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In this study, for the first time, a silver-based metal–organic framework (Ag-MOF) was synthesized and used as the electrochemiluminescence (ECL) emitter for building an ECL sensor. After modification with chitosan (CS) and gold nanoparticles (Au NPs), the ECL stability of Ag-MOF was improved. To detect mercury ions, a biosensor was constructed using the mercury ion aptamer and steric effect of streptavidin. First, the capture strand (cDNA) with terminal-modified sulfhydryl group was attached to the electrode surface by the Au–S bond. Then, the mercury-ion aptamer (Apt-Hg) modified with biotin was anchored to the electrode by complementary pairing with cDNA. Streptavidin (SA) could be fixed on the electrode by linking with biotin, thereby reducing the ECL signal. However, in the presence of mercury ions, the aptamer was removed and streptavidin could not be immobilized on the electrode. Hence, the ECL signal of the sensor increased with the concentration of mercury ions, which was linear in the range from 1 μM to 300 fM. The detection limit could reach 66 fM (S/N = 3). The sensor provided a new method for the detection of mercury ions. [ABSTRACT FROM AUTHOR]

Bimetallic metal–organic frameworks (MOFs) possess two different metal ions as nodes in their molecular frameworks. They are prepared by either one-pot syntheses, wherein different metals are mixed with suitable ligands and linkers, or by adopting post-synthetic modifications by soaking a monometallic MOF in a concentrated solution of a different (but compatible) metal ion. These bimetallic MOFs exhibit synergistic effects and enhanced properties compared to their monometallic counterparts, such as improved adsorption selectivity, selective catalysis and structural stability. Certainly, there are still many open challenges, given that bimetallic MOFs suffer from the typical drawbacks of MOFs, including high moisture sensitivity, easy oxidation due to their varying oxidation states, and possible metal leaching in liquids. In the present perspective, progress in the research on the synthesis and properties of bimetallic MOFs has been reviewed systematically, describing the synthetic strategies adopted to prepare targeted bimetallic MOFs and their applications in gas adsorption, catalysis, energy storage and conversion, and luminescence sensing. Additionally, the challenges facing the synthesis of stable and robust bimetallic MOFs have been discussed with a final outlook on their further development prospects. [ABSTRACT FROM AUTHOR]

[Display omitted] • Zr-Me-PDI was designed as C 2 H 6 -selective adsorbent for effective C 2 H 6 /C 2 H 4 separation. • High C 2 H 6 adsorption capacity of 3.9 mmol·g-1 and C 2 H 6 /C 2 H 4 selectivity of 1.5 was achieved for Zr-Me-PDI at 298 K and 1 bar. • Zr-Me-PDI exhibits multiple C-H···Cl and C-H···O interactions with C 2 H 6 as confirmed by GCMC simulation. • Zr-Me-PDI shows superior stability under aqueous solution of different pH values. Adsorptive separation of ethane (C 2 H 6)/ ethylene (C 2 H 4) mixtures based on C 2 H 6 -selective adsorbents through one-step separation unit has attracted great attention in view of its enormous potential to reduce energy consumption in the petrochemical industry. To achieve this, it is highly demanded to develop C 2 H 6 -selective adsorbents. However, it is challenging to construct C 2 H 6 -selective adsorbents due to the difficulty in building suitable interaction between C 2 H 6 molecules and adsorption active sites. Here, we constructed a robust perylene diimide-based zirconium metal–organic framework (MOF, denoted as Zr-Me-PDI) of superior stability under aqueous solution of different pH values (1.0 ∼ 10.0), for effectively separation of C 2 H 6 from C 2 H 4. Zr-Me-PDI displayed C 2 H 6 -selective adsorption behavior at both 298 and 273 K. High C 2 H 6 adsorption capacity 3.9 mmol·g−1 and C 2 H 6 /C 2 H 4 selectivity (1.5) was achieved for Zr-Me-PDI at 1 bar and 298 K, comparable to most of the high-performance C 2 H 6 -selective MOFs. Calculation results of Grand Canonical Monte Carlo (GCMC) simulation show that the interpenetrated structure of Zr-Me-PDI exhibit multiple C-H···Cl and C-H···O interactions with C 2 H 6 and preferentially binds to C 2 H 6 over C 2 H 4. Therefore, the results demonstrated in this project may provide valuable guidance for the design and synthesis of C 2 H 6 -selective adsorbents. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) for enzyme immobilization have already shown superior tunable and designable characteristics, however, their diverse responsive properties have rarely been exploited. In this work we integrated a responsive MOF into a MOF–enzyme composite with the purpose of designing an "all‐in‐one" multifunctional composite with catalytic and luminescence functions incorporated into a single particle. As a proof‐of‐concept, glucose oxidase (GOx) was encapsulated in situ within an oxygen (O2)‐sensitive, noble‐metal‐free, luminescent CuI triazolate framework (MAF‐2), denoted as GOx@MAF‐2. Owing to the rigid scaffold of MAF‐2 and confinement effect, the GOx@MAF‐2 composite showed significantly improved stability (shelf life of 60 days and heat resistance up to 80 °C) as well as good selectivity and recyclability. More importantly, owing to the O2 sensitivity of MAF‐2, the GOx@MAF‐2 composite exhibited a rapid and reversible response towards dissolved O2, thereby allowing direct and ratiometric sensing of glucose without the need for chromogenic substrates, cascade enzymatic reactions, or electrode systems. High sensitivity with a detection limit of 1.4 μm glucose was achieved, and the glucose levels in human sera were accurately determined. This strategy has led to a new application for MOFs that can be facilely extended to other MOF–enzyme composites due to the multifunctionality of MOFs. Multifunctional composite: The "all‐in‐one" MOF–enzyme composite prepared in this work utilizes MAF‐2 simultaneously as protective matrix and signal transducer and can be applied to the detection of glucose in human serum (see figure). Glucose oxidase (GOx) is encapsulated within the MAF‐2 matrix, and the rapid and reversible response of the latter towards dissolved O2 allows the sensing of glucose. The composite shows good stability, selectivity, and recyclability. [ABSTRACT FROM AUTHOR]

Mixing molecular building blocks in the solid solution manner is a valuable strategy to obtain structures and properties in between the isostructural parent metal-organic frameworks (MOFs). We report nonlinear/synergistic solid-solution effects using highly related yet non-isostructural, phosphorescent CuI triazolate frameworks as parent phases. Near the phase boundaries associated with conformational diversity and ligand heterogeneity, the porosity (+150 %) and optical O2 sensitivity (410 times, limit of detection 0.07 ppm) can be drastically improved from the best-performing parent MOFs and even exceeds the records hold by precious-metal complexes (3 ppm) and C70 (0.2 ppm). [ABSTRACT FROM AUTHOR]

Mixing molecular building blocks in the solid solution manner is a valuable strategy to obtain structures and properties in between the isostructural parent metal-organic frameworks (MOFs). We report nonlinear/synergistic solid-solution effects using highly related yet non-isostructural, phosphorescent CuI triazolate frameworks as parent phases. Near the phase boundaries associated with conformational diversity and ligand heterogeneity, the porosity (+150 %) and optical O2 sensitivity (410 times, limit of detection 0.07 ppm) can be drastically improved from the best-performing parent MOFs and even exceeds the records hold by precious-metal complexes (3 ppm) and C70 (0.2 ppm). [ABSTRACT FROM AUTHOR]

Phosphorescent complexes of precious metal ions are widely studied as optical sensing materials for molecular oxygen. Combining the advantages of luminescent complexes and porous matrixes, porous coordination polymers show great potential for oxygen-sensing, although their sensitivity, requirement of precious metal, and device fabrication remain challenging issues. In this work, the photoluminescence and oxygen-sensing properties of the porous Cu(I) triazolate framework [Cu(detz)] (MAF-2, Hdetz = 3,5-diethyl-1,2,4-trizole) is studied in detail, which shows high chemical stability in moisture and water, very long phosphorescent lifetime (116 μs) and large Stokes shift (14 562 cm−1), as well as considerable oxygen permeability (1.7 × 10−11 mol cm−1 s−1 bar−1) at ambient conditions, giving rise to exceptionally high luminescence quenching efficiency of 99.7% at 1 bar O2 ( I0/ I100 = 356) with a perfectly linear Stern-Volmer plot ( KSV = 356 bar−1, R2 = 0.9998), fast response and good reversibility. Further, a counter-diffusion crystal-growth method was developed to fabricate MAF-2 thin films protected by silicone rubbers as the first example of soft membrane oxygen sensor based on coordination polymer or metal-organic framework, which exhibited extraordinary oxygen-sensing performance (limit of detection = 0.047 mbar) and outstanding mechanical property, as well as outstanding chemical stability even in an acidic atmosphere. [ABSTRACT FROM AUTHOR]

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]

Invited for the cover of this issue are Jie‐Peng Zhang, Zong Dai, and co‐workers at Sun Yat‐sen University. The image depicts the harmonious and synergetic combination of MAF‐2 and glucose oxidase (just like the Tai Chi in the background). Read the full text of the article at 10.1002/chem.201806146. "Since metal–organic frameworks (MOFs) and enzymes both have exhibited diverse functions and properties, we hope this exploratory work will inspire more research on utilizing the multifunctions of MOFs for enzyme‐related applications." Read more about the story behind the cover in the Cover Profile and about the research itself on page 5463 ff. (DOI: 10.1002/chem.201806146). [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs) for enzyme immobilization have already shown some superior characteristics; however, their devisable responsive properties have rarely been exploited. This work adopted a facilely synthesized, oxygen‐sensitive luminescent MOF, MAF‐2, for the immobilization of glucose oxidase (GOx) to give GOx@MAF‐2. The MAF‐2 scaffold played both protective and sensing functions in GOx@MAF‐2, which possessed much improved stability and was applied for glucose detection in human sera without any other additional reagents. More information can be found in the Full Paper by J.‐P. Zhang, Z. Dai, et al. on page 5463. [ABSTRACT FROM AUTHOR]

Review: 148 refs. [ABSTRACT FROM AUTHOR]

A noble‐metal‐free porous coordination polymer is successfully developed as high‐performance sensor for gaseous oxygen. On page 5866, J.‐P. Zhang and co‐workers show that the long‐lifetime phosphorescence of a Cu(I)‐based porous metal azolate framework MAF‐2 is extremely sensitive to molecular oxygen. Moreover, a counter‐diffusion crystal‐growth method is introduced to composite the fragile crystals with silicone rubbers to fabricate mechanically robust and soft membrane sensors. [ABSTRACT FROM AUTHOR]

Cu‐based metal–organic frameworks have attracted much attention for electrocatalytic CO2 reduction, but they are generally instable and difficult to control the product selectivity. We report flexible Cu(I) triazolate frameworks as efficient, stable, and tunable electrocatalysts for CO2 reduction to C2H4/CH4. By changing the size of ligand side groups, the C2H4/CH4 selectivity ratio can be gradually tuned and inversed from 11.8 : 1 to 1 : 2.6, giving C2H4, CH4, and hydrocarbon selectivities up to 51 %, 56 %, and 77 %, respectively. After long‐term electrocatalysis, they can retain the structures/morphologies without formation of Cu‐based inorganic species. Computational simulations showed that the coordination geometry of Cu(I) changed from triangular to tetrahedral to bind the reaction intermediates, and two adjacent Cu(I) cooperated for C−C coupling to form C2H4. Importantly, the ligand side groups controlled the catalyst flexibility by the steric hindrance mechanism, and the C2H4 pathway is more sensitive than the CH4 one. [ABSTRACT FROM AUTHOR]

Cu‐based metal–organic frameworks have attracted much attention for electrocatalytic CO2 reduction, but they are generally instable and difficult to control the product selectivity. We report flexible Cu(I) triazolate frameworks as efficient, stable, and tunable electrocatalysts for CO2 reduction to C2H4/CH4. By changing the size of ligand side groups, the C2H4/CH4 selectivity ratio can be gradually tuned and inversed from 11.8 : 1 to 1 : 2.6, giving C2H4, CH4, and hydrocarbon selectivities up to 51 %, 56 %, and 77 %, respectively. After long‐term electrocatalysis, they can retain the structures/morphologies without formation of Cu‐based inorganic species. Computational simulations showed that the coordination geometry of Cu(I) changed from triangular to tetrahedral to bind the reaction intermediates, and two adjacent Cu(I) cooperated for C−C coupling to form C2H4. Importantly, the ligand side groups controlled the catalyst flexibility by the steric hindrance mechanism, and the C2H4 pathway is more sensitive than the CH4 one. [ABSTRACT FROM AUTHOR]

Single‐cell encapsulation is an emerging technology to endow cells with various functions, of which developing new applications in vivo is in high demand. Currently, metal–organic frameworks (MOFs) that are used as nanometric shells to coat living cells, however, have not realized cell‐selective encapsulation. Here, a biocompatible and selective cell encapsulation strategy based on precursor‐functionalized nucleolin aptamer and in situ MOF mineralization on the aptamer‐identified cancer cell surface are developed. After MOF coating, the encapsulated cancer cells undergo immunogenic cell death, which is found associated with the changed cell stiffness (indicated by Young's modulus). The immunogenic dead cancer cells are used as whole‐cell cancer vaccines (WCCVs), forming the integral WCCV‐in‐shell structure with enhanced immunogenicity ascribing from the surface‐exposed calreticulin to promote dendritic cell recruitment, antigen presentation, and T‐cell activation. The major activation pathways in the immune response are identified including tumor necrosis factor signaling pathway, cytokine–cytokine receptor interaction, and Toll‐like receptor signaling pathway, suggesting the potential adjuvant effect of the MOF shells. After vaccination, WCCV‐in‐shell shows much better tumor immunoprophylaxis than either the imperfectly coated cancer cells or the traditional WCCV. This strategy is promising for the universal and facile development of novel whole‐cell vaccines. [ABSTRACT FROM AUTHOR]

Point-of-care testing (POCT) biosensors are rapidly developing in recent years because of the urgent needs for rapid test and home test. Among various types of POCT biosensors, paper-based biosensors have occupied large market share owing to the advantages of cost-effectiveness, portability and simplicity. To further meet the increasing requirement of POCT in various application scenes, the functionalization of paper is highly demanded. Metal-organic framework (MOF), a multifunctional porous material, is introduced in the design of paper-based biosensors, significantly improving the sensing property and application potential. This review provides a summary of the recent advances and emerging trends of MOF-functionalized paper-based biosensors (MOF@paper), including different types of substrates, fabrication methods, detection mechanisms and applications. On account of the multifunctionality and superior performance of MOF@paper biosensors, this field should possess promising prospect in scientific researches, translational medicine and clinical applications. • Multifunctional MOF endows paper-based biosensors with diverse detection properties. • The substrates and fabrication methods for MOF@paper biosensors are reviewed. • Various detection mechanisms are summarized and discussed. • MOF@paper biosensors are promising in diagnosis, food, environment and other related applications. [ABSTRACT FROM AUTHOR]

Natural enzymes are highly specific biocatalysts that can selectively catalyse specific biological reactions. However, the high preparation cost and easy deactivation of natural enzymes limit their practical applications. In the past ten years, nano-enzymes have been developed rapidly because of their excellent physical and chemical properties, low cost, high stability and easy storage, and can be used as a bridge to natural enzymes. These are a class of enzyme-like nanomaterials, which have some similarities with natural enzymes in terms of their total size, shape and surface charge. They themselves can simulate the bionic catalytic function of enzymes through the catalytic activity of inorganic materials. Metal–organic frameworks (MOFs) and their derivatives are expected to be substitutes for conventional enzymes in enzymatic reactions, and nano-enzymes have shown potential in the field of biomedicine, such as in antimicrobial drugs, biological detection and cancer treatment. In this review, the various types of MOF-derived nano-enzymes and the activities of corresponding simulated enzymes are summarized, and the latest applications of MOF-derived nano-enzymes in biosensing, as antibacterial compounds and in cancer treatment are mainly introduced. In addition, the development prospects of nano-enzymes is introduced in order to provide new ideas for the design and applications of nano-enzymes in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new robust photo-responsive adsorbent Azo-U was designed for controllable CO 2 capture. • The regulation efficiency on CO 2 capacity reaches 25.5% upon ultraviolet and visible light irradiation. • The regulation efficiency can be well-preserved upon alternative light irradiation. • Azo-U possesses good stability under aqueous solutions of different pH values (1.0 to 11.0). Photo-responsive adsorbents (PRAs) have attracted much attention due to their energy efficiency for controllable gas capture. However, the construction of robust PRAs is still full of challenges. In this project, we report the construction of azobenzene-modified UiO-67, namely Azo-U, consisted of hexa-nuclear zirconium clusters and azobenzene derivative ligand Azo-H 2 BPDC. The single crystal X-ray diffraction (SCXRD) analysis demonstrates that Azo-U shows analogous structures to UiO-67 and the specific surface area is up to 1327 m2·g−1 derived from N 2 uptake property at 77 K. The incorporation of Azo-H 2 BPDC imparts Azo-U with reversible photo-responsive properties. Considering its high porosity and photo-responsive properties, Azo-U was evaluated for controllable CO 2 capture and the regulation efficiency can be up to 25.5%. Such a photo-controllable CO 2 capacity of Azo-U is further confirmed by density functional theory (DFT) and Grand Canonical Monte Carlo calculation. Besides, the regulation efficiency can be well-preserved upon alternative ultraviolet and visible light irradiation. Moreover, Azo-U possesses good stability under aqueous solutions of different pH values (1.0 to 11.0). This study might shed light on the design and fabrication of target-specific PRAs to meet the various demands. [ABSTRACT FROM AUTHOR]

Developing advanced nanocatalysts with superior structural and textural characteristics can provide significant potential for CO oxidation. Herein, triple-shelled CuO/CeO2 hollow nanospherical catalysts have been successfully prepared through a metal–organic framework (MOF) engaged strategy, involving two steps: thermal annealing of CeMOF precursors and subsequent deposition–precipitation of CuO. By tuning the loading of CuO species, the composites show a typical volcano-shaped relationship between the composition and the catalytic activity. CuO/CeO2-8% is the most active catalyst with the lowest temperature (130 °C) to achieve complete CO conversion, and it possesses the maximum turnover frequency (TOF) value of 1.72 × 10−3 s−1 at 90 °C. Systematic structural characterization revealed that the remarkably improved catalytic performance can be attributed to a unique porous triple-shelled structure, abundant surface oxygen vacancies, greater Cu+ content, more lattice oxygen and the synergistic effect between two individual components. Furthermore, the superior catalyst also has good cyclic stability. Of significance, this work may open a novel, facile avenue for fabricating desirable multicomponent nanocatalysts from proper MOFs for pollution control and environment protection. [ABSTRACT FROM AUTHOR]

[Display omitted] • The chromogenic paper chip was facilely prepared by one-pot synthesis. • The "all-in-one" strategy fundamentally improves the stability and convenience. • Glucose level can be noninvasively detected with "sample in, result out" manner. • A smartphone App was developed for further improving the accuracy and ease of use. Noninvasive glucose detection for diabetes monitoring, in comparison with the conventional finger-prick test that causes inevitable pain, is on demand. Salivary glucose level that possesses a well-established correlation with blood glucose level can be a promising alternative for noninvasive detection, however, the sensitivity and user-friendliness remained to be improved. Herein, an "all-in-one" paper chip was fabricated by one-pot method for sensitive and user-friendly detection of salivary glucose level. Glucose oxidase (GOx) and the chromogenic reagent, luminol, were both in situ encapsulated in a metal–organic framework, ZIF-67, to form the GOx&luminol@ZIF-67@Paper (G&L@ZIF@Paper). Owing to the specificity of GOx and the peroxidase activity of ZIF-67, the paper chips are highly sensitive and specific for glucose with a linear range from 0.2 to 2 mM, and a limit of detection of 0.12 mM (S/N = 3). Moreover, ascribing to the protection and "all-in-one" structure by ZIF-67, the chip is highly stable that maintains the detection performance after storage at room temperature in air for 4 weeks, and this strategy also facilitates the one-pot detection without multiple steps of sampling and incubation. With the assistance of a smartphone application, the glucose level in saliva can be accurately detected with "sample-in-result-out" manner, and the results were highly consistent with those measured by commercial kit. This paper chip is a promising device for daily glucose monitoring, and the highly-integrated strategy provides an innovative resolution for the construction of colorimetric paper chips. [ABSTRACT FROM AUTHOR]

Abstract: Two‐dimensional (2D) materials and ultrathin nanosheets are advantageous for elevating the catalysis performance and elucidating the catalysis mechanism of heterogeneous catalysts, but they are mostly restricted to inorganic or organic materials based on covalent bonds. We report an electrochemical/chemical exfoliation strategy for synthesizing metal–organic 2D materials based on coordination bonds. A catechol functionalized ligand is used as the redox active pillar to construct a pillared‐layer framework. When the 3D pillared‐layer MOF serves as an electrocatalyst for water oxidation (pH 13), the pillar ligands can be oxidized in situ and removed. The remaining ultrathin (2 nm) nanosheets of the metal–organic layers are an efficient catalyst with overpotentials as low as 211 mV at 10 mA cm−2 and a turnover frequency as high as 30 s−1 at an overpotential of 300 mV. [ABSTRACT FROM AUTHOR]

Abstract: Two‐dimensional (2D) materials and ultrathin nanosheets are advantageous for elevating the catalysis performance and elucidating the catalysis mechanism of heterogeneous catalysts, but they are mostly restricted to inorganic or organic materials based on covalent bonds. We report an electrochemical/chemical exfoliation strategy for synthesizing metal–organic 2D materials based on coordination bonds. A catechol functionalized ligand is used as the redox active pillar to construct a pillared‐layer framework. When the 3D pillared‐layer MOF serves as an electrocatalyst for water oxidation (pH 13), the pillar ligands can be oxidized in situ and removed. The remaining ultrathin (2 nm) nanosheets of the metal–organic layers are an efficient catalyst with overpotentials as low as 211 mV at 10 mA cm−2 and a turnover frequency as high as 30 s−1 at an overpotential of 300 mV. [ABSTRACT FROM AUTHOR]

[Display omitted] • A water-stable luminescent europium MOF (EuUCBA) is fabricated and explored as a sensor for monitoring tetracyclines. • The sensor shows high selectivity and sensitivity, rapid response, low LOD, and good anti-interference toward tetracyclines. • The sensor shows great potential for determination of tetracyclines in wastewater and complex biological samples. Tetracyclines (TCs), a type of antibiotics, are widely used in human therapy and animal husbandry. Public concerns about tetracyclines residues have been raised due to their negative impact on the environment and food, causing bacterias drug resistance and human health concerns. In this work, a luminescent europium MOF (EuUCBA) is constructed via post-synthetic attachment of Eu3+ into a UiO-66 type MOF. The luminescent of EuUCBA exhibits high stability in aqueous media in the pH range of 4–11. Among 36 common veterinary drugs, the synthesized probe is highly selective and sensitive to six tetracyclines with low detection limits of 0.118 μM, 0.228 μM, 0.102 μM, 0.138 μM, 0.206 μM, and 0.078 μM for oxytetracycline (OTC), chlortetracycline (CTC), methylenetetracycline (MTC), minocycline (MOC), tetracycline (TC), and doxycycline (DOXY), respectively. Furthermore, the probe shows good anti-interference ability and fast response. Finally, EuUCBA was successfully to detect DOXY in swine wastewater and pig kidney with good recoveries. This work provides an excellent fluorescent sensor for highly selective and rapid detection of TCs residues in wastewater and complex biological samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • An Eu3+-based sensor has been explored for specific recognizing ST and 5-HI-3-AA. • The detection limit for ST and 5-HI-3-AA is 0.013 and 0.15 µM, respectively. • The sensor can be recycled and reused to monitor ST and 5-HI-3-AA. • The sensor specifically recognizes ST among monoamine neurotransmitters. • This work provides a portable method for visual detection of biomarkers. Monoamine neurotransmitters such as L-epinephrine (EPI), norepinephrine (NE), dopamine (DA), and serotonin (ST) are important biomarkers for neurological diseases. However, specific detection of a single monoamine neurotransmitter is challenging. In this work, a water-stable fluorescent biosensor, Eu3+-doped UiO-66 metal–organic framework (EuUPDC), is constructed for specific recognition of ST and its metabolite, 5-hydroxyindole-3-acetic acid (5-HI-3-AA). The detection limits of EuUPDC for ST and 5-HI-3-AA are 0.013 μM and 0.15 μM, respectively. The LOD value for ST is 10-fold improvement compared to the reported fluorescent sensors. Importantly, the biosensor specifically recognizes ST at very low concentrations in the presence of co-existing monoamine neurotransmitters. Furthermore, the EuUPDC biosensor is successfully applied for the determination of ST and 5-HI-3-AA in human serum and urine with good recoveries. Finally, a EuUPDC -embedded test strip is fabricated and portable smartphone-assisted RGB color values are effectively integrated with a lowest detectable value of 0.6 μM for ST and 6.7 μM for 5-HI-3-AA. The designed biosensor EuUPDC has great potential for the quantitative determination of ST and 5-HI-3-AA, and applicable for early diagnosis of neurological diseases. [ABSTRACT FROM AUTHOR]

A novel dual-emissive Eu3+-loaded metal–organic framework (MOF) is designed and successfully fabricated by introducing 2-hydroxyterephthalic acid (H 2 BDC-OH) and Eu3+ ions into an UiO-66-type MOF material. The obtained MOF, here referred to as EuUCH , exhibits dual emission at 450 and 614 nm, and both emissions are quite stable in aqueous media in the pH range of 4–11. EuUCH is characterized by a high selectivity and sensitivity toward Fe3+ and Al3+, which yield different responsive modes. The two emissions of EuUCH are quenched by Fe3+; by contrast, only the emission at 450 nm is quenched by Al3+ showing a ratiometric fluorescence signal. More importantly, as there is no clear interference between the signals of Fe3+ and Al3+, EuUCH is successfully utilized for the simultaneous detection of Fe3+ and Al3+ in their mixtures. In addition, the simultaneous quantification of Fe3+ and Al3+ is achieved in more complicated swine wastewater with good recoveries. This work provides a water-stable dual-emissive probe and the possibility to achieve the simultaneous quantification of Fe3+ and Al3+ in complicated environment wastewater. [Display omitted] • A highly water-stable dual-emission Eu3+-loaded MOF (EuUCH) has been successfully fabricated. • EuUCH specifically recognizes Fe3+ and Al3+ with two different response signals. • The simultaneous quantification of Fe3+ and Al3+ in their mixture is achieved. • The probe could be practically applied for simultaneous quantification of Fe3+ and Al3+ in environmental wastewater. [ABSTRACT FROM AUTHOR]

Distance-based microfluidic paper-based analytical devices (μ PADs) are simple and user-friendly detection platforms for disease screening, environment monitoring and food safety. However, the current distance-based μ PADs still face major challenges of relatively low sensitivity and accuracy. In this work, we propose a novel chromogenic reaction-free distance-based (CRFD) μ PAD strategy for sensitive and accurate quantitation of microRNAs (miRNAs) via viscosity amplification and surface hydrophobicity modulations. The CRFD μ PAD with sampling, indicator (with red ink), and detection zones is scaled with reference patterns. Target miRNA in sample is pre-amplified with rolling circle amplification (RCA) reaction to specifically enhance its viscosity. The difference of flow between target and control is further enlarged on CRFD μ PADs whose surface hydrophobicity is rationally modulated by in situ metal-organic frameworks (MOFs) modification. Meanwhile, the repeatability and flow shape are significantly improved. For a proof-of-concept demonstration, the miR-221 and miR-222 in liver cells lysis were sensitively detected by naked-eye with limits of detection of 0.33 and 0.37 pM, respectively. A smartphone-based auto-reading system (SAS) was developed to further improve the accuracy and convenience, showing greatly reduced relative standard deviation (RSD) of assay from 12.2% to 1.0%. This facile and extensible strategy is promising for rapid detection in complex biosystem. [Display omitted] • Distance-based μ PADs without chromogenic reaction are used for microRNA detection. • Viscosity is specifically amplified by RCA to generate the flow distance difference. • Sensitivity is improved by in situ MOF modification that modulate the surface. • A smartphone-based system is developed to improve the accuracy and convenience. [ABSTRACT FROM AUTHOR]