A turn-off Eu-MOF@Fe2+ sensor for the selective and sensitive fluorescence detection of bromate in wheat flour

Smartphone-integrated paper-based sensing platform for the visualization and quantitative detection of pymetrozine

Pymetrozine (PYM) is an effective pyridine insecticide for controlling aphids, while its residues pose a serious threat to human health. Herein, a europium complex (Eu-DBPA, DBPA represents deprotonated 2,5-dibromoterephthalic acid ligand) probe was prepared for the detection of PYM via fluorescence quenching. The detection process has the advantages of short response time (2 min), wide linear range (0-4 and 4-45 mg/kg) and low detection limit (2.2 μg/kg). Furthermore, a portable detection platform was designed by integrating Eu-DBPA-based paper strip with smartphone and applied for the visual detection of PYM in real cucumber, tomato, cabbage and apple samples, obtaining satisfactory recovery (99.00 %-107.00 %) and low standard deviation (RSD < 3.4 %). In addition, a logic gate device was designed to simplify the detection process. The smartphone-integrated paper-based probe detection platform provides a new strategy for intelligent and online identification of hazards in environmental and biological samples.

A portable smartphone-assisted Tb-MOF-based agar-slice probe for the rapid and on-site fluorescence assay of malachite green in aquatic products

In this study, a new Tb-MOF fluorescence probe was developed for the detection of malachite green (MG) in real aquatic products. Fluorescence sensing experiments revealed that MG can effectively quench the green fluorescence of Tb-MOF suspensions, and the detection process exhibits the advantages of high sensitivity, a wide linear range (0-80 μM), a low detection limit (10.8 nM) and a rapid response time. Selective detection of MG is achieved primarily through fluorescence resonance energy transfer (FRET) and photoinduced electron transfer (PET) mechanisms. Furthermore, a smartphone-assisted Tb-MOF-based agar slice detection platform was constructed for the visual and quantitative detection of MG. Additionally, the on-site detection of MG in crucian and shrimp samples was accomplished with high recoveries (99.8 %-107.99 %) and low relative standard deviations (RSD < 2.2 %). This developed detection platform introduced a low-cost, portable and user-friendly approach for MG detection.

Highly sensitive ratiometric fluorescence detection of tetracycline residues in food samples based on Eu/Zr-MOF

The development of a simple, rapid, and sensitive method for monitoring antibiotic residues is crucial for maintaining food safety. Herein, a ratiometric fluorescence probe based on bimetallic organic framework (Eu/Zr-MOF) was developed for the detection of tetracycline (TC). The Eu/Zr-MOF was synthesized by the coordination of Eu3+ and Zr4+ with 2-APDC, which exhibited a grape-like cluster morphology and dual-emitting fluorescence at 430 nm/616 nm. Based on the internal filtering effect (IFE), significant fluorescence quenching was observed at 430 nm, whereas only slight changes occurred at 616 nm. The ratiometric sensing offered two broad linear ranges (0.5-8 μg/mL; 10-60 μg/mL) and a low detection limit (26.7 ng/mL). The proposed method was applied to the determination of TC in pork and water samples. Fluorescent sensors have the advantages of simple design, fast response, and high sensitivity, thus providing a promising means for evaluating the safety of food contaminated with TC.

A tetrahedron-shaped polyoxoantimotungstate encapsulating a hexanuclear octahedral lanthanide-oxo cluster for an amperometric bromate sensor

An inorganic hexalanthanide-oxo-cluster-encapsulated antimotungstate, K2Na3H43[Nd6(OH)6(H2O)6(B-α-SbW9O33)4]2·67H2O (1), has been successfully synthesized by a facile one-step hydrothermal reaction method. The tetrahedron-shaped two-shell {Nd6(OH)6(H2O)6(B-α-SbW9O33)4}(1a) polyanion is composed of a novel pure lanthanide-oxo {Nd6(μ3-OH)6(H2O)6} octahedron and {(B-α-SbW9O33)4} tetrahedron. After being effectively loaded onto a glassy carbon electrode (GCE) by electrostatic adsorption using polydiallyldimethyl ammonium chloride (PDDA)-functionalized multi-walled carbon nanotubes (MWCNTs), compound 1 exhibits electrochemical activity for the reduction of bromate ions with good selectivity, a high sensitivity of 186 μA mM-1 and a detection limit that has reached 1.9 μM. To the best of our knowledge, this is the first example of an amperometric bromate sensor based on Ln-containing antimotungstates, which will provide new materials for electrochemical sensors.

A facile fluorescence Eu MOF sensor for ascorbic acid and ascorbate oxidase detection

In this work, a facile fluorescence Eu3+-based metal-organic framework (Eu MOF) sensor for ascorbic acid (AA) and ascorbate oxidase (AAO) detection was developed. The fluorescence of the Eu MOF could be effectively quenched by Ce3+ but not by Ce4+ at an appropriate concentration, and thus, when the reductant AA was added into the solution containing Ce4+, Ce4+ was chemically reduced to Ce3+, which induced the decreased fluorescence signal of the Eu MOF. However, when AAO was introduced, AA was effectively oxidized to dehydroascorbic acid (DHAA) under the catalysis of AAO, and thus, Ce4+ could not be reduced, resulting in the fluorescence restoration of the Eu MOF. Hence, the concentration of AA and AAO could be determined by the fluorescence decrease and restoration of the Eu MOF. The fluorescent platform showed high sensitivity with a limit of detection of 0.32 μM for AA and 1.18 U L-1 for AAO, respectively. Moreover, the proposed method was successfully applied for AA and AAO determination in real samples, indicating great potential for biomedical application in complex matrices.

Fluorescence sensing and device fabrication with luminescent metal-organic frameworks

Metal-organic frameworks (MOFs) are a novel class of hybrid porous multi-functional materials consisting of metal ions/clusters and organic ligands. MOFs have exclusive benefits due to their tunable structure and diverse properties. Luminescent MOFs (LMOFs) exhibit both porosity and light emission. They display abundant host and guest responses, making them conducive to sensing. Currently, LMOF sensing research is gaining more depth, with attention given to their device and practical applications. This work reviews recent advancements and device applications of LMOFs as chemical sensors toward ions, volatile organic compounds, biomolecules, and environmental toxins. Furthermore, the detection mechanism and the correlation between material properties and structure are elaborated. This analysis serves as a valuable reference for the preparation and efficient application of targeted LMOFs.

Histidine-capped copper nanoclusters for in situ amplified fluorescence monitoring of doxycycline through inner filter effect

There is a significant need to accurately measure doxycycline concentrations in view of the adverse effects of an overdose on human health. A fluorescence (FL) detection method was adopted and copper nanoclusters (CuNCs) were synthesized using chemical reduction technology. Based on FL quenching with doxycycline, the prepared CuNCs were used to explore a fluorescent nanoprobe for doxycycline detection. In an optimal sensing environment, this FL nanosensor was sensitive and selective in doxycycline sensing and displayed a linear relationship in the range 0.5-200 μM with a detection limit of 0.092 μΜ. A characterization test demonstrated that CuNCs offered active functional groups for identifying doxycycline using electrostatic interaction and hydrogen bonds. Static quenching and the inner filter effect (IFE) resulted in weakness in the FL of His@CuNCs with doxycycline with great efficiency. This suggested nanosensor was revealed to be a functional model for simple and rapid detection of doxycycline in real samples with very pleasing accuracy.

Rhodamine-based Fluorescent Probe With Quick Response and High Selectivity for Imaging Labile Ferrous Iron in Living Cells and Zebrafish

The transition between its various oxidation states of Iron plays a crucial part in various chemical transformation of cells. Misregulation of iron can give rise to the iron-catalyzed reactive oxygen species disorder which have been linked to a variety of diseases, so it is crucial to monitor the labile iron pool in vivo for clinical diagnosis. According to iron autoxidation and hydrogen abstraction reaction, we reported a novel "off-on" fluorescent probe to response to ferrous (Fe2+) both in solutions and biological systems. The probe responds to Fe2+ with good selectivity toward competing metal ions. What's more, the probe presents significant fluorescent enhancement to Fe2+ in less than 1 min, making real-time sensing in biological system possible. The applications of the probe in bioimaging revealed the changes in labile iron pool by iron autoxidation or diverse stimuli.

An intelligent smartphone-test strip detection platform for rapid and on-site sensing of benzoyl peroxide in flour samples

Benzoyl peroxide (BPO) is a commonly used flour whitener, but its excessive usage can have adverse effects on human health, such as nutrient loss, vitamin deficiencies and certain diseases. In this study, a europium metal organic framework (Eu-MOF) fluorescence probe was prepared, which exhibited a strong fluorescence emission at 614 nm upon excitation at 320 nm, with a high quantum yield of 8.11%. The red fluorescence of the probe could be effectively quenched by BPO through the inner filter effect (IFE) and photoinduced electron transfer (PET) mechanism. The detection process offered several advantages, including a wide linear range of 0-0.95 mM, a low detection limit of 66 nM and a fast fluorescence response of 2 min. Furthermore, an intelligent detection platform was designed to enhance the practical application of the detection method. This platform combined the portability and visuality of a traditional test strip with the color recognition capability of a smartphone, allowing for the visualization and quantitative detection of BPO in a convenient and user-friendly manner. The detection platform was successfully applied to the analysis of BPO in real flour samples with satisfactory recoveries (99.79%-103.94%), suggesting a promising strategy for the rapid and on-site detection of BPO in food samples.

A smartphone-assisted paper-based ratio fluorescent probe for the rapid and on-site detection of tetracycline in food samples

Rapid, sensitive and portable analytical methods for on-site detection of tetracycline (TC) in food samples is of critical importance for food safety and public health. In this study, a dual-emission ratio fluorescent probe (Gd0.9@Eu0.1) was prepared and utilized for the detection of tetracycline (TC) by observing the fluorescence color change from blue to red. The detection process exhibits a wide linear range (0-52.0 μM), good selectivity and low detection limit (14 nM). A paper-based probe and a colorimetric card was constructed for the visual detection of TC. Furthermore, a novel and portable detection platform combining smartphone and test strip was exploited for the quantitative and on-site detection of TC in real pork sample. The developed method was validated through intra- (n = 5) and inter-day (n = 2) measurements, as well as comparison with a traditional HPLC method. These statistical result validate the reliability and accuracy of the developed method. This intelligent detection platform represents a promising approach for the rapid, sensitive and visual detection of TC in food samples.

Sensitive fluorescent detection of phosmet and chlortetracycline in animal-derived food samples based on a water-stable Cd(II) chain-based zwitterionic metal-organic framework

The residues of pesticides and antibiotics have always been a major concern in agriculture and food safety. In order to provide a new method for the rapid detection of organophosphorus pesticides and antibiotics, a novel Cd(II) chain-based zwitterionic metal-organic framework MOF 1 with high sensitivity fluorescence sensing performance was successfully synthesized. A series of researches showed that the water- and pH-stable bifunctional MOF 1 has a great ability to detect phosmet (PSM) and chlortetracycline (CTC) in water through fluorescence quenching effect, with high detection sensitivity, low detection limits (0.0124 μM and 0.0131 μM), short response time (40 s) and reusability. Practical application results revealed that MOF 1 could detect PSM and CTC in milk, beef, chicken and egg samples, with satisfactory recoveries (95.2%-103.7%). As a novel fluorescence probe, MOF 1, is known the first case that can detect PSM in animal-derived samples, and the first dual-function material capable of detecting PSM and CTC. Mechanism studies displayed that competitive absorption and photoinduced electron transfer clearly authenticate the high quenching performance of the material.

A Coordination Polymer for the Fluorescence Turn-On Sensing of Saccharin, 2-Thiazolidinethione-4-carboxylic Acid, and Periodate

A luminescent 1D coordination polymer (CP) [Zn2L2(H2O)4]·H2O (1, H2L = 1-(4-carboxyphenyl)-1H-pyrazole-3-carboxylic acid) was prepared by a solvothermal method. 1 shows excellent fluorescence properties and has an obvious fluorescence "turn-on" phenomenon for saccharin (SAC), 2-thiazolidinethione-4-carboxylic acid (TTCA), and periodate (IO4-). Between 0 and 60 μM concentration range of SAC, the fluorescence enhancement efficiency (KEC) of 1 reaches 1.00 × 105 M-1 with the limit of detection (LOD) of 90 nM. 1 is the first CP-based sensing material for SAC detection. For TTCA detection, the KEC is 2.73 × 105 M-1 at the 25-80 μM concentration range, and the LOD is 33 nM, the lowest LOD among the sensors that detect TTCA at present. For IO4- ion detection, when the IO4- ion concentration ranges from 0 to 10 μM, the KEC is 2.34 × 105 M-1 and the LOD is as low as 39 nM. In order to better understand the sensing phenomenon, we also discuss in detail the sensing mechanisms for SAC, TTCA, and IO4- ions.

Boric acid group-functional Tb-MOF as a fluorescent and captured probe for the highly sensitive and selective determination of propyl gallate in edible oils

This study reports the development of a Tb-metal-organic framework (Tb-MOF)-based fluorescent platform for the detection of propyl gallate (PG). The Tb-MOF using 5-boronoisophthalic acid (5-bop) as the ligand exhibited multiple emissions at 490, 543, 585, and 622 nm under an excitation wavelength of 256 nm. The fluorescence of Tb-MOF was selectively and significantly weakened in the presence of PG due to the special nucleophilic reaction between the boric acid of Tb-MOF and o-diphenol hydroxyl of PG, and the combined effect of static quenching and internal filtering. Furthermore, this sensor enabled the determination of PG within seconds in a wide linear range of 1-150 μg/mL, and with a low detection limit of 0.098 μg/mL, and high specificity against other phenolic antioxidants. This work provided a new route for the sensitive and selective determination of PG in soybean oil, thus was perspective to monitor and reduce the risk of PG overuse.

A highly selective and sensitive europium-organic framework sensor for the fluorescence detection of fipronil in tea

A europium-based metal organic framework (Eu-TFPA-MOF) was used for the fluorescence detection of fipronil in green tea and oolong tea for the first time. The red fluorescence of Eu-TFPA-MOF could be quenched significantly by low concentration (0.24 mM) of fipronil, and the "turn off" process exhibited quick response time (2 min), high sensitivity and selectivity, low detection limits (4.4 nM) and wide linear range (0-0.15 mM). The mechanism of fluorescence quenching was mainly attributed to static quenching process and the competitive absorption of excitation energy. Besides, the spiked and recovery test indicated that Eu-TFPA-MOF could be used in the fluorescence detection of fipronil in real green tea and oolong tea sample and the process had the advantages of simple pretreatment and satisfactory recoveries (98.33-106.17 %). More importantly, a simple, portable and low-cost smartphone-assisted test strip were designed for the visual detection of fipronil in real tea samples. The detection platform will be beneficial for tea quality safety and human heath, and is expected to be applied in other agricultural product safety field.

Two anthracene-based zirconium metal-organic frameworks with fcu and hcp topologies as versatile fluorescent sensors for detection of inorganic ions and nitroaromatics

Two anthracene-based zirconium metal-organic frameworks (UiO-68-AN-fcu and UiO-68-AN-hcp) with blue emission were synthesized by the solvothermal reaction of ZrCl₄ with anthracene-based ligand 4,4'-(9,10-anthracenediyl)dibenzoic acid. The two MOFs inherited the luminescence properties of anthracene-based ligand and exhibited different topologies due to the change of connection mode of Zr-O clusters. The two stable anthracene-based zirconium MOFs served as luminescent sensors for selectively detecting 2-nitrophenol, Fe³⁺ and Cr₂O₇^2-. UiO-68-AN-hcp with flower morphology exhibited stronger quenching effect for 2-nitrophenol, Fe³⁺ and Cr₂O₇^2- by comparing to UiO-68-AN-fcu. Adsorption tests, fluorescence lifetime and spectroscopy studies demonstrated that the fluorescence responses of MOFs for analytes can be primarily attributed to the dynamic quenching mechanism involving energy and electron transfer. These results revealed that the combination of luminescent anthracene-based ligand and Zr-O clusters is a feasible strategy to construst MOFs-based fluorescent sensors.

Fabrication of Two Luminescent Imidazolyl Cadmium-Organic Frameworks and Their Sensing Mechanism for 2,6-Dichloro-4-nitroaniline

2,6-Dichloro-4-nitroaniline, alias dicloran (DCN), is a broad-spectrum pesticide that can cause irreversible damage to the human body. Therefore, it is of great significance to develop a technology for the rapid and convenient detection of DCN. Luminescent metal organic frameworks have attracted extensive attention in the field of sensing and detection due to their excellent optical properties. In this study, two kinds of 2D Cd-MOFs (CdMOF-1 and CdMOF-2) were developed for the detection of residual DCN in the environment. Both CdMOFs exhibit excellent solvent and acid-base stability and can respond to DCN quickly and sensitively in a short time (30 s). CdMOFs not only have good selectivity and anti-interference toward DCN but also have good reusability. Under the conditions of DCN concentrations of 1-15 and 0.3-30 μM, the change in fluorescence intensity of CdMOF-1 and CdMOF-2 showed a good linear relationship with DCN concentration (R² = 0.999/0.991), and the detection limits were 0.36 and 0.12 μM, respectively. Through ultraviolet-visible absorption spectroscopy (UV-Vis), X-ray photoelectron spectroscopy, fluorescence lifetime, and density functional theory calculations, it is revealed that the fluorescence quenching mechanisms of DCN for two kinds of Cd-MOFs are competitive absorption and photoinduced electron transfer, and there may be a weak π-π interaction. Finally, it is demonstrated that by using two types of fluorescent CdMOFs to make the fluorescent test paper and detect actual soil, these can be applied to the actual scene and achieve onsite real-time detection.

A ratiometric fluorescent probe based on a dual-ligand lanthanide metal–organic framework (MOF) for sensitive detection of aluminium and fluoride ions in river and tap water

A dual-emission fluorescent probe towards Al3+ and F− using a Ln-MOF material Eu-BDC-NH2/TDA is employed with exceptional sensitivity, high selectivity, low LOD, excellent anti-interference characteristics and direct visual observation.

Citrate Functionalized Zirconium-Based Metal Organic Framework for the Fluorescent Detection of Ciprofloxacin in Aqueous Media

Ciprofloxacin (CIP) is a commonly used antibiotic for the treatment of infectious diseases in humans and as a prophylactic agent in the livestock industry, leading to the environmental discharge of significant amounts of CIP. CIP is stable in aquatic systems leading to its pseudo-persistence. Constant exposure to these antibiotics results in the generation of antibiotic-resistant pathogens and potential toxicity/hypersensitivity in humans. Therefore, it is necessary to develop a convenient, rapid, and cost-effective method for the monitoring of ciprofloxacin in environmental samples. Rhodamine-based fluorescent receptors have the limitation of aqueous solubility. Therefore, in order to overcome this drawback, we designed a novel fluorescent receptor based on a zirconium-based metal organic framework (MOF-808). The precursor, MOF-808, was synthesized and functionalized by using sodium citrate to obtain a receptor called C-MOF-808. The C-MOF-808 was structurally characterized by XRD and spectroscopic analyses. Thus, this synthesized receptor can be used for the fluorescent detection of CIP in aqueous media with a detection limit of 9.4 µM. The detection phenomena of the receptor were studied by absorption as well as fluorescent spectra. The binding behavior of CIP with the receptor was studied by FT-IR and ¹H-NMR analyses, and a binding mechanism is proposed.

Two novel zinc-based MOFs as luminescence sensors to detect phenylglyoxylic acid

Automobile exhaust gases, plastic pollutants, smoking, and other harmful substances can cause serious harm to human beings and the environment. Styrene, as a common airborne toxin, enters the human body through breathing or the skin and is discharged in the form of phenylglyoxylic acid (PGA). Therefore, specific, sensitive and trace detection of PGA is particularly important. Here, two zinc-based metal-organic frameworks {[Zn₂L₁(DMF)₂H₂O](DMF)₂H₂O}_n, {[Zn₄(L₂)₂(DMF)₂(H₂O)₃](DMF)₈}_n (L₁ = 2,5-bis((3-carboxylphenyl)amino)terephthalic acid, L₂ = 2,5-bis((4-carboxyphenyl)amino)terephthalic acid) have been reported as 1 and 2, respectively. Both 1 and 2 present 3D structures, which can both be simplified as 4,4,4-c net topology. It is worth mentioning that 2 has two different kinds of Zn SBUs as connecting nodes in the structure. Besides, compared with the other materials for the detection of PGA, 1 and 2 exhibit relatively low detection limits (LODs), both in water and in urine (where the LODs for 1 in water and urine were 0.33 μM and 0.43 μM in the range of 0-0.39 mM, and those for 2 were 0.28 μM and 0.49 μM in the range of 0-0.59 mM, respectively). In addition, the sensors have excellent anti-interference ability, high stability, rapid response, and can easily distinguish between different concentrations of PGA with the naked eye. The developed paper probes were suitable for practical sensing applications for portable detection of PGA in urine.

An Overview of the Design of Metal-Organic Frameworks-Based Fluorescent Chemosensors and Biosensors

Taking advantage of high porosity, large surface area, tunable nanostructures and ease of functionalization, metal-organic frameworks (MOFs) have been popularly applied in different fields, including adsorption and separation, heterogeneous catalysis, drug delivery, light harvesting, and chemical/biological sensing. The abundant active sites for specific recognition and adjustable optical and electrical characteristics allow for the design of various sensing platforms with MOFs as promising candidates. In this review, we systematically introduce the recent advancements of MOFs-based fluorescent chemosensors and biosensors, mainly focusing on the sensing mechanisms and analytes, including inorganic ions, small organic molecules and biomarkers (e.g., small biomolecules, nucleic acids, proteins, enzymes, and tumor cells). This review may provide valuable references for the development of novel MOFs-based sensing platforms to meet the requirements of environment monitoring and clinical diagnosis.

Crystal structure of diaqua-bis(μ2-2-carboxy-3,4,5,6-tetrafluorobenzoato-κ2 O:O′)-bis(phenanthroline-κ2 N,N′)-bis(μ2-3,4,5,6-tetrafluorophthalato-κ3 O:O,O′)dieuropium(III) – phenanthroline (1/2), C40H19EuF8N4O9

C40H19EuF8N4O9, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 11.3326(4) Å, b = 12.7652(4) Å, c = 13.2629(4) Å, α = 102.266(2)°, β = 97.689(2)°, γ = 105.630(3)°, V = 1767.93(10) Å3, Z = 2, R gt (F) = 0.0329, wR ref (F 2) = 0.0648, T = 293(2) K.

The crystal structure of ammonium (E)-4-((4-carboxyphenyl)diazenyl)benzoate, C14H13N3O4

C14H13N3O4, monoclinic, I2/a (no. 15), a = 11.4188(4) Å, b = 3.7968(2) Å, c = 30.2320(18) Å, β = 96.037(6)∘, V = 1303.44(11) Å3, Z = 4, R gt (F) = 0.0656, wR ref (F 2) = 0.2073, T = 293(2) K.

A novel 2D metal–organic framework probe: a highly sensitive and visual fluorescent sensor for Al3+, Cr3+ and Fe3+ ions

A novel 2D MOF Tb-DBA was constructed. Tb-DBA could detect Al3+, Cr3+ and Fe3+ ions rapidly, sensitively, selectively, reversibly and visually. Tb-DBA represents a promising material for the quick detection of metal ions in aqueous solution.