Luminescent sensors based on metal-organic frameworks

A multifunctional Tb-MOF constructed with triphenylamine-based hexacarboxylate ligands for highly luminescent sensing toward antibiotics and salicylaldehydes

Antibiotics and salicylaldehydes are major organic pollutants in the environment, and their efficient selection and sensitive detection are of great significance but also challenging. A multifunctional terbium-organic framework (Tb-MOF) with multiple π-conjugated rings and basic sites decorated nanoporous channels was constructed with triphenylamine-based hexacarboxylate ligands. Structure analysis of Tb-MOF revealed that the six carboxyl groups on the skeleton of ligand exhibit considerable degree of distortion and can be regarded as three triangular nodes, which further combined the binuclear [Tb2(COO)6(H2O)4] nodes to form a new (3,3,3,6)-connected 3D net. Importantly, Tb-MOF provided the first example of luminescent MOFs constructed from triphenylamine-based hexacarboxylate ligands with multi-responsive behavior toward antibiotics and salicylaldehydes. Tb-MOF demonstrated excellent performance on the selection and recognition of two antibiotics, metronidazole (MDZ) and dimetridazole (DTZ), with the detection limit (LOD) of 0.60 and 0.95 μM, respectively. More importantly, Tb-MOF can achieve highly sensitive detection of three aldehydes, salicylaldehyde (SA), 5-methylsalicylaldehyde (5-MeSA) and 5-chlorsalicylaldehyde (5-ClSA), with LODs up to 0.58, 0.59 and 0.48 μM, respectively. Regenerated experiments indicated that Tb-MOF can be employed for the efficient detection of MDZ and SA at least five times. Thus, Tb-MOF can be potentially explored as a promising sensor to simultaneously identify antibiotics and salicylaldehydes in chemical detection and biologic environments with ultra-sensitivity, low LODs and extraordinary recycling capacity.

Research progress on electrochemiluminescence nanomaterials and their applications in biosensors - A review

BACKGROUND

Electrochemiluminescence (ECL) is a promising analytical technique that combines electrochemistry with chemiluminescence. The performance of ECL systems depends on luminophores. Nonetheless, conventional luminophores present certain limitations. At first, their ECL efficiencies often fall short of the requirements for accurate detection. Moreover, in complex environments, traditional materials struggle to selectively identify target compounds and are prone to interference. Furthermore, these materials exhibit a deficiency in flexibility and tunability, attributed to their rigid structure and inherent characteristics. Advancing ECL technology necessitates the creation of novel materials that improve efficiency, selectivity, stability, and flexibility.

RESULTS

This review emphasizes the recent advances in ECL nanomaterials and their applications in biosensors. The discussion starts with a comprehensive examination of two main mechanisms of ECL emission: quenching ECL and co-reactant ECL. Various nanomaterials are then discussed, including semiconductor nanomaterials, metal nanoclusters, carbon nanomaterials, nanoscale aggregation-induced emission materials, organic nanomaterials, and composite nanomaterials, with emphasis on their unique ECL properties. Examples illustrate specific applications in disease diagnosis, environmental monitoring, and food safety testing. The review further examines the structural and luminescent characteristics of nanomaterials, which facilitate the advancement of novel ECL detection methodologies. Finally, we examine the existing challenges and propose possible avenues for the future advancement of innovative ECL nanomaterials.

SIGNIFICANCE

ECL nanomaterials possess unique quantum sizes and surface effects. Through the design and selection of appropriate nanomaterials, extremely sensitive, selective, and stable ECL biosensors may be developed for the detection of particular targets, applicable in disease diagnostics, food safety, and environmental monitoring.

Highly Stable Zn(II) Metal-Organic Framework as an "On-Off-On" Fluorescence Sensor toward H2PO4- Anion in the pH-Dynamic System

In a dynamic system, fluorescent probes with dual signals not only efficiently identify target analytes but also resist interference from the system, aiding in further system differentiation. A new three-dimensional (4,6)-connected Zn(II)-based metal-organic framework with the formula {[Zn2(BTDI)(3,5-BBIP)]·2.5H2O·2DMF}n (JXUST-50) was solvothermally used with 5,5'-(benzothiadiazole-4,7-diyl)diisophthalic acid (H4BTDI), which incorporates benzothiadiazole luminescent groups. JXUST-50 displays a fluorescence "turn-on" effect and a blue-shift behavior toward the H2PO4- anion in formamide solution, with a limit of detection of 0.50 μM. Remarkably, in a pH-dynamic system regulated by NaOH/HCl, JXUST-50 demonstrates a fluorescence "on-off-on" effect and a blue-red-blue-shift behavior toward the H2PO4- anion. Furthermore, the fluorescence "turn-on" and blue-shift effect observed between JXUST-50 and H2PO4- may be attributed to host-guest interaction and an absorbance-caused enhancement mechanism.

Respiration Drives Dynamic Metal-Organic Framework for Smart Photoresponse to Volatile Toxic Vapors and Their Photodynamic Sterilization

Using aggregation-induced emission luminous (AIEgens) containing dynamic molecular rotor structures as linkers to construct flexible smart luminescent metal-organic frameworks (MOFs) has become a transformative approach to constructing artificial intelligence color-changing materials. Herein, 4',4″,4'″,4″″-(ethene-1,1,2,2-tetrayl)tetrabiphenyl-4-carboxylic acid (H4TPPE) is selected as a linker, and octahedral Zr6O4(OH)8(H2O)4 cluster are used as secondary building unit (SBU) to construct the first smart luminescent MOF (Zr-TPE-MOF) that can be driven by CH2Cl2 or CH3COOH vapor for respiration. It is worth noting that Zr-TPE-MOF can absorb trace amounts of CH2Cl2 or CH3COOH vapor into the pores through respiration and shows a blue shift of the emission wavelength up to 479 nm and an increase of emission intensity by nearly three times. In addition, the thermochromic behavior of Zr-TPE-MOF is not obvious in the temperature range of 80-350 K, but it has obvious thermofluorochromics behavior in the temperature range of 350-470 K. Zr-TPE-MOF showed highly sensitive and visualized smart photoresponse to the highly toxic Cr2O7 2-, with a detection limit as low as 7.49 µm. Benefiting from the porous framework structure and organic-inorganic hybrid characteristics of Zr-TPE-MOF, it has excellent ROS generation ability and has excellent application prospects in photodynamic sterilization and rapid degradation of colored dyes.

Recent advances in metal-organic frameworks for catalysing organic transformation

Metal-organic frameworks (MOFs) have garnered considerable attention due to their tunable properties, well-defined porosity, and structural versatility, making them effective catalysts for organic transformations. This review explores recent advances in MOF-based catalysis, emphasizing the roles of metal centres and organic linkers, as well as the synergistic effects arising from their combination. Additionally, guest molecule encapsulation and morphology modulation as effective strategies for improving catalytic efficiency are also discussed. Finally, future challenges and opportunities for MOFs as heterogenous catalysts are highlighted.

Nanoarchitectonics of a covalent organic supramolecular cage (COSC) for fluorescent visual detection of macrolides

Macrolides, a major group of antibiotic pollutants, have been widely observed in water and sediments. For onsite identification of macrolides in water environments, we designed and synthesized a quadrangular prism-shaped covalent organic supramolecular cage (COSC) via an aldol-amine condensation. Multiple hydrogen bonding sites were introduced into the building blocks to increase host-guest interactions. Meanwhile, by introducing a stimuli-sensitive module, TPE, the fluorescence of the supramolecule changes upon encapsulation of the clarithromycin guest which was a type of macrolides. The cage structure was fully characterized using NMR and high-resolution ESI mass spectrometry. The fluorescence recognition process and detection limitations of the cage for clarithromycin were investigated using NMR, UV-vis, and fluorescence spectroscopy. This study expands the application of precisely designed covalent supramolecular cages for monitoring antibiotic-based environmental pollutants.

Metal-organic frameworks (MOFs): A review of volatile organic compounds (VOCs) detection

This research presents a systematic review of the application of metal-organic frameworks (MOFs) to detect volatile organic compounds (VOCs). VOCs, compounds with high vapor pressure at ambient temperature and normal pressure, are widely present in a variety of industrial and living environments. VOCs are not only hazardous to the environment but also have a severe impact on human health. Therefore, an excellent research interest is developing efficient and sensitive detection technologies for VOCs. In this article, we first introduce the definition and classification of VOCs and their sources and discuss the environmental and health hazards of VOCs. Then, the discussion focuses on various sensors based on MOFs, including electrochemical sensors, fluorescence sensors, colorimetric sensors, and surface-enhanced Raman spectroscopy (SERS) sensors. In electrochemical detection, MOFs, as sensing materials, exhibit good detection performance due to their ultra-large surface area and highly adjustable pore size structure. In fluorescence detection, MOFs achieve high sensitivity and selective detection of VOCs under their unique optical properties. Colorimetric sensors, on the other hand, achieve the detection of VOCs through color change, which has the advantages of low cost and easy operation. In contrast, SERS sensors utilize the high surface area of MOFs and specific Raman enhancement effect to achieve ultra-high sensitivity detection of VOCs, which is especially suitable for trace analysis. Immediately after that, we describe the research progress of various sensors for VOCs detection and analyze their detection mechanisms and application prospects. Finally, the MOFs-based VOCs detection technology is summarized, and the current challenges and future development directions are pointed out.

A platinum-porphyrin zirconium metal-organic framework as an effective photocatalyst for hydrogen generation

Efficient solar energy storage via light-driven hydrogen (H2) production presents a promising and attractive strategy for addressing the global energy crisis. The integration of platinum (Pt) co-catalyst into metal-organic frameworks (MOFs) to enhance photoinduced charge separation and transfer remains a significant challenge. Herein, a platinum-porphyrin zirconium metal-organic framework (MOF) PCN-223(Pt) is reported, and synthesized using a facile two-solvent strategy. The prepared PCN-223(Pt) is self-sensitized and contains a platinum (Pt) electron-trapping center, which confers excellent visible-light catalytic activity. Under visible-light irradiation, PCN-223(Pt) produced 732 μmol g-1 h-1 of H2, a 7.6-fold increase compared to the isostructural PCN-223, which lacks Pt coordination in its porphyrin rings. This improvement results from the photogenerated electrons' efficient transport to the Pt electron-trapping centers, which improves charge carrier separation. Density functional theory calculations demonstrate the positive role that Pt in PCN-223(Pt) play in optimizing the corresponding hydrogen binding energy. PCN-223(Pt) exhibits excellent recyclability, maintaining its catalytic performance across five cycles without significant degradation. These results offer a new approach for designing MOF-based highly efficient visible-light active catalysts.

Rapid and sensitive detection of malachite green by multifunctional octahedron UiO- 66-NH2/Fe3O4/Ag SERS substrate

Multifunctional nanocomposites have attracted extensive attention in the design of new SERS substrates. In this work, a metal-organic framework (MOF) modified with Ag nanoparticles (Ag NPs) and cysteine functionalized Fe3O4 (UiO-66-NH2/Fe3O4/Ag) was prepared as a SERS substrate (UFAs). The substrate combines the enrichment ability of UiO-66-NH2, the magnetic separation ability of Fe3O4, and the localized surface plasmon resonance (LSPR) effect of Ag NPs to achieve efficient detection of the target analyte. The results of adsorption kinetics showed that the adsorption process of malachite green (MG) was mainly dominated by chemical adsorption. In addition, we further explored the detection mechanism of UFAs for MG. UFAs enriched cation analytes such as MG through π-π stacking and electrostatic interaction and performed SERS detection. The UFA SERS substrate exhibits good detection sensitivity for MG, with a limit of detection (LOD) of 1.35 × 10-10 M (at 1619 cm-1), and the SERS substrate has good uniformity and stability. The SERS substrate was applied to the detection of MG in aquaculture water. The recovery of MG in the sample was 91.2-105%, and the relative standard deviation (RSD) was 3.76-6.06%. This high-performance UFA SERS substrate also has great potential for the detection of food and other environmental pollutants in practical applications.

Water-Stable MIL-MOFs Developed Through a Novel Sacrifice-Protection Strategy Inspired by Butterfly Wings' Scales for Long-Term Turn-On Fluorescence Sensing of H2S

Metal-organic frameworks, which are the desired candidates for biosensing application due to their tunable properties, are significantly hindered by their rapid degradation in aqueous solutions, as well as the loss of their inherent fluorescence. Most studies aim to improve the hydrophobicity of materials by modifying their contact angle, thereby enhancing water stability. However, water droplets poorly adhere to the surface of hydrophobic materials, limiting their application for direct contact and detection in aqueous environments. Drawing inspiration from the sacrificial protection mechanism of butterfly wings used to evade predation and entanglement, a universal approach is successfully developed to protect water-sensitive MIL-MOFs from water molecule attack while preserving good hydrophilicity. Using the organic ligand 2,2'-bipyridine-5,5'-dicarboxylic acid (bpydc) as sacrificial protection scales, the MIL-125-NH2-bpydc demonstrated broad pH structural stability (pH 2-12) and fluorescence stability increased by 10.17 time in aqueous solutions, achieving the highest performance in MILMOFs. The MIL-125-NH2-bpydc is biocompatible enabling it to perform long-term fluorescence imaging in living cells and zebrafish, further detecting hydrogen sulfide (H2S) in the aqueous and biological systems via turn-on fluorescence emission. This study offers a novel and universal sacrifice-protection strategy for the design and development of the luminescent biocompatible MOFs tailored for biosensing applications.

State-of-the-art progress and prospect of metal-organic frameworks and composites for photoelectrochemical amino-drugs sensing

Unregulated discharge of antibiotics in waterbodies has posed a significant threat to the aquatic flora and fauna in post-pandemic times. This alarming situation has ascertained the need for suitable sensors to detect persistent antibiotic residues. In this context, functional hybrid materials centralized on reticular metal-organic frameworks (MOFs)/composites have been a research hot spot for photoelectrochemical host-guest recognition events over the past two decades. The unique amalgamation of the robust framework, ease of synthesis, and tunable photophysical properties complemented with in silico approaches render these materials highly promising for recognition events over other contemporaries. The present review provides a critical analysis of the state-of-the-art advancement of MOFs along with their allied composites toward the detection of targeted amino-drug residues (nitrofurazone, norfloxacin, ciprofloxacin, tetracycline, acetaminophen) within the last quinquennial period (approximately 2019-2024). Detection of the targeted drug residues by electrochemical and fluorometric pathways and their host-guest mechanistic pathways have been precisely described. Additionally, different functionalization methods and luminescence strategies with their structural viewpoint have been concisely summarized. Moreover, we delve into the futuristic possibility of integrating artificial intelligence (AI) and machine learning (ML) for better quantification of antibiotics. Finally, the unmet challenges and future research directions of the current research strategies have been outlined for automatic ML (AutoML) assisted next-generation POCT device fabrication.

New 1,4-naphthalenedicarboxylic acid- and 3,5-bis(benzimidazol-2-yl)pyridine-appended d10-configuration-based coordination polymers as recoverable turn-off luminescent sensors for tetracycline

Coordination polymers (CPs) possessing Zn2+ and Cd2+ display interesting photoluminescent properties, thereby finding utility as luminescent sensors to detect traces of molecular substances. Herein, new Cd(II) and Zn(II)-based coordination polymers (CPs) with formulae [Cd3(L)3(3,5-bipy)6(H2O)3·H2L·5H2O] (1) and [Zn(HL)2(3,5-bipy)2] (2) were synthesized utilizing 1,4-naphthalenedicarboxylic acid (H2L) as the main ligand and 3,5-bis(benzimidazol-2-yl)pyridine (3,5-bipy) as the co-ligand and characterized. These CPs exhibited luminescent properties. Upon exciting their aqueous suspensions at 360 nm, both 1 and 2 exhibited broad emissions at 461 nm and 457 nm, respectively, with 1 displaying more intense emission than 2. Furthermore, employing these CPs as luminescent sensors for sensing antibiotics in aqueous media suggest that both 1 and 2 display selective and sensitive sensing towards tetracycline (TCY). 1 and 2 demonstrated limit of detection (LOD) values of 6.21 × 10-6 M and 1.07 × 10-5 M, respectively, accompanied with Stern-Volmer constants (Ksv) of 2.08 × 104 M-1 and 1.24 × 104 M-1. Additionally, recoveries in the luminescent responses of both 1 and 2 were successfully achieved through titration-back experiments using salicylic acid (SA). The integrated experimental and computational techniques suggest that the decline in emission intensity of CPs in the presence of antibiotics is due to energy/charge transfer and interaction with TCY, inducing minor alterations in the framework. These alterations form a non-fluorescent ground state complex (GSC) that alters the electron communication and decreases the photoluminescent intensity. Also, restoration in the emissive responses of TCY@CP arises due to the SA-assisted release of TCY from TCY@CP, which leads to restoration of the emissive responses.

A Water-Stable Hydrogen-Bonded Organic Framework (HOF) for Selective Sensing of Antibiotics in Aqueous Medium

Although metal organic frameworks (MOFs) and covalent organic frameworks (COFs) have been extensively used as fluorescent-based antibiotic sensors, newly developed hydrogen-bonded organic frameworks (HOFs) are largely unexplored toward this direction. To realize this, the luminescent HOFs must be stable in water as the analytes are mostly found in water-based effluents in environments. In addition, HOFs should be equipped with specific recognition sites in order to direct the discrimination among the antibiotics. Herein, we report a 3D porous HOF, IITKGP-HOF-6, constructed from an aromatic-rich tetratopic carboxylic acid (H4L), which exhibits excellent hydro and prolonged open-air stability (7 and 15 days, respectively). IITKGP-HOF-6 was explored for the highly selective detection of nitrofurans (NFs) family of antibiotics in aqueous medium exhibiting a remarkably low detection limit of 0.75 μM for nitrofurazone (NFZ) through luminescence quenching. Photoinduced electron transfer driven by the presence of low-lying charge-transfer excited state below to theπ π * ${\pi {\pi }^{^{\ast}}}$ and Forster energy transfer between H4L donor and NFZ acceptor are confirmed to be responsible for observed quenching using detailed quantum-chemical studies. This work demonstrates the usage of HOFs as sensory materials toward antibiotics in aqueous medium along with a clear understanding into the sensing mechanism at the molecular level.

Luminescent Metal-Organic Framework with Negative Electrostatic Pores for Highly Selective GDP Sensing

Electrostatic potential (ESP) plays an essential role in studying interactions among molecules. Developing probe materials capable of selectively detecting analytes by aligning their molecular ESP with the electrostatic interaction of the host probe material is critically important for identifying analogous analytes; however, relevant research is extremely lacking. In this work, we synthesized a luminescent metal-organic framework (LMOF, Cd-DBDP) featuring negative electrostatic pore environments achieved by incorporating numerous electronegative oxygen atoms and N-containing aromatic rings from organic linkers. The molecular ESP distributions of Cd-DBDP and RNA-related nucleotides were calculated and employed to predict the sensing results. Fluorescence tests demonstrated that Cd-DBDP represents the first example of an MOF-based sensor for guanosine diphosphate (GDP) sensing, and the experimental observations were highly consistent with the theoretical prediction. The sensing mechanism for GDP was thoroughly studied through Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS), and theoretical calculations. These findings provide valuable insights into understanding the interplay between the molecular ESP distribution condition and the sensing results. This study offers a theoretical guide for future sensory research and provides effective means for the design and synthesis of highly efficient sensing MOFs, lending a solid groundwork for further exploration in this field.

Synthesis of pillar-layered metal-organic frameworks with variable backbones through sequence control

The properties and functions of metal-organic frameworks (MOFs) can be tailored by tuning their structure, including their shape, porosity and topology. However, the design and synthesis of complex structures in a predictable manner remains challenging. Here we report the preparation of a series of isomeric pillar-layered MOFs, and we show that their three-dimensional topology can be controlled by altering the layer stacking. This enables variability on the backbone structure, as well as diverse spatial arrangements of pillars and the partitioning of pore space into several kinds of cages packing in distinct sequences. These sequence-controlled MOFs (SC-MOF-1-6) showcase ultrahigh benzene capture capacities at low-pressure and high volumetric and gravimetric uptake performances in high-pressure methane storage. We provide the construction principles of the SC-MOFs and predict nearly 2,000 possible SC-networks with sophisticated composition sequences at the atomic level by using a Python script.

Synthesis of metal-organic framework-luminescent guest (MOF@LG) composites and their applications in environmental health sensing: A mini review

Metal-organic framework (MOF) materials are three-dimensional structures formed by the combination of metal ions and organic ligands. So far, various typical metal organic framework materials have emerged, such as ZIF-8, MOF-5, UIO-66, etc. These traditional MOF materials have the advantages of simple synthesis, high porosity, and high stability, and have great research potential in the field of fluorescence sensing. However, MOF materials with excellent luminescent properties often involve fine regulation of organic ligands to ensure that fluorescence emission can be achieved between metal ions and organic ligands through energy transfer and photo induced electron transfer. The long synthesis cycle and cumbersome preparation process pose challenges for the research of fluorescent MOF materials. Combining MOF materials with luminescent guests is an effective way to prepare simple fluorescent chemical sensors. These luminescent guests include quantum dots, organic dyes, fluorescent nanoparticles, etc. They have the characteristic of high luminescence quantum yield, but high concentrations often lead to aggregation and collision, which in turn cause emission quenching. MOF materials with excellent porosity and specific surface area can serve as an ideal platform for encapsulating luminescent guests and preventing their aggregation. The preparation of MOF@luminescent guest composite material (MOF@LG) is easy to synthesize, which not only effectively improves the poor fluorescence performance of MOFs themselves, but also preserves the excellent fluorescence performance of luminescent guests. Composite materials often have excellent solid-state luminescence performance, making them a good choice for constructing a simple fluorescence sensing platform.

Trace level detection of Pb2+ ion using organic ligand as fluorescent-on probes in aqueous media

In this study, an optical sensor, JA/(2,6-di((E)-benzylidene)cyclohexan-1-one), was synthesized and characterized using 1H NMR and FT-IR spectroscopy. The sensor exhibited high efficiency and selectivity in detecting Pb2+ ions, even in the presence of potential interfering ions such as Mn2+, Cu2+, Co2+, Cr3+, Ni2+, Ce3+, Hg2+, and Cd2+ in aqueous solutions. The interaction of JA with Pb2+ resulted in a significant enhancement of fluorescence intensity, suggesting the formation of a stable complex. A 2:1 binding ratio between JA and Pb2+ was confirmed through fluorometric analysis, absorption spectra, and theoretical calculations (DFT). The association constant for the complex was calculated to be 3 × 106 M-2. The sensor demonstrated high sensitivity towards Pb2+ with a detection limit of 5 × 10-7 M. Additionally, JA was successfully reused by applying EDTA to release Pb2+ from the sensor. Real sample analysis under optimized conditions of pH, time, and concentration of JA and Pb2+ further validated the practical applicability of the sensor.

Signal Amplification via Nonlinear Femtosecond Laser Filamentation for Trace Metal Ion Detection Using Metal-Organic Framework-Polymer Adsorbents

Signal amplification strategies are essential for enhancing the sensitivity and accuracy of analytical methods. This study introduces an innovative approach that utilizes the nonlinear process of femtosecond laser filamentation as a signal amplifier in combination with metal-organic framework (MOF)-polymer adsorbents. In this method, metal ions adsorbed in the MOF-polymer composite alter the intensity and temporal characteristics of an 800 nm femtosecond laser pulse. These changes significantly impact the spectra produced after filamentation, thus serving as an effective signal amplifier. Using MOF single crystals as metal ion enrichment platforms, we enhance spectral signals and achieve detection limits as low as 0.1 ppb for trace metal ions. The integration of the MOF adsorbent with the extensive spectral modifications induced by femtosecond laser filamentation represents a significant advancement in signal amplification techniques for analytical chemistry and environmental monitoring.

Synthesis and applications of luminescent metal organic frameworks (MOFs) for sensing dipicolinic acid in biological and water samples: a review

The detection of trace quantities of 2,6-dipicolinic acid (DPA) in real-world samples is crucial for early disease diagnosis and routine health monitoring. Metal-organic frameworks (MOFs), recognized for their diverse structural architectures, have emerged as advanced multifunctional hybrid materials. One of the most notable properties of MOFs is their luminescence (L), which can arise from structural ligands, guest molecules, and emissive metal ions. Luminescent MOFs have shown significant promise as platforms for sensor design. This review highlights the application of luminescent MOFs in the detection of DPA in biological and aqueous environments. It provides a comprehensive discussion of the various detection strategies employed in luminescent MOF-based DPA sensors. Additionally, it explores the origins of L in MOFs, their synthesis, and the mechanisms underlying their sensing capabilities. The article also addresses key challenges and limitations in this field, offering practical insights for the development of efficient luminescent MOFs for DPA detection.

Recent Advancements in Electrochemical Sensors Based on MOFs and Their Derivatives

Metal-organic frameworks (MOFs) are composed of metal nodes and organic linkers that can self-assemble into an infinite network. The high porosity and large surface area of MOFs facilitate the effective enrichment and mass transfer of analytes, which can enhance the signal response and improve the sensitivity of electrochemical sensors. Additionally, MOFs and their derivatives possess the properties of unsaturated metal sites and tunable structures, collectively demonstrating their potential for electrochemical sensing. This paper summarizes the preparation methods, structural properties, and applications of MOFs and their derivatives in electrochemical sensing, emphasizing sensors' selectivity and sensitivity from the perspectives of direct and indirect detection. Additionally, it also explores future directions and prospects for MOFs in electrochemical sensing, with the aim of overcoming current limitations through innovative approaches.

Synthesis of highly sensitive and multi-response Eu-MOF, fluorescence sensing properties and anti-counterfeiting applications

A new Europium metal-organic framework (Eu-MOF), namely [Eu(dpa) (H2O)]·0.5(bpy)·4H2O}n (H4dpa = 5-(3,4-dicarboxyphenoxy) isophenic acid, bpy = protonated 4,4'-bipyridine) was synthesized and structurally characterized by elemental analyses, infrared spectroscopy, and X-ray single-crystal diffraction analyses. Eu-MOF shows a three-dimensional network structure based on EuIII ions and (dpa)4- ligands via µ4: η1, η2, η2, η2 coordination mode. Fluorescence analysis shows that Eu-MOF has excellent fluorescence sensing characteristics, which can efficiently and sensitively detect various pollutants in water: the limit of detection (LOD) of ratiometric fluorescence detection of ANI in water was 42.9 nM, which was better than the single-peak detection limit. In addition, the peak detection limits of Eu-MOF for Flu, ORN and NB were 120 nM, 27 nM and 94 nM, respectively. In addition, XPS, LUMO orbital energy level, fluorescence lifetime, ultraviolet absorption and other principles are used to explore the mechanism of fluorescence quenching. Surprisingly, Eu-MOF not only has excellent anti- counterfeiting ability and stability, can be used as anti-counterfeiting material in life, but also has good selectivity to Flu. Eu-MOF has obvious fluorescence quenching effect on Flu on paper under ultraviolet light, which can be used for rapid in situ imaging test paper of pesticide residues.

Construction of luminescent dye@MOF platforms for sensing antibiotics with enhanced selectivity and sensitivity

The fabrication of luminescent dye@MOF composites has received extensive attentions in the development of realistic sensing applications. Herein, based on two anionic In-MOFs with different pore structure (1 and 2), the charge and size dependent ion-exchange of cationic dyes was investigated, and consequently four luminescent dye@MOF composites (DMASM@1/2 and RhB@1/2) were successfully fabricated and importantly can be regarded as ideal platforms for better understanding of the factors affecting the construction of dye@MOF composites, which may closely related to a well match between the intrinsic properties and size/charge of the fluorescent molecules and the porosity, structure character of the MOF hosts. Furthermore, these four dye@MOF composites were utilized for sensing of different kinds of antibiotics, demonstrating enhanced selectivity and sensitivity. DMASM@1/2 demonstrated excellent selectivity and sensitivity for NFT and NFZ antibiotics, while RhB@1/2 exhibited excellent selectivity and sensitivity for MDZ and DTZ antibiotics. Systematic analysis of the detection mechanism revealed that different energy transfer efficiency and interaction between MOF frameworks and different types of guest dyes led to different selectivity and detection mechanisms for antibiotics. Moreover, high selectivity and sensitivity, low LOD and extraordinary recycling capacity of four dye@MOF composites in the detection of antibiotics promote their excellent prospect in the further practical application.

Supramolecular chiroptical sensing of chiral species based on circularly polarized luminescence

Circularly polarized luminescence (CPL) refers to the differentiation of the left-handed and right-handed emissions of chiral systems in the excited state. Serving as an alternative characterization method to circular dichroism (CD), CPL can detect changes in fluorescence in a chiral system, which could be more efficient in recognizing chiral species. Although CPL can be generated by attaching luminophores to a chiral unit through a covalent bond, the non-covalent bonding of fluorescent chromophores with chiral species or helical nanostructures can also induce CPL and their changes. Thus, CPL can be used as an alternative detection technique for sensing chiral species. In this review, we summarize typical recent advances in chirality sensing based on CPL. The determination of the absolute configuration of chiral compounds and encrypted sensing is also discussed. We hope to provide useful and powerful insights into the construction of chemical sensors based on CPL.

Luminescence Thermometry with Eu3+-Doped Y2Mo3O12: Comparison of Performance of Intensity Ratio and Machine Learning Temperature Read-Outs

Accurate temperature measurement is critical across various scientific and industrial applications, necessitating advancements in thermometry techniques. This study explores luminescence thermometry, specifically utilizing machine learning methodologies to enhance temperature sensitivity and accuracy. We investigate the performance of principal component analysis (PCA) on the Eu3+-doped Y2Mo3O12 luminescent probe, contrasting it with the traditional luminescence intensity ratio (LIR) method. By employing PCA to analyze the full emission spectra collected at varying temperatures, we achieve an average accuracy (ΔT) of 0.9 K and a resolution (δT) of 1.0 K, significantly outperforming the LIR method, which yielded an average accuracy of 2.3 K and a resolution of 2.9 K. Our findings demonstrate that while the LIR method offers a maximum sensitivity (Sr) of 5‱ K⁻1 at 472 K, PCA's systematic approach enhances the reliability of temperature measurements, marking a crucial advancement in luminescence thermometry. This innovative approach not only enriches the dataset analysis but also sets a new standard for temperature measurement precision.

Mixed-ligand based water-stable Mn(II)-MOF for quick, sensitive, and reusable IFE-PET-RET facilitated detection of formaldehyde and Cr(VI)-oxoanions in real-field samples like food and industrial water: experimental and theoretical insights

We report the luminescence-based detection of Group-1 carcinogen formaldehyde (FA) and Cr(VI)-oxoanions with a mesoporous Mn(II)-MOF (1), featuring a uninodal 4-c net topology and linear 1D square channels forming a polymeric 2D network. The Mn-MOF i.e., [Mn(phen)(hia)(H2O)]∞ was solvothermally constructed using π-conjugated, chelating phenanthroline (phen) and µ3-η2:η1 binding 5-hydroxyisophthalic acid (hia) ligands. The 2D rod-like crystallites of 1 demonstrated excellent phase purity, high thermal and photostability, and robustness under harsh conditions. The SCXRD and XPS studies established the structural framework and elemental composition, while the Hirshfeld surface analysis and NCI-RDG plot confirmed the presence of π-π stacking and weak interactions in 1. We explored the bright-blue emission of 1 for recyclable and fast-responsive (∼70 s) 'turn-off' detection of FA, with a low limit of detection (LOD) of 8.49 µM. Based on this, a 04-input-03-output molecular logic gate was proposed, which can be useful as a molecular switch for future applications. Furthermore, a unique experimental setup using the MOF film demonstrated ∼57% quenching upon exposure to FA vapor (an indoor VOC). Additionally, 1 exemplified itself as an efficient probe towards Cr(VI)-oxyanions, depicting LODs of 79 and 170 ppb, Stern-Volmer constants (KSV) of 16.13 × 104 and 12.73 × 104 M-1, and response times of ∼48 and ∼40 s for CrO42- and Cr2O72-, respectively. DFT calculations and specific wet-chemical investigations elucidated the FA detection to be triggered by photo-induced electron transfer (PET), while the Cr(VI)-sensing involved a combination of PET, the inner-filter effect (IFE), resonance energy transfer (RET), and electrostatic H-bonding interactions. The FA detection was validated using food samples (fish and meat) and wastewater specimens, achieving excellent recovery rates of ∼92-95%. Furthermore, the MOF's efficacy in recognizing the Cr(VI)-species in complex matrices (coal mine wastewater, sewage, and tap water) was investigated to yield high KSV values (3.10-5.17 × 104 and 2.16-7.03 × 104 M-1 for CrO42- and Cr2O72-), which demonstrated the probe's consistency and reliability.

Applications of Metal-Organic Frameworks (MOFs) in Drug Delivery, Biosensing, and Therapy: A Comprehensive Review

The porous materials known as metal-organic frameworks (MOFs) stand out for their enormous surface area, adaptable pore size and shape, and structural variety. These characteristics make them well-suited for various applications, especially in healthcare. This review thoroughly summarizes recent studies on the use of MOFs in drug delivery, biosensing, and therapeutics. MOFs may encapsulate medications, target certain cells or tissues, and regulate their release over time. Additionally, MOFs have the potential to be used in biosensing applications, allowing for the selective detection of chemical and biological substances. MOFs' optical or electrical characteristics may be modified to make biosensors that track physiological data. MOFs show potential for targeted drug delivery and the regulated release of therapeutic substances in cancer treatment. In addition, they may work as potent antibacterial agents, providing a less dangerous option than traditional antibiotics that increase antibiotic resistance. For practical applications, further research is required as well as more consideration for the problems with toxicity and biocompatibility. In addition to addressing the difficulties and promising possibilities in this area, this study intends to provide insights into the potential of MOFs in healthcare for drug delivery, biosensing, and treatment. Despite several essential reviews in this area, it was necessary to look into the most recent research on drug delivery, biosensing, and therapy as a combined concept.

Luminescent Metal-Organic Framework-Based Fluorescent Sensor Array for Screening and Discrimination of Bisphenols

Extensive applications of bisphenols in industrial products have led to their release into aquatic environments, causing a great threat to human health due to their endocrine-disrupting effects, whereas existing methods are difficult to implement the rapid and high-throughput detection of multiple bisphenols. To circumvent this issue, we constructed a sensor array using two luminescent metal-organic frameworks (LMOFs) (Zr-BUT-12 and Ga-MIL-61) for the rapid discrimination of six bisphenol contaminants (BPA, BPS, BPB, BPF, BPAF, and TBBPA). Wherein, Zr-BUT-12 and Ga-MIL-61 exhibited different fluorescence-emission properties and good luminescent stability. Interestingly, bisphenols with different structures had diverse quenching effects on the fluorescence intensity of Zr-BUT-12 and Ga-MIL-61 via the adsorptive interaction, resulting in unique fluorescent fingerprints. Based on pattern recognition methods, different bisphenols were successfully identified, with the limit of detection in the range of 1.59-16.7 ng/mL for six bisphenols. More importantly, the developed sensor array could be effectively utilized for distinguishing different ratios of mixed bisphenols, which was further applied for bisphenol discrimination in real water samples. Consequently, our finding provides a promising strategy for the simultaneous recognition of multiple bisphenols, which encourages the development of a sensor array for the detection of multiple contaminants in environmental monitoring and food safety.

The design, synthesis and application of metal-organic framework-based fluorescence sensors

Fluorescence-based chemical sensors have garnered significant attention due to their rapid response, high sensitivity, cost-effectiveness and ease of operation. Recently, metal-organic frameworks (MOFs) have been extensively utilized as platforms for constructing fluorescence sensors, owing to their ultra-high porosity, flexible tunability, and excellent luminescent properties. This feature article summarizes the progress made mainly by our research group in recent years in the construction strategies, principles, and types of MOF sensors, as well as their applications in quantitative sensing, qualitative identification analysis, and multimodal/multifunctional analysis. In addition, the challenges and an outlook on the future progression of MOF-based sensors are discussed, highlighting how these studies can contribute to addressing these issues. Hopefully, this feature article can provide some valuable guidance for the construction and application of MOFs in fluorescence sensing, thereby broadening their practical applications.

Luminescent Ln-MOFs for Chemical Sensing Application on Biomolecules

At present, the application of rare-earth organic frameworks (Ln-MOFs) in fluorescence sensing has entered rapid development and shown great potential in various analytical fields, such as environmental analysis, food analysis, drug analysis, and biological and clinical analysis by utilizing their internal porosity, tunable structural size, and energy transfer between rare-earth ions, ligands, and photosensitizer molecules. In addition, because the luminescence properties of rare-earth ions are highly dependent on the structural details of the coordination environment surrounding the rare-earth ions, and although their excitation lifetimes are long, they are usually not burst by oxygen and can provide an effective platform for chemical sensing. In order to further promote the development of fluorescence sensing technology based on Ln-MOFs, we summarize and review in detail the latest progress of the construction of Ln-MOF materials for fluorescence sensing applications and related sensor components, including design strategies, preparation methods, and modification considerations and initially propose the future development prospects and prospects.

Rational construction of luminescent Eu-doped Y-MOF for ratiometric temperature sensing

Introducing lanthanide(iii) ions into a MOF structure is one of the most effective strategies to construct luminescent MOFs with multiple emission centers for fluorescent applications. In this work, a functionalized Eu3+-doped Y-MOF (Eu@SNNU-325) was constructed by using a cation exchange strategy. The photoluminescence result shows that Eu@SNNU-325 exhibits a unique emission spectrum, namely, the absence of the organic ligand peak and the very strong Y3+/Eu3+ characteristic peaks. Interestingly, the smart luminescent Eu@SNNU-325 as a ratiometric thermometer for temperature sensing has good self-calibrated ability and a high maximum relative sensitivity (S m) value (1.2% K-1 at 260 K). This work presents the construction of a smart Eu3+-functionalized Y-MOF thermometer through a cation exchange strategy, providing a good idea for the future development and design of Y-MOF thermometers.

Lanthanide metal-organic frameworks as ratiometric fluorescent probes for real-time monitoring of PFOA photocatalytic degradation process

The assessment of perfluorooctanoic acid (PFOA) photocatalytic degradation usually involves tedious pre-treatment and sophisticated instrumentation, making it impractical to evaluate the degradation process in real-time. Herein, we synthesized a series of lanthanide metal-organic frameworks (Ln-MOFs) with outstanding fluorescent sensing properties and applied them as luminescent probes in the photocatalytic degradation reaction of PFOA for real-time evaluation. As the catalytic reaction proceeds, the fluorescence color changes significantly from green to orange-red due to the different interaction mechanisms between the electron-deficient PFOA and smaller radius F- with the ratiometric fluorescent probe MOF-76 (Tb: Eu = 29:1). The limit of detection (LOD) was calculated to be 0.0127 mM for PFOA and 0.00746 mM for F-. In addition, the conversion rate of the catalytic reaction can be read directly based on the chromaticity value by establishing a three-dimensional relationship graph of G/R value-conversion rate-time (G/R indicates the ratio between green and red luminance values in the image.), allowing for real-time and rapid tracking of the PFOA degradation. The recoveries of PFOA and F- in the actual water samples were 99.3-102.7% (RSD = 2.2-4.4%) and 100.7-105.3% (RSD = 3.9-6.8%), respectively. Both theoretical calculations and experiments reveal that the detection mechanism was attributed to the photoinduced electron transfer and energy transfer between the analytes and the probe. This method simplifies the sample analysis process and avoids the use of bulky instruments, and thus has great potential on the design and development of quantitative time-resolved visualization methods to assess catalytic performance and reveal mechanisms.

Controlled Primary Amine-Enriched SG-Bonded Papain Surface: Synthesis, Characterization, and Extraction of Protonated Dichromate

The single-step synthesis of nitro-derivatized SG using dimethyldichlorosilane in an aprotic solvent dichloromethane at 300 K is efficient and straightforward. Reduction and diazotization effectively functionalize the material for enzyme coupling at the O-carbon of the enzyme's tyrosine. The high extraction efficiency of protonated dichromate ions with a breakthrough capacity of 480 μmol·g-1 is notable. Eco-friendly elution using distilled water achieves a significant enrichment factor of 23.2. Excellent reusability (up to 900 cycles) and stable sorption efficiency (ζ ≥ 0.9) highlight the material's potential for practical applications and future research.

A Thermo-Responsive MOFs for X-Ray Scintillator

Thermo-responsive smart materials have aroused extensive interest due to the particular significance of temperature sensing. Although various photoluminescent materials are explored in thermal detection, it is not applicable enough in X-ray radiation environment where the accuracy and reliability will be influenced. Here, a strategy is proposed by introducing the concept of radio-luminescent functional building units (RBUs) to construct thermo-responsive lanthanide metal-organic frameworks (Ln-MOFs) scintillators for self-calibrating thermometry. The rational designs of RBUs (including organic ligand and Tb3+/Eu3+) with appropriate energy levels lead to high-performance radio-luminescence. Ln-MOFs scintillators exhibit perfect linear response to X-ray, presenting low dose rate detection limit (min ≈156.1 nGyairs-1). Self-calibrating detection based on ratiometric XEL intensities is achieved with good absolute and relative sensitivities of 6.74 and 8.1%K-1, respectively. High relative light yield (max ≈39000 photons MeV-1), imaging spatial resolution (max ≈18 lp mm-1), irradiation stability (intensity ≈100% at 368 K in total dose up to 215 Gyair), and giant color transformation visualization benefit the applications, especially the in situ thermo-responsive X-ray imaging. Such strategy provides a promising way to develop the novel smart photonic materials with excellent scintillator performances.

Multifunctional Lanthanide Metal-Organic Frameworks Are Used for Fluorescence Sensing of Bi3+, HPO42-, Flu, and PNBA and Application

Using a nitrogen-containing tricarboxylic acid ligand (imidazole-1-yl) benzene-2,4,6-tricarboxylic acid (H3ttc) and lanthanide metal elements (Dy, Eu, Nd, and Gd), four lanthanide metal organic frameworks (Ln-MOFs) with the same structure, namely, {[Dy2 (Httc)3]·1.5DMF}n(1), {[Eu2 (Httc)3]·1.5DMF}n(2), {[Nd2 (Httc)3]·1.5DMF}n(3), and {[Gd2 (Httc)3]·1.5DMF}n(4), were synthesized under solvothermal conditions. The characterization analysis showed that the four isomorphic Ln-MOFs were trigonal crystals of the R3̅c space group, with good phase purity and thermal stability. Fluorescence analysis showed that complex 1 can be an excellent fluorescence sensor for Bi3+, HPO42-, and fluridine (Flu), while complex 2 can be an excellent fluorescence sensor for p-nitrobenzoic acid (PNBA). And their sensing mechanisms were discussed in detail. The fluorescent test paper and fluorescent seal were prepared by using the excellent luminescence properties of 1 and 2, and the pesticide on the surface of cherry tomato was detected. The applicability of these MOFs as fluorescence sensors was proved. Therefore, Ln-MOFs are expected to have unpredictable application prospects in the field of environmental detection.

Mixed N,O-donor Directed Blue Emissive Nano-dispersed Mesoporous Mn(II)-MOF: Dual Sensing Probe for Recyclable and Ultrasensitive ppb-Level Recognition of TNP and Cr(VI)-Oxoanions

A new mesoporous Mn(II)-MOF [Mn2(phen)2(nia)2]∞ with 4-c uninodal net topology and reiterating rectangular channels in its cargo-net like extension was synthesized using π-conjugated phenanthroline (phen) and syn-syn bridging 5-nitroisopthalic acid (nia) linkers. The MOF (1) exhibited phase purity, uniform morphology, photo and thermal stability, and robustness; duly triggered by the exceptional framework rigidity via intermolecular H-bonding and interlayer π-π stacking interactions. The bright-blue luminescence of the MOF nano-dispersion was explored for sensitive, specific and ultrafast detection of trinitrophenol (TNP) with extremely low LOD (90.62 nM), high KSV (18.27×104 M-1) and Kq (4×1014 M-1s-1). The vapor-phase TNP sensing was also accomplished. Additionally, 1 served towards discriminatory, aqueous-phase monitoring of Cr(VI)-oxoanions, depicting LODs: 36.08 and 35.70 ppb; KSV: 3.46×104 and 4.87×104 M-1; Kq: 3.26×1013 M-1s-1 and 4.31×1013 M-1s-1; and response time: 32 and 40s for CrO4 2- and Cr2O7 2- respectively. The quenching mechanisms (i. e., RET, PET, IFE, weak interactions, collisional quenching and π⋅⋅⋅π stacking) was explained from several experimental investigations and theoretical DFT calculations. The recyclable sensing events and quantification from complex environmental matrices with admirable recovery rates and high KSV (13.02-22.44×104; ~6.31-10.98×104 and ~6.60-11.42×104 M-1 for TNP, CrO4 2- and Cr2O7 2-) undoubtedly advocated the consistency of the probe.

Water bridges as the trigger in an amino functionalized Zn-MOF for highly selective and sensitive fluorescent sensing of water

Water is a fundamental element for life. The highly selective and sensitive sensing of water is always attractive for mankind in activities such as physiological processes study and extraterrestrial life exploration. Fluorescent MOFs with precise channels and functional groups might specifically recognize water molecules with hydrogen-bond interaction or coordination effects and work as water sensors. As a proof of concept, herein, an amino functionalized Zn-MOF (named as complex 1) with pores that just right for water molecules to form hydrogen bond bridges is revealed for highly selective and sensitive fluorescent sensing of water. The single-crystal X-ray diffraction analysis indicates that the 3D framework of complex 1 is functionalized with free amino groups in the channels. Hydrogen bonds formed in the channel along b-axis as water bridges to connect two adjacent NH2bdc ligands and result in the restriction of intramolecular motions (RIM) which could responsible for the selective turn-on fluorescence response to water. Complex 1 exhibits high sensitive to trace amount of water in organic solvents and could be used for water detection in a wide range water contents. Take advantages of complex 1, portable sensors (complex 1@PMMA) were prepared and used in the highly sensitive water sensing.

Harvesting Multicolor Photoluminescence in Nonaromatic Interpenetrated Metal-Organic Framework Nanocrystals via Pressure-Modulated Carbonyls Aggregation

Interpenetrated metal-organic frameworks (MOFs) with nonaromatic ligands provide a unique platform for adsorption, catalysis, and sensing applications. However, nonemission and the lack of optical property tailoring make it challenging to fabricate smart responsive devices with nonaromatic interpenetrated MOFs based on ligand-centered emission. In this paper, the pressure-induced aggregation effect is introduced in nonaromatic interpenetrated Zn4O(ADC)4(Et3N)6 (IRMOF-0) nanocrystals (NCs), where carbonyl groups aggregation results in O─O distances smaller than the sum of the van der Waals radii (3.04 Å), triggering the photoluminescence turn-on behavior. It is noteworthy that the IRMOF-0 NCs display an ultrabroad emission tunability of 130 nm from deep blue (440 nm) to yellow (570 nm) upon release to ambient conditions at different pressures. The eventual retention of through-space n-π* interactions in different degrees via pressure treatment is primarily responsible for achieving a controllable multicolor emission behavior in initially nonemissive IRMOF-0 NCs. The fabricated multicolor phosphor-converted light-emitting diodes based on the pressure-treated IRMOF-0 NCs exhibit excellent thermal, chromaticity, and fatigue stability. The proposed strategy not only imparts new vitality to nonaromatic interpenetrated MOFs but also offers new perspectives for advancements in the field of multicolor displays and daylight illumination.

Highly Specific Sulfadiazine Detection Using a Two-Dimensional Europium-Organic Coordination Polymer

Sulfadiazine (SFZ) is an inexpensive large-consumption antibiotic used for treat bacterial infections but an excess of residues in food can be harmful. Fast and specific luminescence detection of SFZ is highly challenging because of the interference of structurally similar antibiotics. In this work, we develop a two-dimensional europium-organic coordination polymer with excellent luminescence and water stability for highly specific detection of SFZ in the range of 0-0.2 mM. Structural analysis shows that the high stability of coordination polymer is due to the high coordination number of europium ion and the special chelating coordination structure of ligand. The experiment results revealed that the high selectivity and effectively luminescence quenched behaviour of coordination polymer toward SFZ is caused by highly efficient inner filter effect.

An iron metal-organic framework-based electrochemical sensor for identification of Bisphenol-A in groundwater samples

Bisphenol A (BPA) is an endocrine disruptor that leaches into food and is significantly employed in food and beverage storage, and source water cycles. To ensure an outstanding and sustainable biosphere while safeguarding human health and well-being, BPA detection is essential, necessitating an efficient detection methodology. Here, we describe an easy-to-use, inexpensive, and overly sensitive electrochemical detector that uses Fe-MOF nanotextures for identifying BPA in groundwater. This sensing electrode device combines the excellent guest interaction potential of organic ligands with the substantial surface area of metal. Using various analytical techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and powder X-ray diffraction (XRD), the structural and physicochemical behaviors of the as-synthesized material were evaluated. Electrochemical BPA detection was enabled by a diffusion-controlled oxidation procedure with a comparable number of both protons and electrons. With a 0.1 μM detection limit, the sensor displayed a linear sensitivity of around 0.1 μM and 15 μM. Additionally, the sensors demonstrated an outstanding recovery with actual water samples as well as a repeatable and steady performance over the course of a month exhibiting minimal interference from typical inorganic and organic species. Due to its notable sensitivity, inexpensive cost, robust selectivity, excellent repeatability, and reuse ability, the electroanalytical possibilities of the Fe-MOF-modified GCE suggest that the device can be implemented into real-world applications in its primed condition.

Construction of a novel Eu-MOF material based on different detection mechanisms and its application in sensing pollutants aniline, F- and Hg2

Aniline is an organic pollutant with carcinogenicity and teratogenicity, while F- and Hg2+ are toxic ions that are easily soluble in water. When they are released to the environment, they will pose a threat to human health. Designing a material that can simultaneously detect three types of pollutants is of great significance. In this paper, a novel rare earth metal organic framework material (Eu-MOF) with three-dimensional structure based on 1-methylimidazole-4,5-dicarboxylic acid was synthesized for the first time through solvent thermal method. It has excellent luminescent performance and can be used as a multifunctional fluorescent probe to detect aniline, F-, and Hg2+ based on photoinduced electron transfer, energy competitive absorption, and ion exchange mechanisms, with detection limits of 1.79 × 10-8, 8.13 × 10-8, and 8.83 × 10-7 M, respectively. It is worth noting that Eu-MOF can detect F- and Hg2+ in real water samples, such as lake water and green tea water, with favorable recovery rates.

A three-modal fluorescent sensor harnessing diverse luminescent mechanisms for the purpose of segmented Baijiu identification

The classification and verification of segmented Baijiu hold significant importance as they profoundly influence the blending and overall quality of the Baijiu. Our scholarly investigation yielded a fluorescent sensor with three luminescent modes by integrating Tb3+ and RHB into UiO-66. The interplay between carboxyl-containing compounds and RHB/Tb@TLU-2 orchestrates a harmonious molecular association, where the convergence of carboxyl groups with Tb3+ yields a resonating impact on the antenna effect of BDC-SO3-. Furthermore, the acidity and alkalinity of reactants induced a charge transfer interaction between BDC-NH2 and Zr4+ and led to structural changes in RHB/Tb@TLU-2, resulting in observable fluorescence signal variations across the three emission centers. The sensor array successfully identified eight organic acids, achieving an impressive 97.5 % accuracy in discerning segmented Baijiu samples from four Baijiu pits. This meticulous methodology prioritizes simplicity, swiftness, and effectiveness, paving the path for comprehensive segmented Baijiu analysis in the esteemed realm of Brewing production.

Magnetic properties and magnetocaloric effect of Ln = Dy, Tb carborane-based metal-organic frameworks

We present the synthesis and magneto-thermal properties of carborane-based lanthanide metal-organic frameworks (MOFs) with the formula {[(Ln)3(mCB-L)4(NO3)(DMF)n]·Solv}, where Ln = Dy or Tb, characterized by dc and ac susceptibility, X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and heat capacity measurements. The MOF structure is formed by polymeric 1D chains of Ln ions with three different coordination environments (Ln1, Ln2, Ln3) running along the b-axis, linked by carborane-based linkers thus to provide a 3D structure. Static magnetic measurements reveal that these MOFs behave at low temperature as a system of S* = 1/2 Ising spins, weakly interacting ferromagnetically along the 1D polymeric chain (J*/kB = +0.45 K (+0.5 K) interaction constant estimated for Dy-MOF (Tb-MOF)) and coupled to Ln ions in adjacent chains through dipolar antiferromagnetic interactions. The Dy MOF exhibits slow relaxation of magnetization through a thermally activated process, transitioning to quantum tunneling of the magnetization at low temperatures, while both compounds exhibit field-induced relaxation through a very slow, direct process. The maximum magnetic entropy changes (-ΔSmaxm) for an applied magnetic field change of 2-0 T are 5.71 J kg-1 K-1 and 4.78 J kg-1 K-1, for Dy and Tb MOFs, respectively, while the magnetocaloric effect (MCE) peak for both occurs at T ∼ 1.6 K, approximately double that for the Gd counterpart.

Fluorescent sensor based on bismuth metal-organic frameworks (Bi-MOFs) mimic enzyme for H2O2 detection in real samples and distinction of phenylenediamine isomers

Although peroxidase-like nano-enzymes have been widely utilized in biosensors, nano-enzyme based biosensors are seldom used for both quantitative analysis of H2O2 and differentiation of isomers of organic compounds simultaneously. In this study, a dual-functional mimetic enzyme-based fluorescent sensor was constructed using metal-organic frameworks (Bi-MOFs) with exceptional oxidase activity and fluorescence properties. This mimetic enzyme sensor facilitated quantitative analysis of H2O2 and accurate discrimination of phenylenediamine isomers. The sensor exhibited a wide linear range (0.5-400 μM) and low detection limit (0.16 μM) for the detection of H2O2. Moreover, the sensor can also be used for the discrimination of phenylenediamine isomers, in which the presence of o-phenylenediamine (OPD) leads to the appearance of a new fluorescence emission peak at 555 nm, while the presence of p-phenylenediamine (PPD) significantly quenched its fluorescence due to the internal filtration effect. The proposed strategy exhibited a commendable capability in distinguishing phenylenediamine isomers, thereby paving the way for novel applications of MOFs in the field of environmental science.

Optical Phenomena in Molecule-Based Magnetic Materials

Since the last century, we have witnessed the development of molecular magnetism which deals with magnetic materials based on molecular species, i.e., organic radicals and metal complexes. Among them, the broadest attention was devoted to molecule-based ferro-/ferrimagnets, spin transition materials, including those exploring electron transfer, molecular nanomagnets, such as single-molecule magnets (SMMs), molecular qubits, and stimuli-responsive magnetic materials. Their physical properties open the application horizons in sensors, data storage, spintronics, and quantum computation. It was found that various optical phenomena, such as thermochromism, photoswitching of magnetic and optical characteristics, luminescence, nonlinear optical and chiroptical effects, as well as optical responsivity to external stimuli, can be implemented into molecule-based magnetic materials. Moreover, the fruitful interactions of these optical effects with magnetism in molecule-based materials can provide new physical cross-effects and multifunctionality, enriching the applications in optical, electronic, and magnetic devices. This Review aims to show the scope of optical phenomena generated in molecule-based magnetic materials, including the recent advances in such areas as high-temperature photomagnetism, optical thermometry utilizing SMMs, optical addressability of molecular qubits, magneto-chiral dichroism, and opto-magneto-electric multifunctionality. These findings are discussed in the context of the types of optical phenomena accessible for various classes of molecule-based magnetic materials.

Multifunctional Metal-Organic Frameworks as Catalysts for Tandem Reactions

Owing to well-defined structure as well as easy synthesis and modification, metal-organic frameworks (MOFs) have emerged as promising catalysts for tandem reactions. In this article, we aim to summarize the development of multifunctional MOFs, including mixed metal MOFs, MOFs that are synergistically catalyzed by metal nodes and organic linkers, MOFs loaded with metal nanoparticles, etc, as heterogenous catalysts for tandem reactions over the past five years. This concept briefly discusses on present challenges, future trends, and prospects of multifunctional MOFs catalysts in tandem reactions.

Switchable Anisotropic/Isotropic Photon Transport in a Double-Dipole Metal-Organic Framework via Radical-Controlled Energy Transfer

Directional control of photon transport at micro/nanoscale holds great potential in developing multifunctional optoelectronic devices. Here, the switchable anisotropic/isotropic photon transport is reported in a double-dipole metal-organic framework (MOF) based on radical-controlled energy transfer. Double-dipole MOF microcrystals with transition dipole moments perpendicular to each other have been achieved by the pillared-layer coordination strategy. The energy transfer between the double dipolar chromophores can be modulated by the photogenerated radicals, which permits the in situ switchable output on both polarization (isotropy/anisotropy state) and wavelength information (blue/red-color emission). On this basis, the original MOF microcrystal with isotropic polarization state displays the isotropic photon transport and similar reabsorption losses at various directions, while the radical-affected MOF microcrystal with anisotropic polarization state shows the anisotropic photon transport with distinct reabsorption losses at different directions, finally leading to the in situ switchable anisotropic/isotropic photon transport. These results offer a novel strategy for the development of MOF-based photonic devices with tunable anisotropic performance.

From nano- to macroarchitectures: designing and constructing MOF-derived porous materials for persulfate-based advanced oxidation processes

Persulfate-based advanced oxidation processes (PS-AOPs) have gained significant attention as an effective approach for the elimination of emerging organic contaminants (EOCs) in water treatment. Metal-organic frameworks (MOFs) and their derivatives are regarded as promising catalysts for activating peroxydisulfate (PDS) and peroxymonosulfate (PMS) due to their tunable and diverse structure and composition. By the rational nanoarchitectured design of MOF-derived nanomaterials, the excellent performance and customized functions can be achieved. However, the intrinsic fine powder form and agglomeration ability of MOF-derived nanomaterials have limited their practical engineering application. Recently, a great deal of effort has been put into shaping MOFs into macroscopic objects without sacrificing the performance. This review presents recent advances in the design and synthetic strategies of MOF-derived nano- and macroarchitectures for PS-AOPs to degrade EOCs. Firstly, the strategies of preparing MOF-derived diverse nanoarchitectures including hierarchically porous, hollow, yolk-shell, and multi-shell structures are comprehensively summarized. Subsequently, the approaches of manufacturing MOF-based macroarchitectures are introduced in detail. Moreover, the PS-AOP application and mechanisms of MOF-derived nano- and macromaterials as catalysts to eliminate EOCs are discussed. Finally, the prospects and challenges of MOF-derived materials in PS-AOPs are discussed. This work will hopefully guide the design and development of MOF-derived porous materials in SR-AOPs.

Influence of Humidity on Layer-by-Layer Growth and Structure in Coordination Networks

Metal-organic frameworks (MOFs) are promising materials because of their high designability of pores and functionalities. Especially, MOF thin films and their properties have been investigated toward applications in nanodevices. Typically, MOF thin films are fabricated by using a bottom-up method such as layer-by-layer (LbL) growth in air. Because the water molecules can coordinate and be replaced with organic linkers during synthesis, humidity conditions will be expected to influence the LbL growth processes. In this study, we fabricated MOF thin films composed of Zn2+, tetrakis-(4-carboxyphenyl)-porphyrin (TCPP), and 4,4'-bipyridyl (bpy) at 10 and 40% relative humidity (RH) conditions. Then, we investigated the humidity effects on chemical compositions of TCPP and bpy, periodic structure, orientation, and surface morphology. At high RH, coordination replacement of water with the organic linkers becomes more competitive than that at low RH, resulting in a different TCPP/bpy composition ratio between the two RH conditions. Also, more frequent coordination replacements of water with the organic linkers at high RH led to the formation of phases other than that observed at low RH, loss of growth orientation, and rough surface. The findings clarified the importance of controlling the RH condition during LbL growth to obtain the desired coordination networks.

Spirobifluorene-Based Porous Organic Salts: Their Porous Network Diversification and Construction of Chiral Helical Luminescent Structures

Porous organic salts (POSs) are organic porous materials assembled via charge-assisted hydrogen bonds between strong acids and bases such as sulfonic acids and amines. To diversify the network topology of POSs and extend its functions, this study focused on using 4,4',4'',4'''-(9,9'-spirobi[fluorene]-2,2',7,7'-tetrayl)tetrabenzenesulfonic acid (spiroBPS), which is a tetrasulfonic acid comprising a square planar skeleton. The POS consisting of spiroBPS and triphenylmethylamine (TPMA) (spiroBPS/TPMA) was constructed from the two-fold interpenetration of an orthogonal network with pts topology, which has not been reported in conventional POSs, owing to the shape of the spirobifluorene backbone. Furthermore, combining tris(4-chlorophenyl)methylamine (TPMA-Cl) and tris(4-bromophenyl)methylamine (TPMA-Br), which are bulkier than TPMA owing to the introduction of halogens at the p-position of the phenyl groups with spiroBPS allows us to construct novel POSs (spiroBPS/TPMA-Cl and spiroBPS/TPMA-Br). These POSs were constructed from a chiral helical network with pth topology, which was induced by the steric hindrance between the halogens and the curved fluorene skeleton. Moreover, spiroBPS/TPMA-Cl with pth topology exhibited circularly polarized luminescence (CPL) in the solid state, which has not been reported in hydrogen-bonded organic frameworks (HOFs).

Highly sensitive sensing of DPA by lanthanide metal-organic frameworks and detection of fiber membranes

The detection of 2,6-pyridinecarboxylic acid (DPA), as a biomarker of Bacillus anthracis, has attracted wide attention. In previous reports of DPA detection, fluorescent probes may not have high specificity. Therefore, the rational design and development of fluorescent sensors with excellent performance is of great significance for the detection of DPA. In this study, two novel lanthanide metal-organic frameworks (Ln-MOFs) were synthesized by hydrothermal method using 3-polyfluorobiphenyl-3 ', 4,5 ' -tricarboxylic acid (H2FPTA) as ligand. Studies have shown that Ln-MOFs can detect DPA in real time, with detection limits of 0.54 μM and 0.67 μM, respectively, and have a high recovery rate (95 % -108 %) in fetal bovine serum. As a self-calibration sensor, other substances in the blood can be clearly distinguished by a two-dimensional fluorescence code diagram. After the Ln-MOFs were spun into nanofiber membranes, they responded quickly to DPA. This increases practicability and provides a promising idea for the development of simple and efficient ratio sensors.