A novel microporous Tb-MOF fluorescent sensor for highly selective and sensitive detection of picric acid

Selective sensing of picric acid using a Zn(II)-metallacycle: experimental and theoretical validation of the sensing mechanism and quantitative analysis of sensitivity in contact mode detection

A combination of N,N',N''-tris(3-pyridyl)-1,3,5-benzenetricarboxamide (L1) and p-chlorobenzoic acid (HL2) with Zn(NO3)2·6H2O resulted in the formation of a dinuclear metallacycle [ZnL1(L2)2(DMF)2]2 (1(DMF)4). In 1(DMF)4, the Zn(II) centre adopts a square pyramidal geometry, while one of the pyridyl N out of the three pyridyl groups in L1 remained uncoordinated. Solvated DMF molecules are present in 1(DMF)4. The structural and chemical nature of 1(DMF)4 is effective for it to act as a potential fluorescent probe for the detection of nitroaromatic compounds. It is observed that the probe, 1(DMF)4, could selectively detect picric acid (PA) among various aromatic compounds in solution (DMSO), while the solid state (contact mode) detection showed a positive sensing response for the nitrophenols (PA: 87% quenching efficiency, 2,4-dinitrophenol (2,4-DNP): 57% quenching efficiency and 4-nitrophenol (4-NP): 40% quenching efficiency). The limit of detection (LOD) of PA by the probe in DMSO was found to be 6.8 × 10-11 M while the LOD in contact mode detection was estimated to be 0.49 ng cm-2. The mechanism of selective detection of PA by 1(DMF)4 in DMSO was analyzed through photophysical studies, 1H-NMR experiments and also by density functional theory (DFT) calculations. The effective overlap of the absorption spectrum of 1(DMF)4 and emission spectrum of PA in DMSO suggests that the Förster resonance energy transfer (FRET) is responsible for quenching phenomena in DMSO. The DFT calculations and molecular docking studies showed the adduct formation due to the favorable interactions between 1(DMF)4 and PA in DMSO, while negligible interactions were observed between 1(DMF)4 with other aromatic compounds. The experimental and DFT studies showed that the efficient sensing ability of PA by 1(DMF)4 in the solid-state was due to photoelectron transfer (PET) and FRET phenomena described herein.

Design and Synthesis of an Efficient Fluorescent Probe Based on Oxacalix[4]arene for the Selective Detection of Trinitrophenol (TNP) Explosives in Aqueous System

We present the synthesis of a new oxacalix[4]arene system, DMANSOC, wherein two 5-(dimethylamino)-1-naphthalene sulfonamide subunits are attached to the lower rims of the basic oxacalix[4]arene platform. Extensive spectrophotometric studies were conducted to investigate the selectivity and sensitivity of DMANSOC towards nitroaromatic explosives. Detailed analysis of spectrophotometric data, utilizing techniques such as Stern-Volmer, Benesi-Hildebrand, Job's plot, and interference study, unequivocally demonstrated the effectiveness of DMANSOC as a highly efficient fluorescent sensor for 2,4,6-trinitrophenol explosive (TNP) detection in an aqueous medium. The sensor exhibited a linear concentration range of 7.5 μM to 50 μM, with a low detection limit of 4.64 μM and a high binding affinity of 2.45 × 104 M towards TNP. Furthermore, the efficiency of the sensor in environmental samples contaminated with TNP was evaluated, yielding excellent recovery rates. Complementary DFT calculations and molecular dynamics simulations were performed to elucidate the mechanism behind the selective fluorescence quenching of DMANSOC in the presence of TNP.

A dysprosium(III)-based triple helical-like complex as a turn-on/off fluorescence sensor for Al(III) and 4,5-dimethyl-2-nitroaniline

A novel triple helical-like complex [Dy2K2L3(NO3)2]·3DMF (1) based on a designed Schiff base N'1,N'3-bis((E)-3-ethoxy-2-hydroxybenzylidene)-malonohydrazide (H4L) was synthesized with good chemical and thermal stabilities. Single-crystal X-ray structural analysis showed that 1 presents a tetranuclear triple helical-like structure via the coordination mode of Dy : K : L with 2 : 2 : 3 stoichiometry. Fluorescence measurements showed that 1@EtOH has excellent fluorescence turn-on/off response ability for aluminium ions and 4,5-dimethyl-2-nitroaniline (DMNA) with outstanding selectivity, sensitivity, and anti-interference ability. The calculated limit of detection (LOD) values for 1@EtOH to Al3+ and DMNA were found to be 0.53 and 3.33 μM, respectively. Density functional theory (DFT) calculation showed that the fluorescence response mechanism can be explained by the photoinduced electron transfer (PET) mechanism; meanwhile, the inner filter effect (IFE) of DMNA can also affect the emission of 1@EtOH.

Label-Free Detection of Unbound Bilirubin and Nitrophenol Explosives in Water by a Mechanosynthesized Dual Functional Zinc Complex: Recognition of Picric Acid in Various Common Organic Media

High levels of unconjugated bilirubin (UB) in serum lead to asymptomatic and neonatal jaundice and brain dysfunctions. Herein, we have reported the detection of UB at as low as 1 μM in an aqueous alkaline medium using a Zn(II) complex. The specificity of the complex has been validated by the HPLC in the concentration window 6-90 μM, which is rare. The sensory response of the probe at physiological pH against nitro explosives developed it as an instant-acting fluorosensor for picric acid (PA) and 2,4-dinitrophenol (2,4-DNP). Spectroscopic titration provided a binding constant of 4×105  M-1 with PA. The naked eye detection was found to be 15 μM. The solid-state photoluminescent nature of the complex enabled it for PA sensing in the solid phase. Interestingly, the probe remained fluorescent in various volatile and non-volatile organic solvents. As a result, it can also detect PA and 2,4-DNP in a wide range of common organic media. NMR studies revealed the coordination of PA, 2,4-DNP, and UB to the Zn(II) center of the probe, which is responsible for the observed quenching of the probe with the analytes.

A novel high sensitive Cd-MOF fluorescent probe for acetone vapor in air and picric acid in water: Synthesis, structure and sensing properties

A novel three-dimensional luminescence Cd-MOF sensor with the molecular formula {[(CH₃)₂NH₂]₂ Cd₃(ptptc)₂} (complex 1) has been synthesized by using terphenyl-3,3',5,5'-tetracarboxylic acid (H₄ptptc) and Cd(NO₃)₂·4H₂O under solvothermal conditions. Single crystal X-ray diffraction analysis shows that complex 1 crystallizes in the monoclinic system C2/c space group and consists of one-dimensional channels. Complex 1 exhibits characteristic fluorescence emission (λ_em = 380 nm) both in solid state and solvents upon excitation at 300 nm. Real-time fluorescence quenching of complex 1 was observed in the fluorescence sensing of acetone vapor and picric acid. Intriguingly, ppm scale detection limit for acetone vapor in air and nano-mole scale detection limit for picric acid in water were observed. Moreover, good reusability and liner/nonlinear relationships were observed in the fluorescent titration.

Highly selective detection of TNP over other nitro compounds in water: the role of selective host–guest interactions in Zr-NDI MOF

A fluorescent Zr-NDI based MOF shows the selective sensing of TNP in water, over other classes of nitro compounds. DFT studies reveal favourable host–guest interactions behind this phenomenon.

A novel Cd-MOF with enhanced thermo-sensitivity: the rational design, synthesis and multipurpose applications

A novel thermo-sensitive fluorescent Cd-MOF probe (complex 1) and its multipurpose sensing properties have been revealed.

A Multifunctional Tb-MOF Detector for H2O2, Fe3+, Cr2O7 2-, and TPA Explosive Featuring Coexistence of Binuclear and Tetranuclear Clusters

A novel three-dimensional microporous terbium(III) metal-organic framework (Tb-MOF) named as [Tb10 (DBA)6(OH)4(H2O)5]·(H3O)4 (1), was successfully obtained by a solvothermal method based on terbium nitrate and 5-di(2',4'-dicarboxylphenyl) benzoic acid (H5DBA). The Tb-MOF has been characterized by single crystal X-ray diffraction, elemental analysis, thermogravimetry, and fluorescence properties, and the purity was further confirmed by powder X-ray diffraction (PXRD) analysis. Structural analysis shows that there are two kinds of metal cluster species: binuclear and tetranuclear, which are linked by H5DBA ligands in two μ7 high coordination fashions into a three-dimensional microporous framework. Fluorescence studies show that the Tb-MOF can detect H2O2, Fe3+, and Cr2O7 2- with high sensitivity and selectivity and can also be used for electrochemical detection of exposed 2,4,6-trinitrophenylamine (TPA) in water. The highly selective and sensitive detection ability of the Tb-MOF might make it a potential multifunctional sensor in the future.

Rational design of a functionalized aluminum metal-organic framework as a turn-off fluorescence sensor for α-ketoglutaric acid

A 3D metal-organic framework (MOF) called Al-DUT-5-N2H3 (1) (DUT: Dresden University of Technology) was prepared hydrothermally using Al(iii) salt and a hydrazinyl functionalized linker called 2-hydrazinyl-[1,1'-biphenyl]-4,4'-dicarboxylic acid (BPDC-N2H3). Material 1 was successfully characterized by X-ray powder diffraction (XRPD), FT-IR spectroscopy, N2 sorption (BET) experiment, thermogravimetric analysis (TGA), EDX and FE-SEM analyses. The activated form of material 1 (called 1') was achieved by a direct heating process. Material 1' was successfully employed for the solution-phase fluorescence detection of α-ketoglutaric acid (α-KG). It showed high detection performance even when there were other competitive analytes present in the mixture. Material 1' is the first MOF-based fluorescent turn-off sensor for the detection of α-KG. The response time for α-KG is exceptionally low (60 s) as compared to any other reported α-KG sensor. The limit of detection (LOD) was found to be 0.61 μM, which is far better as compared to any other reported sensor for α-KG to date. The mechanism for α-KG sensing was thoroughly investigated and proposed to be PET (photoinduced electron transfer) process by TD-DFT (time-dependent DFT) calculations.

A Dy(iii)–organic framework as a fluorescent probe for highly selective detection of picric acid and treatment activity on human lung cancer cells

A dysprosium(iii) organic framework, {[Dy(H2O)(BTCTB)]·2H2O}n (1, H3BTCTB = 3,3′,3′′-[1,3,5-benzenetriyltris(carbonylimino)]tris-benzoic acid), was synthesized through the hydrothermal reaction of Dy(NO3)3 with the C3-symmetric organic ligand H3BTCTB at 160°C for 96 h. At the same time, the sensitivity of picric acid in water medium was tested with material 1 as the fluorescent sensor. The detection limit was 0.71 µM and KSV of this experiment was 8.55 × 104 M−1, which might be attributed to the presence of abundant amide groups in the framework of 1. In addition, the treatment effect of compound 1 against the NCI-H292 lung cancer cells was evaluated. The Cell Counting Kit-8 (CCK-8) method was conducted to measure the viability of cancer cell after treated through the compound 1. The DCFH-DA was applied for the determination of ROS. The relative expression of the inflammatory genes was measured with RT-PCR. The western blotting was conducted to detect the effect of the compound against MDM-2 levels in NCI-H292 lung cancer cells. The possible binding interactions in terms of binding poses are probed by performing molecular docking simulations.

A simple and fast protocol for the synthesis of 2-amino-4-(4-formylphenyl)-4H-chromene-3-carbonitrile to develop an optical immunoassay for the quantification of botulinum neurotoxin type F

In this study, a novel optical immunoassay platform using (S)-2-amino-4-(4-formylphenyl)-4H-chromene-3-carbonitrile, which was synthesized by an ultra-sonication method, as an optical probe.

Integration of fluorescent probes into metal–organic frameworks for improved performances

Recent years have witnessed a rapid development of fluorescent probes in both analytical sensing and optical imaging. Enormous efforts have been devoted to the regulation of fluorescent probes during their development, such as improving accuracy, sensitivity, selectivity, recyclability and overcoming the aggregation-caused quenching effect. Metal–organic frameworks (MOFs) as a new class of crystalline porous materials possess abundant host–guest chemistry, based on which they display a great application potential in regulating fluorescent probes. This review summarized the research works on the regulation of fluorescent probes using MOFs, with emphasis on the methods of integrating fluorescent probes into MOFs, the regulation effects of MOFs on fluorescent probes, the superiorities of MOFs in regulating fluorescent probes, and the outlook of this subject. It is desirably hoped that this review can provide a useful reference for the researchers interested in this field.

This review surveyed the research works for the regulation of fluorescent probes with metal–organic frameworks based on host–guest chemistry.

Size-controlled synthesis of metal–organic frameworks and their performance as fluorescence sensors

Fluorescent sensing experiments were carried out to compare the sensing performance for folic acid between bulk and nano Tb-MOFs.

Supramolecular Sensing of 2,4,6-Trinitrophenol by a Tetrapyrenyl Conjugate of Calix[4]arene: Applicability in Solution, in Solid State, and on the Strips of Cellulose and Silica Gel and the Image Processing by a Cellular Phone

A calix[4]arene conjugate possessing a tetrapyrenyl moiety at its upper rim (R) is designed as a receptor for sensing trinitrophenol (TNP). To understand the role of the calix[4]arene platform and that of pyrenyl moieties in R, two other control molecules were synthesized. These are as follows: the one possessing a tetraphenyl moiety in place of tetrapyrenyl (R 1 ) and the other one is a p-pyrenyl-hydroxy benzene (R 2 ) that is devoid of the calix[4]arene platform. The R shows high sensitivity toward TNP in tetrahydrofuran (THF) over eleven other nitroaromatic compounds (NACs) studied by exhibiting large fluorescence enhancement and hence is selective to TNP over the other NACs studied. However, the control molecules R 1 and R 2 showed only marginal fluorescence enhancement, supporting the need of a calixarene platform and the presence of a tetrapyrenyl moiety in the receptor system for the selective sensing of TNP. Further, R 1 and R 2 are not suitable for sensing, since these exhibit similar fluorescence response over several NACs studied. The binding of TNP by R has been addressed by fluorescence titration and isothermal titration calorimetry. The nature of the complexation of TNP by R has been revealed by the computational calculations, wherein the data showed the entrapment of TNP by two adjacent pyrene moieties via π-π stacking interactions. Such host-guest complexation is expected to restrict the mobility of the pyrene moieties present in R. The reduction of the flexibility of the pyrenyl moieties of R upon TNP binding is evidenced by the 1H NMR spectral study, wherein this acts as an additional evidence for the complexation. In the present study, the sensing of TNP by R has been shown in THF solution, on the surface of silica gel and the cellulose paper to result in lowest detection limits (LODs) of 1.5, 3.5, and 6.5 μM, respectively. Even the solid mixture of R and TNP showed LOD of 2.1 μmol. Since R is expected to show supramolecular aggregation that is dependent on the guest species, the corresponding details were probed by microscopy techniques, using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy methods, and significant changes in the aggregation of R upon interaction with TNP were found. Such aggregation is responsible for the observed fluorescence enhancement. Thus, the tetrapyrenyl calix[4]arene conjugate (R) acts as a sensitive and robust platform for selective detection of TNP from a mixture of nitroaromatic compounds (NACs) wherein the fluorescence intensities can be imaged and managed by a cellular phone.

Two zinc(ii) coordination polymers based on flexible co-ligands featuring assembly imparted sensing abilities for Cr2O7 2- and o-NP

Two new Zn(ii) coordination complexes, formulated as [Zn(opda)(pbib)] (1) and [Zn(ppda)(pbib)(H2O)] (2), (H2opda = 1,2-phenylenediacetic acid, H2ppda = 1,4-phenylene-diacetic acid, pbib = 1,4-bis(1-imidazoly)benzene), have been synthesized. The opda ligands extend a 1D chain containing (Zn-pbib) polymer chains into a 2D layer in 1. In 2, the ppda ligands link Zn(ii) atoms to form a 2D network, then the rigid bis(imidazole) ligands give rise to the 3D structure. The fluorescence property application and mechanisms of two complexes for detecting Cr2O7 2- and o-NP have been researched. For two complexes, the high quenching percentage in low concentration aqueous solution are 95.75% (Cr2O7 2-, 1), 95.28% (Cr2O7 2-, 2) and 97.56% (o-NP, 1), 96.59% (o-NP, 2). Compared with 2, complex 1 has higher quenching percentage, this could be because 1 is a 3D supramolecular with a large hole. The detection limits have been measured to be 2.992 × 10-7 M (Cr2O7 2-, 1), and 4.372 × 10-7 M (Cr2O7 2-, 2), 2.103 × 10-7 M (o-NP, 1), 1.862 × 10-7 M (o-NP, 2), respectively. The emissions of two complexes could be effectively and selectively quenched by o-NP and Cr2O7 2-, showing their potential as multi-responsive luminescent sensors.

Functional construction of a water-stable Tb-coordination polymer luminescent sensor for highly selective detection of picric acid in an aquatic environment

In order to achieve convenient and efficient detection of picric acid in a water environment, based on function-oriented strategy, we combine luminescence performance with recognition performance, taking into account the application conditions.

A water-stable europium-MOF as a multifunctional luminescent sensor for some trivalent metal ions (Fe3+, Cr3+, Al3+), PO43− ions, and nitroaromatic explosives

Eu-MOF having a layered structure exhibits high sensitivity, selectivity, and recyclability towards sensing Fe³⁺, Cr³⁺, Al³⁺, and PO₄³⁻ ions and TNP.

A pyrazine core-based luminescent Zr(iv) organic framework for specific sensing of Fe3+, picric acid and Cr2O72−

A new Zr-MOF incorporating a pyrazine core-based tetracarboxylate was used for selective fluorometric sensing of Fe³⁺, picric acid and Cr₂O₇²⁻ with outstanding sensitivity.