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

A captivating approach to elevate the detection of Al3+ ions incorporates the utilization of a tripodal receptor intricately embellishing the surface of zinc oxide

The FDA (Food and Drug Administration, (USA)) lists ZnO as a material that is widely acknowledged to be safe. ZnO NPs with a range of tiny particle sizes were made using the precipitation process. ZnO nanoparticles' surface is embellished with a tripodal sensor containing naphthol units. The assembly with the same receptor decorated on ZnO NPs is contrasted with the cation detection capabilities of the purified tripodal receptor. The UV-visible spectrophotometric analysis was conducted to study the state transitions of the receptor and the decorated ZnO receptor. A positive selectivity to Al3+ cations is determined by the fluorescence study under ideal circumstances. The particle size and surface morphologies are determined by DLS and SEM analysis for the same receptor - TP1 and embellished with a tripodal receptor TP2. Using a fluorescence switch-on Photoinduced Electron Transfer (PET) mechanism, the receptor coated on ZnO detects the presence of Al3+ ions with specificity. The binding constant value was determined using the B-H plot equation. Binding stoichiometry for [TP1-Al3+, TP2-Al3+] showed a 1:1 ratio. The fluorescence switches ON-OFF process of the ZnO surface adorned - TP2 with Tripodal receptor- TP1 was used to create molecular logic gates, which can function as a module for sensors and molecular switches. The addition of Na2EDTA in the solution of the [TP1; TP2 - Al3+] complex resulted in a noticeable reduction in the emission of fluorescence. This finding offers compelling support for the reversibility of the chemosensor. To enable the practical application of this sensor, we have developed a cassette containing receptors TP1 and TP2. Successfully, it can detect Al3+ metal ions. We performed a comprehensive assessment of the dependability and appropriateness of our approach in measuring the concentration of Al3+ ions in wastewater produced by important industrial procedures.

Fluorescent bacterial cellulose@Zr-MOF via in-situ synthesis for efficient enrichment and sensitive detection of Cr(VI)

In this study, for the first time, a new Zr-metal-organic framework (MOF) with strong aggregation-induced emission was successfully grown on bacterial cellulose (BC) using an in situ synthesis method, yielding the fluorescent composite nanofiber BC@Zr-MOF. The BC with abundant hydroxyl groups, which can be uniformly wrapped in the interior of the MOF layer to form BC@Zr-MOF, was used as the growth template. The resulting composite nanofibers had a higher specific surface area (1, 116 m2/g), stronger fluorescence emission and better pH stability than MOF particles. In addition, BC@Zr-MOF exhibited selective recognition and enrichment of Cr2O72- in the aqueous phase and a high adsorption capacity of 90 mg/g. Moreover, because of the high aspect ratio and good tensile strength (6.73 N/mm2), BC@Zr-MOF nanofibers could be readily made into freestanding nanopapers via vacuum filtration, thus solving the molding and recycling problems of MOFs. The facilely prepared test paper could rapidly, sensitively and selectively detect Cr2O72- with the limit of detection (LOD) of 41.8 nM, which is nearly 500 times lower than that of the national drinking water standard. Moreover, the LOD of BC@Zr-MOF nanopapers, when used in combination with circulating filtration, decreases to 6.9 nM owing to the adsorption-enrichment effect.

A dual-emitting Rhodamine B-encapsulated Zn-based MOF for the selective sensing of Chromium(VI)

A Rhodamine B-Zn-MOF composite (RhB-Zn-MOF) with dual emission intensity was synthesized through one pot synthesis by in-situ encapsulation of Rhodamine-B dye on a new Zn-MOF metal-organic framework [(Zn(OAc)2(4-BrIPh) (1,10-phenonthroline)(H2O)].H2O, (4-BrIPh = 4-Bromoisophthalic acid). The synthesized encapsulated material was characterized by elemental analysis, FTIR, UV-Visible spectroscopy, TGA, single crystal and powder X-ray diffraction and photoluminescence spectroscopy. The results showed that the synthesized composite, RhB-Zn-MOF could be used as an efficient probe for the selective sensing of Cr(VI) in the presence of Cr(III) as well as other metal ions.

Recent advances in metal-organic framework (MOF)-based agricultural sensors for metal ions: a review

Metal ions have great significance for agricultural development, food safety, and human health. In turn, there exists an imperative need for the development of novel, sensitive, and reliable sensing techniques for various metal ions. Agricultural sensors for the diagnosis of both agricultural safety and nutritional health can establish quality and safety traceability systems of both agro-products and food to guarantee human health, even life safety. Metal-organic frameworks (MOFs) are utilized widely for the design of diversified sensors due to their distinctive structural characteristics and extraordinary optical and electrical properties. To serve agricultural sensors better, this review is dedicated to providing a brief overview of the synthesis of MOFs, the modification of MOFs, the fabrication of MOF-based film electrodes, the applications of MOF-based agricultural sensors for metal ions, which are centered on electrochemical sensors and optical sensors, and current challenges of MOF-based agricultural sensors. In addition, this review also provides potential future opportunities for the development and practical application of agricultural sensors.

Zinc(II)-Based Ring-and-Rod Coordination Layer as an Excitation-Wavelength-dependent Dual-Emissive Chemosensor for Discriminating Fe3+, Cr3+, and Al3+ in Water

The reactions of Zn(NO3)2, 3,6-bis(pyridin-3-yl)-9H-carbazole (bpycz), and 2,5-dihydroxyterephthalic acid (H4dhbdc) or 2-bromoterephthalic acid (Br-1,4-H2bdc) under hydro(solvo)thermal conditions yielded corresponding coordination polymers (CPs) {[Zn(H2dhbdc)(bpycz)]•0.5H2O}n (1) and [Zn(Br-1,4-bdc)(bpycz)]•2DMAc•H2O (2), respectively, with high thermal stability approaching 350 °C. CP 1 adopts a ring-and-rod layer structure, which is topologically described as a 4-connected net with the point symbol of 2•65. Two layers are interpenetrated in parallel interlocking mode to form a double 2D → 2D polyrotaxane entanglement with extra-framework void space of 19.6%. CP 2 has a non-interpenetrating ring-and-rod layer structure of 4-connected 2•65 net topology, with extra-framework void space of 16.6%. Thermally activated 1 and 2 revealed CO2 uptakes of 101.1 and 98.6 cm3 g-1, respectively, at P/P0 = 1 and 195 K. X-ray powder diffraction (XRPD) patterns confirmed that 1 and 2 both possessed high chemical stability in H2O, CH3OH, acetone, and DMF, and framework stability during gas adsorption-desorption. The H2O suspension of 1 displayed excitation-dependent dual-emissive properties, appearing at 432 nm upon excitation at 300 nm and at 528 nm upon excitation at 365 nm. Of note, 1 was capable of detection of Fe3+, Cr3+, and Al3+ ions in H2O, showing good anti-interference ability, excellent selectivity, and high sensitivity. More interesting, the dual-emissive properties make 1 to be an excellent luminescence chemosensor to screen Fe3+, Cr3+, and Al3+ from a pool of metal ions in H2O upon excitation at 300 nm via luminescence quenching effect and then discriminate Fe3+, Cr3+, and Al3+ upon excitation at 365 nm via luminescence quenching, unaltered, and enhancement responses, respectively. On the other hand, the H2O suspension of 2 demonstrated an excitation-independent emission appearing at around 430 nm, which could be utilized to sensitively detect Fe3+ and Cr3+ ions with good anti-interference ability and excellent selectivity via luminescence quenching effect. Further, 1 and 2 were recyclability and possessed cycling stability. The plausible sensing mechanisms for 1 and 2 toward Fe3+, Cr3+, and Al3+ were also explored in detail.

A dual-function [Ru(bpy)3]2+ encapsulated metal organic framework for ratiometric Al3+ detection and anticounterfeiting application

In this work, a novel composite material (HPU-24@Ru) has been prepared by combining a blue-emission Cd-based metal-organic framework (MOF, [Cd₂(TCPE)(DMF)(H₂O)₃]_n, HPU-24) with a red-emission tris (2,2'-bipyridine) dichlororuthenium(II) hexahydrate ([Ru(bpy)₃]²⁺) molecule for ratiometric fluorescence sensing of Al³⁺ ions in aqueous medium and high-level dynamic anticounterfeiting application. The luminescence measurement results indicated that the fluorescence intensity of HPU-24 at 446 nm showed a red shift in the presence of Al³⁺ ions, and the new peak appeared at 480 nm and continued to increase with an increase in Al³⁺ ion concentration. Meanwhile, the fluorescence intensity of [Ru(bpy)₃]²⁺ almost showed no change. The detection limit was calculated as 11.63 μM, which was better than that for the MOF-based Al³⁺ ions in some reported examples in aqueous media and achieved through strong electrostatic interactions between HPU-24@Ru and Al³⁺ ions. Moreover, owing to the particularity of the tetrastyryl structure in HPU-24, HPU-24@Ru showed intriguing temperature-dependent emission behavior. This unique structure provides the composite material HPU-24@Ru with attributes for high-level information encryption that make it difficult for counterfeiters to identify all of the right decryption measures.

A multifunctional cobalt-organic framework for proton conduction and selective sensing of Fe3+ ions

Developing multifunctional metal-organic frameworks (MOFs) is a new research trend. MOFs have shown remarkable performances in both proton conduction and fluorescence sensing, but the MOFs integrating the two performances are scarce. Herein, a Co-MOF, [Co₆(oba)₄(Hatz)(atz)(H₂O)₂(μ₃-OH)₂(μ₂-OH)]·H₂O (1, H₂oba = 4,4-oxybis(benzoic acid), Hatz = 5-amino-1H tetrazole), has been assembled by Co²⁺ ions with H₂oba and Hatz ligands, providing a unique example of multifunctional MOFs with both proton conduction and fluorescence sensing performances. The framework of 1 displays a pillar-layer structure built by the oba ligand as a pillar and a layer composed of Co-clusters and atz linkers. Because large-scale single crystals of 1 were successfully synthesized, the proton conduction ability of 1 was investigated using single crystal samples. 1 exhibits highly anisotropic conduction with conductivity values of 1.1 × 10^-3 S cm^-1 along the [001] direction and 9.1 × 10^-6 S cm^-1 along the [010] direction at 55 °C and 95% RH, respectively. Meanwhile, the fluorescence sensing of 1 towards metal ions was studied in aqueous solutions. Attractively, 1 may sensitively and selectively detect Fe³⁺ ions in the presence of other interfering ions by fluorescence quenching.

Two Co-Based Metal-Organic Framework Isomers with Similar Metal-Carboxylate Sheets: Turn-On Ratiometric Luminescence Sensing Activities toward Biomarker N-Acetylneuraminic Acid and Discrimination of Ga3+ and In3

Two supramolecular Co-MOF isomers, namely, {[Co(L)_0.5(m-bimb)]·3H₂O}_n (LCU-115) and {[Co(L)_0.5(p-bimb)]·3H₂O}_n (LCU-116), were synthesized from an amide-containing carboxylic acid N,N″-(3,5-dicarboxylphenyl)benzene-1,4-dicarboxamide (H₄L) and two flexible positional isostructural N-containing ligands m-bimb and p-bimb (m-bimb = 1,3-bis((1H-imidazol-1-yl)methyl)benzene; p-bimb = 1,4-bis((1H-imidazol-1-yl)methyl)benzene). The carboxylate ligands connect Co(II) centers to form 2D metal-carboxylate sheets, which are extended further by m-bimb and p-bimb to form a 2D bilayer with parallel stacking (LCU-115) and a 3D framework (LCU-116), respectively. Luminescence measurements indicated that these two complexes exhibited interesting multiresponsive sensing activities toward pH, biomarker N-acetylneuraminic acid, and trivalent cations Ga³⁺/In³⁺. They show highly sensitive turn-on fluorescence responses in the acidic range and can also be regarded as on-off-on vapoluminescent sensors to typical acidic and basic gases HCl and Et₃N. It is worth noting that these complexes have excellent turn-on ratiometric fluorescence sensing ability for N-acetylneuraminic acid (NANA) with detection limits as low as 7.39 and 8.06 μM, respectively. Furthermore, they were successfully applied for the detection of NANA in simulated urine and serum samples with satisfactory results. For ion detection, LCU-116 could detect both Ga³⁺ and In³⁺, while LCU-115 could distinguish Ga³⁺ from In³⁺ with the latter showing luminescence quenching. The sensing mechanism was investigated in detail by XRD, UV-vis, EDS, XPS, SEM, and TEM. The results of interday and intraday precision studies gave low RSD values in the range of 1.19-3.53%, ascertaining the reproducibility of these sensors. The recoveries for the sensing analytes in simulated urine/serum or real water are satisfactory from 96.7 to 103.3% (toward NANA) and 96.6 to 115.0% (toward Ga³⁺ and In³⁺), indicating that these two complexes also possess acceptable reliability for monitoring in real samples. The results indicated that the supramolecular isomers LCU-115 and LCU-116 are promising material candidates for application in biological and environmental monitoring.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Fluorescence-Responsive Detection of Ag(I), Al(III), and Cr(III) Ions Using Cd(II) Based Pillared-Layer Frameworks

Two Cd(II) based coordination polymers, {Cd₃(btc)₂(BTD-bpy)₂]∙1.5MeOH∙4H₂O}_n (1) and [Cd₂(1,4-ndc)₂(BTD-bpy)₂]_n (2), where BTD-bpy = bis(pyridin-4-yl)benzothiadiazole, btc = benzene-1,3,5-tricarboxylate, and 1,4-ndc = naphthalene-1,4-dicarboxylate, were hydro(solvo)thermally synthesized. Compound 1 has a three-dimensional non-interpenetrating pillared-bilayer open framework with sufficient free voids of 25.1%, which is simplified to show a topological (4,6,8)-connected net with the point symbol of (3²4²56)(3⁴4⁴5⁴6²8)(3⁴4²6¹⁹7²8). Compound 2 has a three-dimensional two-fold interpenetrating bipillared-layer condense framework regarded as a 6-connected primitive cubic (pcu) net topology. Compounds 1 and 2 both exhibited good water stability and high thermal stability approaching 350 °C. Upon excitation, compounds 1 and 2 both emitted blue light fluorescence at 471 and 479 nm, respectively, in solid state and at 457 and 446 nm, respectively, in the suspension phase of H₂O. Moreover, compounds 1 and 2 in the suspension phase of H₂O both exhibited a fluorescence quenching effect in sensing Ag⁺, attributed to framework collapse, and a fluorescence enhancement response in sensing Al³⁺ and Cr³⁺, ascribed to weak ion-framework interactions, with high selectivity and sensitivity and low detection limit.

A Highly Selective MOF-Based Probe for Turn-On Luminescent Detection of Al3+, Cr3+, and Fe3+ in Solution and Test Paper Strips through Absorbance Caused Enhancement Mechanism

Trivalent metal ions (Cr³⁺, Al³⁺, and Fe³⁺) constitute a major section of the environmental pollutants, and their excess accumulation has a detrimental effect on health, so their detection in trace quantity has been a hot topic of research. A highly scalable 3D porous Zn-based luminescent metal-organic framework (MOF) has been synthesized by exploiting the mixed ligand synthesis concept. The strategic selection of an aromatic π-conjugated organic linker and N-rich spacer containing the azine functionality as metal ion binding sites immobilized across the pore spaces, have made this MOF an ideal turn-on sensor for Al³⁺, Cr³⁺, and Fe³⁺ ions with very high sensitivity, selectivity, and recyclability. An in-depth study revealed absorbance caused enhancement mechanism (ACE) responsible for such turn-on phenomena. In order to make the detection process straightforward, convenient, portable, and economically viable, we have fabricated MOF test paper strips (the MOF could be simply immobilized onto the paper strips) for naked eye visual detection under UV light, which, thus, manifests its potential as a real-time smart sensor for these trivalent ions.

pH-Stable Luminescent Metal-Organic Frameworks for the Selective Detection of Aqueous-Phase FeIII and CrVI Ions

The development of chemically stable metal-organic framework (MOF)-based luminescent platforms for toxic ion detection in an aqueous medium is highly challenging because most of the classical MOFs are prone to water degradation, and that is the reason why most of the MOF-based luminescent sensors use a nonaqueous medium for sensing. In this contribution, we report two new water-stable luminescent MOFs (Zn-MOF-1 and Zn-MOF-2), assembled from a mixed-ligand synthesis approach. Because of the presence of a hydrophobic trifluoromethyl group to the backbone and stronger metal-N coordination, these MOFs exhibit excellent stability not only in water but also in acidic/alkaline aqueous solutions (pH = 3-10). Here, we report a green sensing approach by exploiting the significant reduction in photoluminescence of these MOFs in the presence of toxic ions. Fe³⁺ and CrO₄^2-/Cr₂O₇^2- ions could be traced with a detection limit (LOD) in the micromolar range (0.045 and 0.745/0.33 μM for Zn-MOF-1; 125.2 and 114.2/83.5 μM for Zn-MOF-2). The mechanistic study reveals that competitive absorption of the excitation energy coupled with fluorescent resonance energy transfer are responsible for the turn-off quenching. The anti-interference ability and recyclability along with the pH stability gave these MOFs high potential to be used as practical sensors toward Fe^III and Cr^VI ions in water as a greenest medium.

Selective luminescent sensing of metal ions and nitroaromatics over a porous mixed-linker cadmium(ii) based metal–organic framework

A potential luminescent sensor based on porous metal organic framework for the detection of metal ions (Al3+, Fe3+ or Cr3+) and nitro-explosive, 2,4,6-tri-nitrophenol has been discovered. MOF is capable of detecting aqueous phase analyte through luminescent sensing.

Smart Metal-Organic Frameworks for Biotechnological Applications: A Mini-Review

In this pandemic situation it is evident that viruses and bacteria, more specifically, multiple drug resistant (MDR) bacteria, endanger human civilization severely. It is high time to design smart weapons to combat these pathogens for the prevention and cure of allied ailments. Metal-organic frameworks (MOFs) are porous materials designed from metal ions or inorganic clusters and multidentate organic ligands. Due to some unique features like high porosity, tunable pore shape and size, numerous possible metal-ligand combinations, etc., MOFs are ideal candidates to design "smart biotechnological tools". MOFs construct promising fluorescence based biosensing platforms for detection of viruses. MOFs also exhibit excellent antibacterial activity due to their ability for sustained release of active biocidal agents. There are several reviews that summarize the antibacterial applications of MOFs, but the biosensing platforms based on MOFs for detection of viruses have scarcely been summarized. This review carefully covers both the aspects including virus detection (nucleic acid recognition and immunological detection) with underlying mechanisms as well as antibacterial application of MOFs and doped MOFs or composites. This review will deliver valuable information and references for designing new, smarter antimicrobial agents based on MOFs.

Highly selective fluorescent turn-on-off sensing of OH-, Al3+ and Fe3+ ions by tuning ESIPT in metal organic frameworks and mitochondria targeted bio-imaging

Herein we report a multifunctional high performance metal organic framework (Zn-DHNDC MOF) based chemosensor that displays an exceptional excited state intramolecular proton transfer (ESIPT) tuned fluorescence turn-on–off response for OH⁻, Al³⁺ and Fe³⁺ ions along with mitochondria targeted bio-imaging. Properly tuning ESIPT as well as the hydroxyl group (–OH) allows Zn-DHNDC MOF to optimize and establish chelation enhanced fluorescence (CHEF) and chelation enhanced quenching (CHEQ) based sensing mechanisms. The MOF benefits from acid-base interactions with the ions which generate a turn-on bluish green fluorescence (λ_Em 492 nm) for OH⁻, an intense turn-on green fluorescence (λ_Em 528 nm) for Al³⁺ and a turn-off fluorescence quenching response for Fe³⁺ ions. The aromatic –OH group indeed plays its part in triggering CHEF and CHEQ processes responsible for the turn-on-off events. Low limits of detection (48 nM of OH⁻, 95 nM for Al³⁺, 33 nM for Fe³⁺ ions), high recyclability and fast response time (8 seconds) further assist the MOF to implement an accurate quantitative sensing strategy for OH⁻, Al³⁺ and Fe³⁺ ions. The study further demonstrates the MOF's behaviour in cellular medium by subjecting it to live cell confocal microscopy. Along with a bio-compatible nature the MOF exhibited successful accumulation inside the mitochondria of MCF7 cancer cells, which defines it as a significant bio-marker. Therefore the present work successfully represents the multidisciplinary nature of Zn-DHNDC MOFs, primarily in sensing and biomedical studies.

ESIPT tuned fluorescence sensing of OH⁻, Al³⁺ and Fe³⁺ ions and mitochondria targeted bio-imaging by a Zn-DHNDC MOF.

Fabrication of two-phase Ca2+-doped LaVO4:Eu3+ structures: morphology modification, tunable optical performance and detection of Fe3+ ions with high sensitivity

Two-phase Ca²⁺-doped LaVO₄:Eu³⁺ nanocrystals were prepared through a hydrothermal method with the help of SOD CITR and EDTA surfactants. The phase and morphology of the products were characterized by XRD and TEM, and the fluorescence performances were also recorded. The results indicated that Ca²⁺ ions were doped into the LaVO₄:Eu³⁺ host lattice, impeding the aggregation of the nanocrystals and enhancing the luminescence intensity. The morphology transformation process and luminescence enhancement were systematacially investigated. The fluorescence intensity of the two selected samples could be completely quenched by Fe³⁺ ions without the disturbance of other ions, with the mechanism being due to the adsorption of Fe³⁺ ions onto the grains and a subsequent energy transfer from Eu³⁺ to Fe³⁺. Therefore, the present two Ca²⁺-doped LaVO₄:Eu³⁺ samples can be applied as appropriate candidates for detecting Fe³⁺ ions with agility and sensitivity in aqueous solution.

Porous Anionic Co(II) Metal-Organic Framework, with a High Density of Amino Groups, as a Superior Luminescent Sensor for Turn-on Al(III) Detection

Accumulation of high concentrations of Al(III) in body has a direct impact on health and therefore, the trace detection of Al(III) has been a matter for substantial concern. An anionic metal organic framework ({[Me₂ NH₂ ]_0.5 [Co(DATRz)_0.5 (NH₂ BDC)] ⋅ xG}_n ; 1; HDATRz=3,5-diamino-1,2,4-triazole, H₂ NH₂ -BDC=2-amino-1,4-benzenedicarboxylic acid, G=guest molecule) composed of two types of secondary building units (SBU) and channels of varying sizes was synthesized by employing a rational design mixed ligand synthesis approach. Free -NH₂ groups on both the ligands are immobilized onto the pore surface of the MOF which acts as a superior luminescent sensor for turn-on Al(III) detection. Furthermore, the large channels could allow the counter-ions to pass through and get exchanged to selectively detect Al(III) in presence of other seventeen metal ions with magnificent luminescence enhancement. The observed limit of detection is as low as 17.5 ppb, which is the lowest among the MOF-based sensors achieved so far. To make this detection approach simple, portable and economic, we demonstrate MOF filter paper test for real time naked eye observation.

Zn-based metal organic framework-covalent organic framework composites for trace lead extraction and fluorescence detection of TNP

A novel dual functional composite (MOF_L-TpBD) was prepared through solvothermal methods, with excellent Pb²⁺ ions separation and stable 2,4,6-Trinitrophenol (TNP) fluorescence detection performance. MOF_L-TpBD was characterized by FTIR, XRD, XPS, SEM and TGA et al. The prepared material was used to extract Pb²⁺ ions, with an adsorption capacity of 21.74 mg g^-1 calculated by Langmuir isotherm model. The limit of detection was 0.32 μg L^-1, along with a linear range from 0.7 to 12 μg L^-1 and a precision of 5.4% (1 μg L^-1, n = 9), respectively, where MOF_L-TpBD was adopted as adsorbent for Pb²⁺ ions preconcentration. The practical samples and reference water sample were measured by the provided method, with the satisfactory recoveries (91-110%) and reliable analytical results. MOF_L-TpBD was capable of fluorescent sensing of TNP, with a linear range from 0.01 to 1 mM and a limit of detection of 3.52 μM, respectively, and a precision of 3.29% was obtained (0.2 mM, n = 11). Meanwhile, the recoveries ranged from 91% to 108% in analysis of TNP for the practical samples. The designed material provided a potential candidate material for the detection of heavy metal ions and explosives in environmental water samples.

Response of a Zn(II)-based metal-organic coordination polymer towards trivalent metal ions (Al3+, Fe3+ and Cr3+) probed by spectroscopic methods

A new zinc-based two-dimensional coordination polymer, [Zn(5-AIP)(Ald-4)]·H2O (5-AIP = 5-amino isophthalate, Ald-4 = aldrithiol-4), 1, has been synthesized at room temperature by the layer diffusion technique. Single-crystal X-ray diffraction analysis of 1 showed a two-dimensional bilayer structure. An aqueous suspension of 1 upon excitation at 300 nm displayed an intense blue emission at 403 nm. The luminescence spectra were interestingly responsive and selective to Al3+, Cr3+ and Fe3+ ions even in the presence of other interfering ions. The calculated detection limits for Al3+, Cr3+ and Fe3+ were 0.35 μM ([triple bond, length as m-dash]8.43 ppb), 0.46 μM ([triple bond, length as m-dash]22.6 ppb) and 0.30 μM ([triple bond, length as m-dash]15.85 ppb), respectively. Notably, with the cumulative addition of Al3+ ions, the luminescence intensity at 403 nm decreased steadily with a gradual red shift up to 427 nm. Afterward, this red shifted peak showed a turn-on effect upon further addition of Al3+ ions. On the other hand, for Cr3+ and Fe3+ ions, there was only drastic luminescence quenching and a large red shift up to 434 nm. This indicated the formation of a complex between 1 and these metal ions, which was also supported by the UV-Visible absorption spectra of 1 that showed the appearance of a new band at 280 nm in the presence of these three metal ions. The FTIR spectra revealed that these ions interacted with the carboxylate oxygen atom of 5-AIP and the nitrogen atom of the Ald-4 ligand in the structure. The luminescence lifetime decay analysis manifested that a charge-transfer type complex was formed between 1 and Cr3+ and Fe3+ ions that resulted in huge luminescence quenching due to the efficient charge transfer involving the vacant d-orbitals, whereas for Al3+ ions having no vacant d-orbital, turn-on of luminescence occurred because of the increased rigidity of 1 upon complexation.

A Photoluminescent Cd(II) Coordination Polymer with Potential Active Sites Exhibiting Multiresponsive Fluorescence Sensing for Trace Amounts of NACs and Fe3+ and Al3+ Ions

The elaborately designed π-electron-rich fluorescent ligand 1,4-bis(1-carboxymethylene-4-imidazolyl)benzene (H₂L), possessing bifunctional groups including the carboxylate groups (building units) and 4-imidazoyl groups (N-donor potential active sites) has been employed to construct fluorescent coordination polymers. A luminescent sensor, namely [Cd(L)(phen)₂]·5H₂O (1), was obtained, which has a one-dimensional structure. The fluorescent material shows a blue emission maximum at 457 nm with a luminescence lifetime of 488 ns and a quantum yield (QY) of 4.56%. Significantly, 1 serves as a promising multiresponsive luminescent sensor to detect trace nitroaromatic compounds (NACs) with the limits of detection (LOD) of 7.21 × 10^-8, 1.85 × 10^-5, and 1.15 × 10^-5 mol/L for 2-nitrophenol (2-NP), 3-nitrophenol (3-NP), and 4-nitrophenol (4-NP), respectively. Furthermore, CP 1 exhibits fluorescent turn-off and turn-on sensing behavior for Fe³⁺ and Al³⁺ metal ions with trace amounts of 1.05 × 10^-7 and 1.13 × 10^-7 mol/L, respectively. Experimental methods and theoretical calculations were employed to elucidate the sensing mechanism in detail.

Porphyrin-Based Metal-Organic Framework Probe: Highly Selective and Sensitive Fluorescent Turn-On Sensor for M3+ (Al3+, Cr3+, and Fe3+) Ions

The development of porphyrin-based metal-organic frameworks (MOFs) has attracted significant interest in the scientific community in recent years because of their versatile applications particularly in optical and electronic fields. In this study, a highly selective and sensitive fluorescent turn-on sensor using a porphyrinic MOF, Tb-TCPP, is presented, which displays a 10-fold fluorescence enhancement in the presence of Al³⁺, Cr³⁺, and Fe³⁺ ions. The detection limit is in the nM region. For the Al³⁺ ion, it could be visually detected at concentrations as low as 5 mM within 15 min. Tb-TCPP could also be used as an indicator for acidic or alkaline solutions at pH values of >9 and <3. The studies on the detection mechanism illustrate that cation exchange proceed between Tb-TCPP and these M³⁺ ions, and consequently, energy transfer from TCPP to Tb³⁺ is suppressed and π*-π energy transfer of the porphyrin ligand is significantly enhanced.

A multifunctional benzothiadiazole-based fluorescence sensor for Al3+, Cr3+ and Fe3+

A benzothiadiazole-based Zn^II MOF (JXUST-3) has been synthesized, which is a good multifunctional chemosensor for the detection of Al³⁺, Cr³⁺ and Fe³⁺.

Turn-on fluorescent probe towards glyphosate and Cr3+ based on Cd(ii)-metal organic framework with Lewis basic sites

Lewis basic site-functionalized porous Cd(ii)-MOF as a bi-functional fluorescent sensor of glyphosate and Cr³⁺ with exceptional LODs.

Distinct solvent-dependent luminescence sensing property of a newly constructed Cu(ii)–organic framework

The distinct solvent-dependent fluorescence sensing behavior of an extremely rare Cu(ii) MOF, showing the fluorescent “turn-off” sensing of Fe³⁺ and HCO₃⁻ in DMF and “turn-on” sensing of Al³⁺ in water.

2D luminescent metal–organic framework: efficient and highly selective detection of 2,4,6-trinitrophenol at the ppb level

A 2D Cd-MOF (CUST-531) was reported as a sensor to detect TNP with high sensitivity and selectivity. The quenching mechanism is the turn-off response of the fluorescence signal, which can be observed by the naked eye under UV-vis lamp irradiation.

Porous and Nonporous Coordination Polymers Induced by Pseudohalide Ions for Luminescence and Gas Sorption

The three-dimensional (3D) coordination polymers [Cd(tpmd)(NCX)₂]_n [X = O (1), S (2), and BH₃ (3); tpmd = N,N,N',N'-tetrakis(pyridin-4-yl)methanediamine] have been determined to display their network structures through coordinated anionic ligands. Polymers 1 and 2 show nonporous structures, whereas polymer 3 shows a porous coordination framework. On the basis of the Cd(II) network structures, the 3D coordination polymer [Zn(tpmd)(NCBH₃)₂]_n·nMeOH (4) was self-assembled. In the cases of polymers 1 and 2, pseudohalide ions acted to form nonporous network structures; however, in polymers 3 and 4, NCBH₃^- helps to construct porous network structures. Polymers 1-4 show strong ultraviolet luminescence emissions, depending on the pseudohalide ions present, compared to the tpmd ligands. Interestingly, coordination polymers 3 and 4 that possess NCBH₃^- ions exhibit high porosities and gas sorption properties. The polymers appeared to absorb N₂, H₂, CO₂, and CH₄. In the case of polymer 4, the structure is almost identical with that of polymer 3, except for the Cd(II) ion. However, polymer 4 has a larger void volume and higher gas absorption ability for N₂ gas than polymer 3. For the sorption of gases, polymers 3 and 4 showed similar behaviors.

A Bifunctional Coordination Polymer for Al3+ Ion Detection and its Treatment Effect on Nonalcoholic Fatty Liver Disease by Promoting Lipoxygenases and Reducing Intrahepatic Triglyceride Content

In this study, a new Cd(II)-bearing coordination polymer with the chemical formula of {[Cd₄(meda)₃(dpe)₄(H₂O)₄]·(NO₃)₂·2(H₂O)}_n (1, H₂meda = 3,3'-methylenedibenzoic acid, dpe = 1,2-di(pyridin-4-yl)ethane) has been successfully prepared by reaction of Cd(NO₃)·4H₂O with a V-shape carboxyl ligand H₂meda along with the linear dipyridine ligand dpe under the hydrothermal conditions. Due to its intensive luminescence, complex 1 could be utilized as the sensor of detecting Al³⁺ ion, and its detection limit is 4 × 10^-6 M. Firstly, the toxicity of the compound on the normal liver cells was determined with Cell Counting Kit-8 detection kit. The triglyceride in liver cells was detected by detection kit after compound treatment and the relative expression of 15-lox and 12-lox in L02 cells was also measured by RT-PCR after compound treatment. In addition, multiple functional groups that provided by the synthesized Cd(II) complex have been studied by using molecular docking simulation for the confirmation of possible binding modes that formed between ligand and receptor.

Amino group decorated coordination polymers for enhanced detection of folic acid

A series of fluorescent coordination polymers (CPs) {[Cd₂(CH₃-bpeb)₂(BDC)₂] CP1, (BDC)_0.5/(NH₂-BDC)_0.5-CP1, (BDC)_0.34/(NH₂-BDC)_0.66-CP1, (BDC)_0.25/(NH₂-BDC)_0.75-CP1, (BDC)_0.2/(NH₂-BDC)_0.8-CP1, (NH₂-BDC)-CP1} were prepared from conjugated ligand 4,4'-((2-methyl-1,4-phenylene)bis(ethene-2,1-diyl))bipyridine (CH₃-bpeb), terephthalic acid (BDC), aminoterephthalic acid (NH₂-BDC) and CdSO₄ under solvothermal conditions. The fluorescence of aqueous suspensions of these CPs was quenched by folic acid (FA) in a concentration dependent manner. The efficiency of quenching increasing with an increased proportion of NH₂-BDC ligand in the CP with (NH₂-BDC)-CP1 exhibiting a low detection limit of 1.7 × 10^-7 M.

A New Zn(II) Complex: Fluorescent Detection of Fe3+ Ions in Water and Prevention Effect on DVT By Regulating Platelets Numbers and Activity of Clotting Factor

[Zn(dima)(H₂O)_0.5]·H₂O (1), a three-dimensional metal organic framework (MOF) with high porosity was formed by self-assembly of 4,6-di(1 h-imidazol-1-yl)isophthalic acid (H₂dima) and Zn²⁺ ion. Owning to its excellent luminescence and excellent water stability, complex 1 can be used as a super sensitive sensor to detect Fe³⁺ ions via the behaviors of fluorescence quenching. At the same time, the mechanism for the fluorescence quenching is also further discussed. Furthermore, the prevention effect of the compound on the deep vein thrombosis of the lower extremities (DVT) after lower venous CHIVA surgery was evaluated in vivo. Firstly, the DVT animal models was constructed and the number of platelets was measured with flow cytometry and content of clotting factor IX and anticoagulant factor III was also detected with Lowry method after compound treatment. The molecular docking simulation results indicate that the Zn(II) complex has activity to protein docking pocket with different sizes.

Constructing Strategies and Applications of Nitrogen-Rich Energetic Metal–Organic Framework Materials

The synthesis of energetic metal–organic frameworks (EMOFs) with one-dimensional, two-dimensional and three-dimensional structures is an effective strategy for developing new-generation high-energy-density and insensitive materials. The basic properties, models, synthetic strategies and applications of EMOF materials with nitrogen-rich energetic groups as ligands are reviewed. In contrast with traditional energetic materials, EMOFs exhibit some interesting characteristics, like tunable structure, diverse pores, high-density, high-detonation heat and so on. The traditional strategies to design EMOF materials with ideal properties are just to change the types and the size of energetic ligands and to select different metal ions. Recently, some new design concepts have come forth to produce more EMOFs materials with excellent properties, by modifying the energetic groups on the ligands and introducing highly energetic anion into skeleton, encapsulating metastable anions, introducing templates and so on. The paper points out that appropriate constructing strategy should be adopted according to the inherent characteristics of different EMOFs, by combining with functional requirements and considering the difficulties and the cost of production. To promote the development and application of EMOF materials, the more accurate and comprehensive synthesis, systematic performance measurement methods, theoretical calculation and structure simulation should be reinforced.

Development of Rhodamine 6G-Based Fluorescent Chemosensors for Al3+-Ion Detection: Effect of Ring Strain and Substituent in Enhancing Its Sensing Performance

Four rhodamine 6G-based chemosensors (H ₃ L1-H ₃ L4) are designed for selective detection of Al³⁺ ion. They are characterized using various spectroscopic techniques and X-ray crystallography. All absorption and emission spectral studies have been performed in 10 mM N-(2-hydroxyethyl)piperazine-N'-ethanesulfonic acid (HEPES) buffer solution at pH 7.4 in H₂O/MeOH (9:1, v/v) at 25 °C. In absorption spectra, chemosensors exhibit an intense band around 530 nm in the presence of Al³⁺ ion. Chemosensors (H ₃ L1-H ₃ L4) are nonfluorescent when excited around 490 nm. The presence of Al³⁺ ion enhances the emission intensity (555 nm) many times. The formation of complexes 1-4 is established with the aid of different spectroscopic techniques. The limit of detection value obtained in the nanomolar range confirms the high sensitivity of the probes toward Al³⁺ ion. It has been observed that the presence of aliphatic spacers in the diamine part and different halogen substituents in the salicylaldehyde part strongly influences the selectivity of the chemosensors toward Al³⁺ ion. The propensity of the chemosensors to identify intracellular Al³⁺ ions in triple-negative human breast cancer cell line MDA-MB-468 by fluorescence imaging is also examined in this study.

Five water-stable luminescent CdII-based metal–organic frameworks as sensors for highly sensitive and selective detection of acetylacetone, Fe3+ and Cr2O72− ions

Five Cd^II-based MOFs with different topologies were prepared, in which 2 and 3 are rare examples which display excellent sensitivity, selectivity, recyclability and structural stability for detection of acac/Fe³⁺ and acac/Cr₂O₇²⁻, respectively.

A dual-functional metal phosphate for high proton conduction and selective luminescence turn-on sensing of Co2+ ions

The {[Zn(H₂PIPZ)](H₂O)}_n (compound 1) detects Co²⁺ ions with turn on fluorescent and proton conductivity of composite membrane 1@PVA10 is ten times higher than compound 1 at 98% RH and 353 K.

Dual-responsive luminescent sensors based on two Cd-MOFs: rare enhancement toward acac and quenching toward Cr2O72−

Two luminescent Cd-MOFs were employed as dual-responsive luminescence sensors to detect acac and Cr₂O₇²⁻ through turn-on and turn-off mechanisms.

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.