Photo- and pH-responsive drug delivery nanocomposite based on o-nitrobenzyl functionalized upconversion nanoparticles

A near infrared (NIR) and pH dual-responsive nanocomposite, composed of a lanthanide-doped upconversion nanoparticle (UCNP) core and a transformable poly-o-nitrobenzyl shell, was prepared by the distillation precipitation polymerization and template method. The poly-o-nitrobenzyl shell can undergo hydrophobic-hydrophilic transformation upon an irradiation of 980 nm, rendering the capability of NIR-activated drug release. The anticancer drug, doxorubicin (DOX), can be loaded into these nanocomposites with a loading efficiency of 7.23 wt%. Furthermore, pH responsiveness caused by the hydrogen bond and charge interactions between DOX and nanocapsules can trigger the release of drugs at low pH. Under visible light irradiation and neutral (pH 7.4) conditions, the cumulative release of DOX was only 8.35% after 300 min, while it reached 59.5% under the synergistic effect of NIR irradiation and acidic conditions. The Baker-Lonsdale model was used to describe the drug release kinetics of this system, and the diffusion coefficient (3DC_s/r₀²C₀) and R² under different conditions were determined to be 4.15 × 10⁻⁶ and 0.98 (pH 7.4 and visible light), 2.64 × 10⁻⁵ and 0.99 (NIR light), 3.26 × 10⁻⁵ and 0.97 (pH 4.5 and visible light), 2.59 × 10⁻⁴ and 0.99 (pH 4.5 and NIR light), respectively. This controlled release feature makes the nanocomposite a promising therapeutic agent for treating diseases.