Long-Term Study of Optical Nanoparticles Doped With Yb3+/Er3+ and Transition Metal Ions and their Real Application for Imaging and Temperature Sensing on Triticum Aestivum L.

Abstract

Upconverting nanoparticles (UCNPs) have incredible potential for countless applications, especially in biology and medicine. These NPs can be used to bioimaging animals and plants and analyze their physiology, metabolic pathways, or intercellular interactions in real-time. However, before reaching such an application, the UCNPs physicochemical properties during prolonged storage and their toxicity to a particular species must be studied. Herein, SrF₂:Yb³⁺, Er³⁺ water colloid, additionally doped with transition metals (Sc³⁺ or Zn²⁺) to enhance observed emission, are tested during 22 weeks of storage in ambient conditions. The obtained compounds presented high stability throughout the entire duration of the experiment, with minor changes in their composition, emission intensity, and thermal sensitivity. After carefully investigating the phytotoxicity of UCNPs on wheat Triticum aestivum L., UC emission plant imaging is successfully observed under 975 nm excitation while overcoming laser heating that can harm the plant. The UC emission from the UCNPs in the plant is also calibrated to monitor temperature. Moreover, it is discovered that SrF₂:Yb³⁺, Er³⁺, Zn²⁺ can positively influence wheat growth. These results indicate that presented UCNPs are among the most promising candidates for biological and agriculture studies and applications.