Highly Selective and Sensitive Luminescence Turn-On-Based Sensing of Al3+ Ions in Aqueous Medium Using a MOF with Free Functional Sites

Dramatic luminescence signal from a Co(ii)-based metal–organic compound due to the construction of charge-transfer bands with Al3+ and Fe3+ ions in water: steady-state and time-resolved spectroscopic studies

A Co(ii)-based metal–organic compound exhibits luminescence turn-on by Al³⁺ and quenching by Fe³⁺ due to the formation of charge-transfer complexes/adducts.

A luminescent terbium coordination polymer as a multifunctional water-stable sensor for detection of Pb2+ ions, PO43− ions, Cr2O72− ions, and some amino acids

It is the first Ln-CP fluorescence probe for synchronous determination of Tyr and Trp in the presence of other amino acids.

A MOF functionalized with CdTe quantum dots as an efficient white light emitting phosphor material for applications in displays

Cysteamine capped CdTe QD functionalized CP1 as a white light emitter in LED applications.

Post-imparting Brønsted acidity into an amino-functionalized MOF as a bifunctional luminescent turn-ON sensor for the detection of aluminum ions and lysine

A novel aldehyde- and amino-functionalized luminescent metal-organic framework, Cd-TCHO, was constructed through the solvothermal reaction of 4,4',4''-tricarboxytriphenylamine, 2-amino-3-pyridinecarboxaldehyde and cadmium nitrate and was characterized. Post-synthetically oxidizing the aldehyde groups into carboxylate groups afforded a new complex, Cd-TCOOH, and this successful conversion process was confirmed by FT-IR and ¹H NMR studies. With the Brønsted acidic sites inside the cavities of Cd-TCOOH, it could be used as a luminescent sensor for Al³⁺ detection with a high selectivity and sensitivity (LOD = 0.54 ppb), which could be attributed to the coordination between free Brønsted acidic sites and Al³⁺. Importantly, it could also detect Lys among 20 kinds of natural amino acids; the selectivity, sensitivity and the sensing mechanism are discussed in detail. Also, both of the sensing processes were carried out in the HEPES buffer.

Aggregation-Induced Emission-Active Hydrazide-Based Probe: Selective Sensing of Al3+, HF2 -, and Nitro Explosives

(E)-N'-((2-Hydroxynaphthalen-1-yl)methylene)picolinohydrazide (H-PNAP) shows aggregation-induced emission (AIE) strictly in a 90% water/MeOH (v/v) mixture at 540 nm, and the solid-state emission is blue-shifted to 509 nm upon excitation at 400 nm. The AIE activity of H-PNAP is selectively quenched by 2,4,6-trinitrophenol (TNP) and 2,4-dinitrophenol (DNP) out of different nitroaromatic compounds with a limit of detection (LOD) of 7.79 × 10-7 and 9.08 × 10-7 M, respectively. The probe is nonemissive in aqueous medium (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, HEPES buffer, pH 7.2); however, it shows a strong emission to Al3+ (λem, 490 nm) in the presence of 17 other biological metal ions, and the LOD is 2.09 nM which is far below the WHO recommended value (7.41 mM). The emission of the [Al(PNAP)(NO3)2] complex is quenched by HF2 - (F- and PO4 3- are weak quencher), and the LOD is as low as 15 nM. The probable mechanism of the sensing feature of the probe has been authenticated by 1H nuclear magnetic resonance titration, mass spectrometry, Fourier transform infrared spectroscopy, Benesi-Hildebrand plot, and Job's plot in each case. The probe has some practical applications such as recovery of Al3+ from the drinking water sample, construction of the INHIBIT logic gate, and detection kits for Al3+ and TNP/DNP by simple paper test strips. The probe, H-PNAP, has successfully been applied to the detection of intracellular Al3+ and HF2 - ions in the human breast cancer cell, MDA-MB-468.

Highly Selective and Sensitive Turn-Off-On Fluorescent Probes for Sensing Al3+ Ions Designed by Regulating the Excited-State Intramolecular Proton Transfer Process in Metal-Organic Frameworks

The concept of high-performance excited-state intramolecular proton transfer (ESIPT)-based fluorescent metal-organic framework (MOF) probes for Al³⁺ is proposed in this work. By regulating the hydroxyl groups on the organic linker step by step, new fluorescent magnesium-organic framework (Mg-MOF) probes for Al³⁺ ions were established based on the ESIPT fluorescence mechanism. It is observed for the first time that the number of intramolecular hydrogen bonds between adjacent hydroxyl and carboxyl groups can effectively adjust the ESIPT process and lead to tunable fluorescence sensing performance. Together with the well-designed porous and anionic framework, the Mg-TPP-DHBDC probe decorating with a pair of intramolecular hydrogen bonds exhibits extra-high quantitative fluorescence response to Al³⁺ through an unusual turn-off (0-1.2 μM) and turn-on (4.2-15 μM) luminescence sensing mechanism. Notably, the 28 nM limit of detection value represents the lowest record among all reported MOF-based Al³⁺ fluorescent sensors up to now. Benefited from the unique turn-off-on ESIPT fluorescence detection process, the Mg-TPP-DHBDC MOF sensor exhibits single Al³⁺ detection compared with other 16 common metal ions including Ga³⁺, In³⁺, Fe³⁺, Cr³⁺, Ca²⁺, and Mg²⁺. Impressively, such an Al³⁺ selective sensing process can even be fulfilled by the reusable MOF test paper detected by naked eyes. Overall, the quantitative Al³⁺ detection, together with the extraordinary sensitivity, selectivity, fast response, and good reusability, strongly supports our concept of ESIPT-based fluorescent MOF Al³⁺ probes and makes Mg-TPP-DHBDC one of the most powerful Al³⁺ fluorescent sensors.

Multifunctional luminescent coordination polymers based on tricarboxylic acid for the detection of 2,4-dinitrophenol and iron(iii) and aluminum(iii) ions

2D Zn(ii)-coordination polymer exhibited highly sensitive and selective detection towards DNP, Fe³⁺ and Al³⁺ ions in the presence of other interfering compounds through luminescence quenching and enhancement, respectively.

Two 2D microporous MOFs based on bent carboxylates and a linear spacer for selective CO2 adsorption

Two new 2D microporous MOFs based on bent carboxylates and an unexplored N,N-donor spacer containing imine and amide functionalities exhibited high IAST selectivity for CO₂/N₂ and CO₂/CH₄ mixtures under ambient conditions.

A water-stable europium-MOF as a multifunctional luminescent sensor for some trivalent metal ions (Fe3+, Cr3+, Al3+), PO43− ions, and nitroaromatic explosives

Eu-MOF having a layered structure exhibits high sensitivity, selectivity, and recyclability towards sensing Fe³⁺, Cr³⁺, Al³⁺, and PO₄³⁻ ions and TNP.

A water-stable terbium-MOF sensor for the selective, sensitive, and recyclable detection of Al3+ and CO32− ions

A layered Tb-MOF structure exhibits high sensitivity, selectivity, and concurrently low limits of detection in relation to Al³⁺ and CO₃²⁻ ions.

2D europium coordination polymer as a regenerable fluorescence probe for efficiently detecting fipronil

Recently, considerable attention has been paid to European eggs that were found to contain the poisonous insecticide fipronil. Excessive consumption of fipronil can harm the human body, in particular, the liver, thyroid, nervous system and kidneys. As a consequence, there is an urgent need to develop a method to detect fipronil. In this work, a lanthanide coordination polymer [Eu(SIP)(H2O)4]n (1) (NaH2SIP = 5-sulfoisophthalic acid monosodium salt) was synthesized and characterized by single-crystal X-ray crystallography, elemental analysis, infrared spectrum and powder X-ray diffractions. The X-ray studies show that 1 is a two-dimensional layered structure, which is constructed of fused {[Eu(H2O)4]3(SIP)3} pseudo-hexagonal grids. The luminescence properties of 1 exhibit effective recognition for fipronil in methanol solution. Furthermore, a wide linear range (10-6-10-4 M), a low detection limit of 0.8 μM, high selectivity and excellent recyclability, reveal that 1 can potentially act as a luminescence-based sensor for quantitative and highly sensitive detection of fipronil. To the best of our knowledge, it is the first time that a metal-organic coordination polymer, as a fluorescent-based probe, has been used for the detection of fipronil. Moreover, fluorescent-based test papers of 1 have also been prepared, which can be regarded as a simple and practical method for detecting fipronil.

Lanthanide-MOFs constructed from mixed dicarboxylate ligands as selective multi-responsive luminescent sensors

Five novel Ln-MOFs associated with the mixed ligands of 4-(pyridin-3-yloxy)-phthalic acid (H₂ppda) and terephthalic acid (H₂bdc), namely, [Ln(ppda)(bdc)_0.5(C₂H₅OH)(H₂O)]_n (Ln = Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)) were synthesized under the solvothermal conditions. Compounds 1-5 exhibit the isostructural 2D layered structures. The solid-state luminescence properties of compounds 1, 2, 4 and 5 were investigated in detail. It was found that compound 4 not only detected nitrobenzene derivatives-based explosives with high selectivity, sensitivity, and recyclability, but also served as an excellent selective sensing material for Fe³⁺ ion and Cr₂O₇^2- ion. In particular, it is worth noting that the detection limit of TNP can reach 3.0 × 10^-8 M. It was found that the free oxygen atoms of the ether bond, which function as the Lewis basic sites in Ln-MOFs, might interact with metal ions. In addition, the sensing mechanisms of 4 for different analytes were explored further.

Morphology-dependent sensing performance of dihydro-tetrazine functionalized MOF toward Al(III)

A pillared MOF, [Zn(OBA)(H₂DPT)_0.5].DMF (TMU-34), based on dihydro tetrazine functionalized pillar spacer (H₂DPT=3,6-di(pyridin-4-yl)-1,4-dihydro-1,2,4,5-tetrazine) and V-shape dicarboxylate linker (H₂OBA=4,4'-oxybis(benzoic acid)) was synthesized by reflux and ultrasonic methods. The effects of sonication time, initial concentration of reagents and sonication power on size and morphology have been optimized. This MOF has been characterized by scanning electron microscopy, FT-IR spectra, X-ray powder diffraction and N₂ adsorption at 77K. Bulk and nano samples of TMU-34 have been applied in cation sensing for detection of Al(III) in presence of other cations (Na(I), Mg(II), Sr(II), Al(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II), Hg(II),Cr(III), Li(I), Fe(III), K(I)). The results show that nano powder of TMU-34 with uniform separated plate-like morphology (TMU-34-F) has higher detection limit and short response time compared to bulk material. So, in this work we show the application of luminescent metal-organic frameworks synthesized by sonochemistry approach in effective cation detection.

Coordination polymer-derived nano-sized zinc ferrite with excellent performance in nitro-explosive detection

Herein, a mixed metal coordination polymer, {(H₂pip)[Zn_1/3Fe_2/3(pydc-2,5)₂(H₂O)]·2H₂O} 1 {where H₂pip = piperazinediium and pydc-2,5 = pyridine-2,5-dicarboxylate}, was successfully synthesized using a hydrothermal technique. To confirm the structure and phase purity of 1, single crystals of an isomorphous pure Fe compound, {(H₂pip)[Fe(pydc-2,5)₂(H₂O)]·2H₂O} 1a, were synthesized based on similar synthetic conditions. Single crystal X-ray data of 1a confirmed the one-dimensional anionic metal-organic coordination polymer hydrogen bonded with protonated piprazine (piperazinediium) and lattice water molecules. The phase purity of 1 and 1a were confirmed via powder X-ray diffraction. Compound 1 was systematically characterized using IR, TGA, SEM, and EDX elemental mapping analysis. Compound 1 was used as a single source precursor for the preparation of nano-sized ZnFe₂O₄via thermal decomposition. The as-obtained ZnFe₂O₄ was fully characterized using PXRD, SEM, TEM, and EDX elemental mapping analysis. It was found that ZnFe₂O₄ was formed in its pure form with particle size in the nano-dimension. The aqueous dispersion of nano-sized ZnFe₂O₄ exhibits a strong emission at 402 nm upon excitation at 310 nm. This emissive property was employed for luminescence-based detection of nitroaromatic explosives in an aqueous medium through luminescence quenching for the first time. Importantly, selective detections have been observed for phenolic nitroaromatics based on differential luminescence quenching behaviour along with a detection limit of 57 ppb for 2,4,6-trinitrophenol (TNP) in water.

Tailoring the Fluorescence of AIE-Active Metal-Organic Frameworks for Aqueous Sensing of Metal Ions

A hydroxyl-functionalized ligand was designed for the construction of metal-organic framework (MOF) materials with the aggregation-induced emission (AIE) feature, in which the fluorescence can be deliberately tailored: quenching the fluorescence to an "off" state by the decoration with heterocyclic auxiliary ligand 4,4'-bypyridine (Bpy) in the framework as a quenching agent and triggering the enhanced fluorescence to an "on" state by removal of Bpy through the metal competitive coordination substitution strategy. Our study shows that the occurrence of exciton migration between the AIE linker and conjugated auxiliary ligand Bpy causes fluorescence quenching. Time-dependent density functional theory was employed to understand the photoinduced electron transfer process and explain the origins of fluorescence quenching. Using this strategy, the prepared MOF material can perform as a fluorescence "off-on" probe for highly sensitive detection of Al³⁺ in aqueous media. The hydroxyl group plays a crucial role in sensing as it can selectively chelate Al³⁺, which is directly related to the dissociation of nonfluorescent MOF and consequent activation of the AIE process.

Multi-responsive luminescent sensor based on three dimensional lanthanide metal–organic framework

A novel multi-functional luminescent MOF was synthesized, which shows excellent recyclable luminescent sensing for acetone, Fe³⁺, Cr₂O₇²⁻ and 4-NP.

Two azo-functionalized luminescent 3D Cd(ii) MOFs for highly selective detection of Fe3+ and Al3+

Two 3D luminescent Cd(ii) MOFs (Cd-MOF-1 and Cd-MOF-2) exposing azo functional sites displayed selective detection of Fe³⁺ and Al³⁺ metal ions with high sensitivities.

A Spectral Probe for Detection of Aluminum (III) Ions Using Surface Functionalized Gold Nanoparticles

A simple green route has been developed for the synthesis of casein peptide functionalized gold nanoparticles (AuNPs), in which casein peptide acts as a reducing as well as the stabilizing agent. In this report, AuNPs have been characterized on the basis of spectroscopic and microscopic results; which showed selective and sensitive response toward Al3+ in aqueous media, and Al3+ induces aggregation of AuNPs. The sensing study performed for Al3+ revealed that the color change from red to blue was due to a red-shift in the surface plasmon resonance (SPR) band and the formation of aggregated species of AuNPs. The calibration curve determines the detection limit (LOD) for Al3+ about 20 ppb (0.067 μM) is presented using both decrease and increase in absorbance at 530 and 700 nm, respectively. This value is considerably lower than the higher limit allowed for Al3+ in drinking water by the world health organization (WHO) (7.41 μM), representing enough sensitivity to protect water quality. The intensity of the red-shifted band increases with linear pattern upon the interaction with different concentrations of Al3+, thus the possibility of producing unstable AuNPs aggregates. The method is successfully used for the detection of Al3+ in water samples collected from various sources, human urine and ionic drink. The actual response time required for AuNPs is about 1 min, this probe also have several advantages, such as ease of synthesis, functionalization and its use, high sensitivity, and enabling on-site monitoring.

Metal-Organic Frameworks Constructed from a New Thiophene-Functionalized Dicarboxylate: Luminescence Sensing and Pesticide Removal

A family of thiophene-based metal-organic frameworks (MOFs), [Zn(L)(BBI)·(H₂O)₂] (1) (BBI = 1,1'-(1,4-butanediyl)bis(imidazole)) and [Cd(L)(TPOM)_0.75]·xS (2) (TPOM = tetrakis(4-pyridyloxy-methylene) methane, S represents noncoordinated solvent molecules) was constructed by employing a new linear thiophene-functionalized dicarboxylic acid (benzo-(1,2;4,5)-bis(thiophene-2'-carboxylic acid, H₂L) to assemble with d¹⁰ ions in the presence of a flexible ancillary ligand under solvothermal conditions, which exhibit diverse structures. Most strikingly, both compounds 1 and 2 could be efficient luminescent sensory materials that are highly selective and sensitive to environmental contaminants, especially for Hg(II), Cu(II), Cr(VI), and salicylaldehyde, and yet remain unaffected by other molecules that may coexit. Furthermore, this is the first report on MOF-based sensors capable of recyclable detection of Hg(II), Cr(VI), and salicylaldehyde so far. The luminescent sensing mechanism was studied in detail as well. In addition, compound 2 is one of the rare examples of high-performance MOFs trapping 2,4-dichlorophenol from the wasted methanol solution.

Facile synthesis of a water-soluble fluorescence sensor for Al3+ in aqueous solution and on paper substrate

In this study, a facile water-soluble fluorescence sensor 2-((2-hydroxybenzylidene)-amino)-2-(hydroxymethyl)propane-1,3-diol (ST) was synthesized via one-step reaction, and its fluorescence sensing performance for Al³⁺ both in aqueous solution and on paper substrate was evaluated. The results showed that ST exhibited an specific fluorescence "turn-on" response to Al³⁺ over other cations in aqueous solution as well as on the test paper. The limit of detection was found to be 3.2×10^-7M, which revealed that the obtained Schiff-base based fluorescence chemosensor ST possessed a great potential for the rapid, quantitative and qualitative detection of Al³⁺.

A highly selective and sensitive Zn(ii) coordination polymer luminescent sensor for Al3+and NACs in the aqueous phase

A novel coordination polymer Zn(DMA)(TBA) (1) (H₂TBA = 4-(1H-tetrazol-5-yl)-benzoic acid) features a unique two-dimensional (2D) network structure, exhibiting excellent luminescence and good stability in both water and other organic solvents.