Function-Oriented: The Construction of Lanthanide MOF Luminescent Sensors Containing Dual-Function Urea Hydrogen-Bond Sites for Efficient Detection of Picric Acid

Two Stable Pillar-Layered Zn-LMOFs for Highly Fluorescence Sensing of Inorganic Pollutants and Nitro Aromatic Compounds in Water

Luminescent metal-organic frameworks (LMOFs) are a potential class of functional materials for the photoluminescent detection of a wide range of analytes as well as for the detection of pollutants in wastewater. Herein, by using the pillar-layered strategy, two new luminescence Zn-LMOFs (JLU-MOF222 and JLU-MOF223) were successfully solvothermal synthesized. The 2D layers are both consisting of Zn2+ and TPHC [TPHC = (1,1':2',1″-terphenyl)-3,3″,4,4',4″,5'-hexacarboxylic acid] ligands and then pillared by the different N-donor ligands to form the 3D Zn-LMOFs with fsh topology. Benefiting from the uncoordinated carboxylate sites, uncoordinated N atom, or -NH2 group in the pillaring ligands and excellent stability in pH = 2-13 aqueous phase, JLU-MOF222 and JLU-MOF223 not only can sensitively detect trace amounts of inorganic pollutants (Fe3+, Cr2O72-) and nitro aromatic compounds TNP and 2,4-DNP (TNP = 2,4,6- trinitrophenol, 2,4-DNP = 2,4-dinitrophenol) through luminescence quenching but also exhibit high selectivity of other anti-interference competing analytes. The two new Zn-LMOFs can be used as potential luminescent sensors for pollutant detection in water due to their high KSV and low limit of detection (LOD).

Synthesis and characterization of cis and trans cobalt(II) nalidixate complexes having a 1-(4-chlorophenyl)-3-(pyridin-4-ylmethyl)urea ligand

The synthesis and characterization of specific cis- and trans-isomers of a cobalt(II) bis-nalidixate complex with a pyridine-based urea, 1-(4-chlorophenyl)-3-(pyridin-4-ylmethyl)urea (L), ligand are reported. The two isomers, cis-[Co(L)2(NALD)2]·0.5DMF·H2O and trans-[Co(L)2(NALD)2]·2DMF·2H2O (the nalidixate anion is abbreviated to NALD) were prepared by anion-guided synthesis. When cobalt(II) chloride was used as one of the reactants, the reaction yielded the trans-isomer under ambient reaction conditions. Whereas a reaction using cobalt(II) nitrate provided only the cis-isomer when the reaction was continued for a prolonged time. On the other hand, the cis-isomer was converted to the trans-isomer in solution upon treatment with chloride ions. The chloride-assisted formation of the trans-isomer was investigated by a UV-visible study, and it passed through a bond reorganization by forming a tetrahedral intermediate complex. A DFT calculation was carried out to show the difference in energy between the isomers as well as the energy of a plausible tetrahedral cobalt complex. The aggregation behavior of the cis-isomer in different solvents was investigated, and solvent-dependent aggregation and a solvent-dependent Cotton effect were observed.

Selective sensing of picric acid using a Zn(II)-metallacycle: experimental and theoretical validation of the sensing mechanism and quantitative analysis of sensitivity in contact mode detection

A combination of N,N',N''-tris(3-pyridyl)-1,3,5-benzenetricarboxamide (L1) and p-chlorobenzoic acid (HL2) with Zn(NO3)2·6H2O resulted in the formation of a dinuclear metallacycle [ZnL1(L2)2(DMF)2]2 (1(DMF)4). In 1(DMF)4, the Zn(II) centre adopts a square pyramidal geometry, while one of the pyridyl N out of the three pyridyl groups in L1 remained uncoordinated. Solvated DMF molecules are present in 1(DMF)4. The structural and chemical nature of 1(DMF)4 is effective for it to act as a potential fluorescent probe for the detection of nitroaromatic compounds. It is observed that the probe, 1(DMF)4, could selectively detect picric acid (PA) among various aromatic compounds in solution (DMSO), while the solid state (contact mode) detection showed a positive sensing response for the nitrophenols (PA: 87% quenching efficiency, 2,4-dinitrophenol (2,4-DNP): 57% quenching efficiency and 4-nitrophenol (4-NP): 40% quenching efficiency). The limit of detection (LOD) of PA by the probe in DMSO was found to be 6.8 × 10-11 M while the LOD in contact mode detection was estimated to be 0.49 ng cm-2. The mechanism of selective detection of PA by 1(DMF)4 in DMSO was analyzed through photophysical studies, 1H-NMR experiments and also by density functional theory (DFT) calculations. The effective overlap of the absorption spectrum of 1(DMF)4 and emission spectrum of PA in DMSO suggests that the Förster resonance energy transfer (FRET) is responsible for quenching phenomena in DMSO. The DFT calculations and molecular docking studies showed the adduct formation due to the favorable interactions between 1(DMF)4 and PA in DMSO, while negligible interactions were observed between 1(DMF)4 with other aromatic compounds. The experimental and DFT studies showed that the efficient sensing ability of PA by 1(DMF)4 in the solid-state was due to photoelectron transfer (PET) and FRET phenomena described herein.

A highly efficient lanthanide coordination polymer luminescent material for the multi-task detection of environmental pollutants

It is challenging to explore novel-structure lanthanide coordination polymers (Ln-CPs) for sensing environmental pollutants. Herein, we designed and synthesized an organic bridging linker 3-(carboxymethoxy)-1-(carboxymethyl) pyrazole-4-carboxylic acid (H3ccpc), and then successfully prepared and characterized a novel Ln-CP, namely [Tb2(ccpc)2(H2O)6]·1.5H2O (ccpcTb). Structural analysis indicates that ccpcTb exhibits a two-dimensional structure, in which Tb ions are in an eight-coordinated environment. The photoluminescence performance of ccpcTb was discussed in detail. The ccpcTb displays bright green luminescence and behaves as a multi-responsive luminescent sensor toward Fe3+ ions, Cr2O72- ions and 2,4,6-trinitrophenol with high selectivity and low detection limits. Furthermore, the possible luminescence sensing mechanisms have been addressed in detail. The luminescence quenching mechanism of sensing Fe3+ and Cr2O72- is attributed to the energy competitive absorption, while that of sensing TNP is due to the synergistic effect of energy competitive absorption and photo-induced electron transfer.

Investigation of the Influence of Functionalization Strategy on Urea 2D MOF Catalytic Performance

Urea-functionalized MOFs with unique properties have recently been used as efficient platforms to conduct organocatalytic reactions. To gain more insight into the key factors which govern an efficient organocatalytic reaction in urea-MOFs, two different urea-containing 2D MOFs TMU-58 ([Zn(L1)(oba)].CH₃CN) and TMU-83 ([Zn(L2)(oba)].DMF), where L1 = (1E,5E)-1,5-bis(1-(pyridine-4-ylethylidene)carbonohydrazide, L2 = (1E,5E)-1,5-bis(1-(pyridine-4-ylmethylene)carbonohydrazide, and oba = 4,4'-oxybisbenzoic acid, with abundant accessible active sites, were selected and examined in the methanolysis of styrene oxide. TMU-58 with the ability to form a two-point H-bond with different substrates revealed a high organocatalytic efficiency in the regioselective ring opening of styrene oxide. The catalytic activation of epoxide oxygen by the urea N-H functional sites, followed by the nucleophilic attack of methanol at the benzylic carbon led to the formation of 2-methoxy-2-phenylethanol as the major product. DFT calculations were also performed to investigate the acidic strength of the urea hydrogens in both TMU-58 and TMU-83 structures as a major factor to conduct an efficient catalytic reaction. The results indicated the more acidic nature of the urea hydrogens in TMU-83; however, its catalytic efficiency was remarkably reduced due to the inappropriate orientation of the active interaction sites within the framework revealing the importance of proper orientation of the urea hydrogens in conducting an efficient organocatalytic reaction. The current study provides a comparative study on the function-property relationship in 2D MOF assemblies which has not been explored so far.

Dy(III)-coordination imprinted self-assembly microspheres based on a silica core for highly sensitive and selective detection of two carbamate pesticides

Carbamate (CB) pesticides possess potential carcinogenic and mutagenic activities towards humans even at very low dosages. Thus, broad-specificity probes with high sensitivity and speed are needed for multiple CB determination. This study is the first to focus on Dy³⁺ ions-coordinated self-assembly on a silica core using a surface imprinting procedure, for the simultaneous fluorometric detection of residues of metolcarb (MC) and pirimicarb (PC) insecticides. A simple and mild solvothermal method was applied for the preparation of fluorescent imprinted microspheres starting from 1,10-phenanthroline (Phen)-ligated Dy³⁺ ions to guide imprinted self-assembly of chitosan (CTS), glutaraldehyde (GA), and two carbamate pesticides (MC and PC) on the silica surface by means of coordinate bonds and hydrogen bonds. The as-prepared microspheres displayed strong fluorescence emissions via the antenna effect derived from the Phen ligand and the Schiff base oligomers for sensitizing the Dy³⁺ ions. An expanded in-depth mechanism study was performed on the fluorescence enhancement involving Förster resonance energy transfer (FRET) from the pesticides (donor) to the acceptor. A linear increase in fluorescence at 483 nm for MC and 574 nm for PC upon the imprinted microspheres was observed under the same 350 nm excitation wavelength. Moreover, the quantitative recognition process could be carried out simultaneously and tolerate strong distractions both from five other similar carbamate insecticides and from complicated matrices (e.g., an extract of Chrysanthemum morifolium Ramat). The detection limit was 4 ng mL^-1 with a range of 10-60 ng mL^-1 for MC and 0.4 ng mL^-1 with a range of 1-30 ng mL^-1 for PC. Further characterization of the material, including TEM, SEM, XPS, and FTIR, Raman, and fluorescence spectra, verified that the Dy³⁺ ions play a decisive role in promoting imprinted self-assembly around the silica core. Hence, a novel polynuclear Ln-organic imprinted probe having high selectivity, stability, and sensitivity for the detection of two carbamate insecticides is presented in this study.

Expanding the Knowledge of the Selective-Sensing Mechanism of Nitro Compounds by Luminescent Terbium Metal-Organic Frameworks through Multiconfigurational ab Initio Calculations

The current research shows that the excited-state dynamics of the antenna ligand, both in the interacting system sensor/analyte and in the sensor without analyte, is a safe tool for elucidating the detection principle of the luminescent lanthanide-based metal-organic framework sensors. In this report the detection principle of the luminescence quenching mechanism in two Tb-based MOFs sensors is elucidated. The first system is a luminescent Tb-MOF [Tb(BTTA)_1.5(H₂O)_4.5]_n (H₂BTTA = 2,5-bis(1H-1,2,4-triazol-1-yl) terephthalic acid) selective to nitrobenzene (NB), labeled as Tb-1. The second system is {[Tb(DPYT)(BPDC)_1/2(NO₃)]·H₂O}_n (DPYT = 2,5-di(pyridin-4-yl) terephthalic acid, BPDC = biphenyl-4,4'-dicarboxylic acid), reported as a selective chemical sensor to nitromethane (NM) in situ, labeled as Tb-2. The luminescence quenching of the MOFs is promoted by intermolecular interactions with the analytes that induce destabilization of the T₁ electronic state of the linker "antenna", altering thus the sensitization pathways of the Tb atoms. This study demonstrates the value of host-guest interaction simulations and the rate constants of the radiative and nonradiative processes in understanding and elucidating the sensing mechanism in Ln-MOF sensors.

Multifunctional luminescent Zr(IV)-MOF for rapid and efficient detection of vanillin, CrO42- and Cr2O72- ions

Fast and efficient detection of pollutants in the food or wastewater is an urgent need for protecting human health and ecological environment. Herein, a luminescent Zr(IV)-MOF (HBU-20) has been conveniently synthesized. It could be used as a fluorescent probe for detection of vanillin, CrO₄^2-, and Cr₂O₇^2- in aqueous medium. All the fluorescence response time is less than 10 s and the detection limits of vanillin, CrO₄^2- and Cr₂O₇^2- achieve 0.38 μM, 0.065 μM and 0.0089 μM, respectively. Interestingly, common anions, cations and amino acids in the solution can not affect the fluorescence detection. Meanwhile, the fluorescence detection process can be successfully implemented even under strong acid or strong alkaline conditions. Further research shows that the inner filter effect (IFE) plays a major role in the sensing process. The rapid and sensitive fluorescence responses indicate that the compound is a promising multifunctional probe for sensing toxic substance. The results can provide an important reference for the design of new fluorescent probes.

Seven Ln(III) coordination polymers with two kinds of geometric coordination but the same 3D topological property: luminescence sensing and magnetic property

Two series of seven lanthanide metal coordination polymers (Ln-CPs) formulated as {[Ln(dttpa)_1.5(H₂O)₂]·H₂O}_n [Ln = La³⁺ (1), Ce³⁺ (2), Nd³⁺ (3), Sm³⁺ (4) and Eu³⁺ (5)] and {[Ln (dttpa)_1.5(H₂O)]·xH₂O}_n [Ln = Tb³⁺ (6) and Er³⁺ (7), x = 0.75] have been successfully constructed using Ln³⁺ ions and 2,5-di(1H-1,2,4-triazol-1-yl)terephthalic acid (H₂dttpa) via a hydrothermal method. Their 3D structures are fully characterised by Fourier transform infrared (FT-IR) spectroscopy, X-ray single-crystal analyses, powder diffraction analyses (PXRD), elemental analyses (EAs) and thermogravimetric analyses (TGAs). All Ln-CPs display the same topological property with the point symbol of {4²·8⁴}{4⁴·6²}₂{4⁹·6⁶}₂, and crystallize in the triclinic space group P1̄. Interestingly, Eu-CP (5) effectively sensitizes the visible emission of Tb³⁺ and shows high selectivity and stable response with the lowest detection limit of 9.88 nM. Furthermore, Tb-CP (6) acts as a good luminescence sensor to detect nitrobenzene (NB) with a detection limit of 12.5 nM. In addition, the magnetic susceptibility measurement for Er-CP (7) further shows that compounds constructed by dttpa^2- are a kind of promising functional material.

Five Mesoporous Lanthanide Metal-Organic Frameworks: Syntheses, Structures, and Fluorescence Sensing of Fe3+, Cr2O72-, and H2O2 and Electrochemical Sensing of Trinitrophenol

When a multicarboxylate aromatic ligand, 3,5-di(2',4'-dicarboxylphenyl)benzoic acid (H₅L), was employed, five structurally similar lanthanide metal-organic frameworks (Ln-MOFs), {[Pr₁₀L₆(OH)₃Cl(H₂O)₆]·4C₂H₈N}_n (1), {[Nd₁₀L₆(OH)₄ (H₂O)₉]·4C₂H₈N}_n (2), {[Gd₁₀L₆(OH)₄(H₂O)₃]·4C₂H₈N}_n (3), {[Ho₁₀L₆(OH)₄ (H₂O)₃]·4C₂H₈N}_n (4) and {[Er₁₀L₆(OH)₄(H₂O)₆]·4C₂H₈N}_n (5), were synthesized and characterized. Single-crystal X-ray structural analyses disclosed that all five Ln-MOFs crystallize in the trigonal R₃ space group. They have three-dimensional mesoporous structure featuring the coexistence of binuclear and tetranuclear species as inorganic building units. The mesoporous structure of 3 was verified by the gas adsorption experiment of N₂. Fluorescence analysis showed that 3 can selectively detect Fe³⁺, Cr₂O₇^2-, and H₂O₂; furthermore, it can be used for the electrochemical detection of trinitrophenol. With the merit of an excellent highly sensitive detection performance, 3 has unpredictable application prospects in future research fields.

A Dihydrotetrazine-Functionalized Metal-Organic Framework as a Highly Selective Luminescent Host-Guest Sensor for Detection of 2,4,6-Trinitrophenol

Pore decoration of metal-organic frameworks (MOFs) with functional groups is a useful strategy to attain high selectivity toward specific analytes, especially in the presence of interfering molecules with similar structures and energy levels, through selective host-guest interactions. In this work, we applied a dihydrotetrazine-decorated MOF, TMU-34, with the formula [Zn(OBA)(H₂DPT)_0.5]_n·DMF, where H₂OBA is 4,4'-oxybis(benzoic acid) and H₂DPT is 3,6-bis(pyridin-4-yl)-1,4-dihydro-1,2,4,5-tetrazine, for the highly selective detection of phenolic NACs, especially TNP (94% quenching efficiency, detection limit 8.1 × 10^-6 M, K_SV = 182663 mol L^-1), in the presence of other substituted NACs especially -NH₂-substituted NACs. Investigations reveal that the quenching mechanism is dominated by photoinduced MOF-to-TNP electron transfer through possible hydrogen-bonding interactions between the phenolic hydroxyl group of TNP and dihydrotetrazine functions of TMU-34. Despite extensive publications on the detection of TNP in the presence of other NACs, the significance of this work will be elucidated if attention is paid to the fact that TMU-34 is among the rare and highly selective MOF-based TNP sensors in the presence of -NH₂-substituted NACs as the serious interferers.

One-dimensional Europium-coordination polymer as luminescent sensor for highly selective and sensitive detection of 2,4,6-trinitrophenol

Three isostructural lanthanide coordination polymers (LnCPs), [Ln(L)₆(DMF)]_n {HL = 2-(2-formylphenoxy) acetic acid, Ln = Sm (1); Eu (2); Tb (3)} have been synthesized by solvothermal reaction and characterized. Single crystal analyses revealed that the architectures of these LnCPs own one dimensional chain which can be further packed into two-dimensional architectures by hydrogen bonds. Moreover, these LnCPs can offer strategically placed uncoordinated formyl groups, which may act as hydrogen-bond acceptor in the sensing of nitro explosives. Luminescence measurements reveal that LnCPs 2 and 3 exhibit strong luminescence in solid states. LnCP 2 shows quick, highly selective and sensitive detection of 2,4,6-trinitrophenol (TNP) with the high quenching constant (2.6 × 10⁴ M^-1) and low detection limit (3.39 μM), which indicates that LnCP 2 is more efficient than most of Eu-based coordination polymers for the sensing of TNP. Furthermore, LnCP 2 represents the first example of one-dimensional Eu-based sensors with formyl group as hydrogen-bonding site in the detection of TNP.

Construction of a series of Ln-MOFs Luminescent sensors based a functional “V” shaped ligand

Abstract: It is necessary for decreasing application cost of luminescent Ln-MOFs sensors to develop multiple functionalities. The ingenious design of ligands and the rational dope of Ln3+ ions are main...

A multi-responsive luminescent sensor based on a stable Eu(iii) metal–organic framework for sensing Fe3+, MnO4−, and Cr2O72− in aqueous solutions

A stable benzothiadiazole-based Eu(iii) metal–organic framework with cco topology has been successfully constructed, and represents the multifunctional fluorescence sensor toward Fe3+, MnO4− and Cr2O72− in aqueous solutions.

Novel mixed ligand coordination compounds of some rare earth metal cations containing acesulfamato/N,N-diethylnicotinamide

The mixed ligand coordination compounds containing acesulfamato and N,N -diethylnicotinamide biomolecules of some rare earth metal cations (Eu3+, Tb3+, Ho3+, Er3+ and Yb3+) were synthesized, and their structural properties were investigated. Possible structural formulas have been proposed by determining the chemical composition of molecules (elemental analysis), binding properties (infrared spectroscopy, mass analysis, solid-state UV-vis spectroscopy), thermal degradation properties (TGA / DTA curves). Based on the data collected, it is suggested that rare earth metal cations with a 3+ oxidation state have sextet coordination. The geometries of the structures were thought to be distorted octahedral. The charge balance of the coordination sphere is balanced by a monoanionic acesulfamato located outside the coordination sphere. When the thermal behaviours of the complexes were examined, it was determined that the compounds with Eu3+, Tb3+, and Yb3+ metal cations contained one hydrate water outside the coordination sphere. Hydrate waters do not exist in the Ho3+ and Er3+ metal cation-centred complexes. At the end of the thermal decomposition analysis of all complex structures, it was determined that they leave the relevant metal oxides in the reaction vessels as final decomposition products.

Noncovalent Interactions at Lanthanide Complexes

Lanthanide complexes have attracted a widespread attention due to their structural diversity, as well as multifunctional and tunable properties. The development of lanthanide based functional materials has often relied on the design of the secondary coordination sphere of the corresponding lanthanide complexes. For instance, usually simple lanthanide salts (solvento complexes) do not catalyze effectively organic reactions or provide low yield of the expected product, whereas the presence of a suitable organic ligand with a noncovalent bond donor or acceptor centre (secondary coordination sphere) modifies the symmetry around the metal centre in lanthanide complexes which then successfully can act as catalysts in both homogenous and heterogenous catalysis. In this minireview, we discuss several relevant examples, based on X-ray crystal structure analyses, in which the hydrogen, halogen, chalcogen, pnictogen, tetrel and rare-earth bonds, as well as cation-π, anion-π, lone pair-π, π-π and pancake interactions, are used as a synthon in the decoration of the secondary coordination sphere of lanthanide complexes.

Two new lanthanide complexes with 5-(Pyrazol-1-yl)nicotinic acid: Structures and their anti-cancer properties

Two new lanthanide complexes [PrL₂(EA)₂]NO₃ (complex 1) and [SmL₂(EA)₂]NO₃ (complex 2) (H₂L = 5-(Pyrazol-1-yl)nicotinic acid, EA = CH₃CH₂OH) were synthesized. The structures were characterized by single crystal X-ray and elemental analysis. The interaction between the complex and fish sperm DNA(FS-DNA) was monitored using ultraviolet and fluorescence spectroscopy, and the binding constants were determined. Both complexes showed the ability to effectively bind DNA, and the molecular docking technology was used to simulate the binding of the complex and DNA. In addition, through the annexin V-Fluorescein Isothiocyanate(FITC)/ Propidium Iodide (PI) test experiment, tetrazollium [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide(MTT) in vitro test, and cell morphology apoptosis studies, it was shown that the complex can effectively induce HeLa tumor cell apoptosis. Compared with cisplatin and complex, complex 1 shows significant cancer cell inhibition, and we hope that this new type of complex will open up new ways for the next generation of drugs in biomedical applications.

A water-stable multi-responsive luminescent Zn-MOF sensor for detecting TNP, NZF and Cr2O72- in aqueous media

The wide prevalence of organic and inorganic pollutants in water from various industries is responsible for serious environmental problems and endangers human beings. Therefore, the search for effective methods to detect these pollutants has gained great importance. In this work, a new luminescent MOF, {[Zn(L)(bpe)_0.5]·DMF}_n (1) [H₂L = 4,4'-((naphthalene-1,4-dicarbonyl)bis(azanediyl))dibenzoic acid, bpe = 1,2-bis(4-pyridyl)ethene], was solvothermally synthesized and structurally characterized. In this MOF, Zn-SBUs (SBUs = secondary building units) were connected by acylamide-containing dicarboxylate L^2- and nitrogen-containing bpe molecules to yield a 3D porous framework with isolated DMF molecules in the pores. The activated solvent-free MOF sample (denoted as 1a) with good water-stability was obtained by the solvent-exchange and vacuum heat treatment techniques. The luminescence sensing experiments showed that 1a could sensitively, selectively and reversibly detect 2,4,6-trinitrophenol (TNP), nitrofurazone (NZF) and Cr₂O₇^2- in aqueous media, and the corresponding luminescence quenching mechanism has also been discussed. In addition, MOF 1a could quantitatively detect TNP, NZF and Cr₂O₇^2- in tap water samples, indicating that MOF 1a has the potential to detect the aforesaid pollutants in various environmental water matrices.

Recent advances in process engineering and upcoming applications of metal-organic frameworks

Progress in metal-organic frameworks (MOFs) has advanced from fundamental chemistry to engineering processes and applications, resulting in new industrial opportunities. The unique features of MOFs, such as their permanent porosity, high surface area, and structural flexibility, continue to draw industrial interest outside the traditional MOF field, both to solve existing challenges and to create new businesses. In this context, diverse research has been directed toward commercializing MOFs, but such studies have been performed according to a variety of individual goals. Therefore, there have been limited opportunities to share the challenges, goals, and findings with most of the MOF field. In this review, we examine the issues and demands for MOF commercialization and investigate recent advances in MOF process engineering and applications. Specifically, we discuss the criteria for MOF commercialization from the views of stability, producibility, regulations, and production cost. This review covers progress in the mass production and formation of MOFs along with future applications that are not currently well known but have high potential for new areas of MOF commercialization.

Luminescence response mode and chemical sensing mechanism for lanthanide-functionalized metal–organic framework hybrids

This comprehensive review systematically summarizes the luminescence response mode and chemical sensing mechanism for lanthanide-functionalized MOF hybrids (abbreviated as LnFMOFH).

Recent Developments in the Field of Explosive Trace Detection

Explosive trace detection (ETD) technologies play a vital role in maintaining national security. ETD remains an active research area with many analytical techniques in operational use. This review details the latest advances in animal olfactory, ion mobility spectrometry (IMS), and Raman and colorimetric detection methods. Developments in optical, biological, electrochemical, mass, and thermal sensors are also covered in addition to the use of nanomaterials technology. Commercially available systems are presented as examples of current detection capabilities and as benchmarks for improvement. Attention is also drawn to recent collaborative projects involving government, academia, and industry to highlight the emergence of multimodal screening approaches and applications. The objective of the review is to provide a comprehensive overview of ETD by highlighting challenges in ETD and providing an understanding of the principles, advantages, and limitations of each technology and relating this to current systems.

A Dy(iii)–organic framework as a fluorescent probe for highly selective detection of picric acid and treatment activity on human lung cancer cells

A dysprosium(iii) organic framework, {[Dy(H2O)(BTCTB)]·2H2O}n (1, H3BTCTB = 3,3′,3′′-[1,3,5-benzenetriyltris(carbonylimino)]tris-benzoic acid), was synthesized through the hydrothermal reaction of Dy(NO3)3 with the C3-symmetric organic ligand H3BTCTB at 160°C for 96 h. At the same time, the sensitivity of picric acid in water medium was tested with material 1 as the fluorescent sensor. The detection limit was 0.71 µM and KSV of this experiment was 8.55 × 104 M−1, which might be attributed to the presence of abundant amide groups in the framework of 1. In addition, the treatment effect of compound 1 against the NCI-H292 lung cancer cells was evaluated. The Cell Counting Kit-8 (CCK-8) method was conducted to measure the viability of cancer cell after treated through the compound 1. The DCFH-DA was applied for the determination of ROS. The relative expression of the inflammatory genes was measured with RT-PCR. The western blotting was conducted to detect the effect of the compound against MDM-2 levels in NCI-H292 lung cancer cells. The possible binding interactions in terms of binding poses are probed by performing molecular docking simulations.

Eu(III) Tetrahedron Cage as a Luminescent Chemosensor for Rapidly Reversible and Turn-On Detection of Volatile Amine/NH3

Because of the involvement of the gas-solid diffusion, device fabrication, and the relatively complex photophysical process, the lanthanide complexes are rarely exploited as fluorescence sensors for volatile compound (VC) detection. Herein, we report the first example of a discrete 3D Ln-based architecture as a sensor for VCs. The designed Eu₄L₄ tetrahedral cage shows highly selective, rapidly reversible, and turn-on emissive responses toward volatile amines/NH₃ in a spin-coated film. Through the comprehensive spectral characteristic and density functional theory calculation, an intermolecular weak nucleophilic interaction is proposed for this response mechanism. Combining this weak interactions with the permeability of the cage, the film presents subsecond to second timescales rapid response; combining the fitting electrophilic capability of the β-diketonate units to amine nitrogen with the tunable intramolecular charge-transfer feature, the cage shows excellent selectivity and turn-on emissive response. This work provides a new clue to develop the lanthanide complexes as luminescence probes for VCs.

Controlled dye release from a metal-organic framework: a new luminescent sensor for water

By introducing the dye Rhodamine 6G (R6G) into a metal-organic framework (MOF), Mn-sdc-2 (H₂sdc = 4,4'-stilbenedicarboxylic acid), with a pore size of 20 × 9.8 Ų, the composite R6G@Mn-sdc-2 was obtained. Subsequently, the MOF Mn-sdc-1 with a smaller pore size of 7.5 × 7.5 Ų can be formed through a single-crystal to single-crystal transformation from Mn-sdc-2, thus tightly locking the dye R6G within the pores. Compared with R6G@Mn-sdc-2, R6G@Mn-sdc-1 exhibits a stronger fluorescence emission of R6G. Because the MOF Mn-sdc-1 can reversibly transform back to Mn-sdc-2 in the presence of trace water, the dye R6G can be released. This enables R6G@Mn-sdc-1 to be used as a new luminescent sensor for trace water in organic solvents by monitoring the fluorescence intensity of released R6G. The limit of detection can reach 0.035% in ethanol (v : v), which is among the most sensitive fluorescent water probes.

A stilbazolium dye-based chromogenic and red-fluorescent probe for recognition of 2,4,6-trinitrophenol in water

Probe DMAS-DP in water shows highly selective decrease in absorbance (475 nm) and fluorescence intensity (615 nm) with 2,4,6-trinitrophenol and colour change from red to yellow (visible light) and red fluorescent to black (365 nm light).

2D chain layer versus 1D chain: rigid aromatic benzoate disassembling flexible alicyclic dicarboxylate-based lanthanide coordination polymers with enhanced photoluminescence and characteristic single-molecule magnet behavior

Used as photosensitizer and structural separator, aromatic benzoate activator was grafted on cyclopropane dicarboxylate-based lanthanide coordination polymers with efficient photoluminescence and characteristic behavior of single molecule magnet.

A water-stable terbium metal–organic framework with functionalized ligands for the detection of Fe3+ and Cr2O72− ions in water and picric acid in seawater

A novel Tb-MOF-A was fabricated by functionalized ligands and Tb³⁺, which displays high fluorescence, water stability up to 21 days and rapid, cyclic, simultaneous detection of Fe³⁺, Cr₂O₇²⁻ ions in water and picric acid in seawater.

A down converting serine-functionalised NaYF4:Ce3+/Gd3+/Eu3+@NaGdF4:Tb3+ photoluminescent probe for chemical sensing of explosive nitroaromatic compounds

In this contribution, we explored a novel serine-functionalised NaYF₄:Ce³⁺/Gd³⁺/Eu³⁺@NaGdF₄:Tb³⁺ core–shell nanophosphor as a down-converting photoluminescent probe for efficient sensing of nitroaromatic explosives.

A highly stable 8-hydroxyquinolinate-based metal–organic framework as a selective fluorescence sensor for Fe3+, Cr2O72− and nitroaromatic explosives

A novel 8-hydroxyquinolinate-based metal–organic framework exhibits excellent sensing performance toward Fe³⁺, Cr₂O₇²⁻ and nitroaromatic explosives.