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A europium-functionalized, dual-emissive, metal–organic framework-based fluorescence sensor (EuUCNDA) was constructed via post-synthetic modification of an UiO-66-type precursor through coordination interactions. EuUCNDA exhibited extremely high selectivity and sensitivity for malachite green (MG) with a low detection limit of 13.01 nM, a wide linear concentration range (0.05–50 μM), excellent anti-interference properties, a rapid response (<1 min), and the possibility of recycling. The good sensing performance of EuUCNDA enables the practical detection of MG in fish pond water and grass carp with good recoveries. Moreover, EuUCNDA can be reused for sensing MG and over 90% of fluorescence intensity can be restored after 7 cycles. Furthermore, EuUCNDA-embedded paper-based sensors combined with smartphone imaging afford portable and visual monitoring of MG in real samples. Notably, besides good sensing performance, EuUCNDA could efficiently remove MG from water. Hence, this work provides a recyclable and sensitive fluorescence sensor for portable, visual, rapid detection and efficient removal of MG. [ABSTRACT FROM AUTHOR]

The development of a rapid and selective method for the identification of dipicolinic acid (DPA), a specific biomarker in Bacillus anthracis spores, is of great importance for the avoidance of anthrax infection. Herein, a chain-based EuIII metal–organic framework with the formula {[Eu3(BTDB)3(μ3-OH)3(H2O)]·solvents}n (JXUST-38, H2BTDB = (benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid) was obtained using 2-fluorobenzoic acid as the pH regulator. JXUST-38 exhibits good chemical and thermal stability and can specifically recognize DPA in N,N-dimethylformamide solution through luminescence enhancement and blue-shift effects with a detection limit of 0.05 μM. Furthermore, the significant luminescence enhancement and blue shift under UV lamps are obviously observable by the naked eye. The luminescence sensing mechanism is attributed to absorbance-induced enhancement between JXUST-38 and DPA. Test paper and mixed-matrix membrane based on JXUST-38 are designed for DPA detection. In addition, the feasibility of using JXUST-38 in biosensing is discussed in detail. [ABSTRACT FROM AUTHOR]

A novel three-dimensional Eu3+-based metal–organic framework with the formula {[(CH3)2NH2][Eu(BTDI)]·H2O·DMF}n (JXUST-25) was prepared by solvothermal method based on Eu3+ and 5,5′-(benzothiadiazole-4,7-diyl)diisophthalic acid (H4BTDI) with benzothiadiazole (BTD) luminescent groups. Due to the presence of Eu3+ and organic fluorescence ligand, JXUST-25 displays turn-on and blue-shift fluorescence toward Cr3+, Al3+ and Ga3+ with limits of detection (LOD) of 0.073, 0.006 and 0.030 ppm, respectively. Interestingly, the alkaline environment can change the fluorescence of JXUST-25 toward Cr3+/Al3+/Ga3+ and the addition of HCl solution realizes the reversible change of the fluorescence of JXUST-25 toward Cr3+/Al3+/Ga3+. It is noteworthy that the fluorescent test paper and light-emitting diode lamp based on JXUST-25 can effectively detect Cr3+, Al3+ and Ga3+ by the visual changes. In addition, the turn-on and blue-shift fluorescence between JXUST-25 and M3+ ions may be caused by the host–guest interaction and the absorbance caused enhancement mechanism. [ABSTRACT FROM AUTHOR]

The development of sensors with high sensitivity, selectivity, long-term stability and other excellent performances is still the focus of current research on gas sensors. In this paper, biomorphic zinc oxide composite reduced graphene oxide nanomaterials (C–Z–ZnO–rGO) based on a metal–organic framework are synthesized by an impregnation calcination method using cotton as a biological template. The microscopic morphologies and structural composition of the composites are characterized. The response value of C–Z–ZnO–rGO to acetic acid gas is much higher than that of other gas sensors. At an operating temperature of 350 °C, the C–Z–ZnO–rGO gas-sensitive sensors have a response value of 410 for 100 ppm acetic acid, a response time of 43 s, and a recovery time of 18 s, and have good repeatability and long-term stability. The response value of 2.614 for 1 ppm of acetic acid gas further indicates that the C–Z–ZnO–rGO sensor has a low detection limit. The hollow structure of the C–Z–ZnO–rGO composites has the advantages of high specific surface area, multiple pores, diverse structures and abundant active sites, which improves the adsorption performance on acetic acid gas. [ABSTRACT FROM AUTHOR]

A novel water-stable CdII-based metal–organic framework, namely {[Cd(BIBT)(TDC)]·2H2O}n (JXUST-28, BIBT = 4,7-bi(1H-imidazol-1-yl)benzo-[2,1,3]thiadiazole and H2TDC = 2,5-thiophenedicarboxylic acid), was synthesized using a mixed-ligand strategy. Structural analysis demonstrates that JXUST-28 exhibits a two-dimensional layer structure with 4-connected sql topology. Intriguingly, JXUST-28 presents good stability in boiling water (at least 5 days), common organic solvents and aqueous solutions with different pH values of 2–12 (more than 24 hours). Furthermore, fluorescence experiments revealed that JXUST-28 could sense Hg2+ ions in aqueous solution via a quenching effect with a detection limit of 0.097 μM. Meanwhile, JXUST-28 can also be regenerated at least 5 times to detect Hg2+ ions. In addition, light-emitting diode lamps, luminescent films, and test papers of JXUST-28 have been successfully developed for practical applications. [ABSTRACT FROM AUTHOR]

Excessive Fe3+ and Bi3+ can cause serious hazards to human-beings and microorganisms. However, it remains a great challenge to exploit more efficient methods to detect them. In this work, a two-dimensional (2-D) metal–organic framework (MOF) [Cd(3-L)(NDA)(H2O)]n (1) (3-L = 3,3′-((9H-fluoren-9-ylidene)-methylene)dipyridine; H2NDA = 1,4-naphthalenedicarboxylic acid) was successfully fabricated by a new fluorenyl-containing aggregation-induced emission (AIE) functional ligand. 1 features a 2-D (4,4) network, and good water and thermal stabilities. In its stacking structure, the fluorene rings from neighboring layers overlap with each other in the opposite direction, and show very weak π–π interactions. Accordingly, 1 exhibits superior luminescence enhancement ("turn-on") sensing of Fe3+ and Bi3+ with extremely high sensitivity in aqueous media. The detection limits of 1 for Fe3+ and Bi3+ are 4.86 × 10−4 and 1.87 × 10−5 mM, respectively, which are significantly lower than the corresponding reported works (only 23.6% and 0.8%). Interestingly, it has obviously enhanced Bi3+ detecting ability because of the larger ionic radius of Bi3+. More importantly, this is the first MOF-based "turn-on" sensor for Bi3+ reported to date. [ABSTRACT FROM AUTHOR]

A new water-stable three-dimensional (3D) Eu(III) metal–organic framework with the formula of {[Eu3(BTDC)4(HCOO)(H2O)2]·solvents}n (JXUST-9) was successfully obtained by the solvothermal reaction of 2,1,3-benzothiadiazole-4,7-dicarboxylic acid (H2BTDC) and Eu(NO3)3·6H2O. The PXRD patterns indicate that JXUST-9 exhibits good stability when soaked in boiling water for at least 24 h. The fluorescence experiments indicate that JXUST-9 could be considered as a good multi-responsive sensing material for detecting Fe3+, MnO4− and Cr2O72− in aqueous solutions via the turn-off effect, and the detection limits are 0.94 μM, 1.23 μM and 1.23 μM, respectively. JXUST-9 can also be regenerated at least five times for sensing Fe3+, MnO4− and Cr2O72−. Moreover, a rapid detection test paper incorporated with JXUST-9 has been produced, which is helpful for carrying out visual detection of Fe3+, MnO4− and Cr2O72− in daily applications. [ABSTRACT FROM AUTHOR]

The effective assembly of hollow nanomaterials is of great importance for the rapid advancement of electroanalytical platforms. Herein, the hollow tubular zeolite imidazolium framework-8 (HTZIF-8) was carefully constructed via the precursor conversion pathway. Subsequently, the predictable assembly of HTZIF-8 with carbon nanotubes (CNTs) occurred to form a unique hollow dual-tube MOF hybrid material (HTZIF-8@CNTs). Meanwhile, the HTZIF-8@CNTs electroanalytical platform was established with dopamine (DA) as the objective biomolecule. In the electrochemical evaluation, the linear intervals of 0.06–600 μmol L−1 and detection limit of 0.02 μmol L−1 (S/N = 3) were determined, which were mainly ascribed to nano-synergistic engineering of HTZIF-8 and CNTs. The HTZIF-8@CNTs hybrid material exhibited superior electrocatalytic performance for DA compared to the solid rod-like MOF composite (SRZIF-8@CNTs), which was majorly based on the faster mass transfer characteristics of hollow MOFs. Additionally, the HTZIF-8@CNTs electrochemical sensor presented outstanding anti-interference capabilities as well as stability and could be utilized for the detection of DA in real samples. The employment of F and t statistics were employed to ensure the reliability of the results. This study will offer novel thoughts toward the application of hollow MOF composites in the area of electroanalytical platforms. [ABSTRACT FROM AUTHOR]

Due to their hazard to biological systems, it is urgent to develop materials that can rapidly and sensitively detect the concentration of H2PO4− and OCN− ions. In this work, a new CdII-based luminescent metal–organic framework with the formula [Cd(BTDB)(2,6-BBIP)]n (JXUST-47, H2BTDB = (benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid, 2,6-BBIP = 2,6-bis(benzimidazol-1-yl)pyridine) and sql topology was successfully synthesized using a mixed-ligand strategy. JXUST-47 shows good chemical and thermal stability. It also exhibits weak quenching and fluorescence blue shift for H2PO4− and red shift for OCN−, with the detection limits of 0.106 and 0.128 mM, respectively. In addition, considering the demand for H2PO4− and OCN− ion detection, by combining this with the functions of a smartphone, the chroma of photographs have been used to realize the consecutive visual detection of the concentration of these ions. [ABSTRACT FROM AUTHOR]

The current luminescent metal-organic framework (MOF) based fluorescence detection mostly focuses on achiral molecules. The stereospecific recognition and determination of MOF-based detection remain challenging. A novel luminescent terbium-based MOF (Tb-MOF) based biosensing system with excellent performance for stereoselective detection of D-amino acids (D-AAs) was introduced in this paper. D-Amino acid oxidase catalyzes stereospecific oxidative deamination of D-AAs, producing H2O2. The generated H2O2 effectively quenches the fluorescence of Tb-MOF. Under optimum conditions, the D-AAs were detected with excellent efficiency. The linear working range was 0.5-100 mM for D-Alanine (D-Ala) and 0. 5-5 mM for D-Proline (D-Pro), respectively. The limit of detection (Ksv detection) for D-Ala and D-Pro was 0.09 mM and 0.14 mM, respectively. The detection can be performed within 30 min with high selectivity and long-term stability. The fluorescent sensing platform required simple fabrication and operation and was free from complicated reaction processes and expensive reagents. The present sensing system was successfully applied in D-AA detection in human serum with good recovery, indicating its potential application in detection in biological samples. [ABSTRACT FROM AUTHOR]

Dipicolinic acid (DPA) is an anthrax biomarker. Its serious consequences make its detection a great need. In this paper, three novel metal–organic frameworks (MOFs) with different coordination modes were synthesized by a simple solvothermal method, which can be used as highly efficient fluorescence sensors for the highly selective and sensitive trace detection of DPA. MOFs 1–3 showed rapid responses to DPA (<30 s), and the limits of detection (LODs) were calculated to be 1.01 × 10−6 M−1 (MOF 1), 1.17 × 10−6 M−1 (MOF 2) and 2.07 × 10−6 M−1 (MOF 3). DPA detection based on MOFs 1–3 in fetal bovine serum is highly reliable based on the high recovery rates (90% to 115%). Hence, the three MOF-based sensors can be used in the real-time detection of DPA. [ABSTRACT FROM AUTHOR]

A fluorescent probe based on single metal–organic framework material without additional fluorophores and active sites can significantly improve the stability of the probe for detection, and has very important application value in environmental analysis and detection. In this paper, a simple and rapid fluorescence detection method was established with Zn-MOF, which realized the highly sensitive detection of tetracycline antibiotics and NH4+ in water. The prepared Zn-MOF has abundant pores and can exist stably in water. When tetracycline antibiotics are present in Zn-MOF aqueous solution, based on the unique coordination ability between Zn and N, tetracycline antibiotics rich in N will be adsorbed into the pore canals of MOF, and aggregation-induced luminescence will occur. The original non-fluorescent Zn-MOF will immediately produce yellow fluorescence, realizing the detection of tetracycline antibiotics in water, with the limit of detection reaching 0.017 μM in a linear range of 0.02–13 μM. Zn-MOF is further used for the detection of tetracycline antibiotics in actual samples of milk and honey. Oxytetracycline (OTC) with the best fluorescence response of tetracycline antibiotics was coated on Zn-MOF to synthesize OTC@Zn-MOF fluorescent probe. NH4+ will replace the original ligand of Zn-MOF, which will disintegrate MOF and release OTC, resulting in a fluorescence decrease. Therefore, NH4+ can be detected with low limit of detection (0.038 μM) in a linear range of 0 to 3 mM. The probe is expected to be able to detect ammonia in the environment. [ABSTRACT FROM AUTHOR]

The introduction of halogen atoms into the skeleton to regulate the intrinsic properties or improve task-specific performance of metal–organic frameworks (MOFs) has developed rapidly in recent years. Herein, a series of halogen-engineered MOFs were designed and prepared for electrochemical glucose sensing. Three isomorphic Ni-MOFs were constructed by using tetra-halogenated-phthalic acids as the organic ligand and incorporating 4,4′-bipyridine as an auxiliary ligand. Halogen atoms can enhance the stability of Ni-MOFs through their hydrophobicity and interlayer halogen bonds (X–X or X–π, X = F, Cl, Br). Combined experimental and theoretical results show that the hydrogen bond between halogen atoms and glucose improves the reaction thermodynamics, enabling the wide linear range of 0.01–5.0 mM, high sensitivity of 4709.9 μA mM−1 cm−2 and low detection limit of 0.043 μM. This work provides practical guidance for the rational design of halogenated MOFs and promotes their applications in electrochemical sensing. [ABSTRACT FROM AUTHOR]

tert-Butylhydroquinone (TBHQ) is a novel synthetic antioxidant with a higher safety profile and antioxidant effect that is more excellent than other synthetic antioxidants and is internationally recognized as one of the best food antioxidants. However, its excessive use in food can have unfavorable effects on the human body. Thus, it is critical to establish a rapid method for the detection of TBHQ in food samples. In this study, a cobalt-based metal–organic framework (Co-MOF) was fabricated by a one-pot hydrothermal method and embedded in multi-walled carbon nanotubes (MWCNTs) to construct an economical and sensitive electrochemical sensor for TBHQ. The results showed that this sensor possessed a wide linear range (0.004–20 μM and 20–300 μM), a low limit of detection (LOD = 2.5 nM, S/N = 3) as well as an ultra-high sensitivity (43.19 μA μM−1 cm−2). Moreover, the sensor also has superior selectivity, repeatability, reproducibility and anti-interference ability and can be successfully applied for the detection of TBHQ in samples of instant noodles and potato chips. [ABSTRACT FROM AUTHOR]

Ratiometric fluorescent nanosensors were developed to detect mercury ions (Hg2+) using enhanced dual emissions from glutathione stabilized gold nanoclusters/indium-based metal–organic frameworks modified with cysteine (AuNCs/MIL-68(In)-NH2/Cys). The nanosensors exhibited bright pink fluorescence with AuNCs evenly distributed on MIL-68(In)-NH2. Under 370 nm excitation, the obtained sensor presented double fluorescence emission around 438 nm and 668 nm, which was attributed to MIL-68(In)-NH2 and GSH-AuNCs, respectively. The fluorescence emission was remarkably enhanced after modification with Cys. In the presence of Hg2+, the red fluorescence peak at 668 nm was quenched, while the blue fluorescence peak at 438 nm was slightly altered. The prepared AuNCs/MIL-68(In)-NH2/Cys nanosensors exhibited two linear ranges for the detection of Hg2+, namely from 20 pM to 0.2 μM and 0.2 μM to 60 μM, with a detection limit of 6.7 pM. They also presented high selectivity towards other ions and good performance in real water samples. Moreover, a radial star-shaped microfluidic paper-based analytical device (μPAD), as a straightforward and convenient platform, was successfully fabricated for the visual detection of Hg2+ with a wide detection range from 5 nM to 50 μM. [ABSTRACT FROM AUTHOR]

In this paper, PS (polystyrene)/Au/ZIF-8 (zeolite imidazole framework-8) hybrid structures were synthesized for the first time as novel SERS active substrates. A series of substrates were successfully prepared by changing the Au sputtering time (5 min, 8 min, 10 min, 15 min and 20 min). When the sputtering time of Au was 10 min, the 4-mercaptobenzoic acid (4-MBA) molecules on the PS/Au/ZIF-8 substrate exhibited the maximum SERS enhancement. Meanwhile, the hybrid SERS substrate exhibited good SERS reproducibility, and we successfully obtained an ultrahigh enhancement factor of 1.67 × 106. Probe molecules can be easily enriched on the surface of the PS/Au/ZIF-8 composite due to their large pore volume and the high surface area of metal organic framework (MOF) materials. ZIF-8 also guides the probe molecules to the "hot-spots" to enhance the SERS signals. Moreover, the detection limit of R6G molecules achieved was 10−12 M when PS/Au(10 min)/ZIF-8 was used as a highly sensitive SERS sensor. This strategy has brought new insights to SERS research, and has also provided a new idea for the application and development of SERS in MOF-based SERS materials and ultra-sensitive analyses. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are a unique class of multifunctional hybrid crystals that have been successfully utilized in diverse ranges of applications. However, since MOFs are prone to aqueous degradation, the development of stable luminescent MOF platforms in aqueous media is still a huge challenge. Here, a novel dual-ligand Eu3+/DUT-52-COOH composite is prepared based on the luminescent DUT-52 prototype structure via a dual-ligand strategy and a post-synthetic modification (PSM) method. The functionalized Eu3+/DUT-52-COOH material exhibits dual emission and good photothermal stability in aqueous media. Thus, Eu3+/DUT-52-COOH is developed as a ratiometric luminescent sensor to achieve highly selective and sensitive detection of Cu2+ and Cr2O72− in aqueous solutions and has a low detection limit of 3.43 μM and 25.7 nM, respectively. This work is one of the few cases of detecting Cu2+ and Cr2O72− in aqueous media based on a DUT-52, and the detection signals can be observed by the bare eye without using sophisticated analytical instruments. The possible sensing mechanism is discussed in detail. The results obtained in this project may provide broad prospects for developing smart sensing systems to accomplish highly efficient, easily operable and quantitative intelligent recognition of Cu2+ and Cr2O72−. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) are composed of metal ions and organic ligands with high specific surface areas, controllable porous structures and abundant metal active sites, showing their extraordinary potential in electrochemical sensors. Here, a 3D conductive network structure (C–Co–N@MWCNTs) is designed by anchoring zeolite imidazole frameworks (ZIF-67) onto multi-walled carbon nanotubes (MWCNTs) and carbonizing them. The C–Co–N@MWCNTs exhibit excellent electron conductivity, a porous structure and considerable electrochemical active sites, which can effectively demonstrate high sensitivity and selectivity in the detection of adrenaline (Ad). The Ad sensor exhibited a low detection limit of 6.7 nmol L−1 (S/N = 3) and a wide linear range of 0.02 μmol L−1–1.0 mmol L−1. The developed sensor also displayed high selectivity, good reproducibility and repeatability. The C–Co–N@MWCNTs electrode was further employed in the detection of Ad in a real sample of human serum, suggesting that it is a promising candidate for electrochemical sensing of Ad. [ABSTRACT FROM AUTHOR]

A novel composite fluorescence probe (oPD-CDs@UiO-66-NH2) was successfully prepared for NO detection in the aqueous phase, where carbon quantum dots (oPD-CDs) with NO recognition units were doped in a hydrothermally stable metal–organic framework material (UiO-66-NH2). oPD-CDs and UiO-66-NH2 combined by electrostatic adsorption, and oPD-CDs were uniformly distributed within the pore channel of UiO-66-NH2. This not only suppressed the aggregate induced fluorescence quenching occurring in carbon quantum dots, but also facilitated the efficient detection of NO. The prepared novel fluorescence probes were more sensitive to NO detection than pure oPD-CDs. NO can be detected in a wide linear concentration range of 6.25–500 μM with a lower limit of detection of 4.27 μM. The probes had high selectivity for NO analogs as well as other common substances. This was mainly attributed to the modification of UiO-66-NH2 by oPD-CDs, which can improve the efficient and selective adsorption of NO. [ABSTRACT FROM AUTHOR]

To improve the peroxidase-like activities of metal–organic frameworks (MOFs) as nanozymes, a ternary MIL-100(Fe)@PMo12@3DGO nanocomposite was designed and fabricated by encapsulating Keggin-type H3PMo12O40 (PMo12) with fast and reversible multi-electron redox processes and an electron-rich structure into MIL-100(Fe), then being covered by three-dimensional graphene (3DGO) with higher conductivity, larger surface area, higher porosity, and better chemical stability. As a consequence, the as-prepared MIL-100(Fe)@PMo12@3DGO nanocomposite exhibits excellent peroxidase-like activities, namely, the lowest limit of detection (0.14 μM) in the range of 1–100 μM for glucose to date, to the best of our knowledge, attributed to the individual and synergistic effects of H3PMo12O40, 3DGO and MIL-100(Fe). [ABSTRACT FROM AUTHOR]

In recent years, antibiotic pollution has become a major concern due to their excessive exposure to humans and the environment. However, the existing instrument-dependent and time-consuming conventional detection approaches are not feasible for the real-time detection of antibiotics at the field level. Herein, two Cu-based metal–organic frameworks (Cu-btc) with the same stoichiometry were synthesized under different reaction conditions. The hydrothermal approach resulted in better structural and crystalline properties of Cu-btc (named as Cu-MOF2) than the preparation under normal laboratory conditions (Cu-MOF1). The high peroxidase-like activity of Cu-MOF2 was further utilized to develop a colorimetric assay for the detection of tetracycline in water. The presence of multiple O- and N-functional groups in tetracycline led the formation of tetracycline–Cu2+ complexes. Tetracycline itself did not cause any change in the color of the TMB-H2O2 system, but it could effectively hinder the colorimetric reaction of TMB with H2O2 in the presence of Cu-MOF2. The designed system demonstrated a low detection limit of 0.23 μM with a limit of quantification of 0.69 μM. The performance of this colorimetric assay was also examined in the presence of other possible interfering antibiotics. The good biocompatibility of this sensing platform increases its potential for in vitro biosensing applications. [ABSTRACT FROM AUTHOR]

A novel three-dimensional Eu3+-based metal–organic framework with the formula {[(CH3)2NH2][Eu(BTDI)]·H2O·DMF}n (JXUST-25) was prepared by solvothermal method based on Eu3+ and 5,5′-(benzothiadiazole-4,7-diyl)diisophthalic acid (H4BTDI) with benzothiadiazole (BTD) luminescent groups. Due to the presence of Eu3+ and organic fluorescence ligand, JXUST-25 displays turn-on and blue-shift fluorescence toward Cr3+, Al3+ and Ga3+ with limits of detection (LOD) of 0.073, 0.006 and 0.030 ppm, respectively. Interestingly, the alkaline environment can change the fluorescence of JXUST-25 toward Cr3+/Al3+/Ga3+ and the addition of HCl solution realizes the reversible change of the fluorescence of JXUST-25 toward Cr3+/Al3+/Ga3+. It is noteworthy that the fluorescent test paper and light-emitting diode lamp based on JXUST-25 can effectively detect Cr3+, Al3+ and Ga3+ by the visual changes. In addition, the turn-on and blue-shift fluorescence between JXUST-25 and M3+ ions may be caused by the host–guest interaction and the absorbance caused enhancement mechanism. [ABSTRACT FROM AUTHOR]

Two novel 2D lanthanide metal–organic frameworks (Ln-MOFs), namely {[Eu2(DBTA)3(DMF)2]·DMF}n (1) and {[Tb2(DBTA)3(DMF)2]·DMF}n (2) (H2DBTA = 2,5-dibromoterephthalic acid), have been successfully synthesized by the solvothermal method. Single-crystal X-ray diffraction results proved that the complexes possess the same topological structure of a (42·6)2(42·84)(47·63)2-connected net. The recognition of CN− from interfering anions with a low detection limit by "turn-off" luminescence makes them promising candidates for the highly selective and sensitive detection of the cyanide ion. The Ln-MOFs 1 and 2 exhibit excellent chemical sensing properties for CN− with efficiency, selectivity, and excellent performance in various mixed anions. The evaluation parameters, including the quenching constant and detection limit, have been investigated to obtain the detection performance for CN−. [ABSTRACT FROM AUTHOR]

Injecting polyoxometalate (POM) clusters into metal organic frameworks (MOFs) can not only provide more additional redox centers, but also solve the problems of easy agglomeration and low stability of POMs. Herein, we prepared {Co3Mo7O24}@[Ag4(μ-Hbtc)(μ-H2btc)]1/2 (shortened as {Co3Mo7O24}@Ag-BTC-2, btc = 1,3,5-benzyltricarboxylic acid) by a simple grinding method and characterized its morphology and composition. {Co3Mo7O24}@Ag-BTC-2 showed high specific capacitance (260.7 F g−1) and high capacitance retention (99.8% after 5000 cycles) in a three-electrode system with nickel foam as a collector. A symmetrical supercapacitor fabricated with {Co3Mo7O24}@Ag-BTC-2 delivers an energy density of 4.9 W h kg−1 at 355.1 W kg−1. The capacitance retention reached 97.6% after 5000 cycles. In addition, {Co3Mo7O24}@Ag-BTC-2 as a H2O2 sensor showed a wide linear range (1 μM to 0.43 mM), a low detection limit (0.33 μM) and a strong anti-interference ability, and can be used to detect H2O2 in real blood serum specimens. These results show that POMOF materials with high performance can be prepared by a simple grinding method. [ABSTRACT FROM AUTHOR]

Nanozymes with the advantages of excellent enzyme-mimicking activity, low cost and high stability have displayed great application potential in diverse fields as replacements for natural enzymes. In this study, a new nanozyme based on an ultrathin two-dimensional metal–organic framework nanomaterial D-ZIF-67 was prepared and characterized. D-ZIF-67 exhibited remarkable oxidase-like activity, which was attributed to the large specific surface area of the two-dimensional sheet structure, as well as its numerous exposed active sites compared with crystal MOFs. In the catalytic process of D-ZIF-67, the hydroxyl radical and superoxide anion played an essential role and facilitated the oxidation of the substrate 3,3′,5,5′-tetramethylbenzidine (TMB) by oxygen. The reducing agent glutathione (GSH) inhibited the catalytic activity of D-ZIF-67 besides reducing the oxidized oxTMB, based on which a simple, sensitive and accurate colorimetric method was developed to determine GSH, with the detection limit of 229.2 nM. This work mainly proposes a new two-dimensional metal–organic framework with high oxidase-like activity and provides a simple and practical platform for visual GSH detection by naked eyes. [ABSTRACT FROM AUTHOR]

Because of the fluorescence properties, lanthanide metal-organic framework (Ln-MOF) materials have potential applications in the detection of metal ions and nitro-aromatic explosives. Herein, a series of isostructural Ln-MOFs [Ln2IJPIA)3IJDMF)3IJCH3OH)] (JLU-MOF201-Ln, Ln = Y, Tb, Yb, Ho and Er, H2PIA = 5-(1H-pyrazol-3-yl)isophthalic acid), and DMF = N,N-dimethylformamide) were successfully synthesized. In these compounds, binuclear secondary building units (SBUs) are formed by two adjacent Ln3+ ions and H2PIA ligands, further linking together to build a 2D structure. The 2D framework can be simplified as a (3,4)-connected network with 3,4L83 topology. The luminescence sensing tests indicated that JLUMOF201-Y and JLU-MOF201-Tb show high sensitivity for Fe3+, 2,4-dinitrophenol (2,4-DNP) and 4-hydroxyderricin (4-NP), respectively. JLU-MOF201-Y and JLU-MOF201-Tb also exhibit high selectivity for detecting Fe3+ among other metal ions in DMF solution. The limits of detection (LOD) toward Fe3+, 2,4-DNP, and 4-NP are calculated to be 2.21, 0.46, and 1.15 µM for JLU-MOF201-Y and 2.17, 2.29, and 1.01 µM for JLU-MOF201-Tb, respectively. [ABSTRACT FROM AUTHOR]

Metal oxide nanostructures hold great promise in biosensors for non-enzymatic detection of H2O2. However, the interfacial or morphological changes of metal oxides during electrochemical reactions due to corrosion greatly reduce the service life and stability of the sensor. In this work, we propose the utilization of zeolite imidazole framework-8 (ZIF-8) as a functional layer to improve the H2O2 detection properties of ZnO nanorod arrays. Benefiting from the synergic interaction of the two materials, the core–shell ZnO@ZIF-8 nanoarrays demonstrate significantly enhanced electrochemical performance compared to pristine ZnO, delivering a wider linear range (20–11 550 μM) at 0.6 V potential, higher sensitivity (4.47 μA mM−1 cm−2) and low detection limit (3 μM), as well as appealing long-term stability of up to 21 days. Post-TEM analysis reveals that the ZIF-8 shells can effectively protect the ZnO cores from corrosion when immersed in electrolyte to detect H2O2. The core–shell structure formed by coating metal–organic frameworks on metal oxides provides a new pathway for high performance chemical detection and other related fields. [ABSTRACT FROM AUTHOR]

Multifunctional metal–organic frameworks (MOFs) as fluorescent probes have been proven to be practical tools for future sensing devices. We herein report a new luminescent MOF, {[Zn3(TLA)2(H2O)2(4-abpt)2]·5CH3OH}n (1) (trimellitic acid = H3TLA, 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole = 4-abpt), which was synthesized under solvothermal conditions and then characterized. 1 has a three-dimensional polymeric coordination structure with a V-shaped trinuclear metal–oxygen [Zn3] unit. The adjacent [Zn3] units are further connected by TLA3− and 4-abpt linkers, resulting in the generation of a 3D coordination polymeric network with obvious 3D channels. Moreover, 1 demonstrates a unique three-fold interpenetrated network and exhibits excellent chemical and thermal stabilities. Interestingly, 1 can be used as a sensitive and recyclable fluorescent probe for the detection of 2,4,6-trinitrophenol (TNP), levofloxacin (LVX), and L -cystine (L -Cys) with low limits of detection (LOD) of 5.24, 7.47 and 5.05 μM, respectively. [ABSTRACT FROM AUTHOR]

Highly selective sensing of Fe3+ is very important due to its great effect on biological systems. A novel ligand [1,1′:4′,1′′:4′′,1′′′:4′′′,1′′′′-quinquephenyl]-2,2′′,2′′′′,5′′-tetracarboxylic acid (H4qptca) was designed and successfully obtained for the first time via three steps in high total yields according to the absorption spectrum of Fe3+. The europium(III)-based metal–organic framework derived from H4qptca, {[Eu(qptca)1/2(H2qptca)1/2(H2O)2]·DMF}n (referred to as SLX-1), was then synthesized and used as a water-stable and highly selective luminescent sensor for Fe3+ in aqueous solution with a comparable detection limit using Ln-MOF probes (6.45 μM) through the antenna effect of SLX-1. Furthermore, the luminescence quenching mechanism was also proposed as a competitive absorption mechanism. [ABSTRACT FROM AUTHOR]

Herein, an amine decorated Cd(II) metal–organic framework (MOF) with a uninodal 6-c topology was synthesized as a suitable platform for facile post-synthetic modification (PSM). The as-synthesized parent d10-MOF (1) with free –NH2 centers, when functionalized with two different carbonyl substituents (1-naphthaldehyde and benzophenone) of varying conjugation, produces two novel luminescent MOFs (LMOFs) viz.PSM-1 and PSM-2. The judicious incorporation of carbonyl substituents into the skeleton of 1 was rationalized via ESI-MS, 1H-NMR, FT-IR and PXRD analyses. Interestingly, both PSM-1 and PSM-2 show 'turn-on' luminescent behaviour in the presence of 1,4-dioxane with the limit of detection (LOD) as 1.079 ppm and 2.487 ppm, respectively, with prompt response time (∼55 s & ∼58 s, respectively). The inhibition of PET is comprehended to be the prime reason for luminescence enhancement upon interaction with the targeted analyte which was further validated from DFT calculations. In continuation, the PSM-MOFs were equally responsive towards 1,4-dioxane in several complex environmental matrices and cosmetic products. Additionally, vapor phase detection of 1,4-dioxane using PSM-MOFs has also been demonstrated as an additional advantage ensuring propagation of future research endeavour. [ABSTRACT FROM AUTHOR]

Reasonable control of the redox states within the catalytic units together with the interconnection degrees of the substrate is of great significance in the modulation of a well-performing transducer. Herein, a novel carbon black (CB)-modified copper metal–organic framework nanomaterial (CB@Cu-MOF) prepared at room temperature was utilized as a precursor to synthesize mixed-valent copper–oxide composite catalysts (NC/CuxO-T). By tuning the carbonization process of the precursor at different temperatures (T = 100 °C, 200 °C, 300 °C and 400 °C), the different ratio configurations of the redox-alternated CuxO portions were successfully controlled with the simultaneous effective tailoring of the defect abundance in the N-doped carbon substrate. As a result, an optimized NC/CuxO-300 electrochemical H2O2 sensor was able to present a low detection limit (0.26 μM) and decent linear ranges (0.02–1.79 mM and 2.29–9.29 mM). Our strategy using easily available initial materials with mild preparation conditions is expected to promote the practical application of the star materials in laboratories. [ABSTRACT FROM AUTHOR]

Two cluster-based metal–organic frameworks {[Cd5L4Br10]·2(CH3)2NH}n (1) and {[MnIII3OL(TA)3]F·sol}n (2) (L = 1,3,5-tris(benzimidazol-1-ylmethyl)-2,4,6-trimethylbenzene, TA = terephthalate anion) containing a semi-rigid tribenzimidazol-based ligand were synthesized and characterized. Single crystal X-ray analyses show that the structure of 1 contains pentanuclear cadmium clusters with an interesting four-fan shape, in which each μ2-Br interlinks two crystallographically unique Cd atoms, while 2 contains a trimanganese cluster with three Mn3+ ions present in an equilateral triangle distribution. Furthermore, 1 exhibits highly selective fluorescent detection of trace Hg2+, with the detection limit of 5.26 × 10−7 M−1. 2 shows antiferromagnetic interactions between Mn3+ ions. [ABSTRACT FROM AUTHOR]

Construction of zeolite-type frameworks is of broad interest and mainly achieved by using imidazolate linkers. Incorporation of multiple linkers/functionalities into these unique types of frameworks would potentially expand their application scope. Herein, a three-dimensional (3D) metal–organic framework, BUT-27, with a unique zeolite A structure (LTA topology) was synthesized by linker exchange via single-crystal-to-single-crystal transformation. Addition of isophthalic acid linker to the two-dimensional double layered BUT-25 changed the whole framework to a 3D structure, BUT-27, containing three kinds of linkers. The strong fluorescence and presence of free O and N atoms in the framework make BUT-27 a good luminescent sensor for the detection of Fe3+ and Cr2O72− ions with high selectivity and sensitivity, i.e. Ksv = 1.1 × 104 and 5.9 × 104, and LOD (limit of detection) of 0.19 and 0.26 μM, respectively. These values are lower than the minimum values specified by US-EPA (United States Environmental Protection Agency) indicating its high potential for practical applications. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) as a peroxidase mimic have been integrated with glucose oxidase (GOx) to achieve one-step glucose detection. However, limited by the loading amount of GOx, the performances of the developed glucose sensing assays still remain to be further improved to meet sensing requirements in diverse biological samples. Herein, with Fe3+ as the metal ion and 2-amino-benzenedicarboxylic acid as a ligand, a fluorescent Fe-based organic framework (NH2-MIL-101) with peroxidase-like activity was synthesized. Due to the large specific surface area (791.75 m2 g−1), 68 μg mg−1 GOx could be immobilized through the amidation coupling reaction, and the product was designated GOx@NH2-MIL-101. With OPD as the substrate, Gox@NH2-MIL-101 achieved highly efficient biomimetic cascade catalysis for one-step glucose detection through an inner filter effect: upon reacting with glucose, GOx@NH2-MIL-101 catalytically oxidized glucose using dissolved O2, and the produced H2O2 concurrently oxidized o-phenylenediamine (OPD) to oxidized OPD (oxOPD), accompanied by the fluorescence of GOx@NH2-MIL-101 at 456 nm being quenched and that of oxOPD at 565 nm being enhanced. With the fluorescent ratio F565/F456 used as a readout signal, a wide linear range of 0.1–600 μM was obtained, and the detection limit was 0.0428 μM. Based on the excellent selectivity and high stability of GOx@NH2-MIL-101, the developed assay was successfully applied to glucose detection in human serum and saliva, presenting potential applications in diverse biological samples and even medical diagnosis. [ABSTRACT FROM AUTHOR]

Due to their ultra-thin morphology, larger specific surface area and more exposed active sites, two-dimensional (2D) metal–organic framework (MOF) nanosheets can break the limitations of three-dimensional (3D) MOFs in sensitivity, response speed and the limit of detection for sensing applications. In this work, fluorescent NH2-MIL-53(Al) nanosheets were developed as a fluoride detection sensor compared with the 3D bulk counterpart. The morphological and structural characteristics of the obtained products were systematically characterized, and the favourable chemical and fluorescence stability of the NH2-MIL-53(Al) nanosheets were explored. The fluorescent NH2-MIL-53(Al) nanosheets showed high sensitivity, fast response speed (as short as 10 seconds), low limit of detection (15.2 ppb), and wide linear detection range (5–250 μM), and all performances were better than those of their bulk counterpart. In addition, the sensing mechanism was investigated to be based on the transformation of the NH2-MIL-53(Al) framework that induced the release of fluorescent ligands, resulting in an exceptionally enhanced fluorescence. This work highlights the advantages of 2D MOF nanosheets in fluorescence sensing applications. [ABSTRACT FROM AUTHOR]

By means of post-synthetic treatment on the UiO-66 derivative with –SO3H, a novel luminescent hybrid material named Tb3+@UiO-66–SO3H has been prepared simply and efficiently. Given its wonderful luminescence properties like intense green emission, a long lifetime, a robust structure and photostability, it is further developed as a fluorescent probe for the sensing of trans,trans-muconic acid (tt-MA, a biomarker of benzene) and Fe3+, which are closely related to human health. Notably, Tb3+@UiO-66–SO3H shows an outstanding recognition ability for Fe3+ among common cations with a low detection limit (0.11 μM, 0.006 ppm). More importantly, Tb3+@UiO-66–SO3H can realize highly sensitive and selective detection of tt-MA (detection limit, 0.58 μM, 0.083 ppm). Besides, this rapid response probe is facilely prepared, non-toxic and reusable, showing the potential of Tb3+@UiO-66–SO3H in the practical monitoring of tt-MA and Fe3+. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemiluminescence (ECL) biosensor was developed based on MIL-53(Al)@CdS QDs and SiO2@AuNPs for trichlorfon detection. Metal–organic frameworks (MOFs) were used as a loading platform that provided a large surface area to load targets and modified materials onto the electrode. At the same time, SiO2@AuNPs loaded plenty of AuNPs which effectively increased the ECL resonance energy transfer between the CdS QDs, so that the ECL signal was strongly quenched and resulted in an amplified response. In the range of 10−11–10−4 M, the ECL response showed a linear relationship with the concentration (logarithm) of trichlorfon, and the detection limit was 5.1 × 10−12 M (S/N = 3). When the biosensor was applied to detect trichlorfon in lettuce, broccoli, cucumber, and chives, the recoveries obtained from the spiked samples were 97%–105%, 102%–104%, 100%–104%, and 98%–104%, respectively. Thus, this novel ECL biosensor has potential applications for the analysis of trichlorfon in food samples. [ABSTRACT FROM AUTHOR]

As one of the significant serum cytokines, platelet-derived growth factor-BB (PDGF-BB) is a crucial protein biomarker overexpressed in human life-threatening tumors, the sensitive identification and quantification of which are urgently desired but challenging. Herein we report a novel core–shell nanoarchitecture consisting of Cu-based metal–organic frameworks (Cu-MOFs) and covalent organic frameworks (denoted as TpBD-COFs), which was used to prepare an aptasensor for the detection of platelet-derived growth factor-BB (PDGF-BB). The central Cu-MOFs function as signal labels with no need for extra redox media, whereas the porous TpBD serves as the shell to immobilize the PDGF-BB-targeted aptamer strands in abundance via strong interactions involving π–π stacking, electrostatic, and hydrogen bonding interactions. The proposed aptasensor based on Cu-MOF@TpBD can achieve a detection limit as low as 0.034 pg mL−1 within the dynamic detection range from 0.0001 to 60 ng mL−1. The hybridization of MOFs and COFs, together with the immobilization with the specific analyte targeted aptamer, provides a promising and propagable approach to prepare an aptasensor for the simple, sensitive, and selective detection of a specific biomarker in clinical diagnosis. [ABSTRACT FROM AUTHOR]

Recently, exploring new luminescent metal–organic frameworks (LMOFs) to selectively detect nitro-aromatic compounds (NACs) has been a hot topic of research. Simultaneously, it is still a challenging issue to understand the sensing mechanism of luminescent MOFs interacting with NACs at the molecular level. In this work, highly fluorescent Sc-tetracarboxylate frameworks (Sc-EBTC) have been successfully synthesized through a solvothermal method. The as-prepared Sc-EBTC crystals have good thermal stability, chemical stability as well as strong fluorescence (λex = 320 nm and λem = 400 nm), and they can detect various NACs rapidly (as short as 30 s), selectively and efficiently by the "turn-off" fluorescence mechanism. The detection limits of Sc-EBTC toward 2,4-DNP and 4-NP are quantified to be 5.71 ppb and 6.26 ppb, respectively. Furthermore, to better understand the sensing mechanism, we attempt to use solid-state NMR and X-ray photoelectron spectroscopy to vividly characterize the charge transfer caused by the interaction between NAC molecules and the MOF at the molecular level. Additionally, test strips were made successfully for the practical detection of the NACs. This study demonstrates that the MOF constructed from the H4EBTC ligands might be a promising candidate for the detection of trace NACs. [ABSTRACT FROM AUTHOR]

Here, we have described the design, preparation and detailed characterization of a new acetoxy functionalized aluminium based metal–organic framework (MOF) called CAU-10-OCOCH3 (1) (CAU stands for Christian-Albrechts-University). The desolvated compound was employed for the detection of perborate in a pure aqueous environment. The presented MOF based perborate sensing probe (1) was synthesized by employing 5-acetoxyisophthalic acid and AlCl3·6H2O as the linker molecule and metal salt source, respectively, in DMF/H2O medium at 120 °C for 12 h. The material (1′) showed a very selective fluorescent turn-on response towards perborate in aqueous medium with the coexistence of several competitive analytes. A dramatic increment (65 fold) in emission intensity of the probe was observed within 5 min of the addition of perborate. A chemo-selective reaction between perborate and the acetoxy functionality and subsequent hydrolysis of the acetoxy group to the hydroxy group is the main cause of the turn-on nature of detection. The material showed a detection limit of 1.19 μM. The probe was also applied for the recognition of perborate in several environmental water samples. The material is the first ever MOF based probe for selective detection of perborate. [ABSTRACT FROM AUTHOR]

In this work, we have developed amino-functionalized copper-based metal–organic frameworks (NH2-Cu-MOFs) for the detection of hypochlorite (ClO−). NH2-Cu-MOFs were synthesized using a one-pot hydrothermal method, and they exhibit strong fluorescence at 455 nm under the excitation of 330 nm. In the presence of ClO−, the fluorescence of NH2-Cu-MOFs was quenched due to the electron transfer between NH2-Cu-MOFs and ClO−. The NH2-Cu-MOFs exhibited 87.6% fluorescence quenching efficiency with 12.5 μM ClO− and the limit of detection is 0.036 μM. NH2-Cu-MOFs exhibited the advantages of high sensitivity, high selectivity, and low response reaction time for ClO− detection. This work developed a novel fluorescent probe for the detection of ClO− and the NH2-Cu-MOFs were successfully applied to analyse ClO− in real water samples. [ABSTRACT FROM AUTHOR]

The phosphate content in water is crucial to all forms of life. Excessive phosphate in water can cause the excessive growth of algae and lower the oxygen content in water, which is a danger to our environment. However, most conventional methods for phosphate detection are time-consuming and instrument-dependent. In this work, three Cu-based metal–organic framework nanomaterials (Cu-MOF(1), Cu-MOF(2), Cu-MOF(3)) were synthesized. And it was found that the obtained three nanomaterials all exhibited peroxidase-like activities. Cu-MOF catalyzed color reaction can be inhibited in the presence of phosphate, and a colorimetric assay is constructed for the determination of phosphate by taking Cu-MOF(3) as an example. Good linearity existed between the absorbance of the Cu–MOF/TMB–H2O2 system at 652 nm and phosphate concentration from 0.05 μM to 5 μM, with the limit of detection down to 20 nM according to the S/N = 3 rule. Besides, the practicality of our assay was also certified by sensing PO43− in local river water samples. [ABSTRACT FROM AUTHOR]

Two series of lanthanide-based metal–organic frameworks, namely {[Ln(BIPA-TC)0.5(DMA)2(NO3)]·DMA·H2O}n (1-Ln, Ln = Eu, Dy, Sm, Nd) and {[Ln2(BIPA-TC)1.5(DMA)3(H2O)2]·2DMA·2H2O}n (2-Ln, Ln = Eu, Dy, Sm, Nd), were successfully constructed via a solvent regulation strategy based on a π-electron rich tetra-carboxylate ligand (H4BIPA-TC). 1-Ln shows a 4-connected lvt topology with the point symbol of {42·84}, but 2-Ln displays a new 4,4,6-connected wxk1 topology with the point symbol of {43·83}4{46·66·83}2{86}. The solid-state luminescence property and the microporous nature of Eu-MOFs (1-Eu and 2-Eu) indicate that they can potentially be used as luminescent sensors. Fluorescence measurements indicate that Fe3+ exhibits the quenching effect for 1-Eu with the quenching efficiency of 93.1%. 2-Eu is the first MOF sensor for Mg2+ with the lowest detection limit of 1.53 × 10−10 mol L−1 and displays good recyclable capability. Simultaneously, in the presence of other metal ions (Ca2+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pd2+, Al3+, Cr3+and Fe3+), 2-Eu can maintain the selective sensing of Mg2+, indicating its potential for Mg2+ turn-on sensing. [ABSTRACT FROM AUTHOR]

Hypochlorite (ClO−) is widely used as a disinfectant, whose residue content in water should be strictly controlled due to the potential threat to human health in an inappropriate concentration. Herein, dual-emissive metal–organic frameworks with a UiO-66 prototype structure, PDA/Eu/PDA-UiO-66-NH2(x), were elegantly designed and prepared by a mixed ligand assembly and sequential post-synthesis strategy. Since blue emission is sensitive to ClO−, PDA/Eu/PDA-UiO-66-NH2(40) was selected as a model nanosensor for ratiometric and turn-on sensing of ClO− while red emission acts as a reference signal. Remarkably, PDA/Eu/PDA-UiO-66-NH2(40) shows high efficiency and specificity toward ClO− detection, as verified by a very short response time of 15 s, a wide linear range of 0.1–60 μM, a low detection limit of 0.10 μM, and excellent selectivity toward common competing ions. The recovery experiments show that the recoveries of spiking ClO− in tap water range from 96 to 103%. The rigidification of the coordinated H2N–BDC2− ligands should be responsible for the turn-on fluorescence of PDA/Eu/PDA-UiO-66-NH2(40). This work not only shows a highly efficient and specific fluorescent nanosensor for ClO− detection but also presents the first MOF-based fluorescent probe for turn-on and ratiometric sensing of ClO−. [ABSTRACT FROM AUTHOR]

To explore a novel colorimetric biosensor with high sensibility and selectivity, a new Wells–Dawson-type polyoxometalate (POM)-based metal–organic framework (MOF) with an eightfold helix, [Cu9(FKZ)12(H2O)8][H3P2W18O62]2·4H2O (CuFKZP2W18) (HFKZ = 1-(2,4-difluorophenyl)-1,1-bis[(1H-1,2,4-triazol-1-yl)methyl] ethanol), was successfully synthesized; then, polypyrrole (PPy) was introduced to fabricate CuFKZP2W18/PPy(n) nanocomposites (n = 7%, 15%, 30%) via a facile in situ oxidation polymerization process. All the results indicate that CuFKZP2W18/PPy(15%) as a colorimetric biosensor exhibits lower limits of detection (0.07 μM towards H2O2 and 0.627 μM towards ascorbic acid), smaller Km values (0.106 mM for H2O2 and 0.042 mM for o-phenylenediamine) and higher sensitivity (0.0227 1 μM−1 towards H2O2 and 0.0025 1 μM−1 to ascorbic acid) than most reported enzyme mimetics to the best of our knowledge. [ABSTRACT FROM AUTHOR]

Detecting trace amounts of copper ions (Cu2+) is of high importance since copper is an essential element in the environment and the human body. Despite the recent advances in Cu2+ detection, the current approaches still suffer from insensitivity and lack of in situ detection in living cells. In the present work, a fluorescent nanosensor based on porphyrinic metal–organic framework nanoparticles (MOF-525 NPs) is proposed for sensitive and selective monitoring of Cu2+ in aqueous solution and living cells. The MOF-525 NPs with attractive properties, including ultrasmall size, good water dispersity and intense red fluorescence, are prepared via a facile and environment-friendly hydrothermal route. The fluorescence signal of MOF-525 NPs could be quenched statically by Cu2+ with high selectivity due to the strong affinity of Cu2+ to the porphyrin ligand in MOF-525. The proposed fluorescent nanosensor has a linear response in the range of 1.0–250 nM with a low detection limit of 220 pM. Furthermore, it is successfully employed for the detection of Cu2+ in water samples and the intracellular imaging of Cu2+ in living cells, demonstrating its great potential in the sensing and biological fields. [ABSTRACT FROM AUTHOR]

Metal–organic framework (MOF) materials with controlled microstructures have become popular in the last few decades. In this study, Zn-MOF precursors with diverse crystallinity and particle size (20–800 nm) were synthesized using an accelerating or retarding nucleation process by introducing various secondary ligands, which were employed as modulators in the coordination and ligand exchange equilibria according to their different acidity coefficients. Thus, the pore size of MOF-derived ZnO clusters was different, resulting in diverse gas sensing properties. Moreover, large precursor-derived ZnO-(2 and 3) assemblies with the micropore sizes of 1 nm and 0.75 nm showed size-selective sensing and better performance, which exhibited a higher and fast response (4 s) to butanone and n-butanol with the lengths of 0.664 nm and 0.499 nm, respectively, and a low limit of detection (0.1 ppm). This simple method of controlling the nucleation of MOFs and the pore size of ZnO assemblies paved a new way towards the design of the microstructure of MOF-based functional materials. [ABSTRACT FROM AUTHOR]

Pyrophosphate (PPi) is a significant biological anion, and its abnormal level in the human body is regarded as a signal of some diseases. Herein, we developed a method for the detection of PPi using a luminescent ZTMOF-1 via the luminescence turn-on effect. PPi formed hydrogen bonds with the phenyl and pyridine rings in the framework, and ZTMOF-1 could discriminately detect PPi among other phosphorus oxides in both an aqueous solution and a physiological environment. In addition, to the best of our knowledge, this is the first report on the use of a regenerable MOF-based luminescent sensor for the detection of PPi. Moreover, ZTMOF-1 showed an excellent luminescence quenching response to nitrofurantoin (NFT) over other drugs with the detection limit of 0.175 μM. This study presents a dual-responsive regenerable luminescent probe for the detection of PPi and NFT. [ABSTRACT FROM AUTHOR]

A solvothermal reaction between Cd(NO3)2·4H2O and the bifunctional ligand 3,5-bis-(1H-1,2,4-triazol-1-yl)benzene carboxylic acid (HTBC) afforded a three-dimensional coordination polymer, namely [Cd0.5(TBC)]n (1). Single-crystal X-ray diffraction analyses exhibited that MOF 1 possesses a 3D framework with rtl topology, which exists in the form of 2-fold interpenetrated networks. Its luminescence properties demonstrated that complex 1 is a very suitable MOF for the luminescence probing of Fe2+ cations over other metal cations with a high quenching-efficiency constant KSV value of 1.35 × 105 M−1 and a low fluorescence detection limit. In addition, complex 1 also exhibits the highly selective and visually sensitive sensing of the organic contaminant PhCHO with good reusability and a low detection limit. What's more, this is a regenerable luminescent sensor for the highly selective, sensitive sensing of Fe2+ over Fe3+. [ABSTRACT FROM AUTHOR]

The dispersion of gold nanoparticles (AuNPs) on a metal–organic framework (MOF) surface greatly affects the catalytic activity of the material. However, regulating the catalytic performance of AuNP–MOF composite-based nanozymes is a great challenge. Herein, poly(dimethylvinyloxazolinone) (PV) was chemically bonded on the surface of UiO-66-NH2 (U66), followed by modification of pepsin (Pep) on the PV chains. U66-PV-Pep@AuNP composite nanozymes were fabricated after the AuNPs formed in situ with Pep as the capping and reducing reagent. Compared to Pep@AuNPs that were physically adsorbed onto the surface of U66, the U66-PV-Pep@AuNP composites exhibited superior peroxidase (POD)-mimetic activity in the oxidation of 3,3′5,5′-tetramethylbenzidine (TMB) with H2O2. Considering the surface dispersion uniformity and local concentration of Pep@AuNPs on the surface of the U66-PV-Pep@AuNP composites, the principle for improving the catalytic performance of the proposed nanozymes was explored. Furthermore, it was observed that the introduction of L -cysteine (L -Cys) into the U66-PV-Pep@AuNP-TMB-H2O2 system significantly reduced its oxidation activity and faded the color, allowing the development of a highly selective and sensitive colorimetric method for L -Cys detection. The UV-vis absorption intensity of oxTMB showed a good linear relationship with the concentration of L -Cys in the range of 2.5–40.0 μM (R2 = 0.996), with a detection limit of 0.33 μM. The proposed protocol using U66-PV-Pep@AuNP nanozymes was applied to monitor rat serum L -Cys following intraperitoneal injection. This study paves the way for the design and construction of MOF-polymer@AuNP nanozymes for drug detection in real bio-samples. [ABSTRACT FROM AUTHOR]