Biodegradable inorganic upconversion nanocrystals developed for in vivo applications
Lanthanide-doped inorganic upconversion nanocrystals (UCNCs) are attracting more attention, as they are potential fluorescent diagnostic and therapeutic agents for in vivo applications including biological imaging and disease theragnostics.
However, all currently available lanthanide-doped inorganic UCNCs, as exemplified by the most presentative b-NaYF4:Yb/Er, are not biodegradable and thus cannot be harmlessly eliminated from the body of living organisms in a reasonable period of time, making their clinical translations nearly impossible.
In a study published in ACS Nano, the research group led by Prof. Hong Maochun from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences reported a new class of red-emitting biodegradable UCNCs based on Yb3+/Er3+-doped inorganic potassium heptafluozirconate (K3ZrF7:Yb/Er) that features dynamically "soft" crystal lattice containing water-soluble [ZrF7]3- cluster and K+ cation.
The researchers found that this arrangement of K3ZrF7 crystal lattice enables the preparation of a family of red-emitting biodegradable inorganic UCNCs after substituted Yb3+/Er3+ doping into the high-symmetry host matrix.
In particular, the red-emitting K3ZrF7:Yb/Er UCNCs exhibit a pH-dependent biodegradation capability upon exposure to water both in vitro and in vivo, and of which the rapid biodegradation rate, monitored by using the intrinsic red upconversion luminescence (UCL), can be tuned by changing the pH value during degradation process.
Through histopathological and elemental analyses, the researchers also found that the final biodegradation products of K3ZrF7:Yb/Er UCNCs can rapidly excrete from the bodies of mice in a short period of time without evident toxicity to their muscles and main organs, in stark contrast to the non-degradable b-NaYF4:Yb/Er UCNCs that primarily accumulate in the main organs of mice.
This study unambiguously offers an opportunity to produce a family of UCL diagnostic and therapeutic agents that are biodegradable in vivo during a reasonable period of time after carrying out their biological applications, which also stimulate an upsurge of research interest on biodegradable Ln3+-doped inorganic UCNCs for various biomedical applications and benefit their future clinical translations.