A single multifunctional nanoplatform based on upconversion luminescence and gold nanorods

Abstract

Lanthanide-doped upconverting nanoparticles (UCNPs), which convert near-infrared (NIR) light to higher energy light have been intensively studied for theranostic applications. Here, we developed a hybrid core/shell nanocomposite with multifunctional properties using a multistep strategy consisting of a gold nanorod (GNR) core with an upconverting NaYF₄:Er³⁺, Yb³⁺ shell (GNR@NaYF₄:Er³⁺, Yb³⁺). To use a single excitation beam, the GNR plasmon was tuned to ∼650 nm, which is resonant with the upconverted red Er³⁺ emission emanating from the ⁴F_9/2 excited state. Thus, under laser irradiation at 980 nm, the intensity ratio of the upconverted green emission (arising from the ²H_11/2 and ⁴S_3/2 excited states of Er³⁺) showed a remarkable thermal sensitivity, which was used to calculate the temperature change due to rapid heat conversion from the GNR core. The red upconversion emission of the GNR@NaYF₄:Er³⁺, Yb³⁺ core/shell nanocomposite decreased compared with the NaYF₄:Er³⁺, Yb³⁺ nanoshell structure (without a GNR core), which indicates that energy transfer from NaYF₄:Er³⁺, Yb³⁺ to the GNR takes place, subsequently causing a photothermal effect. The anticancer drug, doxorubicin, was loaded into the GNR@NaYF₄:Er³⁺, Yb³⁺ nanocomposites and the drug release profile was evaluated. In particular, the release of doxorubicin was significantly enhanced at lower pH and higher temperature caused by the photothermal effect. This multifunctional nanocomposite, which is suitable for local heating and controlled drug release, shows strong potential for use in cancer therapy.