Rapid and facile ratiometric detection of an anthrax biomarker by regulating energy transfer process in bio-metal-organic framework

Smartphone-assisted ratiometric fluorescent sensor to quantitatively detect curcumin in traditional Chinese medicine based on Förster resonance energy transfer

A ratiometric fluorescence sensor (Fe-MIL-88-NH2/curcumin) based on luminescent metal-organic frameworks (LMOFs) for the determination of curcumin was constructed. Upon the addition of curcumin, the 535-nm emission of curcumin was enhanced, while the fluorescence emission at 438 nm was quenched, under 367-nm excitation. This sensor demonstrated a broad linear range from 1.5 to 40 μM, a low detection limit of 35 nM, and a fast response time of at most 30 s. We verified the Förster resonance energy transfer (FRET) mechanism between donor (Fe-MIL-88-NH2) and acceptor (curcumin), which further proved the selectivity of the approach. The sensing system enabled the detection of curcumin in the traditional Chinese medicine (TCM) Turmeric. A smartphone-assisted sensing platform was prepared to visually detect curcumin in a portable manner. This study represents the first attempt to fabricate LMOFs for ratiometric fluorescence detection of curcumin, which has promising potential for application in TCM.

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.

Airborne microbes: sampling, detection, and inactivation

The human living environment serves as a habitat for microorganisms and the presence of ubiquitous airborne microbes significantly impacts the natural material cycle. Through ongoing experimentation with beneficial microorganisms, humans have greatly benefited from airborne microbes. However, airborne pathogens endanger human health and have the potential to induce fatal diseases. Tracking airborne microbes is a critical prerequisite for a better understanding of bioaerosols, harnessing their potential advantages, and mitigating associated risks. Although technological breakthroughs have enabled significant advancements in accurately monitoring airborne pathogens, many puzzles about these microbes remain unanswered due to their high variability and environmental diffusibility. Consequently, advanced techniques and strategies for special identification, early warning, and efficient eradication of microbial contamination are continuously being sought. This review presents a comprehensive overview of the research status of airborne microbes, concentrating on the recent advances and challenges in sampling, detection, and inactivation. Particularly, the fundamental design principles for the collection and timely detection of airborne pathogens are described in detail, as well as critical factors for eliminating microbial contamination and enhancing indoor air quality. In addition, future research directions and perspectives for controlling airborne microbes are also suggested to promote the translation of basic research into real products.

Distinguishing nitroimidazoles from nitrofurans via luminescence sensing

Similarity of nitroimidazole and nitrofuran antibiotics in molecular structure and photophysical properties makes them difficult to distinguish via luminescence sensing technology. Herein, this is solved by a dye-encapsulated lanthanide metal-organic framework luminescent sensor.

Dual-mode detection of 2,6-pyridinedicarboxylic acid based on the enhanced peroxidase-like activity and fluorescence property of novel Eu-MOFs

2,6-Pyridinedicarboxylic acid (DPA) is a significant biomarker of anthrax, which is a deadly infectious disease for human beings. However, the development of a convenient anthrax detection method is still a challenge. Herein, we report a novel europium metal-organic framework (Eu-MOF) with an enhanced peroxidase-like activity and fluorescence property for DPA detection. The Eu-MOF was one-step synthesized using Eu3+ ions and 2-methylimidazole. In the presence of DPA, the intrinsic fluorescence of Eu3+ ions is sensitized, the fluorescence intensity linearly increases with an increase in DPA concentration, and the fluorescence color changes from blue to purple. Simultaneously, the peroxide-like activity of the Eu-MOF is enhanced by DPA, which can promote the oxidation of TMB to oxTMB. The absorbance values increase linearly with DPA concentrations, and the colorimetric images change from colorless to blue. The dual-mode detection of DPA has good sensitivity with a colorimetric detection limit of 0.67 μM and a fluorescent detection limit of 16.67 nM. Moreover, a simple detection method for DPA was developed using a smartphone with the RGB analysis system. A portable kit with standard color cards was developed using paper test strips. The proposed methods have good practicability for DPA detection in real samples. In conclusion, the developed Eu-MOF biosensor offers a valuable and general platform for anthrax diagnosis.

A smartphone-intergrated dual-emission fluorescent nanoprobe for visual and ratiometric detection of anthrax biomarkers

A novel dual-emission fluorescent nanoprobe based on rare-earth nanosheets was fabricated to detect 2,6-pyridine dicarboxylic acid (DPA), which is the biomarker of Bacillus anthracis. 2-amino terephthalic acid (BDC-NH2) and surfactant sodium dodecyl sulfate (SDS) were co-intercalated into layered europium hydroxide (LEuH) to prepare the organic/inorganic composite, which was delaminated to obtain the rare-earth nanosheets. The ratio detection of DPA is possible due to the antenna effect between DPA and Eu3+. The nanoprobe shows high accuracy and sensitivity due to the large specific surface area of the rare-earth nanosheets. The limit of detection (LOD) is 4.4 nM for DPA in the range of 0-20 μM. In addition, a more convenient and faster smartphone-based visual detection platform was established based on the obvious color change. This work offers an effective way for developing visual sensing platforms, which opens a new path for designing fluorescent probes with superior sensing capabilities.

Design and application of dual-emission metal-organic framework-based ratiometric fluorescence sensors

Metal-organic frameworks (MOFs) are novel inorganic-organic hybridized crystals with a wide range of applications. In the last twenty years, fluorescence sensing based on MOFs has attracted much attention. MOFs can exhibit luminescence from metal nodes, ligands or introduced guests, which provides an excellent fluorescence response in sensing. However, single-signal emitting MOFs are susceptible to interference from concentration, environment, and excitation intensity, resulting in poor accuracy. To overcome the shortcomings, dual-emission MOF-based ratiometric fluorescence sensors have been proposed and rapidly developed. In this review, we first introduce the luminescence mechanisms, synthetic methods, and detection mechanisms of dual-emission MOFs, highlight the strategies for constructing ratiometric fluorescence sensors based on dual-emission MOFs, and classify them into three categories: intrinsic dual-emission and single-emission MOFs with luminescent guests, and non-emission MOFs with other luminescent materials. Then, we summarize the recent advances in dual-emission MOF-based ratiometric fluorescence sensors in various analytical industries. Finally, we discuss the current challenges and prospects for the future development of these sensors.

Eu3+ doped ethylenediamine functionalized UiO-66 probe for fluorescence sensing of formaldehyde

The development of probes with selectivity and prompt detection of aldehydes molecules is of great importance for protecting human health and public security. Herein, a system based on ethylenediamine (EDA) functionalized and Eu3+-doped UiO-66, namely EDA-Eu3+@UiO-66, was designed to detect formaldehyde molecules. Based on the "antenna effect" of lanthanide elements, UiO-66 transfers the absorbed energy to Eu3+ ions and emits characteristic fluorescence belonging to Eu3+. By using the fluorescence peaks of UiO-66 and Eu3+ respectively, a ratiometric fluorescence sensing probe can be constructed. Formaldehyde molecules react with the -NH2 on the surface of EDA-Eu3+@UiO-66 through an aldehyde-amine condensation reaction and connect to the functionalized surface of UiO-66. Due to the absorption of excitation light energy by formaldehyde molecules, the energy transfer efficiency from UiO-66 to Eu3+ ions is reduced, resulting in the fluorescence quenching of EDA-Eu3+@UiO-66, thus achieving selective detection of formaldehyde. The fabricated sensing platform successfully detected residual formaldehyde in frozen shrimp tail samples. The system was also used to respond to formaldehyde vapor, and a significant fluorescence quenching effect was observed. This strategy provides a sensitive, selective, and reliable method for the visual sensing of formaldehyde.

A Recent Advancement in Food Quality Assessment: Using MOF-Based Sensors: Challenges and Future Aspects

Monitoring food safety is crucial and significantly impacts the ecosystem and human health. To adequately address food safety problems, a collaborative effort needed from government, industry, and consumers. Modern sensing technologies with outstanding performance are needed to meet the growing demands for quick and accurate food safety monitoring. Recently, emerging sensors for regulating food safety have been extensively explored. Along with the development in sensing technology, the metal-organic frameworks (MOF)-based sensors gained more attention due to their excellent sensing, catalytic, and adsorption properties. This review summarizes the current advancements and applications of MOFs-based sensors, including colorimetric, electrochemical, luminescent, surface-enhanced Raman scattering, and electrochemiluminescent sensors. and also focused on the applications of MOF-based sensors for the monitoring of toxins such as heavy metals, pesticide residues, mycotoxins, pathogens, and illegal food additives from food samples. Future trends, as well as current developments in MOF-based materials.

Polyarylether-based COFs coordinated by Tb3+ for the fluorescent detection of anthrax-biomarker dipicolinic acid

In this study, a rare-earth hybrid luminescent material (lanthanide@COF) was constructed for the detection of a biomarker for anthrax (dipicolinic acid, DPA). JCU-505-COOH was prepared by the hydrolysis of the cyano group in JCU-505 via a post-synthetic modification strategy, then the carboxyl groups in JCU-505-COOH coordinated with Tb3+ ions, similar to pincer vising nut. The prepared Tb3+@JCU-505-COOH exhibited a turn-on response toward DPA, which allowed the lanthanide@COF to serve as a fluorescence sensor with excellent selectivity and high sensitivity (binding constant Ka = 3.66 × 103). The fluorescent probe showed satisfactory performance for the determination of DPA in saliva and urine with a detection limit of 0.6 μM. Moreover, we established a facile point-of-care testing (POCT) using the Tb3+@JCU-505-COOH-based fluorescent test paper together with a smartphone for the initial diagnosis of anthrax. As expected, Tb3+@JCU-505-COOH showed great potential for the rapid screening of anthrax due to low cost, simple operation, and wide applicability.

A pre-oxidized Eu-probe doped into bio-MOF-1 for ascorbic acid emission "off-on" detection in human serum

Ascorbic acid (or widely known as vitamin C, VC) is an essential antioxidant and a free radical scavenger in human body. The appeal for reliable fluorescent nanosensors always promotes the development of VC probe. In this work, a pre-oxidized Eu-probe (denoted as Eu-NO9) was synthesized. Without VC, Eu-NO9 was nearly non-emissive owing to the inefficient ligand energy transfer (ET) to Eu ion (caused by mismatched ligand level and long distance to Eu, as revealed by single crystal analysis and emissive parameters). By adding VC, the pre-oxidized ligand was deoxidized and its ET to Eu ion became efficient (confirmed by electrochemical analysis), with Eu(III) red emission intensity obviously increased. Then Eu-NO9 was doped into a porous host bio-MOF-1 for ascorbic acid detection (denoted as Eu-NO9@MOF). The molecular sieving effect of bio-MOF-1 improved sensing selectivity, and bio-MOF-1 blue emission (421 nm) was applied as a reference for Eu(III) red emission. Linear working curves were obtained within a wide working region of 0-100 μM, with LOD of 1.7 μM. A short response time of 192 s at 25 °C was confirmed. Practical sensing plates were prepared and found applicable for VC detection in fresh human serum. The advantage of this work was the combination of a pre-oxidized probe and a porous host which gave emission "turn on" fluorescence sensing for VC with good selectivity, linear calibration curve and wide working region.

Self-calibrated HAp:Tb-EDTA paper-based probe with dual emission ratio fluorescence for binary visual and fluorescent detection of anthrax biomarker

Development of the portable device is significant for sensitive and rapid detection of an anthrax biomarker dipicolinic acid (DPA), existing in the B. anthracis. In this work, a novel HAp:Tb-EDTA paper-based ratiometric fluorescent sensor was obtained by a simple one-pot method for rapid and sensitive DPA detection. With the increased DPA concentration, the luminescence intensity of HAp (hydroxyapatite) remained constant, and thus applied as the stable reference signal, while the luminescence signal of Tb3+-EDTA was significantly enhanced due to the antenna effect. Therefore, the HAp:Tb-EDTA paper-based sensor was endowed with self-calibrated and ratiometric fluorescent detection performance for DPA. The proposed sensor showed excellent detection performance with a detection limit as low as 10.8 nM in the linear range of 0.5-30 μM. After combination with a smartphone, rapid visual and fluorescent detection of DPA was achieved. The proposed sensor was successfully applied to detect DPA from B. subtilis spore real samples, showing the application prospects of the paper-based sensors and opening a new horizon to develop novel paper-based point-of-care testing (POCT) devices.

Trajectory in biological metal-organic frameworks: Biosensing and sustainable strategies-perspectives and challenges

The ligand attribute of biomolecules to form coordination bonds with metal ions led to the discovery of a novel class of materials called biomolecule-associated metal-organic frameworks (Bio-MOFs). These biomolecules coordinate in multiple ways and provide versatile applications. Far-spread bio-ligands include nucleobases, amino acids, peptides, cyclodextrins, saccharides, porphyrins/metalloporphyrin, proteins, etc. Low-toxicity, self-assembly, stability, designable and selectable porous size, the existence of rigid and flexible forms, bio-compatibility, and synergistic interactions between metal ions have led Bio-MOFs to be commercialized in industries such as sensors, food, pharma, and eco-sensing. The rapid growth and commercialization are stunted by absolute bio-compatibility issues, bulk morphology that makes it rigid to alter shape/porosity, longer reaction times, and inadequate research. This review elucidates the structural vitality, biocompatibility issues, and vital sensing applications, including challenges for incorporating bio-ligands into MOF. Critical innovations in Bio-MOFs' applicative spectrum, including sustainable food packaging, biosensing, insulin and phosphoprotein detection, gas sensing, CO2 capture, pesticide carriers, toxicant adsorptions, etc., have been elucidated. Emphasis is placed on biosensing and biomedical applications with biomimetic catalysis and sensitive sensor designing.

Blue-red emission color change from a heavily-doped Eu@MOF composite: Synthesis, characterization and application for 2,4,6-trinitrophenol sensing

2,4,6-trinitrophenol (TPA) natural degradation is nearly impossible and its accumulation threatens ecosystem. Optical sensing is an attractive detection method for TPA with low demand of equipment and data processing, but still needs to be improved. This work was dedicated to increasing probe-loading content so as to improve sensing sensitivity. Three probes derived from Eu(III)-benzimidazole were designed, with their active H atoms replaced by alkyl groups to eliminate the hydrogen bond with supporting host and thus to improve probe-loading content. Their molecular structure, absorption, emission, and excitation spectra were discussed to confirm their sensing potential to TPA. Then these three probes were loaded into host (bio-MOF-1) via ionic exchange method, which was confirmed by XRD, N2 adsorption/desorption, ICP, and SEM. The loading content and sensing performance of these three probes in bio-MOF-1 were compared. It was found that the elimination of active H atoms indeed increased probe loading content from 44% to 78%, with sensing coefficient increased from 0.010 μM-1 to 0.029 μM-1. A ratiometric sensing towards TPA was observed, with blue emission from bio-MOF-1 host increased and red emission from Eu(III) probe decreased, which was detectable by naked eyes. Linear working equations were fitted with high selectivity.

Dual-Emitting Mixed-Lanthanide Metal-Organic Framework for Ratiometric and Quantitative Visual Detection of 2,6-Pyridine Dicarboxylic Acid

The detection of the major biomarker of Bacillus anthracis, 2,6-dipicolinic acid (DPA), has attracted great interest in recent years. In this work, mixed-lanthanide metal-organic frameworks (M'LnMOFs), TbxEu1-x-cppa (cppa = 5-(5-carboxypyridin-3-yl)isophthalic acid), with different Tb/Eu ratios, were solvothermally synthesized. The results reveal that ratiometric fluorescent probe [Tb0.533Eu0.467-(Hcppa)1.5(H2O)(DMF)]·3H2O is water and acid-base stable and exhibits excellent sensitivity (LOD = 2.286 μM), high selectivity, and fast response (<2 min) for the detection of DPA. Due to the blocked energy transfer from Tb3+ to Eu3+ and the inner filter effect upon the addition of DPA, the fluorescent probe shows a distinct color change from orange-red to green. Furthermore, the visual detection of DPA was realized by identifying the RGB values of MOF-based agarose hydrogel films via a smartphone, highlighting the practical application of the fluorescent probe for DPA detection under aqueous solution conditions.

A highly stable chain-based EuIII metal-organic framework as a turn-on and blue-shift luminescent sensor for dipicolinic acid

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

On the modulation/energy competing of Tb(III)/Eu(III) emission in microporous MOF host for peroxide recognition

Being an important chemical reagent having moderate oxidizability, peracitic acid (PAA) has been applied in modern industries and processing, as well as public safety. These versatile applications make PAA an important analyte to be precisely and sensitively detected. The present work chose the combination of rare-earth-based probe and a microporous host bio-MOF-1 ([Zn₈(ad)₄(BPDC)₆O·2(Me₂NH₂)⁺]·G, ad = adenine, BPDC = 4,4'-biphenyl dicarboxylic acid, G = N,N-dimetylformamide and water). Two β-diketone ligands, 1,3-di(pyridin-3-yl)propane-1,3-dione (DPY) and 1,3-diphenylpropane-1,3-dione (DPP), were coordinated to Tb(III) and Eu(III) ions to form probe [RE(DPY/DPP)₂]Cl which was loaded into bio-MOF-1 micropores with different loading contents via an ionic exchange operation. The resulting composite samples were fully characterized, including synthesis, morphology, composition, sensing performance and mechanism. The protonation/oxidization of DPY and DPP ligands adjusted their triplet energy level (T₁) and consequently affected their energy transfer (ET) efficiency to RE ions, resulting in the variation of RE emission relative intensity. A new pathway for PAA optical sensing was thus proposed. Linear fitting equations were observed for DPY-based samples, showing fluorescence intensity ratio value of 8.80, response time of 9 s, and LOD of 8.08 μM within working region of 0-140 μM.

On the construction and performance of pre-oxidized probe inserted into charged MOF for the in vitro vitamin C detection: A highly selective emission turn-on sensing

Owing to the critical role of ascorbic acid (vitamin C, VC) in human bio-activities as an antioxidant and free radical scavenger, the development for an easy and fast VC detection has always been pushed. In this work, a traditional ligand bipyridine (bpy) was firstly oxidized (denoted as bpy-O) and then coordinated to Eu(III) (denoted as Eu-bpy-O). Due to the oxidization of bpy N atoms, which led to improper triplet ligand energy level and increased ligand-to-Eu distance, the efficient ligand energy transfer (ET) to Eu(III) was suspended, resulting in a low emission quantum yield of 1.6%. Upon being deoxidized by VC, the ligand ET to Eu(III) became efficient, with emission quantum yield recovered to 22.4%, showing emission turn-on effect for VC. To allow smooth analyte dispersion and uniform probe distribution, Eu-bpy-O was loaded into the micropores of bio-MOF-1 (Eu-bpy-O@MOF) with various doping levels. Good sensing selectivity was observed owing to the well-designed probe and bio-MOF-1 sieving effect. Linear fitting equations were obtained for the optimal sample named 5Eu-bpy-O@MOF within VC concentration region of 0-100 μM, showing LOD of 1.7 μM, sensitivity of 0.191 μM^-1, and response time of ∼240 s at 35 °C. The practical sensing performance of 5Eu-bpy-O@MOF was confirmed by its sensing plates upon human serum samples. The novelty of this work was the application of a pre-oxidized probe and a porous host, which offered emission "turn-on" effect for VC with promising performance.

Ln-MOF Based Ratiometric Luminescent Sensor for the Detection of Potential COVID-19 Drugs

Countless people have been affected by the COVID-19 pandemic on a global scale. Favipiravir, has shown potential as an effective drug for SARS-CoV-2, attracting scientists' attention. However, overuse of Favipiravir easily leads to serious side effects, requiring real-time monitoring in body fluids. Given this, a new lanthanide metal-organic framework (MOF) was prepared under solvothermal conditions from either Eu (Eu-MOF or (1)) or Tb (Tb-MOF or (2)) using the highly delocalized imidazoledicarboxylic acid linker H₂ L (H₂ L=5-(4-(imidazol-1-yl) phenyl) isophthalic acid) and could be successfully applied to selective optical detection of Favipiravir. In this MOF framework, the organic linker H₂ L provides a high excitation energy transfer efficiency that can sensitize luminescence in lanthanides. In addition, through deliberate tuning of Eu/Tb molar ratio and reaction concentration in the lanthanide framework, ratiometric recyclable luminescent Eu_x Tb_1-x -MOF nanoparticles with open metal sites have been constructed, which present a high detection sensitivity (K_sv =1×10⁷ [M^-1 ], detection limit is 4.63 nM) for Favipiravir. The detection mechanism is discussed with the help of Density Functional Theory (DFT) calculations that sheds light over the selective sensing of Favipiravir over other related COVID-19 drug candidates. Finally, to explore the practical application of Favipiravir sensing, MOF based thin films have been used for visual detection of Favipiravir and recycled 5 times.

Metal-organic frameworks for food contaminant adsorption and detection

Metal-organic framework materials (MOFs) have been widely used in food contamination adsorption and detection due to their large specific surface area, specific pore structure and flexible post-modification. MOFs with specific pore size can be targeted for selective adsorption of some contaminants and can be used as pretreatment and pre-concentration steps to purify samples and enrich target analytes for food contamination detection to improve the detection efficiency. In addition, MOFs, as a new functional material, play an important role in developing new rapid detection methods that are simple, portable, inexpensive and with high sensitivity and accuracy. The aim of this paper is to summarize the latest and insightful research results on MOFs for the adsorption and detection of food contaminants. By summarizing Zn-based, Cu-based and Zr-based MOFs with low cost, easily available raw materials and convenient synthesis conditions, we describe their principles and discuss their applications in chemical and biological contaminant adsorption and sensing detection in terms of stability, adsorption capacity and sensitivity. Finally, we present the limitations and challenges of MOFs in food detection, hoping to provide some ideas for future development.

Highly selective and multicolor ultrasensitive assay of dipicolinic acid: The integration of terbium(III) and gold nanocluster

A novel multicolor fluorescent nano-probe based on the hybridization of Tb³⁺ ion with gold nanoclusters (Au NCs) was synthesized to monitor and on-site visual assay of 2,6-pyridinedicarboxylic acid (DPA), a biomarker of bacterial spores. DPA can replace the water molecule in the center of Tb³⁺ and strongly coordinate with Tb³⁺ based on the analyte-triggered antenna effect. Simultaneously, the red fluorescence of Au NCs is not influenced after addition of DPA and can be used as steady inside fluorescence reference channel to measure background noise. On this basis, the multicolor fluorescence nano-probe based on Tb³⁺-doped Au NCs for fast analysis of DPA was fabricated. The linear range of this method is 0 to 12.5 μM and the limit of detection is 3.4 nM, which is well below the quantity of DPA concentration of 60 μM released by the spore transmission dose of anthrax infection. The proposed multicolor fluorescence nano-probe was successfully detecting DPA in actual sample with good sensitivity and specificity. In addition, the visual paper-based nano-probe is designed to detect DPA by using the color scanning application of smart phone. This developed platform possesses abroad application prospects with advantages of effective, convenient carrying, simple operation, good selectivity and repeatability.

Ce3+-induced Fluorescence Amplification of Copper Nanoclusters Based on Aggregation-induced Emission for Specific Sensing 2,6-pyridine Dicarboxylic Acid

A straightforward, cost-effective and biocompatible reduction approach was applied to fabricate soluble but non-luminous glutathione-stabilized copper nanocluster (GSH-CuNCs). Surprisingly, as high as 1 × 10³ times fluorescence enhancement was acquired when Ce³⁺ was injected at an extremely low concentration of only 18 µM. Ce³⁺ outperformed other rare-earth metal ions in terms of inducing fluorescence amplification of the non-luminous GSH-CuNCs. Furthermore, Ce³⁺ was employed as inducer for aggregation-induce emission (AIE) effect as well as reactant to coordinate with target of 2,6-pyridine dicarboxylic acid (DPA) due to the stronger coordination ability between Ce³⁺ and DPA than that of Ce³⁺ and GSH. As a result, the Ce³⁺/GSH-CuNCs ensemble was developed as a novel sensor to detect DPA in the "on-off" mode. When DPA was introduced into the sensor, Ce³⁺ failed to interact with GSH and detached from the surface of GSH-CuNCs, leading to fluorescence quenching. In addition, static quenching process and internal filtration effect (IFE) between Ce³⁺/GSH-CuNCs and DPA were also responsible for fluorescence quenching effect. A good linear relationship was obtained from 0.3 µM to 18 µM, with a limit of detection (LOD) of 0.19 µM. The as-proposed probe displayed high specificity to DPA and provided a simple, fast rapid and cheap method for construction this type of ensemble sensors to detect other targets.

A review of synthesis, fabrication, and emerging biomedical applications of metal-organic frameworks

The overwhelming potential of porous coordination polymers (PCP), also known as Metal-Organic Frameworks (MOFs), especially their nanostructures for various biomedical applications, have made these materials worth investigating for more applications and uses. MOFs unique structure has enabled them for most applications, particularly in biomedical and healthcare. A number of very informative review papers are available on the biomedical applications of MOFs for the reader's convenience. However, many of those reviews focus mainly on drug delivery applications, and no significant work has been reported on other MOFs for biomedical applications. This review aims to present a compact and highly informative global assessment of the recent developments in biomedical applications (excluding drug-delivery) of MOFs along with critical analysis. Researchers have recently adopted both synthetic and post-synthetic routes for the fabrication and modification of MOFs that have been discussed and analyzed. A critical review of the latest reports on the significant and exotic area of bio-sensing capabilities and applications of MOFs has been given in this study. In addition, other essential applications of MOFs, including photothermal therapy, photodynamic therapy, and antimicrobial activities, are also included. These recently grown emergent techniques and cancer treatment options have gained attention and require further investigations to achieve fruitful outcomes. MOF's role in these applications has been thoroughly discussed, along with future challenges and valuable suggestions for the research community that will help meet future demands.

Ionic modification on COF with rare earth ions for the selective optical sensing and removal of picronitric acid

In this work, we reported a modified COF material for trinitrophenol (TPA) ratiometric sensing and removal. Here a cationic covalent organic framework (C-COF) was prepared as host, while two Tb(III)-based ions were doped into C-COF as probe by ionic exchange reaction with probe loading level of ∼15%. In the absence of TPA, weak Tb(III) emission (489 nm, 545 nm, 585 nm) and bright red COF emission were observed (633 nm). The addition of TPA increased Tb(III) emission and decreased COF emission, following linear response within TPA concentration region of 0-9 μM. Their limit of detection values were determined as 0.9 μM and 4.5 μM, respectively. Corresponding working equations were fitted as I/I₀ = 1.225 + 6.914 × 10⁵ M^-1[TPA], R² = 0.997 for TbCF₃-COF and I/I₀ = 1.063 + 9.222 × 10⁴ M^-1 [TPA], R² = 0.993 for TbDBM-COF. TbCF₃-COF showed better sensing performance than TbDBM-COF, due to its suitable ligand triplet energy level. Their sensing mechanism was revealed as dopant "replacement", where dopant molecules loaded in COF micropore were replaced by TPA molecules, accompanied with energy competing on Tb(III) ⁵D₄ level, showing ratiometric signals. Good selectivity and removal capacity (∼7.4 wt%) for TPA were achieved.

Recent advances in airborne pathogen detection using optical and electrochemical biosensors

The world is currently facing an adverse condition due to the pandemic of airborne pathogen SARS-CoV-2. Prevention is better than cure; thus, the rapid detection of airborne pathogens is necessary because it can reduce outbreaks and save many lives. Considering the immense role of diverse detection techniques for airborne pathogens, proper summarization of these techniques would be beneficial for humans. Hence, this review explores and summarizes emerging techniques, such as optical and electrochemical biosensors used for detecting airborne bacteria (Bacillus anthracis, Mycobacterium tuberculosis, Staphylococcus aureus, and Streptococcus pneumoniae) and viruses (Influenza A, Avian influenza, Norovirus, and SARS-CoV-2). Significantly, the first section briefly focuses on various diagnostic modalities applied toward airborne pathogen detection. Next, the fabricated optical biosensors using various transducer materials involved in colorimetric and fluorescence strategies for infectious pathogen detection are extensively discussed. The third section is well documented based on electrochemical biosensors for airborne pathogen detection by differential pulse voltammetry, cyclic voltammetry, square-wave voltammetry, amperometry, and impedance spectroscopy. The unique pros and cons of these modalities and their future perspectives are addressed in the fourth and fifth sections. Overall, this review inspected 171 research articles published in the last decade and persuaded the importance of optical and electrochemical biosensors for airborne pathogen detection.

Eye-Visible Oxygen Sensing via In-Situ Synthesizing Blue-Emitting Cu(I) Cluster in Red-Emitting COF: Characterization and Performance

Covalent organic frameworks (COFs) have shown virtues of well-defined and uniform pores with structural diversity, including the shape, size and even chemical nature of pores. These features are excellent for the application of O₂ gas optical sensors. In this paper, two oxygen probes based on halogen-bridged Cu cluster were in-situ synthesized in the micropores of COFs, to allow a uniform distribution. The resulting composite samples were characterized in detail to confirm the successful probe loading. The doping level was determined as ~22%. The halogen-bridged Cu clusters showed blue emission peaking at ~440 nm, while COF host showed red emission peaking at 630 nm. These halogen-bridged Cu clusters had long emissive lifetime of ~6.7 μs and high emission quantum yield of 0.30 in pure N₂ atmosphere. Given pure O₂ atmosphere, lifetime and quantum yield were quenched to 2.5 μs and 0.11, showing oxygen-sensing possibility. A linear oxygen-sensing calibration curve was observed, with sensitivity of 12.25, response time of 13 s and recovery time of 38 s. Sample emission color was changed from blue to red when testing atmosphere was changed from pure N₂ to pure O₂, which was detectable by eyes.

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.

Controllable Enhanced Ru(bpy)32+ Electrochemiluminescence Detection Systems Based on Eu@MOF253@AuNPs/GCE for the Sensitive Detection of Carbaryl in Food

In this study, an electrochemiluminescence detection system for the sensitive detection of carbaryl was constructed based on the dual identification of Eu@MOF253, which has a recognition effect on carbaryl, and the electrochemiluminescence system of Ru(bpy)₃²⁺/S₂O₈^2-, which can react with carbaryl in a redox reaction. This method not only overcame the weakness of the electrochemiluminescence instability of the Ru(bpy)₃²⁺/S₂O₈^2- system but also changed the sensitivity of the sensing detection system to the target by adjusting the concentration of Ru(bpy)₃²⁺ and then proposed a detection strategy with a controllable detection range. After analyzing the electrochemiluminescence signal change mechanism of this system and optimizing the detection conditions, it was concluded that the strategy has good linear detection of carbaryl in the range of 1-1000 and 0.02-0.3 μg L^-1, and the detection limits were 0.058 and 0.014 μg L^-1. Finally, the strategy was also successfully applied to the detection of actual samples.

Rapid and Reliable Excitation Wavelength-Dependent Detection of 2,6-Dipicolinic Acid Based on a Luminescent Cd(II)-Tb(III) Nanocluster

A Cd(II)-Tb(III) nanocluster {[Cd₁₀Tb₉L₈(OH)₁₆(OAc)₂₃(H₂O)₃][Cd₁₀Tb₉L₈(OH)₁₆(OAc)₂₃(H₂O)₄]}·3H₂O (1), which contains two crystallographically independent components, was constructed from a tridentate ligand (HL, 3-ethoxysalicylaldehyde). It exhibits rapid and reliable excitation wavelength-dependent luminescence response to 2,6-dipicolinic acid (DPA) [limit of detection = 0.23 nM], which is not influenced by aromatic carboxylates, amino acids, and ions. The test papers of 1 can be used to check DPA in solution. The equation I_Ex272nm/I_Ex329nm = 0.0109 × [DPA]2 + 0.106 × [DPA] + 2.39 of 1 for the luminescence response could be used to quantitatively measure the concentration of DPA in tap water. 1 displays rapid and stable luminescence response to DPA, with the sensing times shorter than 5 s and no changes for the lanthanide luminescence over 24 h.

A Red-Emitting COF Ionic Exchanged With Green-Emitting Tb(III) Complex Anion: Synthesis, Characterization, Ratiometric Emission Sensing, and Removal of Picric Acid

Picric acid (PA) is an important chemical product which has been widely used in dye manufacturing, antiseptics, and pharmaceuticals. Owing to PA’s extreme electron-deficient structure, its natural degradation is hard, leading to accumulation in the environment and finally threatening the ecosystem and human health. In this case, PA detection and removal becomes more and more important, concerning environmental protection and human health. In this study, an ionic covalent organic framework (I-COF) was synthesized and modified with a luminescent Tb(III) emitter (Tb(DPA)₃^3-, DPA = pyridine-2,6-dicarboxylic acid), via ionic exchange. The resulting composite material (Tb-COF) was fully characterized by geometric analysis, IR, XRD, porosity analysis, SEM/TEM, and elemental analysis. It was found that Tb(DPA)₃^3- was loaded into the hexagonal cage in an I-COF host with an ionic exchange ratio of 41%. The as-synthesized Tb-COF showed weak Tb(III) emission and strong red COF emission, after adding PA, Tb(III) emission was increased whereas COF emission weakened greatly, showing sensing behavior. Linear working curves were observed with good selectivity. The sensing mechanism was revealed as follows. PA molecules replaced the [Tb(PDA)₃]^3- component trapped in Tb-COF, releasing free luminescent [Tb(PDA)₃]^3-. After incorporating PA in the hexagonal cage, the COF emission was quenched. This sensing mechanism ensured a good selectivity over competing species, including cations, anions, and nitrocompounds. The adsorption and removal performance of I-COF for PA were investigated as well.

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.

Energy Transfer in Metal-Organic Frameworks for Fluorescence Sensing

The development of materials with outstanding performance for sensitive and selective detection of multiple analytes is essential for the development of human health and society. Luminescent metal-organic frameworks (LMOFs) have controllable surface and pore sizes and excellent optical properties. Therefore, a variety of LMOF-based sensors with diverse detection functions can be easily designed and applied. Furthermore, the introduction of energy transfer (ET) into LMOFs (ET-LMOFs) could provide a richer design concept and a much more sensitive and accurate sensing performance. In this review, we focus on the recent five years of advances in ET-LMOF-based sensing materials, with an emphasis on photochemical and photophysical mechanisms. We discuss in detail possible energy transfer processes within a MOF structure or between MOFs and guest materials. Finally, the possible sensing applications of the ET-LMOF-based sensors are highlighted.

A biological luminescent metal-organic framework with high fluorescence quantum yield for the selective detection of amino acids and monosaccharides

The biological luminescent metal-organic framework (bio-LMOF), (Me2NH2)2[Zn6O(Ade)4(TCPPE)2] (1) {H4TCPPE = tetrakis[4-(4-carboxyphenyl)phenyl]ethene, Ade = adenine} was successfully designed and synthesized under hydrothermal conditions, with two channels of different sizes. The absolute fluorescence quantum yields of complex 1 and activated 1 are up to 77.6% and 85.9%, respectively. Activated 1 exhibits outstanding water stability and excellent selective luminescence sensing for amino acids and monosaccharides. The fluorescence quenching efficiencies of activated 1 towards L-Nph and D-Nga are 86.35% and 91.60%, respectively. Besides, activated 1 also displays highly quenching responses to L-Nph and D-Nga at fairly low concentrations, and the limits of detection for L-Nph and D-Nga are estimated to be 0.149 ppm and 1.612 ppm, respectively. Meanwhile, in multiple cycling experiments, activated 1 still has excellent cycling stability. These phenomena indicate that activated 1 can be utilized as a fast responsive biological luminescent sensor, which is a rare example for bio-LMOFs.

Metal-Organic Frameworks-Based Sensors for Food Safety

Food contains a variety of poisonous and harmful substances that have an impact on human health. Therefore, food safety is a worldwide public concern. Food detection approaches must ensure the safety of food at every step of the food supply chain by monitoring and evaluating all hazards from every single step of food production. Therefore, early detection and determination of trace-level contaminants in food are one of the most crucial measures for ensuring food safety and safeguarding consumers' health. In recent years, various methods have been introduced for food safety analysis, including classical methods and biomolecules-based sensing methods. However, most of these methods are laboratory-dependent, time-consuming, costly, and require well-trained technicians. To overcome such problems, developing rapid, simple, accurate, low-cost, and portable food sensing techniques is essential. Metal-organic frameworks (MOFs), a type of porous materials that present high porosity, abundant functional groups, and tunable physical and chemical properties, demonstrates promise in large-number applications. In this regard, MOF-based sensing techniques provide a novel approach in rapid and efficient sensing of pathogenic bacteria, heavy metals, food illegal additives, toxins, persistent organic pollutants (POPs), veterinary drugs, and pesticide residues. This review focused on the rapid screening of MOF-based sensors for food safety analysis. Challenges and future perspectives of MOF-based sensors were discussed. MOF-based sensing techniques would be useful tools for food safety evaluation owing to their portability, affordability, reliability, sensibility, and stability. The present review focused on research published up to 7 years ago. We believe that this work will help readers understand the effects of food hazard exposure, the effects on humans, and the use of MOFs in the detection and sensing of food hazards.

In situ ligand-induced Ln-MOFs based on a chromophore moiety: white light emission and turn-on detection of trace antibiotics

Series novel 3D Ln-MOFs containing both carboxyphenyl and pyridinyl moieties have been constructed. Tb-MOF fluorescence turn-on sensor of levofloxacin solution with highly sensitive and excellent selective was achieved through d-PET approach.

A high-nuclearity Cd(ii)–Nd(iii) nanocage for the rapid ratiometric fluorescent detection of quercetin

A 32-metal Cd(ii)–Nd(iii) nanocage was constructed, and it shows rapid and stable ratiometric fluorescent response to quercetin.

A time-resolved ratiometric luminescent anthrax biomarker nanosensor based on Ir(III) complex-doped coordination polymer network

Herein, an Ir(III) complex-doped coordination polymer networks (Ir(III)@GMP-Eu3+) is firstly fabricated for the ratiometric luminescent detection of anthrax biomarker 2,6-dipicolinic acid (DPA) through time-resolved emission spectra (TRES) measurement. The detection...

Construction of a Cd8Tb4 nanoring for luminescence response to 2,6-dipicolinic acid as an anthrax biomarker

One 12-metal Cd(ii)–Tb(iii) nanoring (1.2 × 2.8 × 2.8 nm) was constructed from a flexible Schiff base ligand, and it shows luminescent response to 2,6-dipicolinic acid with high sensitivity and selectivity.

Excited State Energy Transfer in Metal-Organic Frameworks

Excited state energy transfer in metal-organic frameworks (MOFs) is of great interest due to potential application of these materials in photocatalysis and fluorescence sensing. In photocatalysis, a light-harvesting antenna of MOFs can collect energy from a much larger area than a single reaction center and efficiently transport the energy to the active site to enhance photocatalytic efficiency, mimicking nature photosynthesis. In fluorescence sensing, excited state traveling on the framework can search for analyte quencher molecules to give amplified fluorescence quenching, so that one quencher turns off multiple excited states to enhance signal. Key to these designer performances is highly efficient energy transfer on these framework materials that are determined by types of excited states, dimension of the materials, and structure of the frameworks. Advancement of MOF synthetic chemistry provides new tools to control the rate and directionality of energy transfer in these materials, opening opportunities in manipulating excited states at an unprecedented level.

Chiral fluorescence recognition of glutamine enantiomers by a modified Zr-based MOF based on solvent-assisted ligand incorporation

In this study, three types of chiral fluorescent zirconium-based metal-organic framework materials were synthesized using l-dibenzoyl tartaric acid as the chiral modifier by the solvent-assisted ligand incorporation method, which was the porous coordination network yellow material, denoted as PCN-128Y. PCN-128Y-1 and PCN-128Y-2 featured unique chiral selectivity for the Gln enantiomers amongst seven acids and the highly stable luminescence property, which were caused by the heterochiral interaction and aggregation-induced emission. Furthermore, a rapid fluorescence method for the chiral detection of glutamine (Gln) enantiomers was developed. The homochiral crystals of PCN-128Y-1 displayed enantiodiscrimination in the quenching by d-Gln such that the ratio of enantioselectivity was 2.0 in 30 seconds at pH 7.0, according to the Stern-Volmer quenching plots. The detection limits of d- and l-Gln were 6.6 × 10-4 mol L-1 and 3.3 × 10-4 mol L-1, respectively. Finally, both the maximum adsorption capacities of PCN-128Y-1 for the Gln enantiomers (Q e(l-Gln) = 967 mg g-1; Q e(d-Gln) = 1607 mg g-1) and the enantiomeric excess value (6.2%) manifested that PCN-128Y-1 had strong adsorption capacity for the Gln enantiomers and higher affinity for d-Gln.

A simple strategy for the detection of Pb(II) and Cu(II) by an electrochemical sensor based on Zn/Ni-ZIF-8/XC-72/Nafion hybrid materials

In this study, a novel electrochemical sensor for simultaneous detection of Pb(II) and Cu(II) was constructed by using Zn/Ni-ZIF-8/XC-72/Nafion hybrid material as electrode surface modifier. XRD, FT-IR, XPS and SEM were used to study the crystal structure, functional groups, element types and morphologies of the prepared materials. The electrochemical performance of the Zn/Ni-ZIF-8/XC-72/Nafion/GCE sensor were investigated by CV, EIS and DPV. In addition, the effects of various conditions including pH, the type of buffer and the ratio of Zn/Ni-ZIF-8 to XC-72 were also explored for the determination of Pb(II) and Cu(II). Under the optimum conditions, the constructed sensor exhibited outstanding linear response of Pb(II) (0.794-39.6 ppm) and Cu(II) (0.397-19.9 ppm) with detection limits of 0.0150 and 0.0096 ppm, respectively. Finally, the fabricated sensor was further used to detect Pb(II) and Cu(II) in real samples, and the satisfactory recovery was obtained.

A Dual-emitting Two-dimensional Nickel-based Metal-organic Framework Nanosheets: Eu3+/Ag+ Functionalization Synthesis and Ratiometric Sensing in Aqueous Solution

Using two-dimensional (2D) nickel-based metal organic framework (Ni-MOF) nanosheets as a matrix, Eu³⁺ and Ag⁺ were incorporated to synthesize Ag/Eu@Ni-MOF with double luminescence centers of Eu³⁺ ion (615 nm) and organic ligand (524 nm). And a ratiometric luminescence sensor is constructed based on Ag/Eu@Ni-MOF for sensitive detection of biothiols in aqueous solutions. The dual-emissive fluorescence properties can be tuned by changing the amounts of Ag⁺ ions doping. The results of temperature and pH effects on the fluorescence of Ag/Eu@Ni-MOF indicates that the Ag/Eu@Ni-MOF is a temperature-sensitive material and the fluorescence of Ag/Eu@Ni-MOF can keep stable over a wide pH range. Due to the binding of -SH in cysteine (Cys) and glutathione (GSH) with Ag⁺, the ligand luminescence was significantly inhibited by weakening the Ag + influence on the energy transfer process in the MOFs. Therefore, ratiometric fluorescent sensing of biomolecular thiols was realized based on the dual-emission Ag/Eu@Ni-MOF. More importantly, the fluorescence color change can be observed with naked eyes to realize visual detection. The ratiometric fluorescent sensor exhibits high performance for Cys and GSH detection with a wide linear range of 5-250 µM and a relatively low detection limit of 0.20 µM and 0.17 µM, respectively. Furthermore, the biothiols content in human serum was determined with satisfactory results. It proves the Ni-MOF nanosheets can be used as a stable matrix for construction luminescent MOFs for the first time, and validate the great potential of Ag/Eu@Ni-MOF as a ratiometric fluorescent probe for point-of-care testing (POCT) in disease diagnosis.