Degradation of upconverting nanoparticles in simulated fluids evaluated by ratiometric luminescence

Abstract

Lanthanide-doped upconversion nanoparticles can convert long-wavelength near-infrared light into short-wavelength emission, which has been widely used in biomedicine. The key to biomedical applications is their toxicity to organisms and their changes in the physiological environment. Many studies have been conducted to assess the toxicity of upconversion nanoparticles to organisms. However, little is known about their potential transformation in biological media, which seriously hinders their biomedical applications. To understand the fate of these nanoparticles in biological media, NaGdF₄:Eu@NaGdF₄:Yb,Tm@NaGdF₄:Tb nanoparticles were exposed to five different artificial simulated fluids for 28 days and characterized by luminescence spectroscopy, transmission electron microscopy, and inductively coupled plasma mass spectrometry. We found that the decrease in the intensity of the upconversion nanoparticles was highly dependent on the composition of the simulated fluids. By contrast, the ratiometric signal of upconversion emission was nearly unchanged. Our mechanistic investigation reveals that these nanoparticles degrade as nanofragments in phosphate-rich fluids, while these nanoparticles have good stability in protein-rich fluids. This study provides useful information about the fate of lanthanide nanoparticles in biological media, as well as exciting opportunities for the design of biological imaging and sensing probes.