A dual-emitting 4d-4f nanocrystalline metal-organic framework as a self-calibrating luminescent sensor for indoor formaldehyde pollution

Alginate-modified surfactants functionalized metal-organic framework-based fluorescent film sensors for detection and adsorption of volatile aldehydes in water

Volatile aldehydes have an adverse impact on both human health and the environment, therefore, a fast, straightforward, highly accurate detection technique for the simultaneous detection and removal of several aldehydes is eagerly anticipated. Herein, novel APGF@ZIF-8 and APOF@ZIF-8 sensing materials were developed by coating fluorescent alginate-modified surfactants (APGF and APOF) into the ZIF-8 MOFs to produce quite porous fluorescent sensors (SBET up to 1519 m2/g). The detection capacity of the prepared sensors for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde has been examined. The detection mechanism was suggested as hydrogen bonding formation between the sensors and volatile aldehydes as confirmed by Gaussian calculations. All the fluorescence spectra of aldehydes display remarkable linear detection relationships in the range of 0.05-200 μM with the limits of detection (LOD) values in the range of 0.001-0.18 μM (0.106-10.44 ppb). These sensors were utilized successfully to detect multiple volatile aldehydes in river water samples with satisfactory recoveries of 96-107 %. Interestingly, fluorescent APGF@ZIF-8/CS and APOF@ZIF-8/CS films as portable disposable removal techniques for benzaldehyde, glyoxal, formaldehyde, and acetaldehyde from water were fabricated. APOF@ZIF-8/CS exhibited an excellent formaldehyde adsorption capacity of 58.30 mg/g and an adsorption removal efficiency of 93.5 %. The adsorption process of biosorbent on various aldehydes was fitted by Freundlich adsorption isotherm. The adsorption kinetics followed Pseudo-second-order kinetic model.

Portable and Recyclable Luminescent Lanthanide Coordination Polymer Film Sensors for Adenosine Triphosphate in Urine

Adenosine triphosphate (ATP) is a small molecule that is released to the urine from bladder urothelial cells and the bladder mucosal band of the human body. In certain cases, ATP can serve as a biomarker in bladder disease. For the practical applicability of luminescent sensors for ATP in urine, it is significant to find a new strategy for making the detection progress simple and available for in-field urine analysis. Here, a novel luminescent lanthanide coordination polymer (Tb-BPA) was designed and synthesized for quick and sensitive detection of ATP through luminescence quenching with a quenching constant of 4.90 × 103 M-1 and a detection limit of 0.55 × 10-6 M. Besides, Tb-BPA has excellent anti-interference ability and can detect ATP in simulated urine with a small relative standard deviation (<4%). Moreover, the luminescent polyacrylonitrile nanofiber films modified by Tb-BPA were prepared by electrospinning and were used for ATP visual detection. Notably, this film is easy to recover and reuse, and maintains good detection performance after at least 7 cycles.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

A Ratiometric Fluorescent Probe Based on RhB Functionalized Tb-MOFs for the Continuous Visual Detection of Fe3+ and AA

In this study, a red-green dual-emitting fluorescent composite (RhB@MOFs) was constructed by introducing the red-emitting organic fluorescent dye rhodamine B (RhB) into metal-organic frameworks (Tb-MOFs). The sample can be used as a ratiometric fluorescent probe, which not only avoids errors caused by instrument and environmental instability but also has multiple applications in detection. The results indicated that the RhB@MOFs exhibited a turned-off response toward Fe3+ and a turned-on response for the continuous detection of ascorbic acid (AA). This ratiometric fluorescent probe possessed high sensitivity and excellent selectivity in the continuous determination of Fe3+ and AA. It is worth mentioning that remarkable fluorescence change could be clearly observed by the naked eye under a UV lamp, which is more convenient in applications. In addition, the mechanisms of Fe3+- and AA-induced fluorescence quench and recovery are discussed in detail. This ratiometric probe displayed outstanding recognition of heavy metal ions and biomolecules, providing potential applications for water quality monitoring and biomolecule determination.

Film-based fluorescent sensor for visual monitoring and efficient removal of aniline in solutions and gas phase

Aniline has attracted much concern for its long degradation half-life and huge toxicity to the environment and human beings. Therefore, the development of a multi-functional device for visual detection and efficient removal of aniline was highly anticipated. In our work, the small-size Eu@UiO-66(COOH) was obtained by post-synthesis modification (PSM), and then the film-based fluorescent sensor was prepared by crosslinking reaction. The films not only showed incredible mechanical stability and potential for large-scale preparation, but also have excellent fluorescence response to aniline in solutions and gas phase. As the concentration of aniline increased, the fluorescence of films gradually increased at 350 nm, while the fluorescence gradually quenching at 620 nm, and the detection limits (LOD) of aniline in water and air were 0.27 ppb and 0.086 ppb, respectively. In addition, the adsorption performance of the film for aniline has also been confirmed and the maximum adsorption capacity was 32.6 mg/g, which is a strong guarantee for the realization of ultra-trace detection and toxicity reduction of aniline. In summary, the multi-functional film sensor has been designed for ultra-trace detection and efficient removal of aniline in solutions and gas phase, and have significant value for pollutant treatment, ecological restoration and early prevention.

Optical thermometry based on europium doped self-activated dual-emitting LiCa3ZnV3O12 phosphor

In this study, rare-earth-doped self-activated LiCa₃ZnV₃O₁₂ (LCZV) vanadate phosphors were preparation by a high-temperature solid-state reaction. Their crystal structure, non-contact temperature sensing, and luminescence properties were studied deeply. Excited by ultraviolet light at 340 nm, the emission of [VO₄]^3- group and the Eu³⁺ ions were monitored. The highest strength emission peaks at 470 nm and 610 nm for [VO₄]^3- and Eu³⁺, respectively, provide favorable signal identification for estimating temperature. Due to thermal quenching behavior and energy transfer, the FIR (Fluorescence Intensity Ratio) from Eu³⁺ to [VO₄]^3- exhibits excellent sensitivity performance at 303 K - 523 K. In the meantime, the maximum absolute and relative sensitivities of the obtained phosphors are 0.0068 K^-1 and 1.18 % K^-1, which are overtopped to those reported previously. Furthermore, for the luminescent color of the CIE diagram with a strong temperature effect, the color coordinate could be verified from (0.2871, 0.3416) to (0.4121, 0.3420), which was matched well with the linear equation. Consequently, the Eu³⁺ doped LCZV phosphor not only can be used for high-temperature environmental safety signals but also is an extraordinary viable material in the field of optical sensing.

Multi-Emission from Single Metal-Organic Frameworks under Single Excitation

Multi-emission materials have come to prominent attention ascribed to their extended applications other than single-emission ones. General and robust design strategies of a single matrix with multi-emission under single excitation are urgently required. Metal-organic frameworks (MOFs) are porous materials prepared with organic ligands and metal nodes. The variety of metal nodes and ligands makes MOFs with great superiority as multi-emission matrices. Guest species encapsulated into the channels or pores of MOFs are the additional emission sites for multi-emission. In this review, multi-emission MOFs according to the different excitation sites are summarized and classified. The emission mechanisms are discussed, such as antenna effect, excited-state intramolecular proton transfer (ESIPT) and tautomerism for dual-emission. The factors that affect the emissions are revealed, including ligand-metal energy transfer and host-guest interaction, etc. Multi-emission MOFs could be predictably designed and prepared, once the emissive factors are controlled rationally in combination with the different multi-emission mechanisms. Correspondingly, new and practical applications are realized, including but not limited to ratiometric/multi-target sensing and bioimaging, white light-emitting diodes, and anti-counterfeiting. The design strategies of multi-emission MOFs and their extensive applications are reviewed. The results will shed light on other multi-emission systems to develop the structure-derived functionality and applications.

Design and Multiple Applications of Mixed-Ligand Metal-Organic Frameworks with Dual Emission

Herein, we revealed the factors that affect the emission in mixed-ligand metal-organic frameworks (MOFs) with the combination of terephthalic acid (BDC), 2-aminoterephthalic acid (BDC-NH₂), and 2,5-dihydroxylterephthalic acid [BDC-(OH)₂] as models. The -NH₂ and -(OH)₂ groups change the π-conjugation and luminescence behaviors than BDC, so the ligands show different optical behaviors. The Zn²⁺ ion with a 3d¹⁰ full electronic structure shows little effect on the emission of the ligand and is selected as the metal node. We found that the emission of BDC is weak and incompatible to that of BDC-NH₂, so only the emission of BDC-NH₂ was observed in the BDC/BDC-NH₂-MOF. Crosstalk occurs between the emissions from BDC and BDC-(OH)₂ for the single emission from BDC/BDC-(OH)₂-MOFs, even different ratios are selected. The MOFs prepared with BDC-NH₂ and BDC-(OH)₂ show dual emission at 450 and 550 nm, while the relative intensity was easily tuned with the ligand ratio and excitation wavelength. Thus, abundant optical behaviors and extensive applications were realized, including but not limited to (1) dual emission from single MOFs, (2) tunable color from blue to yellow with the excitation from 290 to 370 nm for information encryption and decryption, (3) white emission obtained under an excitation of 330 nm, and (4) response of -NH₂ groups to HCHO and Fe³⁺ ions for ratiometric fluorescence sensing and visual detection. This work revealed the factors that affect the emission in mixed-ligand MOFs, studied their optical behaviors, and realized different applications with single MOFs.

Eu3+-β-diketone functionalized covalent organic framework hybrid material as a sensitive and rapid response fluorescent sensor for glutaraldehyde

A covalent organic framework (named as TpDq) linked by β-ketoamine was prepared by imine condensation reaction with 1,3,5-triformylphloroglucinol (TFP) and 2,6-diaminoanthraquinone (DAAQ) as building blocks. Via employing a functionalized modification strategy, a new lanthanide complex Eu³⁺-β-diketone functionalized covalent organic framework hybrid material, Eu-TTA@TpDq (TTA = 2-thenoyltrifluoroacetone), has been synthesized. After post-synthetic modification (PSM), the shape and structure of the parent framework is well preserved and the modified material shows remarkable luminescence properties. Based on this, we designed it as a fluorescent probe and tried to use it to sense common aldehydes. The results indicate that Eu-TTA@TpDq exhibits a turn-off response toward glutaraldehyde which can distinguish from other common aldehydes. The fluorescent probe has the advantages of reusability, pH stability (4.50-8.52), fast luminescence response (<1 min) and low detection limit. The linear range of this method was 0-100 μM; the detection limit was 4.55 μM; the relative standard deviation was 2.16%. Furthermore, it has broad application prospect in both practical sensing of glutaraldehyde in water environment and simple detection of glutaraldehyde vapor. In addition, we preliminarily discussed the possible sensing mechanism.

2-Dimensional rare earth metal–organic frameworks based on a hexanuclear secondary building unit as efficient detectors for vapours of nitroaromatics and volatile organic compounds

A new family of microporous 2-dimensional rare earth metal organic frameworks based on a hexanuclear secondary building unit with capability to selectively detect vapours of volatile organic compounds and nitroaromatic explosives is reported.

Post-synthetically modified metal-organic frameworks for sensing and capture of water pollutants

Thanks to a bottom-up design of metals and organic ligands, the library of metal-organic frameworks (MOFs) has seen a conspicuous growth. Post-synthetically modified MOFs comprise a relatively smaller subset of this library. Whereas the approach of post-synthetic modification was seminally introduced for MOFs in the early 1990s, the earliest examples of post-synthetically modified MOFs are only congruous with adsorption and catalysis. The utility of PSM-derived MOFs for the sensing and capture of water contaminants is relatively niche. Arguably though, an increasing number of post-synthetically modified MOFs are finding relevance in the context of water pollutant remediation. In this article, we review the recent advances in this area and propose a structure-function relationship-guided blueprint for the future outlook.

PVA-SM microstructure enhanced ratiometric fluorescence probe for formaldehyde detection in solution and gas

Formaldehyde (FA) is one of the most common pollutants, which has tremendous harm to humans and environment. In this work, 4-amino-3-pentene-2-one (Fluoral-p) and SiO₂ coated quantum dot (QD@SiO₂) were combined to implement a new ratiometric fluorescence probe QD@SiO₂-Fluoral-p for FA detection. In addition, by utilization of polyvinyl alcohol (PVA) and SiO₂ microsphere (SM), a kind of PVA-SM microstructure was assembled with QD@SiO₂-Fluoral-p to composite a signal enhanced sensing film. The QD@SiO₂-Fluoral-p exhibited good response to 0-400 mg/L FA solution and an enhancement around 15 folds was realized after introducing PVA-SM. In both situations, the probe showed linear relationship to FA concentration (C_FA), with detection limits of 14 and 0.5 mg/L, respectively. Also, the sensing film showed a good linear response to FA gas in the range of 0 to 2 ppm, with a detection limit 0.03 ppm. As a result, the PVA-SM enhanced ratiometric fluorescence probe features high sensitivity, low detection limit, good selectivity, as well as portable, which can serve as a useful tool for investigating FA in solution and gas at room temperature.

Preparation of Eu0.075Tb0.925-Metal Organic Framework as a Fluorescent Probe and Application in the Detection of Fe3+ and Cr2O72

Luminescent Ln-MOFs (Eu0.075Tb0.925-MOF) were successfully synthesised through the solvothermal reaction of Tb(NO3)3·6H2O, Eu(NO3)3·6H2O, and the ligand pyromellitic acid. The product was characterised by X-ray diffraction (XRD), TG analysis, EM, X-ray photoelectron spectroscopy (XPS), and luminescence properties, and results show that the synthesised material Eu0.075Tb0.925-MOF has a selective ratio-based fluorescence response to Fe3+ or Cr2O72-. On the basis of the internal filtering effect, the fluorescence detection experiment shows that as the concentration of Fe3+ or Cr2O72- increases, the intensity of the characteristic emission peak at 544 nm of Tb3+ decreases, and the intensity of the characteristic emission peak at 653 nm of Eu3+ increases in Eu0.075Tb0.925-MOF. The fluorescence intensity ratio (I653/I544) has a good linear relationship with the target concentration. The detection linear range for Fe3+ or Cr2O72- is 10-100 μM/L, and the detection limits are 2.71 × 10-7 and 8.72 × 10-7 M, respectively. Compared with the sensor material with a single fluorescence emission, the synthesised material has a higher anti-interference ability. The synthesised Eu0.075Tb0.925-MOF can be used as a highly selective and recyclable sensing material for Fe3+ or Cr2O72-. This material should be an excellent candidate for multifunctional sensors.

A Two-Fold Interpenetrated Dual-Emitting Luminescent Metal-Organic Framework as a Ratiometric Sensor for Chromium(III)

A novel two-fold interpenetrated metal-organic framework, namely Co-EDDA, was synthesized by hydrothermal reaction of 5,5'-[ethane-1,2-diylbis(oxy)]diisophthalic acid (H₄EDDA), Co(NO₃)₂·6H₂O, and 1,4-di(1H-imidazol-1-yl)benzene in water in an alkaline environment and structurally characterized. Co-EDDA could display clear dual-emission signals at 350 and 430 nm, representing the charge transfer emission between metal ions and the ligand and the ligand-based emission, respectively, which represents the ratiometric luminescence response to chromium(III) with high selectivity and sensitivity (limit of detection of 0.54 μM). Comprehensive studies indicate that the detection can be attributed to the interaction between the Cr³⁺ ions and the O atoms on the ether bond in Co-EDDA.

Tb3+-Doped Ag-MOFs for fluorescent detection of formaldehyde in a novel smartphone platform and its removal applications in milk products and wastewater

As one kind of reactive carbonyl species (RCS), formaldehyde (FA) with a high concentration could be extremely toxic to living bodies as well as the environment. This paper reports a three-dimensional (3D) Tb3+@Ag-MOFs-based fluorescent probe for fast sensing of FA, which uses a novel turn-on mechanism based on the luminescence induced by Tb3+. The MOF sensor shows broad dynamic ranges of 0.1-1 mM for FA with the detection limit of 1.9 μM. For online and real-time detection of FA, a portable smartphone platform was employed to analyze the RGB values of the fluorescence by a smartphone application. By incorporating this probe into a polyacrylonitrile (PAN) layer, we synthesized a film composite that could effectively remove FA in real samples including milk and chemical factory wastewater, and the removal rate reached 98.52% and 95.38% respectively. Moreover, the potential of the film to remove gaseous FA was confirmed by experiments as well.

A Dual-emitting Two-dimensional Nickel-based Metal-organic Framework Nanosheets: Eu3+/Ag+ Functionalization Synthesis and Ratiometric Sensing in Aqueous Solution

Using two-dimensional (2D) nickel-based metal organic framework (Ni-MOF) nanosheets as a matrix, Eu³⁺ and Ag⁺ were incorporated to synthesize Ag/Eu@Ni-MOF with double luminescence centers of Eu³⁺ ion (615 nm) and organic ligand (524 nm). And a ratiometric luminescence sensor is constructed based on Ag/Eu@Ni-MOF for sensitive detection of biothiols in aqueous solutions. The dual-emissive fluorescence properties can be tuned by changing the amounts of Ag⁺ ions doping. The results of temperature and pH effects on the fluorescence of Ag/Eu@Ni-MOF indicates that the Ag/Eu@Ni-MOF is a temperature-sensitive material and the fluorescence of Ag/Eu@Ni-MOF can keep stable over a wide pH range. Due to the binding of -SH in cysteine (Cys) and glutathione (GSH) with Ag⁺, the ligand luminescence was significantly inhibited by weakening the Ag + influence on the energy transfer process in the MOFs. Therefore, ratiometric fluorescent sensing of biomolecular thiols was realized based on the dual-emission Ag/Eu@Ni-MOF. More importantly, the fluorescence color change can be observed with naked eyes to realize visual detection. The ratiometric fluorescent sensor exhibits high performance for Cys and GSH detection with a wide linear range of 5-250 µM and a relatively low detection limit of 0.20 µM and 0.17 µM, respectively. Furthermore, the biothiols content in human serum was determined with satisfactory results. It proves the Ni-MOF nanosheets can be used as a stable matrix for construction luminescent MOFs for the first time, and validate the great potential of Ag/Eu@Ni-MOF as a ratiometric fluorescent probe for point-of-care testing (POCT) in disease diagnosis.

Smartphone-based ratiometric fluorescent definable system for phosphate by merged metal-organic frameworks

Phosphate plays an important role in a wide range of chemical and biological processes, so the development of a new phosphate optical sensor with high sensitivity, specificity and visual recognition function has important practical significance. Herein, a ratiometric fluorescent (RF) probe and a smartphone-integrated colorimetric test paper sensing platform for assay phosphate was fabricated using hybrid fluorescent UiO-66-NH₂ and Eu³⁺@MOF-808 metal-organic frameworks. After continuous addition of phosphate, the blue fluorescence emission of UiO-66-NH₂ and the red emission of Eu³⁺@MOF-808 were regularly enhanced and quenched respectively, and the fluorescence response of the detection platform to phosphate exhibited a clear color change process (red → pink → blue). More importantly, the probe solution and test paper of the integrated smartphone are converted to digital values through RGB channels and successfully used to visualize semi-quantitative recognition of phosphate. In addition, an RF probe and a smartphone integrated fluorescent test paper were developed separately to devise logic gate devices for detecting phosphate. The multifunctional ratio sensing platform integrated by the smartphone furnishes a new strategy and broad prospects for the intelligent online identification of important targets in biological samples and environmental samples.

Solvothermal Synthesis of High-Performance d10-MOFs with Hydrogel Membranes @ "Turn-On" Monitoring of Formaldehyde in Solution and Vapor Phase

Herein, two luminescent porous networks (CMERI-1 & CMERI-2) have been reported for the efficient detection of formaldehyde (FA) from aqueous medium. Judicious solvent screening using a high-throughput solvothermal procedure leads to two completely different metal-organic framework (MOFs) with different architectures. It is perceived that the framework CMERI-1 shows better sensitivity with a very short response time (1 min) in the realm of FA detection due to the facile imine (-N═CH-) formation, which is restricted in the case of CMERI-2. The fluorescence "turn-on" behavior is ascribed due to the inhibition of photoinduced electron transfer (PET) (from amine subunit to secondary building unit) process. The detection limits of CMERI-1 & CMERI-2 toward FA in aqueous medium were found to be 0.62 μM (0.019 ppm) and 1.39 μM (0.041 ppm), respectively, that lie far below the intracellular concentration of formaldehyde (100-400 μM). In addition, MOF-based hydrogel membrane was fabricated, which shows vapor-phase detection of FA, which is hitherto unexplored in this realm. Moreover, the response mechanisms of MOFs are supported by density functional theory (DFT) and Fukui indices analysis. The high stability of the porous frameworks along with its interesting sensing features such as fast recognition phenomenon, appreciable detection limit, etc. instigated us to explore its real-world applicability in various food sample and water analyses. In view of the modular design principle of our polymeric probe, the proposed approach could open a new horizon to construct powerful sensing materials for the ultrafast detection of other industrial pollutants in the domain of supramolecular and analytical chemistry.

Fluorescent sensors for aldehydes based on luminescent metal-organic frameworks

Volatile aldehydes cause great harm to human health and the living environment, and the detection of aldehydes has attracted much attention from chemists and material scientists. In recent years, as one of the most promising classes of functional materials, luminescent metal-organic frameworks (LMOFs) have bloomed as fluorescent sensors for the detection of aldehydes. Herein, the sensing properties of LMOF sensors toward formaldehyde, benzaldehyde, acetaldehyde and other aldehydes have been reviewed, and the sensing mechanism and applications are also illustrated. Additionally, the current status and its potential development prospects in this field are outlined.

A versatile logic detector and fluorescent film based on Eu-based MOF for swift detection of formaldehyde in solutions and gas phase

Due to the huge threat of formaldehyde (FA) on human beings, the development of chemical sensors for swift detection of FA in solutions and gas phase is highly anticipated. In this paper, a versatile logic detector and a portable fluorescent film based on small-scaled Eu-based MOF were applied successfully to detect FA in solutions and gas phase, respectively. For FA in aqueous solution, the design of logic detector will efficiently identify FA in different concentration ranges: when the FA concentration are 0-500 ppb, 500-1000 ppb and >1000 ppb, the output signals of logic detector are the concentration level of FA ("L", "H" and "VH"), and accompanied by red, purple and blue signal lamps to remind, respectively. For FA in the air, the color of rigid film sensor will gradually change from red to blue with the increase of FA under UV lamp, and the detection limit of gaseous FA is 11.8 ppb. Through the preparation of logic devices and fluorescent films, Eu-based MOF realized swift detection of FA in solutions and gas phase, which will be very helpful to improve the human response level to FA from different emission sources.

Designed Eu3+ functionalized Zr-MOF-808 probe for highly sensitive monitoring multiple dyes

Dyes detection remains a serious task because of their high toxicity. In present work, designed Eu³⁺ functionalized Zr-metal-organic framework (Eu³⁺@Zr-MOF-808) as fluorescent probe was constructed via post-synthetic modification (PSM) for rapid monitoring four most commonly used dyes (malachite green (MG), brilliant green (BG), alizarin red S (ARS), indigo red (IDR)). Systematic exploring on the sensing mechanism reveals that fluorescence resonance energy transfer (FRET) for BG, MG and IDR and inner filter effect (IFE) for ARS contribute to the realization of the fluorescence quenching process. It exhibits excellent sensing performances with low limit of detection (LOD) of 32, 58, 77 and 133 nM for BG, IDR, MG and ARS, respectively. The as-constructed Eu³⁺@Zr-MOF-808 was demonstrated to be a highly sensitive probe for screening of MG in fish pond and IDR in printing wastewater with satisfying results. Moreover, a portable test reagent bottle has been developed for visual on-site screening of sample containing dyes with naked eyes under UV light. This is the first attempt to construct the Eu³⁺@Zr-MOF-808 probe for sensingmultiple dyes in real samples and demonstrates promising applications in water quality monitoring.

Encapsulation of Luminescent Guests to Construct Luminescent Metal-Organic Frameworks for Chemical Sensing

Metal-organic frameworks (MOFs), which are a class of coordination polymers constructed by metal ions or clusters with organic ligands, have emerged as exciting inorganic-organic hybrid materials with the superiorities of inherent crystallinity, adjustable pore size, clear structure, and high degree of functionalization. The MOFs have attracted much attention to develop good luminescent functional materials due to their inherent luminescent centers of both inorganic and organic photonic units. Furthermore, the pores within MOFs can also be used to encapsulate a large number of luminescent guest species, which provides a broader luminescent property for MOF materials. MOFs possess the incomparable multifunctional advantages of inorganic and organic luminescent materials. A large number of luminescent MOFs (LMOFs) have been synthesized for applications in sensing, white-light-emitting diodes (LED), photocatalysis, biomedicine, etc. This paper reviews the encapsulation of various luminescent guests such as lanthanide ions, dyes, quantum dots, and luminescent complexes in metal-organic frameworks to construct luminous sensors with single- or double-emission centers, as well as the research progress of these sensors in chemical sensing. Finally, the challenges in these fields were outlined and the prospects for future development were put forward.

Designed Eu(III)-functionalized nanoscale MOF probe based on fluorescence resonance energy transfer for the reversible sensing of trace Malachite green

An ingenious nanoscale fluorescent sensor derived from Eu³⁺-postfunctionalized MIL-53 (Al) (Eu³⁺@MIL-53 [Al]) was fabricated though a simple and effective approach. Malachite green (MG) effectively turned off the luminescence of Eu³⁺@MIL-53 (Al) via fluorescence resonance energy transfer (FRET), thus enabling MG sensing. The developed probe exhibited instantaneous reusability after being cleaned with deionized water. The fluorescence intensity, quenching efficiency, and crystal structure of the recoverable sensor after five recycling processes were unchanged compared with those of the original sample. Moreover, the potential mechanism of MG detection was revealed in detail. This work represents the first attempt to determine MG in aquaculture water and products by using metal-organic frameworks (MOFs). The Eu³⁺@MIL-53 (Al) probe proved to be a remarkable fluorescence probe for MG with high selectivity, sensitivity, and excellent regeneration capability. It provides a promising functional platform for the recognition of illegal MG addition to aquaculture water and products.

Designed Tb(III)-Functionalized MOF-808 as Visible Fluorescent Probes for Monitoring Bilirubin and Identifying Fingerprints

Abnormal bilirubin (BR) level is a sign of several fatal diseases, so it is of great significance and challenge to develop a facile and effective family routine strategy for BR sensing. Herein, novel water-stable Tb³⁺@MOF-808 has been synthesized using a coordinated postsynthetic modification strategy and designed as a convenient and efficient fluorescence probe. The fabricated fluorescent probe exhibits a remarkable fluorescence quenching effect with the successive addition of BR, which displays fascinating features, such as fast response time, high sensitivity, and excellent selectivity. The quenching mechanism between the fluorescent probe and BR was also illustrated in detail. Importantly, the devised fluorescent probe successfully achieved the determination of BR in serum and urine, which has also been successfully used in the design of portable BR test paper. The developed monitoring platform for BR levels in vivo provides promising application potential for the prevention and early diagnosis of fatal diseases. Additionally, a molecular logic gate device that performs intelligent fluorescent sensing of BR was constructed. More interestingly, Tb³⁺@MOF-808 is used for development of latent fingerprints on different guest surfaces. The lines of the fluorescent fingerprints are clear and coherent, the details are obvious, and even sweat pores can be observed by naked eyes, which provides new means for tracking the criminal clue and handling cases efficiently.

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).

Ultrasensitive and highly selective detection of formaldehyde via an adenine-based biological metal–organic framework

We demonstrate a successful design of an adenine-based BioMOF for highly sensitive formaldehyde recognition without the interference of other VOCs by utilizing its reactivity on Watson–Crick sites and MOF compartmentalization.

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.

The selective and sensitive detection of formaldehyde by ZIF-90-LWvia aza-Cope rearrangement

Formaldehyde (FA), as one of the simplest reactive carbonyl species (RCS), is widely known as an environmental toxin and carcinogen. In this work, a new ZIF-90 type material (ZIF-90-LW) was synthesized and investigated, which combines the two strategies of "2-aza-Cope rearrangement" and "MOF structure", by the combination of a pre-functionalized 2-allylaminoimidazole ligand and Zn²⁺ salt under solvothermal conditions. From this, the hurdle of selectivity over other carbonyl compounds (RCS) could be overcome despite their similar electrophilic reactivities to FA, and a prominent fluorescence turn-on type signal was realized through the 2-aza-Cope rearrangement mechanism. A good linear relationship (R² = 0.9979) was obtained by fitting the fluorescence intensity towards FA from 0 to 25 mM, and the detection limit of ZIF-90-LW for FA was 2.3 μM. In addition, it also showed potentially useful sensing ability for the detection of FA in the gas phase, and might therefore be used to rapidly detect FA with a response time of 28 s in the liquid phase. All of the above features clearly demonstrate that ZIF-90-LW has great potential for sensitive and selective recognition of FA in the environment.

Terbium-based metal-organic frameworks: highly selective and fast respond sensor for styrene detection and construction of molecular logic gate

Volatile organic compounds (VOCs) are extremely harmful to the human body and environment, thus it is greatly meaningful and urgent to detect VOCs. In this work, terbium-based metal-organic frameworks (Tb-MOFs) have been prepared successfully via a facile and efficient route. These well-constructed Tb-MOFs architectures exhibit characteristic green emission of Tb³⁺ ion upon excitation of UV light. It is noteworthy that the Tb-MOFs can act as a convenient and efficient luminescent sensor for VOCs. Especially, the Tb-MOFs displayed high selectivity and superior sensitivity towards the sensing of styrene solution and vapor through fluorescence quenching mechanism. The Tb-MOFs can realize fast detection for styrene vapor with a response time of 30 s. The mechanism of fluorescence quenching of Tb-MOFs induced by styrene was also discussed. More importantly, we have designed a logic gate operation with the combination of the sensor for the intelligent detection of styrene. This developed type of lanthanide luminescent metal-organic frameworks (Ln-MOFs) based on the combination of fluorescence sensor and logic gate has a great application prospect in the detection of VOCs in daily life.

A label-free luminescent assay for tyrosinase activity monitoring and inhibitor screening with responsive lanthanide coordination polymer nanoparticles

In this work, a label-free, selective, and sensitive luminescent sensing platform was established for tyrosinase (TYR) activity monitoring and its inhibitor screening using one kind of lanthanide coordination polymer nanoparticles AMP-Tb/Ag⁺. By taking advantage of the specific binding and redox properties of Ag⁺ incorporated into the AMP-Tb network and dopamine (DA) as the product of the model substrate tyramine, the enzymatic reaction and the signal change of the sensing platform was effectively linked. The cooperative effect of a weakened energy transfer from AMP to Tb³⁺ by altering the electronic structure of Ag⁺ and an efficient photoinduced election transfer (PET) process caused by dopaquinone facilitated the luminescence quenching of Tb³⁺. Thus, this luminescent sensing platform could be employed for quantitative evaluation of TYR activity. There was a good linear range for TYR activity from 0.08 to 0.20 U mL^-1 with a low detection limit of 0.004 U mL^-1. Furthermore, this assay was successfully applied to accurate determination of TYR activity in human serum samples and efficient screening of TYR inhibitors. Considering unique spectral characteristics of lanthanides along with operation simplicity and superior analytical performance, this sensing platform is very promising in clinical diagnosis and drugs screening for TYR-associated diseases.

Zinc(ii)-based coordination polymer encapsulated Tb3+ as a multi-responsive luminescent sensor for Ru3+, Fe3+, CrO4 2-, Cr2O7 2- and MnO4. RSC Adv 2020;10:6022-6029. [PMID: 35497449 PMCID: PMC9049217 DOI: 10.1039/c9ra09541a]

A zinc(ii)-based coordination polymer (CP), namely [Zn(modbc)2] n (Zn-CP) (modbc = 2-methyl-6-oxygen-1,6-dihydro-3,4'-bipyridine-5-carbonitrile), has been synthesized and characterized. Single-crystal structural determination reveals that Zn-CP is a two-dimensional framework structure with tetranuclear homometallic Zn4(modbc)4 units cross-linked by modbc. The excellent luminescence as well as good stability of Zn-CP do not enable it to have selective sensing capability for different ions. After encapsulation of Tb3+ in Zn-CP, the as-obtained fluorescent functionalized Tb3+@Zn-CP maintained excellent luminescence as well as stability, which made it a highly selective and sensitive multiresponsive luminescent sensor for Ru3+, Fe3+, CrO4 2-, Cr2O7 2-, and MnO4 - with high sensitivity, good anti-interference performance, and quick response time (∼10 s). The detection limits are 0.27 μM, 0.57 μM, 0.10 μM, 0.43 μM and 0.15 μM, respectively. A possible sensing mechanism was discussed in detail.

A selective and sensitive fluorescent probe for bilirubin in human serum based on europium(III) post-functionalized Zr(IV)-Based MOFs

In the present study, a kind of Eu(III) post-functionalized Zr(IV)-based metal-organic framework (UiO-66(COOH)₂, Zr-MOF: Eu³⁺) was synthesized and utilized as an independently luminescent probe for sensing bilirubin (BR) in human serum, a biomarker of jaundice hepatitis. It can be served as a turn-off fluorescent switch for BR because its red emission from Eu³⁺ can be easily quenched by BR through a fluorescent resonant energy transfer (FRET) process between BR and its ligands, and as a result, BR is recognized successfully. Particularly, Zr-MOF: Eu³⁺ has shown many appealing properties, such as high sensitivity, quick response (less than 1 min), broad response window (0-15 μM), and excellent selectivity. Most importantly, a kind of portable test paper based on Zr-MOF: Eu³⁺ probe has been developed for directly assessing the level of BR in real human serum and further diagnosing bilirubin-related diseases via visually observing the luminescent color variation.

Lanthanide functionalized MOF thin films as effective luminescent materials and chemical sensors for ammonia

A series of Lanthanide functionalized MOF thin films on Al₂O₃ are fabricated using designed linkers, whose unique luminescence performance is shown to be a sensitive probe toward ammonia.

Multicenter Metal-Organic Framework-Based Ratiometric Fluorescent Sensors

Metal-organic frameworks (MOFs) with multiple emission centers are newly emerging as ratiometric sensors owing to their high sensitivity and high selectivity toward a wide range of targeted functional species. Energy transfer between the light-absorbing group and emission centers and between different emission centers is the key to rationally design and synthesize MOF-based ratiometric sensors. A good match between the energy levels of the light-absorbing groups and emission centers is the prerequisite for MOF-based sensors to exhibit multiple emissions, and a good match of the MOF-based sensors and those of the targeted species can increase the sensitivity and selectivity, but this match is highly challenging to obtain via synthesis. MOFs with multiple emission centers can be produced by functionalizing MOFs with multiple lanthanide centers, organic luminophores, dyes, carbon dots, and other such emissive groups. In this progress report, recent advances in the strategies for synthesizing MOFs with multiple emission centers and their applications for ratiometric sensing of solution conditions, including the pH value, and ion, organic molecule, and biomolecule concentrations, are summarized, as are the related sensing mechanisms.

Post-synthetic modification of a metal–organic framework with a chemodosimeter for the rapid detection of lethal cyanide via dual emission

A post-synthetically modified chemodosimeter grafted MOF is presented for the selective, visual and fluorogenic detection of cyanide via dual emission.

Functional metal–organic frameworks as effective sensors of gases and volatile compounds

This review summarizes the recent advances of metal organic framework (MOF) based sensing of gases and volatile compounds.