Imparting Biodegradability to Highly-Efficient Upconversion Nanoparticles via Facet-Selective Zirconium Doping.

Area of Science:

• Materials Science
• Nanotechnology
• Biophotonics

Background:

• Alkali rare-earth fluorides (e.g., UCNPs) are crucial in biophotonics but raise concerns regarding long-term bioretention and toxicity due to their stability.
• There is a need for upconversion nanoparticles that balance high photonic performance with biological safety for clinical applications.

Purpose of the Study:

• To engineer biodegradable upconversion nanoparticles (UCNPs) by modifying the LiREF4 lattice.
• To maintain the structural integrity and luminescent efficiency of UCNPs while introducing biodegradability.
• To explore the potential of these modified UCNPs for safe biomedical applications.

Main Methods:

• Substitution of rare-earth ions with Zr4+ on the [001] facet of LiREF4 (RE = Yb3+).
• Density functional theory (DFT) calculations to analyze the stability and coordination of Zr4+ within the modified lattice.
• Assessment of degradation lifetime for bare and silica-coated UCNPs using the Stöber process.

Main Results:

• The incorporation of Zr4+ created a biodegradable domain within the LiREF4 lattice, preserving the UCNP's structure and luminescence.
• DFT calculations confirmed the stable hosting of Zr4+ as hydrolytically active zirconium fluoride complexes with varying coordination numbers.
• The modified UCNPs exhibited a degradation lifetime of 4 days (bare) and over 1 month (silica-coated), demonstrating controlled biodegradability.

Conclusions:

• A novel strategy was developed to impart biodegradability to highly efficient upconversion nanoparticles.
• This approach establishes a new design principle for creating safer UCNPs by controlled degradation.
• The biodegradable UCNPs show promise for clinically translatable optical imaging and therapeutic applications.