Lanthanide Metal-Organic Framework Isomers with Novel Water-Boosting Lanthanide Luminescence Behaviors

Lanthanide Antenna Amplifier Multiplies the Optical Sensing Efficiency in Phototautomeric Metal-Organic Frameworks

Metal-organic frameworks (MOFs) incorporating phototautomeric ligands have shown significant potential for new-generation optical sensing devices. It is challenging to enlarge the energy difference of tautomers, which is crucial for improving the sensing efficiency. Herein, we report a novel tactic to amplify the excited-state intramolecular proton transfer (ESIPT) effect via the "antenna effect" in lanthanide sensitization. Specifically, by leveraging the enol (E)-keto (K) phototautomerization process, we achieve precise manipulation of the energy gap between the lowest ligand triplet state and the Eu(III) emitting level through fine-tuning. As a result, the small wavelength shift (10 nm) between the E* and K* emissions is amplified into an approximately 65-fold intensity change in Eu(III) emission. This enhancement is accompanied by a significantly lowered limit of detection (LOD: 0.53 μg/L) and improved sensitivity (0.6955% RH-1) in real-time humidity monitoring across a broad linear detection range (0-95.0% RH). Computational simulations and single-crystal analyses demonstrate two key mechanisms: (1) the appropriate hydrophilic/hydrophobic distribution in the MOF cavity facilitates rapid hydration/dehydration and (2) H2O desorption/adsorption-dependent ESIPT switching governs the deactivation/activation of the Eu(III) 4f excited state. This work presents an optimization approach to enhance energy utilization in MOF-based optical sensing.

Hydrogen-Bond-Regulated Tb3+-Centered Emission in a ZnII-TbIII Heterometallic Compound for Water Sensing in Ethanol and Gasoline

Luminescent lanthanide compounds stand out for their distinctive characteristics including narrow emission bands, substantial Stokes shifts, high quantum yields, and unique luminescent colors. However, Ln3+ is highly susceptible to vibrational quenching from X-H (X = O/N) high-energy oscillators in the embedded organic antenna, resulting in significant nonradiative energy dissipation of the 5D excited states of Ln3+. Herein, we introduce a strategy based on supramolecular interactions to modulate the nonradiative transitions in a new ZnII-TbIII heterometallic compound, [ZnTb(HL)2(NO3)Cl2]·2CH3CN·H2O (ZnTb), based on a phenyl-substituted pyrazolinone-modified salicylamide-imide ligand (H2L). The regulation mechanisms are explored in detail both experimentally and theoretically. With the N,N'-dimethylformamide (DMF)-boosted Tb3+ luminescence, ZnTb⊃DMF (1 mg of ZnTb + 2 mL of DMF) realizes a rapid (3s) and sensitive detection of water in DMF with a detection limit of 0.021%. Further, ZnTb⊃DMF can detect trace amounts of water in ethanol and ethanol gasoline with a low detection limit of 0.023% and 0.048%. In addition, portable paper strips of ZnTb⊃DMF are prepared to improve its practicability, which can afford real-time and faster (1 s) in situ visual sensing of trace amounts of water in common organic solvents and ethanol gasoline with sensitivity comparable to the titration results. This study provides a new idea for the lanthanide luminescence modulation and application in the field of fluorescence sensing.

Water-Induced Turn-on of Lanthanide Photoluminescence Emission and Application in Colorimetric Sensing of Trace Water

To examine the water-induced photoluminescence turn-on and its potential application in trace water sensing, a new series of [LnIII(dmba)3(H2O)2]·2H2O, where LnIII = LaIII (I), PrIII (II), NdIII (III), SmIII (IV), EuIII (V), GdIII (VI), TbIII (VII), DyIII (VIII), HoIII (IX), and ErIII (X), were synthesized using dimethoxybenzoic acid (Hdmba). Their single-crystal structures and thermal and chemical robustness were investigated, and the effects of lanthanide contraction and noncovalent interactions were discussed. The photoluminescence and colorimetric properties of I-X were investigated. Their dependence on dehydration and rehydration was disclosed, from which the significant role of noncovalent interactions was proposed. Based on the dehydration-rehydration-dependent responses in the forms of photoluminescence emission and color, the turn-off (dehydration) and turn-on (rehydration) of the red emission of EuIII (V) were demonstrated. Using a mobile phone camera and freeware application, its use in the colorimetric sensing of trace water in polar organic solvents was successfully achieved. With respect to ethanol, acetonitrile, and acetone, linear correlations were established from 0 to 3-5% by volume of water with an R 2 of over 0.98. The detection and quantification limits were less than 0.5 and 1.5%, respectively. The percentage recoveries were 92 and 110%. The underlying mechanism was postulated.

Eu3+-Doped Mixed-Ligand UiO-66-Type Metal-Organic Framework for Ratiometric Fluorescence Sensing Fluoride Ions with Ultralow Detection Limit

Metal-organic frameworks (MOFs) have emerged as a highly promising platform for various sensing applications due to their tunable structures and functionalities. In the present work, a Eu3+-doped mixed-ligand MOF, namely, the Eu3+@UiO-66-IPA, exhibited excellent luminescent properties and high fluorescence stability in aqueous media, displaying dual-emission peaks under 395 and 615 nm excitation that were readily visible to the naked eye. Importantly, the presence of fluoride ions (F-) promoted the "antenna effect" between the ligand and the Eu3+ centers, which significantly enhanced the emission intensity of the Eu3+ characteristic peak. In addition, the addition of F- also inhibited the quenching effect of high-energy O-H bonds existing in the aqueous environment. Notably, Eu3+@UiO-66-IPA demonstrated exceptional selectivity for F- over a range of competing anions, with a remarkable limit of detection as low as 0.22 μM. The developed Eu3+-doped mixed-ligand MOF system offers a highly promising strategy for the simple and accurate sensing of F- in practical applications.

Aptamer-Based Electrochemical Biosensing Platform for Analysis of Cardiac Biomarkers

Monitoring biomarkers secreted by cardiomyocytes is critical to evaluate anticancer drug-induced myocardial injury (MI). Cardiac troponin I (cTnI) is considered the gold standard biomarker for MI. Herein, an electrochemical aptasensor is engineered for cTnI detection based on lanthanide europium metal-organic frameworks (Eu-MOFs) and a hybridization chain reaction-directed DNAzyme strategy. Three types of Eu-MOF morphologies were easily synthesized by changing the solvent, and the Eu-MOF modulated by mixing the solvent of dimethylformamide and H2O (D-Eu-MOF) exhibited the best performance compared to other morphologies of the Eu-MOFs. Multifunctional nanoprobes were constructed from D-Eu-MOF@Pt loaded with natural horseradish peroxidase and combined with an aptamer-initiated nuclear acid hybridization chain reaction to form G-quadruplex/hemin DNAzymes for signal amplification. A novel capture probe is constructed on the basis of DNA nanotetrahedrons modified on screen-printed gold electrodes to enhance the capture of the target and multifunctional nanoprobes for signal amplification. It exhibits a detection limit of 0.17 pg mL-1 and a linear range from 0.5 pg mL-1 to 15 ng mL-1. The practicality of the platform is evaluated by measuring cTnI in real samples and secreted by cardiomyocytes after drug treatment, which provides great potential in drug-induced MI evaluation for clinical application.

Multi-functional GdEuxTb1-xO3 (x = 0 to 1) nanoparticles: colour tuning optical properties, water proton spin relaxivities, and X-ray attenuation properties

Multi-functional nanoparticles are useful for various applications, such as biomedical imaging, detection, and display technologies. Colour-tunable GdEuxTb1-xO3 nanoparticles were synthesized with emission colour ranging from green (545 nm) to red (616 nm) by varying x (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1). These nanoparticles were surface-grafted with polyacrylic acid and a small quantity of 2,6-pyridinedicarboxylic acid. This modification aimed to ensure long-term colloidal stability (>1 year without precipitation) and high quantum yields (>30%) in aqueous media. Additionally, they exhibited long emission lifetimes (∼1 ms), high longitudinal water proton spin relaxivities (>30 s-1mM-1), and high X-ray attenuation efficiencies (∼10 HU mM-1). These multiple exceptional properties within a single nanoparticle make them highly valuable for applications in biomedical imaging, noise-free signal detection, and colour display.

Polymorphism and Its Influence on Catalytic Activities of Lanthanide-Glutamate-Oxalate Coordination Polymers

To study the relationship between polymorphism and catalytic activities of lanthanide coordination polymers in the cycloaddition reactions of CO2 with epoxides, the monoclinic and triclinic polymorphs of [LnIII(NH3-Glu)(ox)]·2H2O, where LnIII = LaIII (I), PrIII (II), NdIII (III), SmIII (IV), EuIII (V), GdIII (VI), TbIII (VII), and DyIII (VIII), NH3-Glu- = NH3+ containing glutamate, and ox2- = oxalate, were synthesized and characterized. Factors determining polymorphic preference, the discrepancy between the two polymorphic framework structures, potential acidic and basic sites, thermal and chemical stabilities, active surface areas, void volumes, CO2 sorption/desorption isotherms, and temperature-programmed desorption of NH3 and CO2 are comparatively presented. Based on the cycloaddition of CO2 with epichlorohydrin in the presence of tetrabutylammonium bromide under solvent-free conditions and ambient pressure, catalytic activities of the two polymorphs were evaluated, and the relationship between polymorphism and catalytic performances has been established. Better performances of the monoclinic catalysts have been revealed and rationalized. In addition, the scope of monosubstituted epoxides was experimented and the outstanding performance of the monoclinic catalyst in the cycloaddition reaction of CO2 with allyl glycidyl ether under ambient pressure has been disclosed.