH. About 10 wt% of the anticancer drug, doxorubicin (DOX), can be loaded into the drug carrying layer under pH 7.4 by electrostatic force. The NIR and pH responsive features of the polyspiropyran shell were shown by the dynamic light scattering (DLS) results, in which the size of nanocomposites (UCNPs@SP-MA/MAA) became larger under NIR irradiation and pH 4.5. The hydrophobic to hydrophilic surface transformation alters the permittivity of the polyspiropyran shell and the release behavior. The cumulative release rate of the DOX-loaded UCNPs@SP-MA/MAA reached 53.8% under pH 4.5 and NIR irradiation. The cytotoxicity of the bare UCNPs@SP-MA/MAA and the DOX-loaded UCNPs@SP-MA/MAA were evaluated against breast cancer cells and the results confirmed that the toxicity of UCNPs@SP-MA/MAA nanocomposites was minimal, even at high dosage (100 μg/mL), while the toxicity of DOX can be triggered by NIR light.