Lanthanide-doped inorganic upconversion nanocrystals (UCNCs) are promising as fluorescent diagnostic and therapeutic agents for in vivo applications ranging from biological imaging to disease theranostics. However, all currently available lanthanide-doped inorganic UCNCs are not biodegradable and thus cannot be harmlessly eliminated from the body of living organism during a reasonable period of time, making their clinical translations nearly impossible. Here, we report a class of red-emitting biodegradable UCNCs based on Yb³⁺/Er³⁺-doped inorganic potassium heptafluozirconate (K₃ZrF₇:Yb/Er) that features a dynamically “soft” crystal lattice containing water-soluble [ZrF₇]^3– cluster and a K⁺ cation. The red-emitting K₃ZrF₇:Yb/Er UCNCs exhibit a pH-dependent biodegradation capability upon exposure to water both in vitro and in vivo, and the rapid biodegradation rate, monitored using the intrinsic red upconversion luminescence, can be tuned particularly in a mild acidic tumor microenvironment (pH ∼5–6). More importantly, the final biodegradation products of K₃ZrF₇:Yb/Er UCNCs can be excreted from the body of mice in a short period of time with no evidence of toxicity, in stark contrast to the nondegradable β-NaYF₄:Yb/Er UCNCs that primarily accumulate in the main organs of mice. These findings described here unambiguously would benefit the future biomedical applications and clinical translations of lanthanide-doped inorganic UCNCs.

中文翻译：

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用于体内应用的可生物降解无机上转换纳米晶体。

镧系元素掺杂的无机上转换纳米晶体 (UCNCs) 有望作为荧光诊断和治疗剂用于从生物成像到疾病治疗学的体内应用。然而，目前所有可用的镧系元素掺杂无机 UNCs 均不可生物降解，因此无法在合理的时间内从生物体内无害地消除，使其临床转化几乎是不可能的。^{在这里，我们报告了一类基于 Yb 3+} /Er ³⁺掺杂的无机七氟锆酸钾 (K ₃ ZrF ₇ :Yb/Er)的可发红光的可生物降解 UCNC ，其具有动态的“软”晶格，含有水溶性 [锆F ₇ ]^3–簇和一个 K ⁺阳离子。发红光的 K ₃ ZrF _{7 :Yb/Er UCNCs}在体外和体内暴露于水时都表现出 pH 依赖性的生物降解能力，并且使用固有的红色上转换发光监测的快速生物降解速率可以特别调整在温和的酸性肿瘤微环境（pH ∼5-6）。_{更重要的是，与不可降解的β-NaYF 4}形成鲜明对比的是，K ₃ ZrF ₇ :Yb/Er UCNCs 的最终生物降解产物可以在短时间内从小鼠体内排出，没有毒性迹象。:Yb/Er UCNCs 主要在小鼠的主要器官中积累。这里明确描述的这些发现将有利于镧系元素掺杂的无机 UCNC 的未来生物医学应用和临床转化。