Biodegradable Inorganic Upconversion Nanocrystals for In Vivo Applications

Area of Science:

• Biomedical Nanotechnology
• Materials Science
• Inorganic Chemistry

Background:

• Lanthanide-doped inorganic upconversion nanocrystals (UCNCs) show promise for in vivo diagnostics and therapeutics.
• Current UCNCs lack biodegradability, hindering clinical translation due to accumulation in organs.

Purpose of the Study:

• To develop novel biodegradable UCNCs for biomedical applications.
• To address the limitations of non-biodegradable UCNCs in vivo.

Main Methods:

• Synthesized Yb³⁺/Er³⁺-doped K₃ZrF₇ UCNCs with a "soft" crystal lattice.
• Investigated pH-dependent biodegradation in vitro and in vivo.
• Monitored biodegradation using intrinsic red upconversion luminescence.
• Compared biodegradation and toxicity with non-biodegradable β-NaYF₄:Yb/Er UCNCs.

Main Results:

• Developed red-emitting, biodegradable K₃ZrF₇:Yb/Er UCNCs.
• Demonstrated pH-dependent biodegradation, tunable in acidic tumor microenvironments (pH 5-6).
• Showed rapid excretion of biodegradation products in mice with no observed toxicity.
• Contrasted with non-biodegradable UCNCs that accumulated in organs.

Conclusions:

• Biodegradable K₃ZrF₇:Yb/Er UCNCs offer a safe alternative for in vivo applications.
• The tunable biodegradation rate is advantageous for targeting specific physiological conditions.
• These findings pave the way for clinical translation of UCNCs in theranostics and imaging.