Fluorescent Aromatic Tag-Functionalized MOFs for Highly Selective Sensing of Metal Ions and Small Organic Molecules

The Application of Metal-Organic Frameworks in Water Treatment and Their Large-Scale Preparation: A Review

Over the last few decades, there has been a growing discourse surrounding environmental and health issues stemming from drinking water and the discharge of effluents into the environment. The rapid advancement of various sewage treatment methodologies has prompted a thorough exploration of promising materials to capitalize on their benefits. Metal-organic frameworks (MOFs), as porous materials, have garnered considerable attention from researchers in recent years. These materials boast exceptional properties: unparalleled porosity, expansive specific surface areas, unique electronic characteristics including semi-conductivity, and a versatile affinity for organic molecules. These attributes have fueled a spike in research activity. This paper reviews the current MOF-based wastewater removal technologies, including separation, catalysis, and related pollutant monitoring methods, and briefly introduces the basic mechanism of some methods. The scale production problems faced by MOF in water treatment applications are evaluated, and two pioneering methods for MOF mass production are highlighted. In closing, we propose targeted recommendations and future perspectives to navigate the challenges of MOF implementation in water purification, enhancing the efficiency of material synthesis for environmental stewardship.

Current advancements and prospects of enzymatic and non-enzymatic electrochemical glucose sensors

This review discusses the most current developments and future perspectives in enzymatic and non-enzymatic glucose sensors, which have notably evolved over the preceding quadrennial period. Furthermore, a thorough exploration encompassed the sensor's intricate fabrication processes, the diverse range of materials employed, the underlying principles of detection, and an in-depth assessment of the sensors' efficacy in detecting glucose levels within essential bodily fluids such as human blood serums, urine, saliva, and interstitial fluids. It is worth noting that the accurate quantification of glucose concentrations within human blood has been effectively achieved by utilizing classical enzymatic sensors harmoniously integrated with optical and electrochemical transduction mechanisms. Monitoring glucose levels in various mediums has attracted exceptional attention from industrial to academic researchers for diabetes management, food quality control, clinical medicine, and bioprocess inspection. There has been an enormous demand for the creation of novel glucose sensors over the past ten years. Research has primarily concentrated on succeeding biocompatible and enhanced sensing abilities related to the present technologies, offering innovative avenues for more effective glucose sensors. Recent developments in wearable optical and electrochemical sensors with low cost, high stability, point-of-care testing, and online tracking of glucose concentration levels in biological fluids can aid in managing and controlling diabetes globally. New nanomaterials and biomolecules that can be used in electrochemical sensor systems to identify glucose concentration levels are developed thanks to advances in nanoscience and nanotechnology. Both enzymatic and non-enzymatic glucose electrochemical sensors have garnered much interest recently and have made significant strides in detecting glucose levels. In this review, we summarise several categories of non-enzymatic glucose sensor materials, including composites, non-precious transition metals and their metal oxides, hydroxides, precious metals and their alloys, carbon-based materials, conducting polymers, metal-organic framework (MOF)-based electrocatalysts, and wearable device-based glucose sensors deeply.

Metal organic frameworks as promising sensing tools for electrochemical detection of persistent heavy metal ions from water matrices: A concise review

Water bodies are being polluted rapidly by disposal of toxic chemicals with their huge entrance into drinking water supply chain. Among these pollutants, heavy metal ions (HMIs) are the most challenging one due to their non-biodegradability, toxicity, and ability to biologically hoard in ecological systems, thus posing a foremost danger to human health. This can be addressed by robust, sensitive, selective, and reliable sensing of metal ions which can be achieved by Metal organic frameworks (MOF) based electrochemical sensors. In the present era, MOFs have caught greater interest in a variety of applications including sensing of hazardous pollutants such as heavy metal ions. So, in this review article, types, synthesis and working mechanism of MOF based sensors is explained to give general overview with updated literature. First time, detailed study is done for sensing of metal ions such as chromium, mercury, zinc, copper, manganese, palladium, lead, iron, cadmium and lanthanide by MOFs based electrochemical sensors. The use of MOFs as electrochemical sensors has attractive success story along with some challenges of the area. Considering these challenges, we attempted to highlight the milestone achieved and shortcomings along with future prospective of the MOFs for employing it in electrochemical sensing devices for HMIs. Finally, challenges and future prospects have been discussed to promote the development of MOFs-based sensors in future.

Study on Fluorescence Recognition of Fe3+, Cr2O72- and p-Nitrophenol by a Cadmium Complex and Related Mechanism

The effective detection of environmental pollutants is very important to the sustainable development of human health and the environment. A luminescent Cd(II) coordination complex, {[Cd(dbtdb)(1,2,4-H3btc)]·0.5H2O}n (1) (dbtdb = 1-(2,3,5,6-tetramethyl-4-((2-(thiazol-4-yl)-2H-benzo[d]imidazol-3(3aH)-yl)methyl)benzyl)-2,7a-dihydro-2-(thiazol-4-yl)-1H-benzo[d]imidazole, 1,2,4-H3btc = 1,2,4-benzenetricarboxylic acid), was obtained by hydrothermal reactions. Complex 1 has a chain structure decorated with uncoordinated Lewis basic O and S donors and provides good sensing of Fe3+, Cr2O72-, and p-nitrophenol with fluorescence quenching through an energy transfer process. The calculated binding constants were 3.3 × 103 mol-1 for Fe3+, 2.36 × 104 mol-1 for Cr2O72-, and 9.3 × 103 mol-1 for p-nitrophenol, respectively. These results show that 1 is a rare multiresponsive sensory material for efficient detection of Fe3+, Cr2O72-, and p-nitrophenol.

Advances in Metal-Organic Framework (MOFs) based biosensors for diagnosis: An update

Metal-organic frameworks (MOFs) have significant advantages over other candidate classes of chemo-sensory materials owing to their extraordinary structural tunability and characteristics. MOF-based biosensing is a simple, and convenient method for identifying various species. Biomarkers are molecular or cellular processes that link environmental exposure to a health outcome. Biomarkers are important in understanding the links between environmental chemical exposure and the development of chronic diseases, as well as in identifying disease-prone subgroups. Until now, several species, including nanoparticles (NPs) and their nanocomposites, small molecules, and unique complex systems, have been used for the chemical sensing of biomarkers. Following the overview of the field, we discussed the various fabrication methods for MOFs development in this review. We provide a thorough overview of the previous five years of progress to broaden the scope of analytes for future research. Several enzymatic and non-enzymatic sensors are offered, together with a mandatory measuring method that includes detection range and dynamic range. In addition, we reviewed the comparison of enzymatic and non-enzymatic biosensors, inventive edges, and the difficulties that need to be solved. This work might open up new possibilities for material production, sensor development, medical diagnostics, and other sensing fields.

Carbazole-Equipped Metal-Organic Framework for Stability, Photocatalysis, and Fluorescence Detection

The useful yet underutilized backfolded design is invoked here for functionalizing porous solids with the versatile carbazole function. Specifically, we attach carbazole groups as backfolded side arms onto the backbone of a linear dicarboxyl linker molecule. The bulky carbazole side arms point away from the carboxyl links and do not disrupt the Zr-carboxyl framework formation; namely, the resultant MOF solid ZrL1 features the same net as that of the unfunctionalized dicarboxyl linker, also known as the PCN-111 net or UiO-66 net. The ZrL1 structure features only half linker occupancy (about 6 out of the 12 linkers around the Zr₆O₈ cluster being missing) and partially collapses upon activation (acetone exchange and evacuation). Notably, the stability improves after heating in diphenyl oxide at 260 °C (POP-260 treatment; to form ZrL1-260), as indicated by the higher crystallinity and surface area of the activated ZrL1-260 sample. The ZrL1-260 samples achieve 72% yield in photocatalyzing reductive dehalogenation of phenacyl bromide; ZrL1 can detect nitro-aromatic compounds via fluorescence quenching, with selectivity and sensitivity toward 4-nitroaniline, featuring a limit of detection of 96 ppb.

Gas sensing based on metal-organic frameworks: Concepts, functions, and developments

Effective detection of pollutant gases is vital for protection of natural environment and human health. There is an increasing demand for sensing devices that are equipped with high sensitivity, fast response/recovery speed, and remarkable selectivity. Particularly, attention is given to the designability of sensing materials with porous structures. Among diverse kinds of porous materials, metal-organic frameworks (MOFs) exhibit high porosity, high degree of crystallinity and exceptional chemical activity. Their strong host-guest interactions with guest molecules facilitate the application of MOFs in adsorption, catalysis and sensing systems. In particular, the tailorable framework/composition and potential for post-synthetic modification of MOFs endow them with widely promising application in gas sensing devices. In this review, we outlined the fundamental aspects and applications of MOFs for gas sensors, and discussed various techniques of monitoring gases based on MOFs as functional materials. Insights and perspectives for further challenges faced by MOFs are discussed in the end.

Fabrication of Hierarchical Quaternary Architectures of Metal-Organic Frameworks through Programmed Transformation

A new method to construct hierarchical architectures has been developed by programmed transformation of metal-organic frameworks (MOFs). A MOF precursor was fabricated by reaction of Cu(OAC)₂ and 2,5-dihydroxyterephthalic acid (H₄DOBDC), which could perform transformation in pure methanol solvent and the sodium dodecyl benzene sulfonate (SDBS) solution of methanol, respectively. Interestingly, two kinds of immersion solutions could induce the transformation of the MOF precursor into MOF-74, which resulted in different morphologies: nanoneedles for the methanol and nanosheets for the SDBS. Herein, nanosheets-mesorods-microcuboid hierarchical quaternary architectures of MOF have been successfully achieved by sequential immersion of the precursor in two kinds of transformation solutions, which demonstrates well-defined hierarchy from the nanoscale to mesoscale to microscale. A unique hierarchical architecture could be recognized as quaternary structures, taking the MOF unit cell as the primary structure, the nanosheets as the secondary structure, the mesorods as the tertiary structure, and the microcuboid as the quaternary structure. Our study indicated the potential of programmed transformation between MOFs in the construction of hierarchical architectures, offering a new approach to sophisticated materials.

A reusable fluorescence Eu-based coordination polymer for the detection of Zr4+ ions in aqueous media

A fluorescence coordination polymer [Eu(L)1.5(phen)(H2O)] (1, H2L = 9,10-anthracenedicarboxylic acid) was prepared. 1 represents a fluorescence turn-off sensing material for Zr4+ ions with an excellent detection performance.

Four MOFs with isomeric ligands as fluorescent probes for highly selective, sensitive and stable detection of antibiotics in water

Four complexes showed excellent discriminative probes for cefixime (CEF) and tetracycline (TEC) based on their sensitive fluorescence quenching. The PET and IFE effects resulted in high sensitivity and selectivity for the detection of CEF and TEC.

Ligand isomerism fine-tunes structure and stability in zinc complexes of fused pyrazolopyridines

Fused-ring pyrazoles offer a versatile platform for derivitization to give finely tuned and functional ligands in coordination assemblies. Here, we explore the pyrazolo[4,3-b]pyridine (HL1) and pyrazolo[3,4-c]pyridine (HL2) backbones and their N-substituted derivatives, using their coordination chemistry with zinc(II) in the solid state and in solution to examine the steric and electronic effects of varying their substitution pattern. The parent heterocycles HL1 and HL2 both generate robust and permanently porous isomeric MOFs on reaction with zinc and a dicarboxylate co-ligand. The subtle geometric change offered by the position of the backbone pyridyl nitrogen atom leads to substantial changes in the pore size and total pore volume, which is reflected in both their surface areas and CO₂ uptake performance. Both materials are also unusually resilient to atmospheric water vapour by virtue of the strong metal-azolate bonding. The isomeric chelating ligands L3-L6, generated by N-arylation of the parent heterocycles with a 2-pyridyl group, each coordinate to zinc to give either mononuclear or polymeric coordination compounds depending on the involvement of the backbone pyridine nitrogen atom. While crystal packing influences based on the steric preferences of the ligands are dominant in the crystalline phase, fluorescence spectroscopy is used to show that the 2H isomers L4 and L6 show distinct coordination behaviour to the 1H isomers L3 and L5, forming competing [ML] and [ML₂] species in soution. The first stability constant for L6 with zinc(II) is an order of magnitude larger than for the other three ligands, suggesting an improved binding strength based on the electron configuration in this isomer. These results show that careful control of remote substitution on fused pyrazole ligands can lead to substantial improvements in the stability of the resulting complexes, with consequences for the design of stable coordination assemblies containining labile metal ions.

Design and synthesis of three new copper coordination polymers: efficient degradation of an organic dye at alkaline pH

Three new coordination polymers (CPs) based on Cu(II), namely {[Cu₆(H₂L)₄(4,4'-bpy)₆(H₂O)₂]·16H₂O}_n(1), {[Cu(H₃L)(1,4-bib)]·3H₂O}_n(2), and {[Cu₂(H₂L)₂(1,4-bib)₂][Cu(1,4-bib)(H₂O)₂]}_n·4nH₂O(3) (H₅L = 6-(3',4'-dicarboxyphenoxy)-2,3,5-benzene tricarboxylic acid, 4,4'-bpy = 4,4'-bipyridine and 1,4-bib = 1,4-bis(1H-imidazol-1-yl)benzene) were synthesized under hydrothermal conditions and characterized. 1 adopts a three-dimensional structure and can be described with the point symbol {4·5²}₂{4²·5⁴·6⁴·8³·9²}{5·10⁴·12} whereas 2 shows a layered structure. 3 can be perceived as a complex salt of two coordination polymers: the cationic component [Cu(1,4-bib)(H₂O)₂]_n²⁺ (3a) represents a chain polymer and the second anionic moiety [Cu₂(H₂L)₂(1,4-bib)₂]_n^2- (3b) corresponds to a 2D sub-structure. In the presence of H₂O₂, all complexes 1-3 act as efficient photocatalysts for the degradation of the dye methylene blue (MB). The effects of properties such as initial MB concentration, catalyst dosage, pH value, and H₂O₂ concentration on MB degradation were also investigated and analyzed in detail. Compounds 1-3 exhibit excellent structural stability during the catalytic process and can be reused at least three times. The hydroxyl radical (OH˙) and holes (h⁺) were confirmed as the main active species in the degradation process.

A dual-emissive europium-based metal-organic framework for selective and sensitive detection of Fe3+ and Fe2

A dual-emissive optical material as a ratiometric fluorescent probe has been demonstrated to be remarkably superior in precise and quantitative analyses. Herein, a novel dual-emissive fluorescent probe Eu-BDC-OH was designed and successfully synthesized using Eu³⁺ and 2-hydroxyterephthalic acid (H₂BDC-OH) at room temperature. Eu-BDC-OH has a three-dimensional interpenetrating network structure with a large number of exposed hydroxyl functional groups, providing abundant active sites for molecular recognition. In particular, the as-obtained Eu-BDC-OH serves as a unique fluorescent probe, and the double emission peaks of both the ligand and Eu³⁺ are completely quenched by Fe³⁺. However, it is worth noting that the dual emissions of Eu-BDC-OH enable the ratiometric detection of Fe²⁺, which leads to an increase in ligand emission and a decrease in Eu³⁺ emission, accompanied by a distinct red to blue color transition. The relative fluorescence intensity ratio (I_{618 nm}/I_{433 nm}) decreased linearly with increasing Fe²⁺ concentration in the 0-50 μM range with a superior detection limit of 0.32 μM. In this work, a fluorescent probe based on a MOF was developed for the recognition of Fe²⁺ and Fe³⁺, providing a promising strategy for the synthesis of novel dual-emission materials by integrating suitable luminescent ligands with lanthanide metal ions.

A Porous Metal-Organic Framework as an Electrochemical Sensing Platform for Highly Selective Adsorption and Detection of Bisphenols

The design of artificial receptors with a specific recognition function and enhanced selectivity is highly desirable in the electrochemical sensing field, which can be used for detection of environmental pollutants. In this facet, metal-organic frameworks (MOFs) featured adjustable porosities and specific host-guest recognition properties. Especially, the large hydrophobic cavity formed in the porous MOFs may become a potential artificial receptor. We herein designed a new porous MOF [Zn₂(L)(IPA)(H₂O)]·2DMF·2MeOH·3H₂O (Zn-L-IPA) by using a functionalized sulfonylcalix[4]arene (L¹) and isophthalic acid (H₂IPA) (DMF = N,N'-dimethylformamide). The specific pore size and pore shape of Zn-L-IPA made it efficiently selective for absorption of bisphenol A (BPA), bisphenol F (BPF), and bisphenol S (BPS). Therefore, a rapid, highly selective, and ultrasensitive electrochemical sensing platform Zn-L-IPA@GP/GCE was fabricated by using Zn-L-IPA as a host to recognize and absorb bisphenol guests (GP = graphite powder, GCE = glassy carbon electrode). Most strikingly, the extremely low detection limits were up to 3.46 and 0.17 nM for BPA and BPF, respectively, using the Zn-L-IPA@GP/GCE electrode. Furthermore, the "recognition and adsorption" mechanism was uncovered by density functional theory with the B3LYP function. This work offered a prospective strategy for selective absorption and detection of harmful bisphenols with the MOF-based porous material.

Highly sensitive detection of nitrobenzene by a series of fluorescent 2D zinc(ii) metal-organic frameworks with a flexible triangular ligand

Four fluorescent zinc(ii) metal–organic frameworks, namely [Zn(HCIA)(4,4′-bipy)] (1), [Zn₂(CIA)(OH)(1,4-bibz)_1.5]·H₂O (2), [Zn(CIA)(OH) (4,4′-bbpy)] (3), and [Zn₂(HCIA) (4,4′-bimp)]·H₂O (4), were prepared hydrothermally with a flexible triangular ligand (H₃CIA) and a series of linear N-donor ligands (H₃CIA = 5-(2-carboxybenzyloxy) isophthalic acid, 4,4′-bipy = 4,4′-bipydine, 1,4-bibz = 1,4-bis(1-imidazoly)benzene; 4,4′-bbpy = 4,4′-bis (imidazolyl) biphenyl; 4,4′-bimp = 4,4′-bis (imidazole-1-ylethyl) biphenyl). Structural analyses revealed that complex 1 exhibited a 2D brick-like network structure based on the basic bimetallic ring, 2 was also a 2D interspersed structure from the 1D tubular structure, compound 3 possessed a 2D (4,4) network with 4,4′-bbpy occupying the holes, and complex 4 displayed a 2D network from the 1D ladder-like chain. The thermal stabilities and fluorescent properties of these complexes were investigated in the solid state. The fluorescent sensing experiments revealed that all Zn-MOFs could highly sensitively detect nitrobenzene in aqueous solution, which indicated that these materials can be used as fluorescent probes for the detection of nitrobenzene.

Four fluorescent 2D Zn-MOFs based on a flexible triangular ligand and linear N-donor ligands are hydrothermally prepared and used to detect nitrobenzene in aqueous solution with high sensitivity, demonstrating their potential as fluorescent sensors.

Magnetic Switching in Vapochromic Oxalato-Bridged 2D Copper(II)-Pyrazole Compounds for Biogenic Amine Sensing

A new two-dimensional (2D) coordination polymer of the formula {Cu(ox)(4-Hmpz)·1/3H2O}n (1) (ox = oxalate and 4-Hmpz = 4-methyl-1H-pyrazole) has been prepared, and its structure has been determined by single-crystal X-ray diffraction. It consists of corrugated oxalato-bridged copper(II) neutral layers featuring two alternating bridging modes of the oxalate group within each layer, the symmetric bis-bidentate (μ-κ2O1,O2:κ2O2′,O1′) and the asymmetric bis(bidentate/monodentate) (μ4-κO1:κ2O1,O2:κO2′:κ2O2′,O1′) coordination modes. The three crystallographically independent six-coordinate copper(II) ions that occur in 1 have tetragonally elongated surroundings with three oxygen atoms from two oxalate ligands, a methylpyrazole-nitrogen defining the equatorial plane, and two other oxalate-oxygen atoms occupying the axial positions. The monodentate 4-Hmpz ligands alternatively extrude above and below each oxalate-bridged copper(II) layer, and the water molecules of crystallization are located between the layers. Compound 1 exhibits a fast and selective adsorption of methylamine vapors to afford the adsorbate of formula {Cu(ox)(4-Hmpz)·3MeNH2·1/3H2O}n (2), which is accompanied by a concomitant color change from cyan to deep blue. Compound 2 transforms into {Cu(ox)(4-Hmpz)·MeNH2·1/3H2O}n (3) under vacuum for three hours. The cryomagnetic study of 1–3 revealed a unique switching from strong (1) to weak (2 and 3) antiferromagnetic interactions. The external control of the optical and magnetic properties along this series of compounds might make them suitable candidates for switching optical and magnetic devices for chemical sensing.

Thiosemicarbazone modified zeolitic imidazolate framework (TSC-ZIF) for mercury(ii) removal from water

Zeolitic imidazolate frameworks (ZIF-8), and their derivatives, have been drawing increasing attention due to their thermal and chemical stability. The remarkable stability of ZIF-8 in aqueous and high pH environments renders it an ideal candidate for the removal of heavy metals from wastewater. In this study, we present the preparation of novel aldehyde-based zeolitic imidazolate frameworks (Ald-ZIF) through the integration of mixed-linkers: 2-methylimidazole (MIM) and imidazole-4-carbaldehyde (AldIM). The prepared Ald-ZIFs were post-synthetically modified with bisthiosemicarbazide (Bisthio) and thiosemicarbazide (Thio) groups, incorporating thiosemicarbazone (TSC) functionalities to the core of the framework. This modification results in the formation of TSC-functionalized ZIF derivatives (TSC-ZIFs). Thiosemicarbazones are versatile metal chelators, hence, adsorption properties of TSC-ZIFs for the removal of mercury(ii) from water were explored. Removal of mercury(ii) from homoionic aqueous solutions, binary and tertiary systems in competition with lead(ii) and cadmium(ii) under ambient conditions and neutral pH are reported in this study. MIM3.5:Thio1:Zn improved the removal efficiency of mercury(ii) from water, up to 97% in two hours, with an adsorption capacity of 1667 mg g-1. Desorption of mercury(ii) from MIM3.5:Thio1:Zn was achieved under acidic conditions, regenerating MIM3.5:Thio1:Zn for five cycles of mercury(ii) removal. TSC-ZIF derivatives, designed and developed here, represent a new class of dynamically functionalized adsorption material displaying the advantages of simplicity, efficiency, and reusability.

Stimuli -triggered fluoro-switching in metal-organic frameworks: applications and outlook

The design and synthesis of efficient sensor materials with fast-responsive and ultrasensitive detection ability is critical to monitor ecological safety, supervise human health, control industrial wastes, and govern food quality among others. Metal-organic frameworks (MOFs) or coordination polymers (CPs) are a new class of porous crystalline materials that have emerged in several potential applications in last two decades. In particular, applications of MOFs as sensory scaffolds for the detection of hazardous pollutants have attracted researchers due to their fabulous structural characteristics and wide range of pore environment tunability. Among several transducer procedures, the luminescence detection of a particular analyte is immensely desirable as it is easy to handle and cost effective, where visual changes in physicochemical attributes can be comprehended via a quick naked eye detection. The porous nature of MOFs facilitates the pre-concentration of target analytes within the pore structure and provides superior host-guest interaction with good detection limits when compared to conventional materials. To this end, guest-induced fluorescence switching in sensory MOFs with good recyclability and unique detectable fingerprints are of particular importance to benefit futuristic monitoring aptitudes and promises environmental remediation. In this review, we present the latest literature based on the analyte-responsive modulation of fluorescence intensity in MOFs towards the detection of target pollutants and discuss the underlying sensing mechanism, which can assist in developing new useful nano-scale devices and sensors.

Three-dimensional assembly and disassembly of Fe3O4-decorated porous carbon nanocomposite with enhanced transversal relaxation for magnetic resonance sensing of bisphenol A

The design and construction of a novel magnetic resonance sensor (MRS) is presented for bisphenol A (BPA) detection. The MRS has been built based on the core component of magnetic Fe₃O₄ nanoparticles (~ 40 nm), which were uniformly distributed in nanoporous carbon (abbreviated as Fe₃O₄@NPC). The synthesis was derived from the calcination of the metal organic framework (MOF) precursor of Fe-MIL-101 at high temperature. Fe₃O₄@NPC was confirmed with enhanced transversal relaxation with r₂ value of 118.2 mM^-1 s^-1, which was around 1.7 times higher than that of the naked Fe₃O₄ nanoparticle. This enhancement is attributed to the excellent proton transverse relaxation rate of Fe₃O₄@NPC caused by the reduced self-diffusion coefficient of water molecules in the vicinity of Fe₃O₄ nanoparticles in the nanoporous carbon. BPA antibody (Ab) and antigen (Ag)-ovalbumin (OVA) were immobilized onto the Fe₃O₄@NPC to form Ab-Fe₃O₄@NPC and Ag-Fe₃O₄@NPC, respectively. These two composites can cause the three-dimensional assembly of Fe₃O₄@NPC via immunological recognition. The presence of BPA can compete with antigen-OVA to combine with Ab-Fe₃O₄@NPC, thereby breaking the assembly process (disassembly). The difference in the change of the T₂ value before and after adding BPA can thus be used to monitor BPA. The proposed MRS not only revealed a wide linear range of BPA concentration from 0.05 to 50 ng mL^-1 with an extremely low detection limit of 0.012 ng mL^-1 (S/N = 3), but also displayed high selectivity towards matrix interferences. The recoveries of BPA ranged from 95.6 to 108.4% for spiked tea π, and 93.4 to 104.7% for spiked canned oranges samples, respectively, and the RSD (n = 3) was less than 4.4% for 3 successive assays. The versatility of Fe₃O₄@NPC with customized relaxation responses provides the possibility for the adaptation of magnetic resonance platforms for food safety development. The magnetic Fe3O4 nanoparticles are uniformly dispersed in the nanoporous carbon (Fe3O4@NPC), which derived from the calcinating of the metal organic framework (MOF) precursor of Fe-MIL-101. And the magnetic Fe₃O₄@NPCs are adopted for the construction of magnetic resonance sensor (MRS) for bisphenol A (BPA) detection.

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.

A newly-constructed hydrolytically stable Co(ii) coordination polymer showing dual responsive fluorescence sensing of pH and Cu2+

A novel CP (1), showing distinct dual responsive fluorescence sensing of pH in three continuous stages as well as efficient and selective sensing of Cu²⁺.

Two Cd(ii)-based metal–organic frameworks for the highly effective detection of Fe3+ ions and levofloxacin in aqueous media

Two new Cd(ii)-MOFs are hydrothermally synthesized and can be applied as dual-response sensors to identify Fe3+ and levofloxacin (LVX) with high selectivity, sensitivity and excellent reusability.

Conformational isomerism involving the carboxylate groups of a linker in metal organic frameworks and its distinctive influence on the detection of ketones

Selective sensing of various ketones by Zn(ii) based conformational MOF isomers.

A luminescent Cd(ii) coordination polymer as a multi-responsive fluorescent sensor for Zn2+, Fe3+ and Cr2O72− in water with fluorescence enhancement or quenching

A luminescent Cd(ii) coordination polymer can act as a multi-responsive sensor for efficiently detecting Zn²⁺, Fe³⁺ and Cr₂O₇²⁻ ions.

Two-dimensional metal organic frameworks for biomedical applications

Two-dimensional (2D) metal organic frameworks (MOFs), are an emerging class of layered nanomaterials with well-defined structure and modular composition. The unique pore structure, high flexibility, tunability, and ability to introduce desired functionality within the structural framework, have led to potential use of MOFs in biomedical applications. This article critically reviews the application of 2D MOFs for therapeutic delivery, tissue engineering, bioimaging, and biosensing. Further, discussion on the challenges and strategies in next generation of 2D MOFs are also included. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Recent Advances in Transition Metal Carbide Electrocatalysts for Oxygen Evolution Reaction

The electrolysis of water is considered to be a primary method for the mass production of hydrogen on a large scale, as a substitute for unsustainable fossil fuels in the future. However, it is highly restricted by the sluggish kinetics of the four-electron process of the oxygen evolution reaction (OER). Therefore, there is quite an urgent need to develop efficient, abundant, and economical electrocatalysts. Transition metal carbides (TMCs) have recently been recognized as promising electrocatalysts for OER due to their excellent activity, conductivity, and stability. In this review, widely-accepted evaluation parameters and measurement criteria for different electrocatalysts are discussed. Moreover, five sorts of TMC electrocatalysts—including NiC, tungsten carbide (WC), Fe3C, MoC, and MXene—as well as their hybrids, are researched in terms of their morphology and compounds. Additionally, the synthetic methods are summarized. Based on the existing materials, strategies for improving the catalytic ability and new designs of electrocatalysts are put forward. Finally, the future development of TMC materials is discussed both experimentally and theoretically, and feasible modification approaches and prospects of a reliable mechanism are referred to, which would be instructive for designing other effective noble-free electrocatalysts for OER.

Anthracene-Tagged UiO-67-MOF as Highly Selective Aqueous Sensor for Nanoscale Detection of Arginine Amino Acid

In the present paper, new functionalized UiO-67 metal-organic frameworks (MOF) which contain aromatic tagged groups such as phenyl, naphthyl, and anthracene have been synthesized, characterized, and used for sensing water-soluble amino acids. The results show that anthracene-tagged UiO-67-MOF is shown to act as a highly efficient and selective aqueous sensor for arginine over other water-soluble amino acids in nanoscale. Upon adding an increasing amount of arginine, PL bands of the anth-UiO-67 MOF quenched completely, while there is no perturbation in the PL bands for other amino acid observed. This MOF allows a selective ratiometric detection of arginine without any interference from other amino acids.