Fluorescent Metal-organic Framework Research Articles

Sensitive and Selective Detection of Bisphenol Compounds in a Fluorescent Metal-Organic Framework

Bisphenol compounds (BPs), as a group of endocrine disrupted compounds, have been posing serious risk on ecological environment and human health. The sensing of BPs is quite significant, but still in challenge. Here, we report, for the first time, a metal-organic framework (MOF) directly and alone, enables the selective and sensitive detection of BPs on its unique fluorescent change. This MOF is based on Ga(III) ion, and interestingly represents specific fluorescent behavior of “turn on” and “turn off”. It exhibits not only good sensing capability with the detection limits as low as 26.36 nM (6.02 μg/L) for the typical BPs (bisphenol A), but also excellent selectivity toward the BPs on the synchronous fluorescent changes of “turn on” at 320 nm and “turn off” at 382 nm. Where, this phenomenon is caused by π-π stacking and hydrogen bonding interactions between adsorbed bisphenol molecules and the MOF host, demonstrated by molecular simulations. More importantly, the proposed sensing method based on this MOF is applicable in the detection of BPs in drinking water, showing excellent performance.

Fluorescent Metal–Organic Framework Constructed from Semi-rigid Ligand for the Sensitive Sensing of 2,4,6-Trinitrophenol

A Cd(II)-based metal–organic framework as fluorescent chemical sensor, formulated as {[Cd3(bmipia)2]·10DMF·5H2O}n (FCS-2), was synthesized through a hydrothermal process and structurally characteri...

RETRACTED: A water-stable Zn(II)-based metal-organic framework for selective detection of Fe3+ ion and treatment effect on children asthma by reducing apoptosis of eosinophil

Abstract The selective detection of metal ion is of high importance to the environmental protection and the safety of human health. In this paper, a novel fluorescent metal-organic framework containing Zn(II) ions as the metal nodes based {Zn3(OH)} clusters as the secondary building unit (SBU) and a rigid hexacarboxylic acid linker of 5,5′,5″-(methylsilanetriyl)triisophthalic acid (H6L) has been triumphantly prepared under the solvothermal conditions, and its chemical formula is established to be {[Zn3HL(μ3-OH)(H2O)2]∙3(H2O)∙DMA}n (1, DMA = N,N-dimethylacetamide). Due to its considerable water stability, the high sensitivity and selectivity of complex 1 as the fluorescent sensor for the detection of the Fe3+ ion in aqueous solution were studied. Furthermore, the treatment function of complex against the children asthma was evaluated and the related mechanism was explored. Firstly, the reverse transcription-polymerase chain reaction (RT-PCR) was carried out in order to determine the bcl-2 gene relative expression level, and the cell apoptosis level was determined with cell apoptosis detection kit. Finally, for the in vivo detection, the children asthma model was constructed and the release of the MBP and EDN from eosinophils was detected by the enzyme linked immunosorbent assay (ELISA).

A luminescent Eu(III)-MOF for selective sensing of Ag+ in aqueous solution

A 3D open structure FeIII(OH)[C6H2(CO2)2(CO2H)2]·xH2O(MIL-82) with carboxyl-rich groups is designed as a parent metal-organic framework (MOF). A stable lanthanide fluorescent MOF was successfully constructed by doping the Eu3+ cation on the coordination site of MIL-82. The intense luminescence of Eu3+ incorporated MIL-82 indicates that uncoordinated carboxyl group is an efficient framework for accommodating and sensitizing Eu3+ cations. The luminescent MOF can be developed as a chemical sensor for Ag+ in aqueous solution. The sensor also displays high selectivity towards Ag+, excellent sensitivity with a relatively low detection limit (0.09 μM) and fast response time within 3 min. In addition, the framework has excellent water stability and thermal stability, which provides a rare method for detecting Ag in daily water samples.

A rht‐Type Luminescent Zn (II)‐MOF Constructed by Triazine Hexacarboxylate Ligand: Tunable Luminescent Performance and White‐light Emission Regulation through doping Eu3+/Tb3+

White‐light emitting materials have become a hot research field of luminescent MOF (Metal–Organic Framework) because of its high practical application value. Herein, we successfully synthesized and characterized a rht‐type fluorescent MOF Zn‐TDPAT [H6TDPAT = 2,4,6‐tris(3,5‐dicarboxylphenylamino)‐1,3,5‐triazine] with a topology of (3, 24) connected nodes. A series of MOFs materials x%Tb + y%Eu@Zn‐TDPAT were prepared by incorporating different concentrations of green emission center Tb3+ and red emission center Eu3+ into the blue‐emitting Zn‐MOF. The luminescence properties of MOFs materials x%Tb + y%Eu@Zn‐TDPAT can be effectively adjusted by incorporating different concentrations of Tb3+ and Eu3+ and can obtain multi‐color luminescence properties from blue, blue‐green, green, yellow green, yellow, blue‐red, yellow‐red and white. According to trichromatic mechanism, by reasonably matching the intensity of blue light, green light and red light emitted by x%Tb + y%Eu@Zn‐TDPAT at 420, 543 and 616 nm, MOFs materials 0.75%Tb + 5%Eu@Zn‐TDPAT, 0.65%Tb + 5.5%Eu@Zn‐TDPAT and 0.5%Tb + 7.5%Eu@Zn‐TDPAT with white‐light emission are obtained. Their CIE coordinates are 0.3162, 0.3345 (0.3162, 0.3345), (0.3138, 0.3339) and (0.3329, 0.3222), respectively, which are very close to ideal white‐light emission (0.3333,0.3333).

Sensitive Ratiometric Fluorescent Metal-Organic Framework Sensor for Calcium Signaling in Human Blood Ionic Concentration Media.

A two-dimensional fluorescent metal-organic framework (MOF) sensor, TMU-5S, was synthesized by introducing rhodamine B into the framework of TMU-5. This dye-sensitized MOF was explored as a ratiometric fluorescent sensor for Ca2+ signaling in the presence of interfering cations in ionic concentrations similar to that of blood plasma that exhibits exceptional sensitivity and selectivity to Ca2+ and faster response and recovery times than any other reported fluorescent sensor. This can be attributed to strong electrostatic interactions between basic azine groups in the narrow pore walls of TMU-5S and Ca2+ as hard-hard acid-base interactions. The results show that the two-dimensional signal transduction can reduce interfering responses from the environment and thus create exceptional sensitivity.

Bismuth-Carboxylate Ligand 1,3,6,8-Tetrakis(p-benzoic acid)pyrene Frameworks, Photophysical Properties, Biological Imaging, and Fluorescent Sensor for Biothiols

The tetracarboxylate ligand H4TBAPy based on the strongly fluorescent pyrene cores and bismuth iodide constructed a permanently 3D microporous fluorescent metal–organic framework Bi-TBAPy first . I...

A highly fluorescent post-modified metal organic framework probe for selective, reversible and rapid carbon dioxide detection

The monitoring of the arterial and exhaled CO2 is of great importance. Despite of many reports on metal organic frameworks (MOFs) in adsorbing and separating CO2, the application of fluorescent MOFs probes for CO2 detection was rarely reported. A new fluorescent MOF probe UIO-66-ONa for CO2 detection was developed via post-synthesis of UIO-66-NH2 through a Schiff base reaction with salicylaldehyde and further treatment with sodium hydroxide. This probe exhibited a remarkable fluorescence color change from green to blue and showed excellent sensitivity and selectivity for CO2 sensing in solution. The detection limit was as low as 3.5 × 10−7 M. The excellent sensing performance of UIO-66-ONa was ascribed to the efficient reaction between sodium phenolic group and CO2, which led to the transformation of UIO-66-ONa to UIO-66-OH as evidenced by the emission spectra. This post-synthetic modification idea provided a new strategy for designing fluorescent MOFs probes for CO2 detection.

Green synthesis of fluorescent PEG-ZnS QDs encapsulated into Co-MOFs as an effective sensor for ultrasensitive detection of copper ions in tap water.

In this work, a novel and highly fluorescent (FL) metal-organic framework (MOF)-based host-guest hybrid system was developed through encapsulation of polyethylene glycol (PEG)-capped ZnS quantum dots (QDs) into zeolitic imidazolate framework (ZIF)-67 at ambient temperature. This new composite material was characterized by FT-IR, XRD, TEM, UV-Vis absorption and FL spectroscopy, and then exploited as fluorescence sensor for highly sensitive and selective detection of Cu (II) ions in water samples. The as-prepared PEG-ZnS QDs@ZIF-67 nanohybrids took advantages of both accumulation effect in ZIF-67 and FL sensitivity and selectivity in ZnS QDs toward analyte-Cu2+. In this regard, ZIF-67 was treated as absorbents to capture and enrich Cu (II) ions, and ZnS QDs were exploited as tentacle to selectively and sensitively sense the bonding interactions between ZIF-67 and Cu (II) ions, and further transduce these chemical events to the detectable fluorescence signals. By this approach, Cu2+ could be detected in a wide concentration range of 3 to 500 nM with a LOD as low as 0.96 nM. The proposed FL-sensor can be promising in the field of preparation of various QDs@MOFs platforms for application in high-performance optical sensing.

ZnMOF-74 responsive fluorescence sensing platform for detection of Fe3+

Fluorescent metal-organic frameworks (MOFs) have attracted wide attention in fluorescence detection. Herein, a novel sensing platform for highly selective and sensitive detection of Fe3+ in aqueous solution was proposed based on 2,5-dihydroxyterephthalic acid (DOBDC)-Zn2+ MOFs (ZnMOF-74). The as-prepared ZnMOF-74 exhibited uniform clavicorn nanostructures and high day-to-day stability in acidic aqueous solution (pH 4.0). Because of the special response of phenolic hydroxyl groups of DOBDC with Fe3+, the cation exchange between Fe3+ and Zn2+ occurred, which caused collapse of the skeleton and formed a blue weak-fluorescent iron(III)-phenol salt complex (Fe-DOBDC), which led to the effective fluorescence quenching of ZnMOF-74. ZnMOF-74 was used as a probe for detection of Fe3+ under relatively acidic condition with a good linear range of 0.1–100 μM and a low detection limit of 40 nM. The fluorescence probe was also applied to determine Fe3+ in real river water and human serum with good recovery and accuracy. This work provided a good Fe3+ sensor based on ZnMOF-74 due to high affinity between phenolic hydroxyl group and Fe3+.

Metal–Organic Framework with Color-Switching and Strongly Polarized Emission

Hybrid fluorescent metal–organic frameworks (MOFs) use long-range intermolecular structural motifs in which the properties of the scaffold molecular system can be designed for specific applications...

An adjustable dual-emission fluorescent metal-organic framework: Effective detection of multiple metal ions, nitro-based molecules and DMA.

A novel multifunctional Pb(II)-based MOF, [Pb1.5(DBPT)]2·(DMA)3(H2O)4 (1), with excellent chemical stability, was successfully assembled by connecting {Pb2O10} unit with a multi-topic polycarboxylate ligand of 3-(3,5-dicarboxylphenyl)-5-(4-carboxylphenyl)-1-H-1,2,4-triazole (H3DBPT). It exhibits dual fluorescence emissions at 380 nm (λex = 280 nm) and 540 nm (λex = 380 nm), respectively. Through the adjustable dual fluorescence emissions, it could act as a turn-off and turn-on switch for detecting N,N-dimethylacetamide (DMA) molecule. Moreover, Fe3+ ions exert luminescence quenching role on compound 1 at both excitation lengths in water, among which the quenching at λex = 280 nm is of high sensitivity (KSV = 1.2 × 105), and the quenching at λex = 380 nm is of wide-range. The sensing for metal ions of In3+, Zr4+, and Al3+ is also effective at λex = 280 nm, with the KSV constants of 1.6 × 105, 1.6 × 105, and 4.3 × 104, respectively. More importantly, a series of nitroaromatic compounds (TNP, 2,4,6-trinitrophenol; 4-NA, 4-nitroaniline; NB, nitrobenzene) and nitro-based drugs (MNZ, metronidazole; DMZ, dimetridazole) could be detected at both excitation lengths, demonstrating the advantage of broad range response of fluorescence sensing. Thanks to the excellent chemical stability and unusual dual emission luminescence properties for chemical detection of various metal ions, nitro-based molecules and DMA solvent, the Pb-based MOF reported in this work is, therefore, a very promising multi-response sensor.

Highly sensitive and selective detect of p‐arsanilic acid with a new water‐stable europium metal–organic framework

The p‐arsanilic acid (p‐ASA), as an aromatic organoarsenic compounds, had received considerable concerns for their potential toxicity and carcinogenic properties. It was essential to detect p‐ASA with a facile method. In this paper, an europium based fluorescent metal–organic framework (MOF) [Eu2(clhex)·2H2O)]·H2O (BUC‐69) was successfully prepared under hydrothermal conditions with 1,2,3,4,5,6‐cyclohexanehexacarboxylic acid (H6clhex) as organic linker. BUC‐69 displayed superior fluorescence capability to achieve selective and sensitive detection toward p‐ASA in water, which presented the first example of a MOF‐based sensor to detect p‐ASA. BUC‐69 showed excellent chemical stability in solutions under pH ranging from 4 to 12, which makes it be a potential sensor both in acidity and alkalinity condition. Significantly, BUC‐69 performed well in fluorescent sensing of p‐ASA at a low concentration (10−6 M) in the simulated wastewater prepared with real lake water, and the results were comparable to the values detected by Inductively Coupled Plasma Optical Emission Spectrometer (ICP‐OES). The corresponding mechanism of fluorescent sensing toward p‐ASA with BUC‐69 was proposed and affirmed.

A highly fluorescent metal organic framework probe for 2,4,6-trinitrophenol detection via post-synthetic modification of UIO-66-NH2

Metal organic frameworks (MOFs) have been hotly concerned due to their unique structure and properties. A new highly fluorescent MOF was developed via post-synthesis of UIO-66-NH2 through an efficient click reaction with 1-ethynylpyrene for the 2,4,6-trinitrophenol (PA) detection which named UIO-66-Py. It exhibited a significantly enhanced fluorescence intensity than UIO-66-NH2 and showed excellent selectivity and sensitivity for sensing PA in solution via the fluorescence quenching mechanism. The UIO-66-Py showed an 85% fluorescence quenching efficiency with 0.203 mM PA and the detection limit was 4.5 × 10−7 M. The excellent selectivity of the probe was ascribed to the hydrogen bond interaction between UIO-66-Py and PA as evidenced by FT-IR. The hydrogen bond interaction promoted the photo-induced electron transfer (PET) between UIO-66-Py and PA which leading to the better selectivity of UIO-66-Py for PA detection over TNT. This post-synthetic modification idea provided a strategy for the development of MOFs with multifunctional sensing.

Mechanistic insight into the sensing of nitroaromatic compounds by metal-organic frameworks

There has been extensive research on the sensing of explosive nitroaromatic compounds (NACs) using fluorescent metal-organic frameworks (MOFs). However, ambiguity in the sensing mechanism has hampered the development of efficient explosive sensors. Here we report the synthesis of a hydroxyl-functionalized MOF for rapid and efficient sensing of NACs and examine in detail its fluorescence quenching mechanisms. In chloroform, quenching takes place primarily by exciton migration to the ground-state complex formed between the MOF and the analytes. A combination of hydrogen-bonding interactions and π–π stacking interactions are responsible for fluorescence quenching, and this observation is supported by single-crystal structures. In water, the quenching mechanism shifts toward resonance energy transfer and photo-induced electron transfer, after exciton migration as in chloroform. This study provides insight into florescence-quenching mechanisms for the selective sensing of NACs and reduces the ambiguity regarding the nature of interactions between the MOF and NACs.

Highly sensitive fluorescent metal-organic framework as a selective sensor of MnVII and CrVI anions (MnO4−/Cr2O72−/CrO42−) in aqueous solutions

A luminescent ZnII-MOF named TMU-41, [Zn2(BDC)1.5(L)(DMF)]·1.5DMF, (L = pyridine 4-carboxylic acid and BDC = benzene-1,4-dicarboxylate), has been successfully assembled and well characterized by single-crystal X-ray crystallography, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and N2 adsorption-desorption isotherms, which shows good stability especially in aqueous solutions. To fabricate open metal sites (OMS) of TMU-41(OMS), the coordinated DMF molecules were exchanged and removed by using acetonitrile as exchanging solvent and drying at 250 °C. The values of obtained surface areas after removing the coordinated DMF molecules are in the range of 740 m2/g. This MOF indicates high potential ability in detection of anions due to its strong luminescence effect and stability in water. All these results suggest TMU-41(OMS) to be a highly selective and recyclable luminescent sensing material for the quantitative detection of CrVI and MnVII anions in aqueous solutions.TMU-41(OMS) has the highest sensing ability in comparison to the reported MOFs-based fluorescent and the detection limits towards MnO4−, Cr2O72− and CrO42− ions are about 5 ppb which is among the lowest reported detection limits for the LMOFs.

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.

Guest-Induced Ultrasensitive Detection of Multiple Toxic Organics and Fe3+ Ions in a Strategically Designed and Regenerative Smart Fluorescent Metal-Organic Framework.

Luminescent metal-organic frameworks (LMOFs) are promising functional materials for sustainable applications, where an analyte-induced multiresponsive system with good recyclability is beneficial for detecting numerous lethal pollutants. We designed and built the dual-functionalized, three-dimensional Zn(II)-framework [Zn3( bpg)1.5( azdc)3]·(DMF)5.9·(H2O)1.05 (CSMCRI-1) using an -OH group-integrated bpg linker and a -N═N- moiety containing H2 azdc ligand, which functions as a unique tetrasensoric fluorescent probe. The activated CSMCRI-1 (1') represents the hitherto unreported pillar-layer framework for extremely selective fluorescence quenching by nitrofurazone antibiotics as well as explosive nitro-aromatic 2,4,6-trinitrophenol, where ultrasensitive detection is achieved for both the electron-lacking analytes. Impressively, 1' represents the first ever MOF for significant fluorescence "turn-on" detection of toxic and electron-rich 4-aminophenol in the concurrent presence of isomeric analogues. Density functional theory calculations highlight the specific importance of pillar functionalization in the "turn-on" or "turn-off" responses of 1' by electronically divergent toxic organics and provide further proof of supramolecular interactions between the framework and analytes. The fluorescence intensity of 1' dramatically quenches by a trace amount of Fe3+ ions over other competing metal ions, alongside visible colorimetric change of the framework in solid and solution phase upon Fe3+ encapsulation. The sensing ability of 1' remains unaltered for multiple cycles toward all lethal pollutants. The sensing mechanism is attributed to both dynamic and static quenching as well as resonance energy transfer, which strongly comply with the predictions of theoretical simulations. Considering the long-term and real-time monitoring, AND as well as OR molecular logic gates are constructed based on the discriminative fluorescence response for each analyte that provides a platform to fabricate smart LMOFs with multimode logic operations.

Nanoscale fluorescent metal–organic framework composites as a logic platform for potential diagnosis of asthma

Asthma is a common chronic disorder, and the decreased hydrogen sulfide (H2S) production in the lung has been considered as an early detection biomarker for asthma. However, the detection of H2S in biological systems remains a challenge; because it requires the designed sensors to have the following features: nanoscale size, good biocompatibility, real-time detection, high selectivity/sensitivity, and good water stability. Here, we propose the potential of using nanoscale fluorescent metal–organic framework (MOF) composites Eu3+/Ag+@UiO-66-(COOH)2 (hereafter denoted as EAUC) as a logic platform for tentative diagnosis of asthma by detecting the biomarker H2S. This INHIBIT logic gate based on Eu3+@UiO-66-(COOH)2 (EUC) can be produced by choosing Ag+ and H2S as inputs and by monitoring the fluorescent signal (I615) as an output. Our fluorescent studies indicate that the EAUC exhibits excellent selectivity, extreme sensitivity (limit of detection: 23.53 μM), and real-time in situ detection of H2S. Further, MTT analysis in PC12 cells shows that the EAUC possesses low cytotoxicity and favourable biocompatibility that are suitable for the detection of biomarker H2S in vivo, as demonstrated by the successful detection of spiked H2S in the diluted serum samples. This work represents the possibility of using MOF-based logic platform for tentative diagnosis of asthma in clinical medicine.

Fluorescent metal-organic frameworks based on mixed organic ligands: new candidates for highly sensitive detection of TNP.

In this study, by employing mixed organic ligands through rational design and metal ions as the initial reactants, a series of novel metal-organic frameworks (AHU-TW1 to 6) were synthesized by a solvothermal method. Herein, accessible Lewis base sites originating from organic ligands within MOFs act as functional sites that can interact with the analyte possessing protons and then lead to obvious variations in the fluorescence spectra. Due to their superiority, AHU-TW1, 3, 4 and 6 are able to recognize trinitrophenol (TNP) with high sensitivity and a low detection limit.