Metal–organic frameworks (MOFs) featured with flexible design and versatile properties are finding increasing applications. In particular, integrating multiple functions into one framework can bring them improved detection efficiency towards various analytes. Herein, for the first time, a Fe–Zr bi-metal–organic framework (UiO-66(Fe/Zr)-NH₂) with three functions (intrinsic fluorescence, peroxidase-mimicking activity, and specific recognition) is designed to establish a ratiometric fluorescent platform for high-performance phosphate ion (Pi) sensing. The use of a fluorescent organic ligand endows the MOF material with a strong intrinsic fluorescence at 435 nm. The presence of Fe³⁺/Fe²⁺ nodes offers good enzyme-like capacity to catalyze the o-phenylenediamine (OPD) substrate to fluorescent OPDox (555 nm), which then quenches the intrinsic fluorescence of UiO-66(Fe/Zr)-NH₂ due to the inner filter effect. The Zr⁴⁺ nodes in the MOF material act as selective sites for Pi recognition. When Pi exists, it specifically adsorbs onto UiO-66(Fe/Zr)-NH₂ and decreases the latter's peroxidase-mimetic activity, resulting in the less production of fluorescent OPDox. As a consequence, the intrinsic fluorescence of UiO-66(Fe/Zr)-NH₂ at 435 nm is restored, and the signal from OPDox at 555 nm is reduced inversely. With the ratiometric strategy, efficient determination of Pi with outstanding sensitivity and selectivity was realized, giving a detection limit down to 85 nM in the concentration range of 0.2–266.7 μM. Accurate measurement of the target in practical water matrices was also validated, indicating its promising application for Pi analysis in environmental and other fields.

中文翻译：

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三功能Fe-Zr双金属有机框架可实现高性能的磷酸根离子比率荧光检测。

具有灵活设计和多功能特性的金属有机框架（MOF）正在得到越来越多的应用。特别是将多种功能集成到一个框架中，可以提高它们对各种分析物的检测效率。本文首次设计了具有三种功能（内在荧光，过氧化物酶模拟活性和特异性识别）的Fe-Zr双金属有机框架（UiO-66（Fe / Zr）-NH ₂）用于高效磷酸根离子（Pi）感应的比例荧光平台。荧光有机配体的使用使MOF材料在435 nm处具有很强的固有荧光。Fe的存在³⁺ / Fe的²⁺节点提供了良好的酶样容量催化Ò-苯二胺（OPD）底物形成荧光OPDox（555 nm），由于内部滤镜效应，该荧光终止了UiO-66（Fe / Zr）-NH ₂的固有荧光。MOF材料中的Zr ⁴⁺节点充当Pi识别的选择性位点。当存在Pi时，它会特异性吸附到UiO-66（Fe / Zr）-NH _2上，并降低UiO-66（Fe / Zr）-NH ₂的过氧化物酶模拟活性，从而导致荧光OPDox的产量降低。结果，UiO-66（Fe / Zr）-NH ₂的固有荧光435 nm处的信号被恢复，来自OPDox 555 nm处的信号被反向减小。通过比例分析策略，可以高效测定具有出色灵敏度和选择性的Pi，在0.2–266.7μM的浓度范围内，检测限低至85 nM。还验证了实际水基质中目标的准确测量，表明其在环境和其他领域的Pi分析中很有希望的应用。