With the introduction of Eu 3+ ions as the secondary fluorescent signal reporter and sensing active sites, a dual-emission ratiometric sensor of Eu 3+ @NiMOF (Eu 3+ functional NiMOF) for hippuric acid (HA) detection in urine and serum was fabricated via the postsynthetic encapsulating strategy. Based on the two emission signals at 441 nm (turn-on) and 628 nm (turn-off), the produced Eu 3+ @NiMOF ratiometric sensor provided enhanced sensitivity, higher selectivity, and 9.7 times lower limits of detection (LOD) for the detection of HA (2.38 μM, 0.42 μg•mL −1 ) than that of the pristine NiMOF. Considering the high sensitivity and visualization results, further exploration of intelligent applications in the HA sensing process was carried out by constructing a tandem combinational logic gate to improve the practicability and convenience with the help of a smartphone. This work provides a promising approach for developing MOF-based ratiometric sensors to detect biomarkers.
Aggregated multilamellar spheres with enhanced luminescence and stimulus-responsiveness were co-assembled from Na9(EuW10O36)·32H2O (EuW10) and myristoylcholine chloride (Myr).
In recent years, aggregates formed in deep eutectic solvents (DESs), especially micelles, have attracted much attention. In this study, the phase behaviours of a cationic surfactant, cetylpyridinium bromide (CPBr), in two DESs, choline chloride + glycerol (ChG) and choline chloride + ethylene glycol (ChEG), were investigated in wide concentration and temperature ranges. With the help of small angle X-ray scattering, polarized optical microscopy and rheological measurements, the structures and properties of various aggregates were characterized. The micelles, hexagonal phase, bicontinuous cubic phase and lamellar phase were observed with the increase of CPBr concentration. Such rich phase behaviours were due to the large cohesive energy densities of DESs. Comparative studies in water and ethylammonium nitrate were carried out to explore how well DESs acted as self-assembly media.
Recently, hybrid
coassembly between polyoxometalates (POMs) and
cationic building blocks provides an efficient strategy to greatly
optimize POMs’ functionality as well as their aggregate structural
diversity. Adaptive hybrid supramolecular materials with enhanced
luminescence have then been obtained from lanthanide-containing POMs.
In this work, a commercially available and pH-switchable zwitterionic
surfactant, tetradecyldimethylamine oxide (C14DMAO), was
chosen to coassemble with a lanthanide-containing anionic POM [Na9(EuW10O36)·32H2O, abbreviated
as EuW10] in water. The much improved red-emitting luminescent
nanobelts at a C14DMAO/EuW10 molar ratio (R) of 20 were obtained, which exhibited longer luminescence
lifetime and higher quantum yield compared with EuW10 aqueous
solution. After careful characterization of morphology and structure
of nanobelts, an unusual axial lamellar aggregation arrangement mechanism
was proposed. It was the partial protonation of C14DMAO
at the solution pH of about 6.5 that led to positively charged micelles,
being bridged by anionic EuW10 clusters to aggregate into
such novel nanobelts under the synergetic effects of appropriate electrostatic,
hydrogen-bonding, and hydrophobic interactions. The resulted pH-responsive
luminescent nanobelts and their aggregation model should offer attractive
references for preparing smart optical supramolecular materials.
Hybridization of polyoxometalates (POMs) with cationic surfactants offers the opportunity to greatly improve their functionalities as well as processabilities. Here, a surfactant-encapsulated Eu-containing POM complex (SEP) was formed via electrostatic interaction between 1-octadecyl-3-methylimidazolium bromide (OB) and Na(EuWO)·32HO (EuW). SEP was first self-assembled in a protic ionic liquid to prepare the soft aggregates to fundamentally avoid the fluorescence quenching by water molecules. The structures and photophysical properties of SEP or aggregates were investigated thoroughly by NMR and FTIR spectroscopy, optical and electron microscopy, small-angle X-ray scattering, and fluorescence measurements. The formed gel-like aggregates were found to compose of three-dimensional networks of microribbons with an interdigitated layered molecular packing of SEP, which was different from the usual inverse bilayer model of POM hybrids in common organic solvents. Compared to EuW solid or its aqueous solution, both SEP and its aggregates exhibited intense red luminescence with much improved lifetime and quantum efficiency. In addition, the soft aggregates exhibited an efficient energy transfer and an obviously enhanced monochromaticity, owning to the organized arrangement of EuW units and a confined microenvironment to isolate them from each other between adjacent layers. The obtained results will not only present a useful reference to the aggregation behavior of POM hybrids in ionic liquids, but also provide an easy way to design EuW luminescent soft materials based on the nonaqueous media.
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