A novel Co-based metal–organic framework (MOF) with the formula of {[Co3(BIBT)3(BTC)2(H2O)2]·solvents} n (JXUST-2, where JXUST denotes Jiangxi University of Science and Technology, BIBT = 4,7-bi­(1H-imidazol-1-yl)­benzo-[2,1,3]­thiadiazole, and H3BTC = 1,3,5-benzenetricarboxylic acid) has been solvothermally prepared, which takes 3D structure with a rare 3,4,6-c topology and contains intramolecular hydrogen bonds. Interestingly, the sensing investigations suggest that JXUST-2 could be considered as a multifunctional fluorescence sensor toward Fe3+, Cr3+, and Al3+ via a turn-on effect with good reusability and detection limits of 0.13, 0.10, and 0.10 μM, respectively. The turn-on effect of JXUST-2 could be ascribed to an absorbance caused enhancement (ACE) mechanism. Notably, JXUST-2 is the first turn-on MOF fluorescent sensor for Fe3+, Cr3+, and Al3+ simultaneously.

A Zn II -based metal−organic framework (MOF) with a rare tcj topology has been solvothermally synthesized and displays relatively good thermal and chemical stabilities. Interestingly, the MOF can sensitively and selectively sense acetylacetone (acac) via a fluorescence enhancement effect with a detection limit of 0.10 ppm and good reusability, which demonstrates the first example of a MOF-based turn-on fluorescent sensor for acac.

Polypyrrole (PPy)-coated Ag composites were synthesized through an immiscible organic/inorganic biphasic system in the presence of polyvinylpyrrolidone (PVP). Highly dispersed PPy/Ag was obtained by using interface polymerization and controlling the reactive conditions. The presence of PVP could realize the effective coating of PPy on the surface of Ag. The core-shell structure was directly confirmed by transmission electron microscopy and also characterized by techniques such as Fourier transform infrared spectroscopy and X-ray diffraction. Furthermore, three-layered Au-modified PPy-coated Ag nanocomposite was prepared through the reaction of Au colloidal solution and PPy/Ag. Moreover, Au/PPy/Ag nanocomposite was immobilized on the surface of a glassy carbon electrode and applied to construct a dopamine (DA) biosensor. The biosensor exhibited a fast amperometric response to DA with the linear range from 1 × 10 -4 to 5 × 10 -3 mol/L.

Activatable imaging probes as alternatives to "always on" imaging probes have attracted more and more attention due to their improved sensitivity and specificity. They are commonly designed to amplify or boost imaging signals only in response to specific biomolecular recognition or interaction. Thus, the design strategies play a vital role in the fabrication of activatable imaging probes. In this review, we focus on the design mechanisms and biological applications of those nanomaterial-based activatable imaging probes reported in the past five years, benefitting greatly from the good development of nanotechnology. These probes not only include the most studied activatable fluorescence imaging probes, but also cover more activatable MR imaging probes based on nanoparticle contrast agents and activatable photoacoustic imaging probes, providing more bases for clinical translation.

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