Dual excitable upconversion nanoparticle@polydopamine nanocomposite with intense red emission and efficient photothermal generation

Abstract

Integration of strong upconversion emission with deep tissue penetration and stable photothermal generation is of great significance for imaging-guided photothermal therapy under infrared excitation. Herein, the NaYF4:Yb3+,Ho3+,Ce3+@NaGdF4:Yb3+,Nd3+@NaGdF4 core-shell-shell upconversion nanoparticles (UCNPs) with increasing Ce3+ doping concentration were firstly synthesized, in which the size manipulation, enhanced red to green emission intensity ratio (IR/IG), 980 and 808 nm dual-modal excitations, as well as improved total upconversion emission intensity can be achieved. After the coating of polydopamine (PDA) through dopamine spontaneous polymerization on the UCNPs surface under alkaline condition, the obtained UCNP@PDA nanocomposites show efficient photothermal effect under 808 nm excitation, while the thickness variation of PDA can be indicated by the upconversion spectra under 980 nm excitation. Interestingly, the photothermal effect of the UCNP@PDA nanocomposites with high IR/IG ratio is more stable with PDA thickness variation, which benefits from the structure design that allows PDA to simultaneously absorb the visible emission from inside UCNPs and the external 808 nm infrared light. Further in vitro cytotoxicity assay and photothermal therapy demonstrate that the UCNP@PDA nanocomposite has good biocompatibility and ability to kill tumor cells by photothermal effect under 808 nm excitation. This research may provide a nanoplatform for integrating deep bioimaging with highly stable photothermal therapy without the sacrifice of radiative transitions of rare earth ions.