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Residual antibiotic tetracycline (TC) that is hard to degrade and active has adversely affected public health and ecosystems. Therefore, developing straightforward, rapid, and sensitive probes for TC detection is highly desirable. Herein, we present a facile yet versatile strategy to design and fabricate luminescence turn-on TC sensors by applying the concept of indicator displacement to metal–organic frameworks (MOFs). It is illustrated by an elaborated dual-emitting nanoporous europium–MOF (Eu–MOF) constructed by Eu3+ cations and 2-aminoterephthalic acid (BDC-NH2), in which the former serves as receptors and the latter acts as luminescent indicators. The indicator displacement is based on the competitive interactions within Eu–MOF, which is confirmed by high-resolution mass spectrometry, photoluminescence, and UV–vis spectroscopy. Once Eu–MOF contacts TC, the competitive coordination effect induces the release of BDC-NH2 molecules and the accompanying turn-on blue emission, whereas the red emission of Eu3+ barely changes, thereby resulting in a remarkable ratiometric luminescence response and luminescence color switching from red to blue that is readily observed by the naked eye. The sensitive and quantitative determination of TC is accomplished through multiple readouts involving ratiometric emission intensity and emission color, exhibiting detection limits of 0.08 and 0.95 μM, respectively. Notably, the visual detection of TC is achieved using a smartphone color-scanning app. Considering the excellent tunability in the composition and structure of MOFs and their compatibility with various host–guest interactions applicable to indicator displacement assays, this study helps to create a universal avenue for leveraging MOFs in constructing luminescence turn-on sensors. [ABSTRACT FROM AUTHOR]

Hollow discontinuous Ge/GeO2 nanotubes are successfully prepared after the facile oxidization process in air, which are derived from the C/Ge core–shell nanofibers. Electrospinning and chemical vapor deposition techniques are used to fabricate the carbon nanofiber templates and the Ge shell electrode, respectively. Compared with the C/Ge nanocomposites, the Ge/GeO2 nanotube anode demonstrates improved electrochemical performance due to the enlarged surface area and enough space, which can effectively retard the Ge electrode large volume change during repeated cycling. Full‐battery Ge/GeO2||LiCoO2 is also configured and displays good Li‐ion storage ability. [ABSTRACT FROM AUTHOR]