A bi-functionalized metal-organic framework based on N-methylation and Eu3+ post-synthetic modification for highly sensitive detection of 4-Aminophenol (4-AP), a biomarker for aniline in urine

Ratiometric sensor based on Ag+-mediated luminescence of Tb-DNA complexes for visual detection of 4-aminophenol

Development of accurate, convenient and portable methods for monitoring 4-aminophenol (4-AP) is extremely important because of its strong toxicity. Here, a ratiometric fluorescence sensor based on Ag+-enhanced luminescence of Tb-DNA complexes has been presented for the detection of 4-AP. The luminescence of Tb-DNA complexes is enhanced about 30 times by Ag+, which can trigger energy transfer from DNA to Tb3+ more efficiently. In the presence of 4-AP, Ag+ can be reduced into Ag0 owing to its strong reducibility, inducing the decrease of Tb-DNA complexes at 545 nm remarkably. Besides, 4-AP exhibits intrinsic fluorescence at 375 nm under the same conditions. Therefore, ratiometric detection of 4-AP can be achieved using F375/F545 as readout with a detection limit of 0.4 μM. Real water samples have been tsted to evaluate this method in practical application and satisfactory results have been obtained. Furthermore, the addition of 4-AP into Tb-DNA-Ag+ system induces a visible color variation from green to bluish violet, enabling visual detection of 4-AP under the assistance of a smartphone.

Hg2+ detection and information encryption of new [1+1] lanthanide cluster

The sensing of heavy metal ion and information encryption are two very important research areas. Therefore, developing multi-functional materials capable of sensing heavy metal ions and encrypting information is highly important. In this work, three [1 + 1] lanthanide clusters [Ln(TFBA)3(dmp) (H2O)2]2 (Ln = Tb3+Tb1+1, Eu3+Eu1+1, Gd3+Gd1+1, HTFBA = 2,3,4,5-tetrafluorobenzoic acid, dmp = 4,7-dimethyl-1,10-phenanthroline) were designed and synthesized. Among them, Tb1+1 shows excellent luminescence sensing towards Hg2+ (Ex = 350 nm, Em = 545 nm). Results demonstrates the sensing with high selectivity, strong anti-interference, 20-s response time, high accuracy, excellent linear relationship in 0-20.0 μM, and a very low limit of detection (0.02 ppb). Furthermore, paper strips based on Tb1+1 is fabricated for visual detection of Hg2+ in real samples of tap water, lake water, human urine, and human serum. More interestingly, a new method for confidentiality of information is realized through multi-color anti-counterfeiting patterns with the [1 + 1] lanthanide cluster ink, based on the luminescence "on-off" sensing towards Hg2+.

Achiral Sm(III)-Based Metal-Organic Framework as a Luminescence Sensor for Enantiodiscrimination of Quinine and Quinidine

The effective discrimination and determination of the chiral antimalarial drugs quinine (QN) and quinidine (QD) are extremely important for human health. Herein, a 2D achiral Sm-based metal-organic framework (IMU-MOF1 = [Sm(tpba)(L)]n, where Htpba = 4-(2,2':6″,2'-terpyridin)-4'-ylbenzioc acid and H2L = 2,2'-biquinoline-4,4'-dicarboxylic acid) was successfully prepared by the solvothermal method. More importantly, IMU-MOF1 was designed as an ultrasensitive fluorescent probe for the identification of chiral enantiomer drugs. The limits of detection for QN and QD are 4.24 × 10-11 and 7.54 × 10-12 M, respectively. Furthermore, it was demonstrated that the stronger hydrogen-bonding interactions between IMU-MOF1 and quinine furnish a more efficient energy transfer to the ligands in the sensing process, resulting in a significant fluorescence enhancement of IMU-MOF1.

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.

Flumequine-mediated fluorescent zeolitic imidazolate framework functionalized by Eu3+ for sensitive and selective detection of UO22+, Ni2+ and Cu2+ in nuclear wastewater

Currently, antibiotics and heavy metal contaminants have posed a great threat for ecological security and human health. Herein, the lanthanide functionalized ZIF (named ZIF-90-PABA-Eu) is constructed by coordinating with Eu³⁺ via p-aminobenzoic acid intermediate. Due to the excellent fluorescence properties, the novel fluorescent probe can selectively monitor flumequine based on "turn on" mode. Furthermore, the obtained new material (named ZIF-90-PABA-Eu-Flu) can be used as "turn off" sensor for selective detection of both radioactive and nonradioactive heavy metal ions (UO₂²⁺, Ni²⁺ and Cu²⁺) which are the main component of nuclear industrial wastewater. ZIF-90-PABA-Eu-Flu shows ultra-short fluorescence response time (3 s) and ultra-low limit of detection (9.0 × 10^-3, 1.3 × 10^-2 and 6.1 × 10^-4 ppm) for three metal ions, which may be attributed to its good affinity with UO₂²⁺, Ni²⁺ and Cu²⁺. Moreover, principal component analysis (PCA) is applied to distinguish the three metal ions. Additionally, the possible sensing mechanism is investigated by the UV-vis spectra, luminescence lifetimes and theoretical calculation analysis. Based on these results, ZIF-90-PABA-Eu possesses promising potential in practical application and provides insight for the design of novel probes to continuously monitor flumequine, radioactive and nonradioactive heavy metal ions.

Detection of different chemical moieties in aqueous media by luminescent Europium as sensor

Detection of different chemical moieties especially trace metals is important for humans as well as water safety. In this review, different detectors synthesized by the combination of different ligands with luminescent europium complexes were discussed for the separation of metals and chemical moieties in aqueous media. These detectors displayed high sensitivity and selectivity. The limit-of-detection values were very low indicating that these detectors are best suitable for the sensing of chemical moieties and trace metals. These detectors’ luminescent changes could be noticed with the naked eye.

A red-emitting Europium(III) complex as a luminescent probe with large Stokes shift for the sequential determination of Cu2+ and biothiols in real samples

In this work, a novel Eu³⁺-DTPA-bis(AMC) complex with red luminescence was designed and synthesized for sequential detection of Cu²⁺ and biothiols (Cys/Hcy/GSH) based on the displacement strategy with the good selectivity, high sensitivity, and large Stokes shift (288 nm). The possible detection mechanism was verified by UV-vis, the high-resolution mass spectrometry, and the fluorescence decay curve. The experimental parameters, including the solution pH, the incubation time, the concentration ratio of Eu³⁺-DTPA-bis(AMC) to Cu²⁺ and biothiols concentration, were optimized. Under the optimal conditions, it shows a good linear relationship between the concentration (0-10 μM) of Cu²⁺ and the fluorescence intensity of Eu³⁺-DTPA-bis(AMC), with a low detection limit of 0.065 μM. The linear range and the limit of detection of the Eu³⁺-DTPA-bis(AMC)/Cu²⁺ system for Cys/Hcy/GSH were 2.5-22.5/5-45/5-50 μM and 0.11/0.07/0.05 μM, respectively. Surprisingly, the high or low concentration of Eu³⁺-DTPA-bis(AMC)/Cu²⁺ can significantly affect the selectivity of the sensing system to biothiols (Cys/GSH/Hcy). When the concentration of the Eu³⁺-DTPA-bis(AMC)/Cu²⁺ system is 10.0 μΜ, it could recognize biothiols (Cys/GSH/Hcy) from other substances, but when the concentration is as low as 3.3 μM, it could further specifically distinguished Cys from Hcy/GSH. Owing to the high anti-interference characteristics, accuracy and specificity, the sensing system was well applied to the cascade detection of Cu²⁺ in actual environmental samples and Cys in biological and food samples, including FBS, urine, milk, beverage, fresh juice with the satisfactory recoveries from 96.20 to 106.80 %.

A Ratiometric Fluorescent Sensor Based on Dye/Tb (III) Functionalized UiO-66 for Highly Sensitive Detection of TDGA

Thiodiglycolic acid (TDGA) is a biomarker for monitoring vinyl chloride exposure. Exploring a facile, rapid and precise analysis technology to quantify TDGA is of great significance. In this research, we demonstrate a fluorescent sensor based on dual-emissive UiO-66 for TDGA detection. This ratiometric fluorescent material named C460@Tb-UiO-66-(COOH)₂ was designed and synthesized by introducing organic dye 7-diethylamino-4-methylcoumarin (C460) and Tb³⁺ into UiO-66-(COOH)₂. The as-obtained C460@Tb-UiO-66-(COOH)₂ samples showed highly selective recognition, excellent anti-interference and rapid response characteristics for the recognition of TDGA. The detection limit is 0.518 mg·mL^-1, which is much lower than the threshold of 20 mg·mL^-1 for a healthy person. In addition, the mechanism of TDGA-induced fluorescence quenching is discussed in detail. This sensor is expected to detect TDGA content in human urine.

A Novel Turn-On Fluorescence Probe Based on Cu(II) Functionalized Metal–Organic Frameworks for Visual Detection of Uric Acid

As an important biomarker in urine, the level of uric acid is of importance for human health. In this work, a Cu(II) functionalized metal–organic framework (Cu²⁺@Tb-MOFs) is designed and developed as a novel fluorescence probe for wide-range uric acid detection in human urine. The study shows that this fluorescence platform demonstrated excellent pH-independent stability, high water tolerance, and good thermal stability. Based on the strong interaction between metal ions and uric acid, the designed Cu²⁺@Tb-MOFs can be employed as efficient turn-on fluorescent probes for the detection of uric acid with wide detection range (0~10⁴ µM) and high sensitivity (LOD = 0.65 µM). This probe also demonstrates an anti-interference property, as other species coexisted, and the possibility for recycling. The sensing mechanisms are further discussed at length. More importantly, we experimentally constructed a molecular logic gate operation based on this fluorescence probe for intelligent detection of uric acid. These results suggest the Cu(II) functionalized metal–organic framework can act as a prominent candidate for personalized monitoring of the concentration of uric acid in the human urine system.

A new three-dimensional zinc(II) metal-organic framework as a fluorescence sensor for sensing the biomarker 3-nitrotyrosine

3-Nitrotyrosine (3-NT), an oxidative stress biomarker, is closely associated with various diseases. Thus, rapid and sensitive detection of 3-NT is of great significance for preventing and treating diseases. Herein, we reported a new 3D zinc-based metal-organic framework (Zn-MOF) [Zn(L)(HBTC)] (L = (E)-4,4'-(ethene-1,2-diyl)bis[(N-pyridin-3-yl)benzamide], H₃BTC = 1,3,5-benzenetricarboxylic acid), which was structurally characterized by single crystal X-ray diffraction, IR, PXRD and TG. The Zn-MOF can be used as a highly efficient fluorescence sensing material to provide a direct and low-cost method for the rapid detection of 3-NT and shows high sensitivity with a K_SV value of 6.596 × 10⁴ M^-1, a rapid luminescence response within 24 s, excellent selectivity, high anti-interference ability and good recyclability. It is the first example of a MOF being used to directly detect 3-NT as a luminescence sensor to our knowledge. The sensing mechanism of the Zn-MOF towards 3-NT is discussed in detail, which provides a basis for the rational design of MOF sensing materials and their application in biomarker detection.

Two Multiresponsive Luminescent Zn-MOFs for the Detection of Different Chemicals in Simulated Urine and Antibiotics/Cations/Anions in Aqueous Media

Two Zn-MOFs, namely, {[Zn(L)_0.5(bpea)]·0.5H₂O·0.5DMF}_n [LCU-113 (for Liaocheng University)] and {[Zn(L)_0.5(ibpt)]·H₂O·DMF}_n (LCU-114), were synthesized based on flexible tetracarboxylic acid 1,3-bis(3,5-dicarboxyphenoxy)benzene (H₄L) and different N-ligands [bpea = 1,2-dipyridyl ethane; ibpt = 3-(4'-imidazolobenzene)-5-(pyridine-4'-yl)-1,2,4-triazole]. LCU-113 and LCU-114 possess twofold interpenetrating three-dimensional pillared layer structures, in which a two-dimensional layer formed by carboxylic acid and Zn²⁺ ions was pillared by bpea and ibpt, respectively. The two complexes show high water stability and high luminescence sensing performance toward organic solvents, ions, and antibiotics, as well as chemicals, in simulated urine. The investigation showed that (1) LCU-113 and LCU-114 could detect uric acid (UA, 2,6,8-trihydroxypurine, metabolite of purine) and p-aminophenol (PAP, biomarker of phenamine) in simulated urine by luminescence quenching, respectively, and (2) luminescence quenching of LCU-113 and LCU-114 occurred in aqueous solutions of nitrofurazone (NZF), Fe³⁺, and CrO₄^2-/Cr₂O₇^2-. All the above detections have excellent anti-interference ability and recyclability. The luminescence mechanism analysis indicates that weak interactions between the framework structures and the target analytes as well as the energy competition (inner filter effect) play an important role in sensing the above analytes. The practical application for monitoring NZF/Fe³⁺ in water samples was also tested.

Cd (II) coordination polymer as a strip based fluorescence sensor for sensing Fe3+ ions in aqueous system

The design and construction of a sensor that can sensitively and conveniently recognize metal ions are essential for the treatment of industrial wastewater. In this work, {[Cd₄(HL)₂(pyp)₂(H₂O)₂]·2H₂O·1.5Diox}_n (1) was synthesized under solvothermal condition and presented a 2D 3,5-connected layered network with the point symbol of {3.4.5} {3².4.5.6².7⁴}, which was coated on the surface of polyvinylidene fluoride (PVDF) to construct a novel paper sensor (1@PVDF). Meanwhile, the stability of 1@PVDF was characterized by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). In addition, fluorescence sensing experiments of 1@PVDF sensor for cations in aqueous system indicated that it has high sensitivity for sensing Fe³⁺ ions with the detection limit (DL) of 4.0 × 10^-8 M. By the characterization of PXRD, UV-vis spectra, ICP, XPS, time-resolved excited-state decay measurements, the sensing mechanisms of 1@PVDF for Fe³⁺ ions were attributed to the competitive absorption and interaction between 1 and Fe³⁺. And the sensing process of 1@PVDF for Fe³⁺ ions was static in the Fe³⁺ concentration of 0 to 0.05 mM. In addition, the binding energies of Fe³⁺ and Zn²⁺ with the framework of 1 were calculated by density functional theory (DFT), which further proved that there was an obvious interaction between Fe³⁺ and the uncoordinated O atom in 1. Based on the thin film technology, a portable and convenient paper-based probe has been developed for practical applications.

The postsynthetic renaissance of luminescent lanthanide ions on crystalline porous organic framework materials

A series of crystalline porous organic framework materials (CPOFs), such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen bonded organic frameworks (HOFs) have received extensive attentions due to...

Dye functionalized lanthanide metal-organic framework as a multifunctional luminescent hybrid material for visual sensing of biomarker 2-methoxyaceticacid and sulfide anion

Based on the anionic Slug-47 [Gd(bpdc)₂^-] [NH₂(CH₃)₂⁺], a multifunctional fluorescent material with ultra-high stability has been fabricated successfully. Firstly, Eu_0.04Tb_39.96Gd₆₀ with white light emission is prepared by adjusting the doping ratio of Eu³⁺ ions and Tb³⁺ ions. Then, the dye acriflavine (ACF) is further introduced into the framework of Eu@ Slug-47 (1) via cation exchange to obtain ACF@1, which can be used as a ratio fluorescence sensor to detect 2-methoxyaceticacid (Maa), a toxic metabolite of glycol monomethyl ether, with the limit of detection (LOD) as low as 0.27 μg/mL. It is impressive that the emissions of ACF and biphenyl-4,4'-dicarboxylicacid ligands are gradually enhanced with the gradual weakening of the emission of Eu³⁺ ions during the detection of Maa. Under the superposition of three different colors, the sensing process undergoes a distinct color change from red to white and then to blue. These rich and colorful colors provide conditions for accurate visual detection of Maa. In addition, the material can also respond well to the pollutant S^2- ions and the LOD can reach 11.3 μmol /L. It is worth mentioning that the available quenching effect can be observed even if Maa and S^2- ions are detected in urine and tap water respectively, indicating that the multifunctional material has a brilliant application prospect. Finally, the quenching mechanism of Maa, S^2- ions toward ACF@1 is discussed in detail.

Dual-Functional Metal-Organic Framework for Luminescent Detection of Carcinoid Biomarkers and High Proton Conduction

It remains a challenge to exploit dual-functional metal-organic frameworks (MOFs) for applications, including luminescence detection and proton conduction. With the deliberate selection of the bifunctional organic ligand 5-sulfoisophthalic acid monosodium salt (NaH₂bts), and the phosphonic acid ligand N,N'-piperazine (bismethylenephosphonic acid; H₄L), a robust three-dimensional (3D) noninterpenetrating dual-functional MOF, [Tb(H₂L)(H₂bts)(H₂O)]·H₂O (1), has been synthesized hydrothermally. On the basis of the excellent thermal and chemical as well as superior luminescence stabilities in water and solutions with different pHs, 1 can serve as the simple, rapid, and highly selective and sensitive luminescence detection of the carcinoid biomarkers 5-hydroxytryptamine (HT) and its metabolite 5-hydroxyindole-3-acetic acid (HIAA) with detection limits of nanomolar magnitude in water and in simulated blood plasma and urine systems. Due to the change in the signals that could be readily differentiated by the naked eye under a UV lamp, a portable test paper has been developed. The probable quenching mechanisms are discussed in detail. In addition, a great number of hydrogen-bonding networks are formed among the uncoordinated carboxylic oxygen atoms, sulfonate oxygen atoms, protonated nitrogen atoms, and water molecules, which provide potential proton-hopping sites for proton conduction, leading to a maximum proton conductivity of 2.3 × 10^-4 S cm^-1 at 368 K and 95% relative humidity. The above results suggest that rationally designed dual-functional MOFs can open an avenue for the development of occupational diagnostic tools and alternative energy technology.

A turn-on fluorescence sensing strategy for rapid detection of flumequine in water environments using covalent-coordination functionalized MOFs

With high output and large use of antibiotics in the process of aquaculture, pollution caused by antibiotics in water environments is becoming a thorny problem, and its ecological risk has aroused widespread concern.