Turn-on and Ratiometric Luminescent Sensing of Hydrogen Sulfide Based on Metal-Organic Frameworks

Bifunctional Tb(III)-modified Ce-MOF nanoprobe for colorimetric and fluorescence sensing of α-glucosidase activity

α-Glucosidase, which directly involves in the metabolism of starch and glycogen and causes an increase in blood sugar level, is the major target enzyme for the precaution and therapy of type II diabetes. Based on the previous work, we adopted a post-synthetic modification method to encapsulate Tb3+ into Ce-MOF nanozyme which owned mixed valence states. Tb@Ce-MOF displayed induced luminescence characteristic and exceptional oxidase-like activity that could oxidize colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue ox-TMB. α-Glucosidase can hydrolyze the substrate l-ascorbic acid-2-O-α-d-glucopyranosyl (AAG) to generate ascorbic acid (AA), which could increase the Ce3+/Ce4+ redox valence mode in Tb@Ce-MOF, leading to the inhibition of the allochroic reaction of TMB and the decreased absorption of ox-TMB at 652 nm. The energy transfer (EnT) process from Ce3+ to Tb3+ will enhance due to the increased Ce3+/Ce4+ mode in Tb@Ce-MOF, which will result in an enhanced fluorescence signal of Tb@Ce-MOF at 550 nm. But the addition of inhibitor acarbose will inhibit the above process. We have constructed a dual-mode detection platform of α-glucosidase and its inhibitor via colorimetric and fluorometric method. The linear range of α-glucosidase were 0.01-0.5 U/mL (colorimetric mode) and 0.8-1.5 U/mL (fluorometric mode), respectively, with a detection limit as low as 0.0018 U/mL. Furthermore, our approach was also successfully employed to the analysis of α-glucosidase in serum samples.

A Piezoelectric Nanogenerator-Driven Dual-Mode Platform for Visualization and Impedance Sensing

Traditional visual biosensing platforms rely on color to display detection results, which can be influenced by individual visual abilities, equipment, parameters, and lighting conditions during photo capture. This limitation significantly impedes the advancement of next-generation portable electrochemical biosensors. Therefore, we propose a visual biosensing device that utilizes distance as an indicator, enabling the facile determination of the length of discoloration, which is inversely proportional to the concentration of the target analyte. The separation of the Signal Generation (SG) and Signal Output (SO) regions effectively mitigates potential interference from the sample color. Additionally, the SG region can be disassembled to facilitate electrochemical impedance spectroscopy (EIS) detection in laboratory settings, enabling dual-mode detection. Meanwhile, the utilization of piezoelectric nanogenerators (PENG) empowers the entire point-of-care testing (POCT) sensing device, effectively addressing the issue of a limited battery life. The biosensing device exhibited a satisfactory linear range (EIS mode, 5 pg/L to 5 mg/L; visual mode, 0.5 ng/L to 5 mg/L) and a low limit of detection (EIS mode, 2.3 pg/L; visual mode, 0.14 ng/L) with S/N = 3 for ochratoxin A (OTA) under optimized conditions. The self-powered and cost-effective dual-mode biosensing platform developed for OTA detection offers clear and easily interpretable results, demonstrating a high accuracy in laboratory settings.

MOF-Based Platform for Kidney Diseases: Advances, Challenges, and Prospects

Kidney diseases are important diseases that affect human health worldwide. According to the 2020 World Health Organization (WHO) report, kidney diseases have become the top 10 causes of death. Strengthening the prevention, primary diagnosis, and action of kidney-related diseases is of great significance in maintaining human health and improving the quality of life. It is increasingly challenging to address clinical needs with the present technologies for diagnosing and treating renal illness. Fortunately, metal-organic frameworks (MOFs) have shown great promise in the diagnosis and treatment of kidney diseases. This review summarizes the research progress of MOFs in the diagnosis and treatment of renal disease in recent years. Firstly, we introduce the basic structure and properties of MOFs. Secondly, we focus on the utilization of MOFs in the diagnosis and treatment of kidney diseases. In the diagnosis of kidney disease, MOFs are usually designed as biosensors to detect biomarkers related to kidney disease. In the treatment of kidney disease, MOFs can not only be used as an effective adsorbent for uremic toxins during hemodialysis but also as a precise treatment of intelligent drug delivery carriers. They can also be combined with nano-chelation technology to solve the problem of the imbalance of trace elements in kidney disease. Finally, we describe the current challenges and prospects of MOFs in the diagnosis and treatment of kidney diseases.

Multiple-Emitting Luminescent Metal-Organic Framework as an Array-on-a-MOF for Rapid Screening and Discrimination of Nitroaromatics

Fluorescence array technologies have attracted great interest in the sensing field because of their high sensitivity, low cost, and capability of multitarget detection. However, traditional array sensing relies on multiple independent sensors and thus often requires time-consuming and laborious measurement processes. Herein, we introduce a novel fluorescence array strategy of the array-on-a-metal-organic framework (MOF), which integrates multiple array elements into a single MOF matrix to achieve facile sensing and discrimination of multiple target analytes. As a proof-of-concept system, we constructed a luminescent MOF containing three different emitting channels, including a lanthanide ion (europium/Eu3+, red emission), a fluorescent dye (7-hydroxycoumarin-4-acetic acid/HCAA, blue emission), and the MOF itself (UiO-66-type MOF, blue-violet emission). Five structurally similar nitroaromatic compounds (NACs) were chosen as the targets. All three channels of the array-on-a-MOF displayed rapid and stable fluorescence quenching responses to NACs (response equilibrium achieved within 30 s). Different responses were generated for each channel against each NAC due to the various quenching mechanisms, including photoinduced electron transfer, energy competition, and the inner filter effect. Using linear discriminant analysis, the array-on-a-MOF successfully distinguished the five NACs and their mixtures at varying concentrations and demonstrated good sensitivity to quantify individual NACs (detect limit below the advisory concentration in drinking water). Moreover, the array also showed feasibility in the sensing and discrimination of multiple NACs in real water samples. The proposed "array-on-a-MOF" strategy simplifies multitarget discrimination procedures and holds great promise for various sensing applications.

Efficient removal of microcystin-LR from contaminated water using water-stable MIL-100(Fe) synthesized under HF-free conditions

Cyanobacterial algal hepatotoxins, called microcystins (MCs), are a global health concern, necessitating research on effective removal methods from contaminated water bodies. In this study, we synthesized non-fluorine MIL-100(Fe) using an environmentally friendly room-temperature method and utilized it as an adsorbent to effectively remove microcystin-LR (MC-LR), which is the most toxic MC congener. MIL-100(Fe) was thoroughly characterized, and its adsorption process was investigated under various conditions. Results revealed rapid MC-LR adsorption, achieving 93% removal in just 5 min, with the pseudo-second-order kinetic model indicating chemisorption as the primary mechanism. The Langmuir isotherm model demonstrated a monolayer sorption capacity of 232.6 µg g-1 at room temperature, showing favorable adsorption. Furthermore, the adsorption capacity increased from 183 µg g-1 at 20 °C to 311 µg g-1 at 40 °C, indicating an endothermic process. Thermodynamic parameters supported MC-LR adsorption's spontaneous and feasible nature onto MIL-100(Fe). This study highlights MIL-100(Fe) as a promising method for effectively removing harmful biological pollutants, such as MC-LR, from contaminated water bodies in an environmentally friendly manner.

Transformational Modulation of Fluorescence to Room Temperature Phosphorescence in Metal-Organic Frameworks with Flexible C-S-C Bonds

Photoluminescent metal-organic frameworks (MOFs) have been a subject of considerable interest for many years. However, the regulation of excited states of MOFs at the single crystal level remains restricted due to a lack of control methods. The singlet-triplet emissive property can be significantly influenced by crystal conformational distortions. This review introduces an intelligent responsive MOF material, denoted as LIFM-SHL-3a, characterized by flexible C-S-C bonds. LIFM-SHL-3a integrates elastic structural dynamics with fluorescence and room temperature phosphorescence (RTP) modulation under heating conditions. The deformable carbon-sulfur bond essentially propels the distortion of molecular conformation and alters the stacking mode, as illustrated by single-crystal-to-single-crystal transformation detection. The deformation of flexible C-S-C bonds leads to different noncovalent interactions in the crystal system, thereby achieving modulation of the fluorescence (F) and RTP bands. In the final state structure, the ratio of fluorescence is 66.7%, and the ratio of RTP is 32.6%. This stands as a successful demonstration of modulating F/RTP within the dynamic MOF, unlocking potential applications in optical sensing and beyond. Especially, a PL thermometer with a relative sensitivity of 0.096-0.104%·K-1 in the range of 300-380 K and a H2S probe with a remarkably low LOD of 125.80 nM can be obtained using this responsive MOF material of LIFM-SHL-3a.

Thiadiazole-Functionalized Th/Zr-UiO-66 for Efficient C2H2/CO2 Separation

Adsorptive separation technology provides an effective approach for separating gases with similar physicochemical properties, such as the purification of acetylene (C2H2) from carbon dioxide (CO2). The high designability and tunability of metal-organic framework (MOF) adsorbents make them ideal design platforms for this challenging separation. Herein, we employ an isoreticular functionalization strategy to fine-tune the pore environment of Zr- and Th-based UiO-66 by the immobilization of the benzothiadiazole group via bottom-up synthesis. The functionalized UPC-120 exhibits an enhanced C2H2/CO2 separation performance, which is confirmed by adsorption isotherms, dynamic breakthrough curves, and theoretical simulations. The synergy of ligand functionalization and metal ion fine-tuning guided by isoreticular chemistry provides a new perspective for the design and development of adsorbents for challenging gas separation processes.

Evaluating the Role of Functional Groups in the Selective Capture of Ag(I) onto UiO-66-Type Metal-Organic Frameworks

UiO-66-type metal-organic frameworks have been considered as promising adsorbents for capturing Ag(I) from wastewater. However, uncertainties persist regarding the specific absorptivity of individual functional groups to the UiO-66 framework structure. In this study, UiO-66-type metal-organic frameworks (UiO-66-X), featuring diverse functional groups (X = -(OH)2, -(COOH)2, -NO2, -NH2, -SO3H, -(SH)2), were synthesized in situ for Ag(I) capture. The findings revealed that functionalization significantly enhanced the adsorption capacity of Ag(I). Notably, quantitative analysis showed that 1 mol of -SH functional group onto the UiO-66 framework structure can adsorb 0.73 mol of Ag(I) ions, surpassing those of -COOH, -OH, -NH2, -SO3H, and -NO2 by 2.4-, 3.5-, 3.8-, 9.1-, and 24.3-fold, respectively. This represents the first assessment of the adsorption capacity of functionalized UiO-66 for Ag(I) based on each effective functional group, addressing limitations in traditional unit mass calculations. Further, the adsorption mechanism of UiO-66-X for selectively capturing Ag(I) was elucidated through experimental and theoretical analyses. Additionally, selectivity and practical applications confirm that UiO-66-(SH)2 exhibits strong anti-interference ability, whether in natural water bodies with complex compositions or in industrial wastewater under harsh conditions. We anticipate that this study will enhance our understanding of structure-performance dependencies of multivariate MOFs for designing novel adsorbents for Ag(I) capture.

The construction of dual-emissive ratiometric fluorescent probes based on fluorescent nanoparticles for the detection of metal ions and small molecules

With the rapid development of fluorescent nanoparticles (FNPs), such as CDs, QDs, and MOFs, the construction of FNP-based probes has played a key role in improving chemical sensors. Ratiometric fluorescent probes exhibit distinct advantages, such as resistance to environmental interference and achieving visualization. Thus, FNP-based dual-emission ratiometric fluorescent probes (DRFPs) have rapidly developed in the field of metal ion and small molecule detection in the past few years. In this review, firstly we introduce the fluorescence sensing mechanisms; then, we focus on the strategies for the fabrication of DRFPs, including hybrid FNPs, single FNPs with intrinsic dual emission and target-induced new emission, and DRFPs based on auxiliary nanoparticles. In the section on hybrid FNPs, methods to assemble two types of FNPs, such as chemical bonding, electrostatic interaction, core satellite or core-shell structures, coordination, and encapsulation, are introduced. In the section on single FNPs with intrinsic dual emission, methods for the design of dual-emission CDs, QDs, and MOFs are discussed. Regarding target-induced new emission, sensitization, coordination, hydrogen bonding, and chemical reaction induced new emissions are discussed. Furthermore, in the section on DRFPs based on auxiliary nanoparticles, auxiliary nanomaterials with the inner filter effect and enzyme mimicking activity are discussed. Finally, the existing challenges and an outlook on the future of DRFP are presented. We sincerely hope that this review will contribute to the quick understanding and exploration of DRFPs by researchers.

Chemical Strategies Toward Prodrugs and Fluorescent Probes for Gasotransmitters

Three gaseous molecules are widely accepted as important gasotransmitters in mammalian cells, namely NO, CO and H2S. Due to the pharmacological effects observed in preclinical studies, these three gasotransmitters represent promising drug candidates for clinical translation. Fluorescent probes of the gasotransmitters are also in high demand; however, the mechanisms of actions or the roles played by gasotransmitters under both physiological and pathological conditions remain to be answered. In order to bring these challenges to the attention of both chemists and biologists working in this field, we herein summarize the chemical strategies used for the design of both probes and prodrugs of these three gasotransmitters.

A new dual-ligand DUT-52-type metal-organic framework for ratiometric luminescence detection of aqueous-phase Cu2+ and Cr2O72

Metal-organic frameworks (MOFs) are a unique class of multifunctional hybrid crystals that have been successfully utilized in diverse ranges of applications. However, since MOFs are prone to aqueous degradation, the development of stable luminescent MOF platforms in aqueous media is still a huge challenge. Here, a novel dual-ligand Eu³⁺/DUT-52-COOH composite is prepared based on the luminescent DUT-52 prototype structure via a dual-ligand strategy and a post-synthetic modification (PSM) method. The functionalized Eu³⁺/DUT-52-COOH material exhibits dual emission and good photothermal stability in aqueous media. Thus, Eu³⁺/DUT-52-COOH is developed as a ratiometric luminescent sensor to achieve highly selective and sensitive detection of Cu²⁺ and Cr₂O₇^2- in aqueous solutions and has a low detection limit of 3.43 μM and 25.7 nM, respectively. This work is one of the few cases of detecting Cu²⁺ and Cr₂O₇^2- in aqueous media based on a DUT-52, and the detection signals can be observed by the bare eye without using sophisticated analytical instruments. The possible sensing mechanism is discussed in detail. The results obtained in this project may provide broad prospects for developing smart sensing systems to accomplish highly efficient, easily operable and quantitative intelligent recognition of Cu²⁺ and Cr₂O₇^2-.

Synthesis, characterization, and electrocatalytic behaviour of hydrothermally grown nanostructured La2 O3 and La2 O3 /K-complex

Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium-potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2-4-N,N-dimethylaminobenzoate-κO)(μ2-4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La2 O3 nanomaterials to obtain a nanohybrid La2 O3 /K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and 1 H and 13 C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La2 O3 /K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La2 O3 /K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour.

Smartphone-assisted ratiometric sensing platform for on-site tetracycline determination based on europium functionalized luminescent Zr-MOF

Accurate on-site analysis of tetracycline (TC) is of great research value for ensuring food safety and estimating environmental pollution. Herein, a smartphone-based fluorescent platform for TC detectionhas been developed based on a europium functionalized metal-organic framework (Zr-MOF/Cit-Eu). Based on the inner filter and antenna effect between Zr-MOF/Cit-Eu and TC, the probe exhibited a ratiometric fluorescent response toward TC, resulting in an emission color change from blue to red. Excellent sensing performance was achieved with a detection limit of 3.9 nM, consistent with the linear operation spanning nearly four orders of magnitude. Subsequently, visual test strips based on Zr-MOF/Cit-Eu were prepared, possessing the potential for accurate testing of TC via RGB signals. Finally, the proposed platform was well applied in actual samples with satisfied recoveries (92.27 to 110.22%). This MOF-based on-site fluorescent platform holds great potential on constructing intelligent platform for visual and quantitative detection of organic contaminants.

Stable Lanthanide-Organic Frameworks: Crystal Structure, Photoluminescence, and Chemical Sensing of Vanillylmandelic Acid as a Biomarker of Pheochromocytoma

Several isostructural lanthanide metal-organic frameworks, viz. [Ln(DCHB)_1.5phen]_n (Ln-MOFs, where Ln = Eu for 1, Tb for 2, Sm for 3 and Dy for 4), are successfully synthesized through the hydrothermal reactions of 4'-di(4-carboxylphenoxy)hydroxyl-2, 2'-bipyridyl (H₂DCHB) and lanthanide nitrates as well as chelator 1,10-phenantroline (phen). These structures are characterized by single-crystal X-ray diffraction, and the representative Ln-MOF 1 is a fivefold interpenetrated framework with the uncoordinated Lewis base N sites form DCHB^2- ligands. The photoluminescence research studies reveal that Ln-MOFs 1-4 exhibit characteristic fluorescent emissions from ligand-induced lanthanide Ln(III) ions, while the single-component emission spectra of Ln-MOF 4 are all located in a white region under different excitations. The absence of coordinated water and the interpenetration property of the structures are conducive to the structure rigidity, and the results display that Ln-MOF 1 has high thermal/chemical stabilities in common solvents and a wide pH range as well as the boiling water. Notably, luminescent sensing studies reveal that Ln-MOF 1 with prominent fluorescence properties can perform in highly sensitive and selective sensing of vanillylmandelic acid (VMA) in aqueous systems (K_SV = 562.8 L·mol^-1; LOD = 4.6 × 10^-4 M), which can potentially establish a detection platform for the diagnosis of pheochromocytoma via multiquenching mechanisms. Moreover, the 1@MMMs sensing membranes comprised of Ln-MOF 1 and a poly(vinylidene fluoride) (PVDF) polymer can also be facilely developed for VMA detection in aqueous media, suggesting the enhanced convenience and efficiency of practical sensing applications.

Numerical Recognition System and Ultrasensitive Fluorescence Sensing Platform for Al3+ and UO22+ Based on Ln (III)-Functionalized MOF-808 via Thiodiglycolic Acid Intermediates

Continuous accumulation of Al³⁺ in the human body and unintended leakage of UO₂²⁺ have posed a great threat to human health and the global environment; thus searching an efficient probe for the detection of Al³⁺ and UO₂²⁺ is of great importance. Herein, we designed and synthesized two hydrolytically stable Eu³⁺- and Tb³⁺-functionalized MOF materials Eu@MOF-808-TDA and Tb@MOF-808-TDA via thiodiglycolic acid (TDA) intermediates by the postsynthetic modification method. Among them, Tb@MOF-808-TDA was applied to construct numerical recognition systems of multiples of three and four by the combination of fluorescent signals, hierarchical cluster analysis, and logical gates. In addition, Tb@MOF-808-TDA exhibits good selectivity and sensitivity for the detection of Al³⁺ and UO₂²⁺. The detection limit is calculated to be 0.085 ppm for Al³⁺ and 0.082 ppm for UO₂²⁺ in aqueous solutions, which is lower than or close to that of latest reported Ln-MOFs. Moreover, the probe shows excellent hydrolytic stability and luminescence stability in the pH range of 4-11, further providing solid evidence for the practical application of Tb@MOF-808-TDA. More importantly, a mixed matrix hydrogel PVA-Tb@MOF-808-TDA was prepared to achieve the visual detection of Al³⁺, which broadens the potential in real-world sensing applications.

A ratiometric fluorescent probe based on a dual-ligand lanthanide metal–organic framework (MOF) for sensitive detection of aluminium and fluoride ions in river and tap water

A dual-emission fluorescent probe towards Al3+ and F− using a Ln-MOF material Eu-BDC-NH2/TDA is employed with exceptional sensitivity, high selectivity, low LOD, excellent anti-interference characteristics and direct visual observation.

Cation-Exchange in Metal-Organic Framework as a Strategy to Obtain New Material for Ascorbic Acid Detection

Ascorbic acid (AA) is an important biomolecule, the deficiency or maladjustment of which is associated with the symptoms of many diseases (e.g., cardiovascular disease or cancer). Therefore, there is a need to develop a fluorescent probe capable of detecting AA in aqueous media. Here, we report the synthesis, structural, and spectroscopic characterization (by means of, e.g., XRD, XPS, IR and Raman spectroscopy, TG, SEM, and EDS analyses), as well as the photoluminescent properties of a metal-organic framework (MOF) based on Cu²⁺ and Eu³⁺ ions. The ion-exchange process of the extraframework cation in anionic Cu-based MOF is proposed as an appropriate strategy to obtain a new material with a nondisturbed structure and a sensitivity to interaction with AA. Accordingly, a novel Eu[Cu₃(μ₃-OH)(μ₃-4-carboxypyrazolato)₃] compound for the selective optical detection of AA with a short detection time of 5 min is described.

Ratiometric Fluorescent Sensor Based on Tb(III) Functionalized Metal-Organic Framework for Formic Acid

Formic acid is a common chemical raw material, the effective detection of which is of importance to food safety and environmental quality. In this work, the lanthanide functionalized dual-emission metal-organic framework (TH25) was prepared as a ratiometric fluorescent sensor for formic acid. This ratiometric sensor has a good detection performance with high selectivity, sensitivity, and reproducibility. Together with a low limit of detection of 2.1 ppm, these characters promise the ability to sense at low levels as well as a practical detection ability. This work provides ideas for the design and synthesis of effective chemical sensors for organic acids.

Dual-ligand lanthanide metal-organic framework for ratiometric fluorescence detection of the anthrax biomarker dipicolinic acid

Dipicolinic acid (DPA) is a unique biomarker of Bacillus anthracis. Development of a simple, fast, sensitive and timely DPA detection method is of great importance and interest for preventing mass disease outbreaks and treatment of anthrax. In this work, a novel lanthanide-doped fluorescence probe was constructed by coordination of Eu³⁺ with bifunctional UiO-66-(COOH)₂-NH₂ MOFs materials for efficient monitoring DPA. UiO-66-(COOH)₂-NH₂ MOFs were prepared using Zr⁴⁺ as a metal node, 1,2,4,5-benzenetetracarboxylic acid (H₄BTC) and 2-aminoterephthalic acid (NH₂-BDC) as bridging ligand through a simple one-pot synthesis method. By virtue their abundant carboxyl groups, UiO-66-(COOH)₂-NH₂ can readily grasp Eu³⁺ to form UiO-66-(COOH)₂-NH₂/Eu with coordinated water molecules at Eu sites. Upon interaction with DPA molecules, the coordinated H₂O molecules were replaced by DPA molecules which transfer energy to Eu³⁺ in UiO-66-(COOH)₂-NH₂/Eu and sensitize Eu³⁺ luminescence. Meanwhile, DPA has a characteristic absorption band at 270 nm, which overlapped with the excitation spectrum of NH₂-BDC, allowing the fluorescence of UiO-66-(COOH)₂-NH₂/Eu at 453 nm to be greatly quenched by DPA through inner filter effect (IFE). Therefore, the rationally designed UiO-66-(COOH)₂-NH₂/Eu complex not only exhibits strong hydrophilicity and high dispersion, but also serves as ratiometric fluorescence sensing platform for monitoring DPA concentration. This sensing platform showed a satisfactory linear relationship from 0.2 μM to 40 μM with a limit of detection of 25.0 nM and a noticeable fluorescence color change from blue to red, holding a great promise in practical applications.

Highly Sensitive Adsorption and Detection of Iodide in Aqueous Solution by a Post-Synthesized Zirconium-Organic Framework

Effective methods of detection and removal of iodide ions (I^-) from radioactive wastewater are urgently needed and developing them remains a great challenge. In this work, an Ag⁺ decorated stable nano-MOF UiO-66-(COOH)₂ was developed for the I^- to simultaneously capture and sense in aqueous solution. Due to the uncoordinated carboxylate groups on the UiO-66-(COOH)₂ framework, Ag⁺ was successfully incorporated into the MOF and enhanced the intrinsic fluorescence of MOF. After adding iodide ions, Ag⁺ would be produced, following the formation of AgI. As a result, Ag⁺@UiO-66-(COOH)₂ can be utilized for the removal of I^- in aqueous solution, even in the presence of other common ionic ions (NO₂^-, NO₃^-, F^-, SO₄^2-). The removal capacity as high as 235.5 mg/g was calculated by Langmuir model; moreover, the fluorescence of Ag⁺@UiO-66-(COOH)₂ gradually decreases with the deposition of AgI, which can be quantitatively depicted by a linear equation. The limit of detection toward I^- is calculated to be 0.58 ppm.

Reversible acidochromism of a benzoxazole based scaffold and construction of reconfigurable dual output molecular logic gates

This report explores the reversible acidochromism of a benzoxazole-based scaffold (BPP), which is highly sensitive to the acid-base in the liquid and gas phases. With the addition of acid, the solution of BPP changes its color from yellow to pink fuchsia due to the transformation of its imine into quinonoid form. Colour change is completely reversible in the presence of the base, confirming the reversible acidochromic behavior of the present BPP system. Further, a paper strips-based test kit has been demonstrated for the practical utility of the present acidochromic BPP to identify a trace amount of acid-base in solution and gas-phase, respectively. The mechanistic aspect of detection of acid-base and colorimetric change in the presence of acid-base have been explored by density functional theoretical investigations and ¹H NMR experiments. Moreover, we have constructed a reconfigurable dual-output combinatorial logic circuit by utilizing the spectral shift between two wavelengths at 404 nm and 552 nm, respectively, and colorimetric change of the BPP in the presence and absence of acid-base.

Tunable Competitive Absorption-Induced Signal-On Photoelectrochemical Immunoassay for Cardiac Troponin I Based on Z-Scheme Metal-Organic Framework Heterojunctions

Recently emerged Z-scheme heterostructure-based immunoassays have presented new opportunities for photoelectrochemical (PEC) biosensing development. Here, we described a tunable signal-on PEC biosensor for the detection of cardiac troponin I (cTnI), which exploited a competitive absorption effect between Cu(II) ions and a Zr metal-organic framework (Zr-MOF) constructed on TiO₂ nanorods (Cu²⁺@Zr-MOF@TiO₂ NRs). Water-stable Zr-MOF was coated onto TiO₂ NRs on fluorine-doped tin oxide to form a Z-scheme heterostructure substrate (Zr-MOF@TiO₂ NRs), which exhibited a high photoelectric response. Cu²⁺@Zr-MOF@TiO₂ NRs, constructed by loading Cu(II) ions onto the architecture of Zr-MOF by electrostatic interaction, demonstrated a low background signal. After sandwich immunorecognition within a 96-well plate, H₂S, generated by confined alkaline phosphatase on zeolitic imidazolate framework-8, was directed to react with Cu(II) ions to form CuS. This resulted in an in situ change in the photoelectrode and an enhanced photoelectric signal. The developed PEC biosensing platform exhibited high sensitivity and selectivity for the cTnI immunoassay with a detection limit of 8.6 pg/mL. The Z-scheme-based competition absorption modulation of photoelectrochemistry provides a new strategy for general PEC biosensing development.

Unique Fluorescence Turn-On and Turn-Off-On Responses to Acids by a Carbazole-Based Metal-Organic Framework and Theoretical Studies

Distinct from predominately known fluorescence quenching (turn-off) detection, turn-on response to hazardous substances by luminescent metal-organic frameworks (LMOFs) could greatly avoid signal loss and susceptibility to environmental stimulus. However, such detection rarely occurs and lacks theoretical elucidations. Here, we present the first example of unique turn-on and unprecedented turn-off-on responses to a variety of acids by a stable 12-connected hexanuclear Y(III)-cluster-based LMOF material─JLU-MOF111, featuring the nondefault pcu topology. Benefiting from the "pocket" structures formed by the carbazole-containing ligands, JLU-MOF111 can sense multiple inorganic and organic acids via different degrees of fluorescence turn-on behaviors. Particularly, turn-on sensing of HNO₃, HCl, HBr, and TFA is hypersensitive with LODs as low as the ppb level. Theoretical calculations confirm weak interactions in acid-ligand complexes, which lead to constrained rotations of benzene moieties of the ligands when the complexes decay from excited states. These account for the turn-on response through reduced nonradiative energy consumption that competes with emissive decay. The turn-off-on response to 4-NBA and 3,5-DNBA involves an excited-state electron transfer process that dominates the turn-off stage and prohibited nonradiative decay that competes with the intrinsic emission of the ligand and dominates the turn-on stage. This work has a guiding significance for the full-scale understanding of turn-on and turn-off-on sensing performance in LMOF materials and beyond.

Dual-emissive EY/UiO-66-NH2 as a ratiometric probe for turn-on sensing and cell imaging of hypochlorite

Hypochlorite plays a vital role in biological systems and our daily life. The rapid and convenient detection of hypochlorite is imperative and significant for disease treatment and human health. In this work, EY/UiO-66-NH₂ (EY = eosin Y) was prepared through a hydrothermal process and could be applied to the detection and bioimaging of hypochlorite as a self-calibrating sensing nanoprobe. EY/UiO-66-NH₂ features two emissions at 432 nm and 533 nm, and the emission intensity of 533 nm is enhanced with increasing ClO^- concentration. EY/UiO-66-NH₂ could be utilized as a ratiometric fluorescence sensor of ClO^-. The linear range of EY/UiO-66-NH₂ towards ClO^- is 0.1-200 μM and its detection limit is 46.4 nM. In comparison with previously reported probes for ClO^-, EY/UiO-66-NH₂ has the advantages of a wide linear range, low detection limit, turn-on fluorescence and ratiometric response. This work provides a new method for ClO^- detection in living cells.

Confinement of Luminescent Guests in Metal-Organic Frameworks: Understanding Pathways from Synthesis and Multimodal Characterization to Potential Applications of LG@MOF Systems

This review gives an authoritative, critical, and accessible overview of an emergent class of fluorescent materials termed "LG@MOF", engineered from the nanoscale confinement of luminescent guests (LG) in a metal-organic framework (MOF) host, realizing a myriad of unconventional materials with fascinating photophysical and photochemical properties. We begin by summarizing the synthetic methodologies and design guidelines for representative LG@MOF systems, where the major types of fluorescent guest encompass organic dyes, metal ions, metal complexes, metal nanoclusters, quantum dots, and hybrid perovskites. Subsequently, we discuss the methods for characterizing the resultant guest-host structures, guest loading, photophysical properties, and review local-scale techniques recently employed to elucidate guest positions. A special emphasis is paid to the pros and cons of the various methods in the context of LG@MOF. In the following section, we provide a brief tutorial on the basic guest-host phenomena, focusing on the excited state events and nanoscale confinement effects underpinning the exceptional behavior of LG@MOF systems. The review finally culminates in the most striking applications of LG@MOF materials, particularly the "turn-on" type fluorochromic chemo- and mechano-sensors, noninvasive thermometry and optical pH sensors, electroluminescence, and innovative security devices. This review offers a comprehensive coverage of general interest to the multidisciplinary materials community to stimulate frontier research in the vibrant sector of light-emitting MOF composite systems.

Homochiral Eu3+@MOF Composite for the Enantioselective Detection and Separation of (R/S)-Ornidazole

The development of homochiral materials for the enantioselective detection and separation of chiral drugs is in high demand for the pharmaceutical industry. Herein, an anionic homochiral metal-organic framework (HMOF) with in situ generated [Me₂NH₂]⁺ counterions, {[Me₂NH₂]₂[Zn₂(d-L)₂(HCO₂)(OH)]·5H₂O}_n (HMOF-1), was synthesized using a d-camphorate-derived enantiopure dicarboxylate ligand, 4,4'-[[(1R,3S)-1,2,2-trimethylcyclopentane-1,3-dicarbonyl]bis(azanediyl)]dibenzoic acid (d-H₂L) via a simple solvothermal method. Interestingly, HMOF-1 could be used as a parent framework to encapsulate Eu³⁺ cations via an ion-exchange process, yielding an Eu³⁺@HMOF-1 composite with dual-luminescent centers. The obtained Eu³⁺@HMOF-1 has high chemical stability and good luminescence stability in water. Importantly, Eu³⁺@HMOF-1 exhibits enhanced enantioselectivity and sensitivity in the detection of an important chiral nitroimidazole antibiotic, (R/S)-ornidazole (ONZ) in comparison to HMOF-1 under the same aqueous conditions. The enantiomeric excess (ee) value of the ONZ enantiomers can be accurately determined by the ratio of dual emission from the ligand and Eu³⁺. In addition, Eu³⁺@HMOF-1 shows the enantioselective separation of racemic ONZ enantiomers with an ee value of 86.6%. This work provides a simple strategy for the preparation of Ln^III-incorporated HMOF composite materials for the simultaneous enantioselective detection and separation of chiral drugs.

Multi-Emission from Single Metal-Organic Frameworks under Single Excitation

Multi-emission materials have come to prominent attention ascribed to their extended applications other than single-emission ones. General and robust design strategies of a single matrix with multi-emission under single excitation are urgently required. Metal-organic frameworks (MOFs) are porous materials prepared with organic ligands and metal nodes. The variety of metal nodes and ligands makes MOFs with great superiority as multi-emission matrices. Guest species encapsulated into the channels or pores of MOFs are the additional emission sites for multi-emission. In this review, multi-emission MOFs according to the different excitation sites are summarized and classified. The emission mechanisms are discussed, such as antenna effect, excited-state intramolecular proton transfer (ESIPT) and tautomerism for dual-emission. The factors that affect the emissions are revealed, including ligand-metal energy transfer and host-guest interaction, etc. Multi-emission MOFs could be predictably designed and prepared, once the emissive factors are controlled rationally in combination with the different multi-emission mechanisms. Correspondingly, new and practical applications are realized, including but not limited to ratiometric/multi-target sensing and bioimaging, white light-emitting diodes, and anti-counterfeiting. The design strategies of multi-emission MOFs and their extensive applications are reviewed. The results will shed light on other multi-emission systems to develop the structure-derived functionality and applications.

Recent Progress in Metal-Organic Framework Based Fluorescent Sensors for Hazardous Materials Detection

Population growth and industrial development have exacerbated environmental pollution of both land and aquatic environments with toxic and harmful materials. Luminescence-based chemical sensors crafted for specific hazardous substances operate on host-guest interactions, leading to the detection of target molecules down to the nanomolar range. Particularly, the luminescence-based sensors constructed on the basis of metal-organic frameworks (MOFs) are of increasing interest, as they can not only compensate for the shortcomings of traditional detection techniques, but also can provide more sensitive detection for analytes. Recent years have seen MOFs-based fluorescent sensors show outstanding advantages in the field of hazardous substance identification and detection. Here, we critically discuss the application of MOFs for the detection of a broad scope of hazardous substances, including hazardous gases, heavy metal ions, radioactive ions, antibiotics, pesticides, nitro-explosives, and some harmful solvents as well as luminous and sensing mechanisms of MOF-based fluorescent sensors. The outlook and several crucial issues of this area are also discussed, with the expectation that it may help arouse widespread attention on exploring fluorescent MOFs (LMOFs) in potential sensing applications.

Iron(II) Immobilized within a Metal-Organic Framework Mixed-Matrix Membrane as a H2O2 Turn-On Sensor

H2O2 detection is closely relevant to human health; however, most of the H2O2 probes suffer from low accuracy and sensitivity because of the aggregating nature of solid sensors. In contrast, a mixed-matrix membrane (MMM) with high processability and flexibility is a suitable H2O2 probe to overcome these drawbacks. Herein, we fabricated MOF-based MMMs by using a robust UiO-66-(COOH)2 with carboxylate-chelating moieties, which were utilized for binding Fe (II) metal centers. The Fe (II)-immobilized MOF-MMM involved in a Fenton reaction when treated with H2O2, exhibiting a fluorescence turn-on property. Compared to the bulk-state MOF powder, the MOF-MMM sensor showed much-improved sensitivity (detection limit down to 0.0215 μM) because of the uniform dispersion of the probe and a sufficient contact with the analyte. This MOF-MMM sensor combinedly exhibited a turn-on fluorescence response and outstanding sensing properties with flexibility and processability, providing a novel platform suitable for practical sensing applications.

Cd (II) coordination polymer as a strip based fluorescence sensor for sensing Fe3+ ions in aqueous system

The design and construction of a sensor that can sensitively and conveniently recognize metal ions are essential for the treatment of industrial wastewater. In this work, {[Cd₄(HL)₂(pyp)₂(H₂O)₂]·2H₂O·1.5Diox}_n (1) was synthesized under solvothermal condition and presented a 2D 3,5-connected layered network with the point symbol of {3.4.5} {3².4.5.6².7⁴}, which was coated on the surface of polyvinylidene fluoride (PVDF) to construct a novel paper sensor (1@PVDF). Meanwhile, the stability of 1@PVDF was characterized by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA). In addition, fluorescence sensing experiments of 1@PVDF sensor for cations in aqueous system indicated that it has high sensitivity for sensing Fe³⁺ ions with the detection limit (DL) of 4.0 × 10^-8 M. By the characterization of PXRD, UV-vis spectra, ICP, XPS, time-resolved excited-state decay measurements, the sensing mechanisms of 1@PVDF for Fe³⁺ ions were attributed to the competitive absorption and interaction between 1 and Fe³⁺. And the sensing process of 1@PVDF for Fe³⁺ ions was static in the Fe³⁺ concentration of 0 to 0.05 mM. In addition, the binding energies of Fe³⁺ and Zn²⁺ with the framework of 1 were calculated by density functional theory (DFT), which further proved that there was an obvious interaction between Fe³⁺ and the uncoordinated O atom in 1. Based on the thin film technology, a portable and convenient paper-based probe has been developed for practical applications.

High-performance TFNC membrane with adsorption assisted for removal of Pb(II) and other contaminants

Rapid and thorough removal of heavy metal ions in wastewater is critical for the urgent need of clean water. Herein, we prepared a high-performance thin film nanofibrous composite (TFNC) membrane consisting of a polyacrylonitrile (PAN)-UiO-66-(COOH)₂ composite nanofibrous substrate (CPAN) and a calcium alginate (CaAlg) skin layer. Owing to abundant adsorption sites of UiO-66-(COOH)₂ MOF, the optimal CPAN-2 nanofibrous substrate showed excellent adsorption capacity for lead ions. The maximum Pb²⁺ adsorption capacity of CPAN-2 substrate calculated by Langmuir isotherm model was 254.5 mg/g. Meanwhile, due to the relatively loose structure of CaAlg skin layer, this TFNC membrane showed high water permeate flux about 50 L m^-2h^-1 at 0.1 MPa, and the rejection for dyes was higher than 95%. Therefore, CaAlg/CPAN TFNC membranes were appropriate for dynamic adsorption/filtration to remove Pb²⁺. Compared with original CaAlg/PAN membrane, the optimal CaAlg/CPAN TFNC membrane showed much better ability to treat Pb(II)-containing wastewater and had good recyclability. Most importantly, the CaAlg/CPAN TFNC membrane could treat 7659 L m^-2 wastewater containing single lead ions under WHO drinking water standard, and effectively deal with more simulated lead-containing wastewater. This work could provide a substitutable solution for effective removal of heavy metal ions and other various contaminants in wastewater.

Rare-Earth Doping in Nanostructured Inorganic Materials

Impurity doping is a promising method to impart new properties to various materials. Due to their unique optical, magnetic, and electrical properties, rare-earth ions have been extensively explored as active dopants in inorganic crystal lattices since the 18th century. Rare-earth doping can alter the crystallographic phase, morphology, and size, leading to tunable optical responses of doped nanomaterials. Moreover, rare-earth doping can control the ultimate electronic and catalytic performance of doped nanomaterials in a tunable and scalable manner, enabling significant improvements in energy harvesting and conversion. A better understanding of the critical role of rare-earth doping is a prerequisite for the development of an extensive repertoire of functional nanomaterials for practical applications. In this review, we highlight recent advances in rare-earth doping in inorganic nanomaterials and the associated applications in many fields. This review covers the key criteria for rare-earth doping, including basic electronic structures, lattice environments, and doping strategies, as well as fundamental design principles that enhance the electrical, optical, catalytic, and magnetic properties of the material. We also discuss future research directions and challenges in controlling rare-earth doping for new applications.

Fluorescent Zn(II) frameworks with multicarboxylate and pyridyl N-donor ligands for sensing specific anions and organic molecules

Three novel fluorescent Zn(II) frameworks, namely [Zn(DPA)(NDA)]2·2DMF (1), [Zn2(DPA)(OBA)2]·2DMF·4H2O (2) and [Zn(DPA)(HNTB)]·H2O (3) (DPA = 2,5-di(pyridin-4-yl)aniline, H2NDA = 1,4-naphthalenedicarboxylic acid, H2OBA = 4,4'-oxydibenzoic acid, H3NTB = 4,4',4''-nitrilotribenzoic acid, DMF =...

Progress on the reaction-based methods for detection of endogenous hydrogen sulfide

Hydrogen sulfide (H₂S) is a biologically signaling molecule that mediates a wide range of physiological functions, which is frequently misregulated in numerous pathological processes. As such, measurement of H₂S holds great attention due to its unique physiological and pathophysiological roles. Currently, a variety of methods based on the H₂S-involved reactions have been reported for detection of endogenous H₂S, bearing the advantages of good specificity and high sensitivity. This review describes in detail the types of reactions, their mechanisms, and their applications in biological research, thus hopefully providing some guidelines to the researchers in this field for further investigation.

Visualizing the degradation of nerve agent simulants using functionalized Zr-based MOFs: from solution to hydrogels

Visual monitoring of the degradation of nerve agent simulants based on the switchable fluorescence of UiO-66-NH₂ was developed. In the hydrolysis, the decomposition products perturbed the linker-to-cluster charge transfer and stimulated the fluorescence recovery. Moreover, a "soft" solid-state platform utilizing agarose hydrogels was proposed to visualize the degradation of gaseous simulants without bulk water.

Recent advances in molecular logic gate chemosensors based on luminescent metal organic frameworks

Luminescent metal-organic frameworks (LMOFs) as chemosensors, can sense various analytes, such as heavy metal ions, antibiotics, pesticides, and small biological molecules. Based on the fluorescence characteristics of LMOFs, a variety of logic gates have been developed. In this review, we mainly discuss some common logic systems based on LMOFs, and then summarize the strategies of constructing logic gates from two perspectives. One is based on superior characteristics of MOFs, which can be synthesized from Ln3+ based MOFs (Ln-MOFs) or form hybrids by encapsulating different materials, including metal ions, dyes, and quantum dots (QDs). The other is to control the presence of inputs by reactions between different reactants and then further control switches of logic gates. Additionally, the common sensing mechanisms of LMOFs in logic gates are discussed. In the end, we have envisioned MOFs that possess a promising future in logic computing areas.