Dual-Ligand Lanthanide Metal-Organic Framework for Sensitive Ratiometric Fluorescence Detection of Hypochlorous Acid

Fabrication of Dual-Ligand Zn-MOFs with Asynchronous Fluorescence Response for Efficient Ratiometric/Visual Sensing of Tetracycline Antibiotics in Animal-Derived Foods

The extensive use of tetracyclines in livestock poses health risks due to their residues in animal-derived food; therefore, developing simple detection methods to replace complex traditional approaches is of paramount importance. Here, we developed a dual-ligand zinc-based metal-organic framework material, Zn-BTC-BDC-NH2 (denoted as ZTD), for the detection of tetracyclines. The intrinsic blue fluorescence of ZTD was quenched upon the introduction of tetracyclines due to electron transfer from -NH2 of ZTD to -CO- and -OH groups of tetracycline molecules; meanwhile, the new green fluorescence emission was generated through π-π stacking between aromatic rings and the formation of complexes between Zn2+ and C-O/C═O groups. In real food samples, ZTD exhibited recovery rates ranging from 93.62 to 110.66%, with detection limits as low as 0.011 μmol·L-1. Additionally, a ZTD fluorescence test paper was developed for portable detection. This study presents a novel tetracycline detection method, offering insights into multiligand metal-organic framework preparation and future sensing method design.

Ultrasensitive "On-Off" Ratiometric Fluorescence Biosensor Based on RPA-CRISPR/Cas12a for Detection of Staphylococcus aureus

Staphylococcus aureus (S. aureus) is a major pathogenic bacterium responsible for bacterial foodborne diseases, making its rapid, specific, and accurate detection crucial. In this study, we develop a ratiometric biosensor based on the recombinase polymerase amplification-clustered regularly interspaced short palindromic repeats/CRISPR associated protein 12a (RPA-CRISPR/Cas12a) system and Eu-metal-organic framework (Eu-MOF) fluorescent nanomaterials for the high-sensitivity detection of S. aureus, combining with RPA for efficient isothermal amplification, this sensor enhances specificity and sensitivity by utilizing the target activation of CRISPR/Cas12a. The Eu-MOF serves a dual function, providing stable red fluorescence as a reference signal and adsorbing FAM-labeled probes for fluorescence quenching, forming a dual-signal system that significantly reduces background interference. This ratiometric design enables accurate and quantitative detection over a wide range (7.9 × 100 to 7.9 × 108 CFU/mL) with a low detection limit of 3 CFU/mL. Overall, with these merits of simplicity, rapid response, high sensitivity, and specificity, this dual-signal biosensor offers a promising method for accurately evaluating S. aureus contamination in food under complex substrate conditions.

Low background dual-ligand Cu-MOF nanoprobe for plant tissue imaging and fast screening as well as sensitive detection of glyphosate in environmental samples

The monitoring of glyphosate residue in environmental samples is critically important due to its high environmental risk. Here, we reported a low background dual-ligand and fast response copper-based metal organic framework (Cu-MOF) nanoprobe for imaging glyphosate in plant tissue, rapid screening of glyphosate-contaminated samples, and sensitive detection of glyphosate in environmental samples. The Cu-MOF nanoprobe was prepared with 2-Aminoisophthalic Acid (AIA) and trimesic acid (H3BTC) as ligands, and Cu2+ as a metal node. Thanking to both ligand-to-metal charge transfer (LMCT) and photoinduced electron transfer (PET) effects, the fluorescence of ligand AIA could be fully quenched in Cu-AIA/BTC probe. Upon the addition of glyphosate, it competed with the ligands in Cu-AIA/BTC probe, causing the collapse of MOF structure and the release of ligand AIA with obvious fluorescence recovery. This nanoprobe exhibited a desirable linear response for glyphosate in the concentration range of 0.1-80 μM, with a low detection limit of 33 nM, much lower than the maximum contaminant level (4.1 μM) set by the U.S. Environmental Protection Agency (EPA). Furthermore, it was also successfully applied for plant tissue imaging, fast screening of glyphosate-contaminated samples and monitoring of the degradation of glyphosate on tea leaves and in soil, indicating the broad application prospect of the nanoprobe.

Amino-functionalized HPU-23@Ru@Tb as light-driven oxidase-like nanozyme for colorimetric recognition of Hg2+ and ratiometric fluorescence sensing of ClO- and PO43

A HPU-23@Ru@Tb-NH2 sensor array with light-driven oxidase-mimicking activity and triple-emission fluorescence was developed. It was composed of a Tb3+-functionalized metal organic framework and Ru(bpy)32+ and applied to the simultaneous detection of Hg2+, ClO-, and PO43- via differently responsive channels. HPU-23@Ru@Tb-NH2 had a photoresponsive colorimetric response toward Hg2+ with a LOD as low as 4.18 nM. In addition, the three emissions of the HPU-23@Ru@Tb-NH2 sensor array were influenced by ClO- and PO43- to varying degrees, causing remarkably distinguishable responses for the fluorescence channels to discriminate ClO- and PO43- from each other. The detection limits of ClO- and PO43- were 12.26 µM and 0.197 nM, respectively. Therefore, this work demonstrates the feasibility of multi-emission and multi-mode sensing platform, which is able to combine the advantages of different strategies for solving the problems of various toxic substances coexisting in the environment while meeting the needs of accurate and precise results and no side interferences.

A Multifunctional Tb(III)-Based Metal-Organic Framework for Chemical Conversion of CO2, Fluorescence Sensing of Trace Water and Metamitron

The utilization of metal-organic frameworks (MOFs) as fluorescent sensors for the detection of environmental and chemical reagent pollutants as well as heterogeneous catalysis for CO2 conversion represents a crucial avenue of research with significant implications for the protection of human health. In this work, a Tb(III)-based three-dimensional metal-organic framework, [Tb(L)·4DMF]n (Tb-MOF) (H3L = 5'-(4-carboxy-3-hydroxyphenyl)-3,3″-dihydroxy-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid), has been structurally conformed by single-crystal X-ray crystallography. It possesses a 1D rhombus channel along the [010] direction, featuring a pore size of 6.02 × 9.13 Å. Tb-MOF was proved to be a multifunctional material for a fluorescent sensor and CO2 cycloaddition heterogeneous catalyst material. Fluorescence sensing studies revealed that Tb-MOF demonstrates high sensitivity, selectivity, and favorable regeneration properties, making it an effective chemosensor for detecting the metamitron (MMT) pesticide and trace water in organic solvents. The mechanism of fluorescence quenching by MMT and water was elucidated by a combination of XRD, UV-vis absorption spectra, IR spectra, theoretical calculations, and fluorescence lifetimes. The material was also utilized for the sensing of MMT and water in paper strips. Additionally, the open Tb3+ site as Lewis acidic centers makes Tb-MOF achieve efficiently catalytic conversion for CO2 and epoxides to cyclic carbonates. Moreover, a possible catalytic mechanism for the conversion of carbon dioxide to cyclic carbonates was proposed by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments. It also exhibited recyclability for up to five cycles without noticing an appreciable loss in sensing or catalytic efficiency.

A Multimode Optical Sensor for Highly Selective and Sensitive Detection of Hypochlorous Acid in Water and Body Fluid

Hypochlorous acid (HClO), as an important reactive oxygen species (ROS), plays a crucial role in our daily life and in biological systems, and its convenient and accurate detection is significant and imperative. In this work, a self-calibrated multimode optical sensor for convenient and accurate HClO detection was elaborately fabricated based on a multifunctional metal-organic framework platform with catalytic active metal nodes, fluorescent responsive bridging ligands, and intrinsic pores for functional molecule accommodation. The sensor shows not only turn-on and ratiometric fluorescence response but also color change in response to HClO. The detection limits are as low as 16.9, 17.3, 66.5, and 63.2 nM for ratiometric fluorometry, absorbance-based colorimetry, and smartphone-based fluorescenceand color analysis, respectively. The accuracy and practicability of this sensor were also demonstrated by the detection of hypochlorous acid in actual water and body fluid samples, and the recovery rates ranged from 97.8 to 103.8%.

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

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

Dual-Response Visual Fluorescent Probes for the Determination of Vanadate and Morphology over a Wide pH Range

Vanadate has become an important indicator for environmental testing due to its high toxicity, mobility, and difficulty in degradation. In addition, depending on its dynamic aggregation, analyzing vanadate is not a single content test; it needs further morphological analysis. Previous research has tended to construct a single functional platform with complicated procedures and expensive equipment, making it difficult to obtain a comprehensive picture of vanadate in a short time. Herein, we constructed a dual-response fluorescent probe EuTAT@Rh B formed by Eu3+, 2-aminoterephthalic acid (TAT), and rhodamine B, which could generate structural changes based on the morphology distribution characteristics of vanadate with pH. In the concentration range from 5 × 10-7 to 2 × 10-4 mol/L, the detection limits (3σ/slope, σ = s/I0) of orthovanadate VO43- and metavanadate VO3- were 1.67 × 10-8 and 2.0 × 10-9 mol/L, respectively. In addition, under 254 nm UV light, the spirolactam ring-controlled structures varied with pH and vanadate concentration, producing different types of photochromic structures, which were able to correspond essentially to the pH range of vanadate morphology distribution. Thus, a window with both vanadate and pH signals was constructed under the dual channels of UV and fluorescence, and we successfully achieved the visual integrated analysis of vanadate. This dual-channel visualization method has the advantages of simplifying the analysis process and improving the detection efficiency, which is of great significance in practical applications and provides a way to identify other polymeric substances.

A handheld fluorescent platform integrated with a Sm(III)-CdTe quantum dot-based ratiometric nanoprobe for point-of-use determination of phosphate

Phosphate (Pi) is crucial for various physiological processes and aquatic environments, which emphasizes the need for a simple, on-site sensor to promptly detect Pi for human health and environmental conservation. In this study, we propose a dual-emission ratiometric fluorescence sensor for highly sensitive and visual Pi detection. The sensor employs samarium ions (Sm3+) as a core component, with cadmium telluride quantum dots (CdTe QDs) and ofloxacin (OFL) serving as signal carriers. The CdTe-Sm(III)-OFL nanoprobe emits a purple fluorescence resulting from the red fluorescence of CdTe QDs and the blue-green fluorescence of OFL. The fluorescence of OFL is quenched by Sm3+ through fluorescence resonance energy transfer (FRET). Upon Pi interaction, the FRET process is disrupted due to the competitive Pi-Sm3+ binding, which leads to the fluorescence recovery of OFL while the red fluorescence of CdTe remains steady. This enables the construction of a ratiometric fluorescent sensor for Pi detection, manifesting as a color change from purple to blue. The sensor demonstrated a linear response for Pi detection within the range of 0.1-75 μM, with a low detection limit of 17.0 nM. By utilizing the distinct fluorescence responses of various physiological phosphates and employing chemometrics, this innovative dual-emission sensor accurately distinguishes among different physiological phosphates. Furthermore, a portable lab-on-paper device based on CdTe-Sm(III)-OFL, coupled with a smartphone-integrated mini-device, is developed for swift Pi detection using an ordinary smartphone. Analytical performance validated on environmental and biological samples demonstrates the sensor's excellent robustness and adaptability. This study introduces a pioneering approach to fabricate ratiometric fluorescence sensors and customize portable, cost-effective mini-devices for precise target detection, thus opening avenues for advanced sensing strategies in various applications.

Eu3+-Doped Mixed-Ligand UiO-66-Type Metal-Organic Framework for Ratiometric Fluorescence Sensing Fluoride Ions with Ultralow Detection Limit

Metal-organic frameworks (MOFs) have emerged as a highly promising platform for various sensing applications due to their tunable structures and functionalities. In the present work, a Eu3+-doped mixed-ligand MOF, namely, the Eu3+@UiO-66-IPA, exhibited excellent luminescent properties and high fluorescence stability in aqueous media, displaying dual-emission peaks under 395 and 615 nm excitation that were readily visible to the naked eye. Importantly, the presence of fluoride ions (F-) promoted the "antenna effect" between the ligand and the Eu3+ centers, which significantly enhanced the emission intensity of the Eu3+ characteristic peak. In addition, the addition of F- also inhibited the quenching effect of high-energy O-H bonds existing in the aqueous environment. Notably, Eu3+@UiO-66-IPA demonstrated exceptional selectivity for F- over a range of competing anions, with a remarkable limit of detection as low as 0.22 μM. The developed Eu3+-doped mixed-ligand MOF system offers a highly promising strategy for the simple and accurate sensing of F- in practical applications.

Metal-Organic Frameworks for Sustainable Crop Disease Management: Current Applications, Mechanistic Insights, and Future Challenges

Efficient management of crop diseases and yield enhancement are essential for addressing the increasing food demands due to global population growth. Metal-organic frameworks (MOFs), which have rapidly evolved throughout the 21st century, are notable for their vast surface area, porosity, and adaptability, establishing them as highly effective vehicles for controlled drug delivery. This review methodically categorizes common MOFs employed in crop disease management and details their effectiveness against various pathogens. Additionally, by critically evaluating existing research, it outlines strategic approaches for the design of drug-delivery MOFs and explains the mechanisms through which MOFs enhance disease resistance. Finally, this paper identifies the current challenges in MOF research for crop disease management and suggests directions for future research. Through this in-depth review, the paper seeks to enrich the understanding of MOFs applications in crop disease management and offers valuable insights for researchers and practitioners.

Fabrication of a two-dimensional bi-lanthanide metal-organic framework as a ratiometric fluorescent sensor based on energy competition

Bimetallic lanthanide metal-organic frameworks (bi-Ln-MOFs) exhibit great appeal for ratiometric luminescent sensors due to their unique advantages. Specially, the low-lying energy of the empty 4f band of Ce4+ ions benefits Ce-MOFs with robust and broad fluorescent emission. Therefore, constructing ratiometric sensors based on Ce-MOFs is of significance but remains a challenge. Here, a two-dimensional (2D) bi-Ln-MOF is fabricated using Eu3+/Ce4+ and 5-boronoisophthalic acid (5-bop) via a crystal phase transformation strategy to construct a ratiometric luminescent Hg2+ sensor. Due to the lower energy gap of Ce4+ compared to Eu3+ and the corresponding stronger energy-absorption ability, the Ce4+ in bi-Ln-MOF shows a stronger and broader fluorescent emission than that of Eu3+. The substitution of the boric acid group in the bi-Ln-MOF by Hg2+ amplifies the difference between the two lanthanide ions. Therefore, the fluorescence intensity of Ce4+ increases whereas that of Eu3+ decreases accordingly, a behavior distinct from individual Eu-MOF or Ce-MOF performance. This novel bi-Ln-MOF sensor not only achieves a wide linear response range from 0.5 to 120 μM with a low detection limit of 167 nM for Hg2+, but also demonstrates exceptional selectivity and stability. The intriguing sensing mechanism of energy competition and the novel synthesis approach for 2D bi-Ln-MOF are anticipated to broaden the application possibilities of bi-Ln-MOFs for designing ratiometric sensors.

Dimensional regulation of lanthanide metal-organic frameworks and their application in bacterial detection

Low-dimensional (LD) lanthanide metal-organic frameworks (Ln-MOFs) have attracted considerable attention in different fields due to their exceptional optical properties and numerous accessible active sites. Through the dimensional regulation effect of dipicolinic acid (DPA), a new LD Ln-MOF crystal is synthesized to monitor nitroreductase (NTR) activity in living bacteria.

A Dy(III) Coordination Polymer Material as a Dual-Functional Fluorescent Sensor for the Selective Detection of Inorganic Pollutants

A Dy(III) coordination polymer (CP), [Dy(spasds)(H2O)2]n (1) (Na2Hspasds = 5-(4-sulfophenylazo)salicylic disodium salt), has been synthesized using a hydrothermal method and characterized. 1 features a 2D layered structure, where the spasda3- anions act as pentadentate ligands, adopting carboxylate, sulfonate and phenolate groups to bridge with four Dy centers in η3-μ1: μ2, η2-μ1: μ1, and monodentate coordination modes, respectively. It possesses a unique (4,4)-connected net with a Schläfli symbol of {44·62}{4}2. The luminescence study revealed that 1 exhibited a broad fluorescent emission band at 392 nm. Moreover, the visual blue color has been confirmed by the CIE plot. 1 can serve as a dual-functional luminescent sensor toward Fe3+ and MnO4- through the luminescence quenching effect, with limits of detection (LODs) of 9.30 × 10-7 and 1.19 × 10-6 M, respectively. The LODs are relatively low in comparison with those of the reported CP-based sensors for Fe3+ and MnO4-. In addition, 1 also has high selectivity and remarkable anti-interference ability, as well as good recyclability for at least five cycles. Furthermore, the potential application of the sensor for the detection of Fe3+ and MnO4- was studied through simulated wastewater samples with different concentrations. The possible sensing mechanisms were investigated using Ultraviolet-Visible (UV-Vis) absorption spectroscopy and density functional theory (DFT) calculations. The results revealed that the luminescence turn-off effects toward Fe3+ and MnO4- were caused by competitive absorption and photoinduced electron transfer (PET), and competitive absorption and inner filter effect (IFE), respectively.

Multiple Stimulus Response Material Based on Sr-tcbpe MOF for Mechanochromism, Visualization Labeling, and Etching Toward TNP

The abuse and excessive discharge of organic pollutants such as nitroaromatic compounds (NACs) have become a hot topic of concern for all humanity and society, and the development of fast, effective, and targeted technical means for detecting NACs also faces many challenges. Here, we reported a strontium-based metal-organic framework (MOF) {[Sr2(tcbpe)(H2O)4]}n (Sr-tcbpe), in which tcbpe represents deprotonated 4',4‴,4″‴,4‴‴-(ethene-1,1,2,2-tetrayl)tetrakis(([1,1'biphenyl]-4-carboxylic acid)). In Sr-tcbpe, Sr-O polyhedron and deprotonated tcbpe4- ligand have a staggered connection to form a self-assembled three-dimensional network structure. In addition, it is found that Sr-tcbpe undergoes no luminescent color change when grinding under solvent protection, while mechanochromic fluorescence behavior is observed when grinding directly, leading to luminescent color changes from cyan to green (Sr-tcbpe-G). Additionally, Sr-tcbpe and Sr-tcbpe-G could selectively detect PNP, DNP, and TNP, and Sr-tcbpe achieves visual fluorescence sensing detection toward TNP at a limit of detection as low as 2.25 μM. Moreover, during the detection process, unexpectedly, TNP exhibits a selective etching effect on Sr-tcbpe, which could drill nano holes with different sizes on the surface area of MOF materials to a certain extent, achieving the conversion of chemical energy to mechanical energy. In addition, the successful preparation of a portable sensor Sr-tcbpe@gypsum block provides a platform for the perfect combination of mechanochromic fluorescence behavior and visualization detection toward TNP. It lays the foundation for the practical application of MOF materials in daily life.

Construction of CDs@β-CD@CCM ratiometric fluorescence probe for FRET-based ClO--sensing

β-Cyclodextrin (β-CD)-functionalized carbon quantum dots (CDs) loaded with curcumin (CCM) were used for ClO-sensing with high sensitivity and selectivity. This fluorescence resonance energy transfer (FRET)-based sensor was created through attaching CCM to the CDs via β-CD linker. CCM could get into the interior of β-CD triggering the FRET from CDs to CCM, providing an 'off' state of the CDs. However, the effect of FRET was weakened by the ClO-, because the o-methoxyphenol structure from CCM was oxidized to be benzoquinone. The fluorescence intensity of CDs@β-CD@CCM at 440 nm can be heightened and 520 nm from CCM can decrease along with the increased ClO-. Therefore, a ratiometric fluorescence probe for ClO-sensing is successfully constructed. It conforms to a polynomial curve equation which is I440/I520= -0.0268 + 0.0315 CClO-+ 0.0055[CClO-]2(R2= 0.9958) between 0 and 18.4μM ClO-. Furthermore, we also obtain excellent results using this spectrophotometric method for ClO--sensing in pure water and commercial disinfectants, which afford potential in the environment monitoring area. We expect this sensing platform could be helpful in other analogous probes in relevant fields.

Dual-ligand lanthanide metal-organic framework based ratiometric fluorescent platform for visual monitoring of aminoglycoside residues in food samples

Herein, a dual-emission Eu metal-organic framework (Eu-MOF) is prepared and used as the ratiometric fluorescence probe for ultrasensitive detection of aminoglycoside antibiotics (AGs). Due to the strong hydrogen bond interactions between AGs and Eu-MOF, the blue emission is enhanced while the red emission has little fluctuation in Eu-MOF with the addition of AGs, thus a good linear relationship with the logarithm of AGs concentrations from 0.001 to 100 μg/mL can be established for quantitative analysis. Good sensitivity with the detection limit of 0.33 ng/mL for apramycin, 0.32 ng/mL for amikacin and 0.30 ng/mL for kanamycin is achieved. The proposed assay demonstrates good selectivity and applicability for determination of AGs in real milk and honey samples. The Eu-MOF materials are further fabricated as fluorescent test papers for facile visual detection. The as-established ratio fluorescence platform offers a portable and economical way for rapid monitoring AGs residues in complex food samples.

Dual-ligand Eu-MOF/CuS@Au Heterostructure Array-based ECL Sensor for MiRNA-128 Detection in Glioblastoma Tissues

In this work, the dual-ligand lanthanide metal-organic framework (MOF)-based electrochemiluminescence (ECL) sensor was constructed for the detection of miRNA-128 in glioblastoma (GBM) diagnosis. The luminescent Eu-MOF (EuBBN) was synthesized with terephthalic acid (BDC) and 2-amino terephthalic acid (BDC-NH2) as dual-ligand. Due to the antenna effect, EuBBN with conjugated-π structure exhibited strong luminescent signal and high quantum efficiency, which can be employed as ECL nanoprobe. Furthermore, the novel plasmonic CuS@Au heterostructure array has been prepared. The localized surface plasmon resonance coupling effect of the CuS@Au heterostructure array can amplify the ECL signal of EuBBN significantly. The EuBBN/CuS@Au heterostructure array-based sensing system has been prepared for the detection of miRNA-128 with a wide linear range from 1 fM to 1 nM and a detection limit of 0.24 fM. Finally, miRNA-128 in the clinic GBM tissue sample has been analysis for the distinguish of tumor grade successfully. The results demonstrated that the dual-ligand MOF/CuS@Au heterostructure array-based ECL sensor can provide important support for the development of GBM diagnosis.

Regulation of the Metal Center in Lanthanide Nanoparticles to Achieve Multifunctional Sensing

Development of a multifunctional sensor is highly desirable. In this work, traces of a carcinoid cancer biomarker of 5-hydroxyindole-3-acetic acid (5-HIAA) in real human urine can be detected by lanthanide nanoparticle Eu-CFC (CFC = 7-chloro-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid) and the sensing devices of the test paper and agarose gel, achieving an ultralow LOD of 0.8 × 10-3 ppm within a sensing time of 2.0 min. Interestingly, by metal center regulation of Tb and Eu codoping, nanoparticle TbEu2-CFC shows high-sensitivity and low-LOD (0.019% v/v) sensing of water in ethanol. The sensing mechanisms are revealed by both experiments and quantum chemical studies.

Oxolinic Acid Generated Green Fluorescence Based on a Terbium-Functionalized Covalent Organic Framework

Oxolinic acid (OXO), a classic environmental contaminant, has a terrible detrimental effect on human health. The exploration of efficient strategies to detect and detecting OXO has remarkable significance. Herein, we reported a novel terbium(III)-functionalized covalent organic framework (Bpy-DhBt-COF@Tb3+) by fixing Tb3+ on the bipyridine-connecting COF (Bpy-DhBt-COF) as a turn-on fluorescent switch toward OXO for the first time. In this platform, Tb3+ acts as the specific recognition units for OXO and the response signal, while Bpy-DhBt-COF acts as the safehaven for Tb3+. Once introducing OXO to Bpy-DhBt-COF@Tb3+, OXO can instead water molecules coordinate with Tb3+ and sensitize Tb3+ instantly, thereby producing a significant fluorescence signal. Profiting from the excellent porosity of Bpy-DhBt-COF@Tb3+, it can obtain optimal response toward OXO only within 10 s with an ultrasensitive detection limit of 12.5 nM. Furthermore, Bpy-DhBt-COF@Tb3+ displayed outstanding selectivity toward OXO than other general quinolones. Based on these, a Tb3+-based COF was explored for the first time for the turn-on fluorescence detection of an OXO with rapid response, high sensitivity, and outstanding selectivity. In this work, we not only exhibit the attractive performance of Tb3+-functionalized COF to detect OXO but also propose a prospect strategy for creating other fluorescent sensors for multiple targets.

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

A Zn(II) Coordination Polymer for Fluorescent Turn-Off Selective Sensing of Heavy Metal Cation and Toxic Inorganic Anions

A novel coordination polymer [Zn(atyha)2]n (1) (Hatyha = 2-(2-aminothiazole-4-yl)-2- hydroxyiminoacetic acid) was constructed by hydrothermal reaction of Zn2+ with Hatyha ligand. CP 1 exhibits a 2D (4,4)-connected topological framework with Schläfli symbol of {44·62}, where atyha- anions serve as tridentate ligands, bridging with Zn2+ through carboxylate, thiazole and oxime groups. CP 1 displays a strong ligand-based photoluminescence at 390 nm in the solid state, and remains significantly structurally stable in water. Interestingly, it can be utilized as a fluorescent probe for selective and sensitive sensing of Fe3+, Cr2O72- and MnO4- through the fluorescent turn-off effect with limit of detection (LOD) of 3.66 × 10-6, 2.38 × 10-5 and 2.94 × 10-6 M, respectively. Moreover, the efficient recyclability for detection of Fe3+ and Cr2O72- is better than that for MnO4-. The mechanisms of fluorescent quenching involve reversible overlap of UV-Vis absorption bands of the analytes (Fe3+, Cr2O72- and MnO4-) with fluorescence excitation and emission bands for CP 1, respectively.

An Oxidative Cleavage-Based Cruciform DNA Nanostructure for In Vivo Hypochlorous Acid Visualization to Monitor Intestinal Inflammation

Ulcerative colitis is a persistent inflammatory bowel disease characterized by inflammation and ulceration in the colon and gastrointestinal tract. It was indicated that the generation of hypochlorous acid (HClO) through the enzymatic activity of myeloperoxidase is significantly linked to ulcerative colitis. In this study, by assembling two hairpins (Hpa and Hpb) onto a quadrivalent cruciform DNA nanostructure, a novel HClO-activatable fluorescent probe was developed based on DNA nanomaterials (denoted MHDNA), which is sensitive, economic, simple, and stable. In the presence of HClO, the Trigger (T) was liberated from the MHDNA probe through a hydrolysis reaction between HClO and phosphorothioate (PS), which is modified on the MHDNA probe and has proved to exhibit particular susceptibility to the HClO. The liberated T subsequently initiated the opening of Hpa and Hpb to facilitate the catalyzed hairpin assembly (CHA) reaction, resulting in the changes of fluorescence and releasing T for recycled signal amplification to achieve sensitive detection of HClO (with a limit of detection 9.83 nM). Additionally, the MHDNA-based spatial-confinement effect shortens the physical distance between Hpa and Hpb and yields a high local concentration of the two reactive hairpins, achieving more rapid reaction kinetics in comparison to conventional CHA methods. Inspirationally, the MHDNA probe was effectively utilized for imaging HClO in ulcerative colitis mice, yielding valuable diagnostic insights for ulcerative colitis.

MOFs as versatile scaffolds to explore environmental contaminants based on their luminescence bustle

Metal-Organic Frameworks (MOFs) with luminescent properties hold significant promise for environmental remediation. This review critically examines recent research on these materials design, synthesis, and applications, mainly focusing on their role in combating environmental pollutants. Through a comprehensive analysis of metal ions, ligands, and framework compositions, the review discusses the importance of tailored design and synthesis approaches in achieving desired luminescent characteristics. Key findings highlight the effectiveness of luminous MOFs as fluorescent sensors for a wide range of contaminants, including heavy metals, reactive species, antibiotics, and explosives. Considering all this, the review discusses future research needs and opportunities in the field of luminous MOFs. It emphasizes the importance of developing multifunctional materials, refining design methodologies, exploring sensing mechanisms, and ensuring environmental compatibility, scalability, and affordability. By providing insights into the current state of research and outlining future directions, this review is a valuable resource for researchers seeking to address environmental challenges using MOF-based solutions.

Dual-emission Tb-based coordination polymer as a ratiometric fluorescence probe for the detection of phosphate

A simple, sensitive dual-emission probe was developed for the detection of phosphate (Pi). The probe Tb-BTB/DPA was synthesized by mixing dual-ligand, 1,3,5-tri(4-carboxyphenyl) benzene (H3BTB) and dipicolinic acid (DPA), with metal ions Tb3+ in ethanol-water solution at 40℃ for 2 h. Tb-BTB/DPA exhibits two emission peaks, the emission at 362 nm is attributed to H3BTB, an energy transfer between Tb3+ nodes, and DPA further enhances the fluorescence of Tb3+ at 544 nm. Pi competes with ligand H3BTB to coordinate Tb3+, resulting in partial collapse of the Tb-BTB/DPA structure and interrupting the electron transfer between H3BTB and Tb3+. Therefore, the emission at 362 nm is enhanced, while the emission at 544 nm is unchanged, and a ratiometric fluorescence method is developed to detect Pi. Tb-BTB/DPA exhibits good linearity within the Pi concentration range (0.1-50 µmol/L), and the detection limit was 25.8 nmol/L. This study provides a new way to prepare probes with dual emission sensing properties.

Metal-organic framework-based ratiometric point-of-care testing for quantitative visual detection of nitrite

Nitrite (NO2-) is categorized as a carcinogenic substance and is subjected to severe limitations in water and food. To safeguard the public's health, developing fast and convenient methods for determination of NO2- is of significance. Point-of-care testing (POCT) affords demotic measurement of NO2- and shows huge potential in future technology beyond those possible with traditional methods. Here, a novel ratiometric fluorescent nanoprobe (Ru@MOF-NH2) is developed by integrating UiO-66-NH2 with tris(2,2'-bipyridyl)ruthenium(II) ([Ru(bpy)3]2+) through a one-pot approach. The special diazo-reaction between the amino group of UiO-66-NH2 and NO2- is responsible for the report signal (blue emission) with high selectivity and the red emission from [Ru(bpy)3]2+ offers the reference signal. The proposed probe shows obviously distinguishable color change from blue to red towards NO2- via naked-eye. Moreover, using a smartphone as the detection device to read color hue, ultra-sensitive quantitative detection of NO2- is achieved with a low limit of detection at 0.6 μΜ. The accuracy and repeatability determined in spiked samples through quantitative visualization is in the range of 105 to 117% with a coefficient of variation below 4.3%. This POCT sensing platform presents a promising strategy for detecting NO2- and expands the potential applications for on-site monitoring in food and environment safety assessment.

A novel ratiometric sensor for fluorimetric and visual dual-mode detection of Al3+ in environmental water based on the target-regulated formation of Eu MOFs

Herein, a novel ratiometric sensor for fluorimetric and smartphone-assisted visual detection of Al3+ in environmental water was developed based on the target-regulated formation of Eu metal-organic frameworks (Eu MOFs). By employing 2-[4-(2-hydroxyethyl) piperazin-1-yl] ethanesulfonic acid (Hepes), Eu3+ and tetracycline (TC) as raw materials, Eu MOFs with red emission were facilely synthesized through the coordination of Eu3+ with Hepes and TC. However, upon the introduction of Al3+, a higher affinity of TC towards Al3+ resulted in the formation of a TC-Al3+ complex with green fluorescence and inhibited the generation of Eu MOFs. This led to an increase in green fluorescence and a decrease in red fluorescence accompanied by the fluorescence color of the solution changing from red to green under the illumination of the UV lamp. Thus, a ratiometric sensor for fluorimetric and the smartphone-assisted visual detection of Al3+ was established. The ratiometric sensor exhibited high sensitivity for Al3+ detection with a detection limit of 0.14 μM for fluorescence detection and 1.21 μM for visual detection. Additionally, the proposed strategy was successfully applied to detect Al3+ in the environmental water samples with satisfactory results, indicating great application prospects for environmental monitoring.

Tri-mode Responses to Reactive Oxygen Species In Vivo by Chiral Vanadium-Based Nanoparticles

Reactive oxygen species (ROS) are closely associated with the redox balance of the physiological environment, and monitoring ROS can aid in the early diagnosis of many diseases, including cancer. In this study, chiral vanadium trioxide/vanadium nitride (V2O3/VN) nanoparticles (NPs) modified with an organic dye (cyanine 3 [Cy3]) were prepared for ROS sensing. Chiral V2O3/VN NPs were prepared with the "ligand-induced chirality" strategy and showed a g-factor of up to 0.12 at a wavelength of 512 nm. To the best of our knowledge, this g-factor is the highest value of all chiral ceramic nanomaterials. The very high g-factor of the nanoprobe confers very high sensitivity, because the higher g-factor, the higher sensitivity. In the presence of ROS, V3+ in the chiral V2O3/VN nanoprobe undergoes a redox reaction to form V2O5, reducing the circular dichroism and absorbance signals, whereas the fluorescence signal of Cy3 is restored. With this nanoprobe, the limits of detection for the circular dichroic and fluorescence signals in living cells are 0.0045 nmol/106 and 0.018 nmol/106 cells, respectively. This chiral nanoprobe can also monitor ROS levels in vivo by fluorescence. This strategy provides an innovative approach to the detection of ROS and is expected to promote the wider application of chiral nanomaterials for biosensing.

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

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

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.

Fabrication of Eu-MOFs rod-shaped nanospheres with dual emissions for ratiometric fluorescence detecting Hg2+ in water

The incorporation of novel nanostructure has been proven to significantly improve the performance of fluorescence-based sensors in terms of sensitivity, selectivity, and detection capability. Herein, a lanthanide metal-organic framework (BTC-Eu-BDC-NH2) with dual ligands of 2-aminobenzoic acid (BDC-NH2) and 1,3,5-benzene tricarboxylic acid (BTC) has been prepared for ratiometric fluorescent detection of Hg2+ through the rational one-step synthetic approach. Through adjusting the ratio of two ligands, this dual-ligands strategy not only provided two independent emissions at peaks of 435 nm and 615 nm to resist the influence of external conditions, but also introduced the visual detection with an obvious color change. Moreover, the specific rod-shaped nanospheres morphology substantially enlarged the surface area of BTC-Eu-BDC-NH2 to ensure good dispersion and rapid response during sensing. Upon the addition of Hg2+, the fluorescence at 435 nm of BTC-Eu-BDC-NH2 was obviously quenched because of the interaction between Hg2+ and -NH2 from the ligand, while the red fluorescence at 615 nm remains almost unchanged. As a result, the synthesized BTC-Eu-BDC-NH2 showed excellent performances for visual sensing detection of Hg2+ with a clear luminescent color conversion from blue to red, and the detecting range was 0-40 μM with a low detection limit of 67 nM. Finally, the developed sensor was applied to actual tap water, and a handy sensing kit was constructed by hydrogel with BTC-Eu-BDC-NH2, demonstrating its potential practical applications.

Cd-MOF and Its Ln3+-Post Modification Products: Regulation of Luminescence Properties and Improved Detection of Uric Acid, Quinine, and Quinidine

One 3D Cd-MOF, namely, {[(HDMA)2][Cd3(L)2]·5H2O·2DMF}n (LCU-124, LCU indicates Liaocheng University), was synthesized from an ether-containing ligand 1,3-bis(3,5-dicarboxylphenoxy)benzene (H4L). Its Ln3+-postmodified samples, Eu3+@LCU-124 and Tb3+@LCU-124, were obtained through cation exchange of dimethylamine cation (HDMA) with Eu3+ and Tb3+. The successful entry of rare earth into LCU-124 by cation exchange modification was verified by IR, XRD, XPS, EDS mapping, and luminescence spectra. The proportion of Eu3+/Tb3+ was adjusted during the modification process, leading to fluorescent materials with different emissions. Luminescence measurements indicated that these complexes exhibited interesting multiresponsive sensing activities toward biomarkers urine acid (UA), quinine (QN), and quinidine (QND). First, LCU-124 has a pronounced quenching effect toward UA with the detection limit of 31.01 μM. After modification, the visualization of the detection was improved significantly and the detection limit of Eu3+@LCU-124 was reduced to 0.868 μM. Second, when QN and QND were present in the suspensions of Eu3+@LCU-124 and Tb3+@LCU-124, strong blue light emission peaks occurred, while the characteristic emission of Eu3+/Tb3+ decreased, forming ratiometric fluorescent sensors with the detection limit in the range of 0.199-9.49 μM. The fluorescent probes have high selectivity, excellent sensitivity recycling, and fast response time (less than 1 min). Besides, a simple logic gate circuit and a range of luminescent mixed matrix membranes were designed to provide simple and fast detection of above biomarkers. Our work indicated that modification of Eu3+/Tb3+ could improve the detection ability significantly.

Multifunctional Luminescent 3D Ln-MOFs with High Sensitivity for Trace Detection of Micronutrients

The synthesis of two versatile fluorescent metal-organic frameworks (MOFs), [Eu(4-NCP)(1,4-bdc)]n·0.5H2O (1) and [Eu(4-NCP)(4,4'-bpdc)]n·0.75H2O (2) (HNCP = 2-(4-carboxyphenyl)imidazo(4,5-f)-(1,10)phenanthroline, 1,4-H2bdc = benzene-1,4-dicarboxylic acid, 4,4'-H2bpdc = 4,4'-biphenyldicarboxylic acid), was carried out using a hydrothermal method. These MOFs were characterized through various advanced technologies to determine their structural information. The results indicate that both MOFs exhibited 3D network structures with specific topologies. Furthermore, these MOFs demonstrated exceptional thermal stabilities and adsorption capabilities. Additionally, complex 2 was utilized for studying the fluorescence sensing properties of various micronutrients including metal ions, nitro aromatic compounds, and biological small molecules. Notably, complex 2 showed promising potential as a multifunctional sensor for selectively detecting Fe3+, nitrobenzene, and ascorbic acid in aqueous solutions through fluorescence quenching with low limits of detection (LODs ∼ 10-7 M) and high quenching constants (Ksv ∼ 103 M-1). Moreover, the detection mechanism of complex 2 was further investigated by using experimental methods and DFT calculations.

Ratiometric fluorescence sensor based on europium-organic frameworks for selective and quantitative detection of cerium ions

BACKGROUND

Due to the unavoidable use of cerium in daily life, the accumulation of cerium in the environment increases health risks for humans. Therefore, it is crucial to develop a chemical sensing technology for the rapid, sensitive, and selective detection of cerium ions.

RESULTS

In this research work, a novel two-dimensional chain structure of a europium-based metal organic framework (Eu-MOF) [Eu2(tcpa)(Htcpa)2] was synthesized by using 3,4,5,6-tetrachloro-1,2-benzenedicarboxylic acid (H2TCPA) as the ligand and europium nitrate as the metal source. The results of powder X-ray diffraction and thermogravimetric analysis show that the synthesized Eu-MOF has excellent chemical and thermal stability. When the Eu-MOF suspension was excited by ultraviolet light at 292 nm, four fluorescence emissions were observed at 420, 595, 620 and 705 nm. It was particularly interesting that when cerium ions (Ce3+/Ce4+) were added to the Eu-MOF suspension, the fluorescence intensity at 420 nm was enhanced, while the fluorescence at 620 nm was quenched. On this basis, a ratiometric fluorescent sensor for detecting cerium ions was constructed, which has a good linear relationship in the range of 0.05-15 μM and a detection limit of 16 nM. The plausible mechanism of the change in the fluorescence characteristics of Eu-MOF caused by cerium ions was discussed in detail. Through the study of fluorescence lifetime and ultraviolet absorption, it was proven that the mechanism of Ce3+-quenching Eu-MOF fluorescence is the inner filter effect. Photoinduced electron transfer and internal filtering effects lead to fluorescence quenching at 620 nm, while redox reactions lead to fluorescence enhancement of the ligand at 420 nm.

SIGNIFICANCE

The proposed ratiometric fluorescence sensor was successfully employed for the detection of cerium ions in real water samples, confirming that it can be used as an alternative method for the detection of Ce3+ and Ce4+ in environmental samples.

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.

Dual-state dual emission from precise chemically engineered bi-ligand MOF free from encapsulation and functionalization with self-calibration model for visual detection

Synthesis of dual-state dual emitting metal-organic frameworks (DSDE-MOFs) is uncommon and challenging. Additionally, DSDE-MOFs can fulfil the expanding need for on-site detection due to their stability and self-reference for a variety of non-analyte variables. In the present work, a novel intrinsic DSDE of chemically engineered bi-ligand Eu-based MOF (UoZ-1) was designed. The prepared UoZ-1 spherical particles were small-sized around 10-12 nm and displayed blue (425 nm) and red fluorescence (620 nm) at both states, dispersed in liquid and in solid state, when excited at 250 nm. A ratiometry platform was developed since the red emission was quenched by the addition of folic acid and the blue emission was almost remained unaffected. In the fluorometric ratiometric-mode, a dynamic linear range was recorded from 10 to 200 µM with LOD about 0.4 µM. Visual-based detection with assistance of smartphone was developed for quantification based on RGB analysis using Color Grab App. In the visual-mode, LOD as small as 2.3 µM was recorded. By utilizing the intrinsic dual-emitting UoZ-1, highly stable, recyclable, sensitive, and selective on-site visual detection of folic acid can be achieved. UoZ-1, a DSDE-MOF with no encapsulation or functionalization requirements, exhibits great potential for diverse applications.

Ratiometric Lanthanide Metal‐Organic Frameworks (MOFs) for Smartphone‐Assisted Visual Detection of Food Contaminants and Water: A Review

Developing a reliable portable biosensor is crucial for ensuring food safety and human health. This involves accurately detecting contaminants in food and water at their source. Smartphone cameras have recently become useful for capturing color or fluorescence changes that occur when a probe interacts with specific molecules on paper or in a chemical solution. Ratiometric designs, which self‐calibrate and minimize the impact of environmental changes, are gaining popularity. These designs rely on color changes or fluorescence shifts, which are easily assessable with smartphones. This overview highlights advances in ratiometric optical sensing using Metal‐organic frameworks (MOFs) with lanthanide components coupled with smartphones. These advancements allow contaminants in food and water to be visually identified. The article explains the principles, properties, and applications of color changes for visual detection in food safety. Using lanthanide metal‐organic frameworks with smartphones offers a potent method to detect contaminants, enhancing food safety and safeguarding human health.

A turn-on fluorescence strategy for hypochlorous acid detection based on DNAzyme-assisted cyclic signal amplification

Hypochlorous acid (HClO) is a crucial active oxygen component and one of the innate immunity's barrier substances in the body. Abnormal fluctuations in HClO concentration can lead to increased oxidative stress, cellular dysfunction, and the onset of various diseases. Thus, developing convenient, affordable, efficient, and sensitive methods to monitor HClO concentration in healthcare and pathophysiology research is highly significant. In this study, we developed a novel fluorescence strategy for HClO detection based on nucleic acid oxidative cleavage and Pb2+-dependent DNAzyme. By introducing a phosphorothioate site in the hairpin-structured nucleic acid sequence, the nucleic acid probe specifically recognized HClO and underwent oxidative cleavage. Upon cleavage, the enzyme strand is liberated, forming DNAzyme. This DNAzyme then cleaves the substrate strand, liberating the initially quenched fluorescent dyes and generating a turn-on fluorescent signal. The enzyme strand produced by the oxidative cleavage of HClO can be repeatedly utilized, thus realizing the cyclic signal amplification to reduce background noise. We verified the detection mechanism of this strategy through stepwise fluorescence spectroscopy analysis and electrophoresis. Under optimal experimental conditions, the method achieved a detection limit of 5.38 nM and a linear range of 1 nM-800 nM. This method demonstrated exceptional performance in actual biological sample testing and presented an exciting opportunity for expanded utilization in clinical diagnosis and medical research.

A smartphone-based visual ratiometric fluoroprobe for rapid and sensitive detection hypochlorous acid based on dual-emission metal organic frameworks

Herein, we designed/developed a mixed fluorescence system with europium metal-organic framework (EDB) and zinc metal-organic framework (ZBNB). At the 270-nm excitation wavelength, the EDB-ZBNB dually emitted at 425 and 615 nm and displayed blue solution under 365-nm UV lamp. When HOCl was fortified, the 425-nm blue emission dropped progressively, while the 615-nm red emission was relatively stable. Upon addition of ClO-, the shortened fluorescence lifetime demonstrated that the quenched 425-nm fluorescence of ZBNB was owing to the occurrence of dynamic quenching effect. Besides, amino groups are protonated in water to form -NH3+, which interact with ClO- to form hydrogen bonds, reduce the distance between -NH3+ and ClO-, produce energy transfer and result in fluorescence quenching. The ratiometric fluoroprobe provided a significant color change from blue to red, making HOCl detection visual and rapid. This fluorescent probe overcome the disadvantage of conventional redox-based fluorescent probes that can be interfered by MnO4- and other oxidants with stronger oxidizing capacity than free ClO-. Furthermore, a smartphone-based portable sensing platform was developed based on EDB-ZBNB. By using a "Thingidentify" software on smartphone, the sensing platform was used to detect HOCl in waters with a low detection limit of 28.0 nM and the fortified recoveries of 98.87-103.60%. Thus, this study provides a novel and promising platform for the detection of free ClO- in monitoring water quality.

An intelligent smartphone-test strip detection platform for rapid and on-site sensing of benzoyl peroxide in flour samples

Benzoyl peroxide (BPO) is a commonly used flour whitener, but its excessive usage can have adverse effects on human health, such as nutrient loss, vitamin deficiencies and certain diseases. In this study, a europium metal organic framework (Eu-MOF) fluorescence probe was prepared, which exhibited a strong fluorescence emission at 614 nm upon excitation at 320 nm, with a high quantum yield of 8.11%. The red fluorescence of the probe could be effectively quenched by BPO through the inner filter effect (IFE) and photoinduced electron transfer (PET) mechanism. The detection process offered several advantages, including a wide linear range of 0-0.95 mM, a low detection limit of 66 nM and a fast fluorescence response of 2 min. Furthermore, an intelligent detection platform was designed to enhance the practical application of the detection method. This platform combined the portability and visuality of a traditional test strip with the color recognition capability of a smartphone, allowing for the visualization and quantitative detection of BPO in a convenient and user-friendly manner. The detection platform was successfully applied to the analysis of BPO in real flour samples with satisfactory recoveries (99.79%-103.94%), suggesting a promising strategy for the rapid and on-site detection of BPO in food samples.

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.

Fabrication of CdS quantum dots with egg white and application in the assay of hypochlorous acid and myeloperoxidase activity and inhibition

The myeloperoxidase (MPO)/H2O2-Cl- enzymatic reaction system and its product hypochlorous acid (HOCl) are closely related to many disease processes, and new methods to detect the levels of HOCl and MPO are being focused on. MPO is the only known enzyme for the catalytic production of HOCl in biological systems; therefore, monitoring the HOCl levels is a selective and direct readout of MPO activity. This study reported a simple and efficient fluorescence assay of HOCl and MPO activity and inhibition. Highly fluorescent CdS quantum dots (CdS QDs) were prepared in one pot where NaOH-pretreated egg white served as a stabilizer. These CdS QDs exhibit strong green emission centered at ca. 550 nm and enable rapid and selective fluorescence response to HOCl with a linear detection range of 8.0-250 μM and a limit of detection (LOD) of 2.5 μM. Moreover, the CdS QDs were further applied for sensing MPO based on the fluorescence quenching exerted by its reaction product HOCl. Detection of MPO is accomplished with a linear range from 0.1 to 40 mU mL-1 (1 U is the MPO concentration for catalysis of 1 micromolar substrate per minute) and a LOD of 0.06 mU mL-1. The developed synthesis method can be applied to large-scale synthesis of CdS QDs, and the strategy to sense HOCl and MPO activity and inhibition has potential biomedical applications such as clinical diagnosis and drug screening.

Lanthanide-MOFs as multi-responsive photoluminescence sensor for sensitively detecting Fe3+, Cr2O72- and nitrofuran antibiotics

Fast and selective detection of contaminants plays a key role in meeting human health and environmental concerns. Herein, two groups of isostructural lanthanide MOFs, [Ln(Hpta)(oxalic acid)]·H2O (1-Eu, 2-Gd) and [Ln(pta)(oxalic acid)0.5(H2O)2]·2H2O (3-Eu, 4-Gd) (H2pta = 2-(4-pyridyl)-terephthalic acid, C2O4- = oxalic acid), were synthesized by solvothermal method. Single crystal X-ray diffraction reveals that 1 and 2 are 3D neutral frameworks, while 3 and 4 consist of 2D layers with parallelogram holes and stack into 3D networks through O-H⋯N and O-H⋯O hydrogen bonding interactions. All complexes remain crystalline and stable below 400 °C, suggesting preeminent thermostability. Noteworthily, only 3 shows excellent chemical stability in water and organic solvent. Therefore, the solid-state fluorescence spectrum was used to characterize 3 which exhibited intense red luminescence. The N active sites in the pore channels of 3 are conducive to displaying a distinct quenching effect for Fe3+ cations in aqueous solutions, Cr2O72- anions in DMF and DMA solutions, and nitrofuran antibiotics in the DMF solvent. Overall, 3 is a prospective luminescent sensor for detecting Fe3+, Cr2O72- and nitrofuran antibiotics.

Dual-ligand lanthanide metal-organic framework probe for ratiometric fluorescence detection of mercury ions in wastewater

By serving dipyridylic acid (DPA) and 2,5-dihydroxyterephthalic acid (DHTA) as the biligands, a novel lanthanide (Eu3+) metal-organic framework (MOF) namely Eu-DHTA/DPA was prepared for specific Hg2+ fluorescence determination. The dual-ligand approach can endows the resulting luminescent MOF with dual emission of ratiometric fluorescence and uniform size. Eu3+ produces intense red fluorescence when activated by the ligand DPA, while the other ligand DHTA produces yellow fluorescence. Under 273 nm excitation, the presence of Hg2+ in the monitoring environment causes an increase in the intensity of the DHTA fluorescence peak at 559 nm and a decrease in the intensity of the Eu3+ fluorescence peak at 616 nm. Hg2+ effectively quenches the fluorescence emission of the central metal Eu3+ in Eu-DHTA/DPA at 616 nm through a dynamic quenching effect. This recognition process occurs due to the coordination of Hg2+ with ligands such as benzene rings, carboxyl groups, and pyridine N in three-dimensional space. Hg2+ was detected by measuring the ratio between two fluorescence peaks (I559 nm/I616 nm) within the range 2-20 μM, achieving a remarkably low detection limit of 40 nM. The established ratiometric fluorescence method has been successfully applied to the determination of Hg2+ in industrial wastewater of complex composition. The method plays a crucial role in the rapid and sensitive monitoring of Hg2+ in real environmental samples. The recoveries ranged from 92.82% to 112.67% (n = 3) with relative standard deviations (RSD) below 4.8%. This study offers a convenient and effective method for constructing probes for Hg2+ monitoring, with practical applications in environmental monitoring.

Stable Europium(III) Metal-Organic Framework Demonstrating High Proton Conductivity and Fluorescence Detection of Tetracyclines

A europium(III) metal-organic framework (MOF), namely, {[[(CH₃)₂NH₂]₃Eu₂(DTTP-2OH)₂(HCOO)(H₂O)]·4H₂O}_n (Eu-MOF, H₄DTTP-2OH = 2',5'-dihydroxy-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid) has been assembled through solvothermal method. The Eu-MOF is a three-dimensional (3D) (4,4,8)-connected topological framework with binuclear Eu(III) clusters as secondary building units, in which a richly ordered hydrogen bonding network formed among the free H₂O molecules, dimethylamine cations, and phenolic hydroxyl groups provides a potential pathway for proton conduction. The proton conductivity reaches the category of superionic conductors (σ > 10^-4 S cm^-1) at room temperature with a maximum conductivity of 1.91 × 10^-3 S cm^-1 at 60 °C and 98% RH. Moreover, it also can be used as a fluorescence sensor in aqueous solution with detection limits of 0.14 μM for tetracycline, 0.13 μM for oxytetracycline and 0.11 μM for doxycycline. These results pave new methods for constructing MOFs with high proton conductivity and responsive fluorescence.

Fluorescence detection of dopamine based on the peroxidase-like activity of Fe3O4-MWCNTs@Hemin

A novel Fe₃O₄-MWCNTs@Hemin nanocomposite was synthesized using hemin and Fe₃O₄ with multi-walled carbon nanotubes (MWCNTs) by one-step hydrothermal methods. The as-prepared Fe₃O₄-MWCNTs@Hemin nanocomposites exhibited excellent peroxidase-like activities in the activation of H₂O₂. The mechanisms, kinetics, and catalytic performances of Fe₃O₄-MWCNTs@Hemin were systematically studied. Fe₃O₄-MWCNTs@Hemin can oxidize dopamine (DA) to dopaquinone in the presence of H₂O₂, and the intermediate products dopaquinone can further react with β-naphthol to generate a highly fluorescent derivative at 415 nm excitation wavelength. Therefore, an innovative fluorescence platform for the detection of DA was developed. The fluorescence intensity increased linearly with DA concentration in the range 0.33 to 107 μM, with a low detection limit of 0.14 μM. Due to the excellent activity, substrate universality, fast response, high selectivity, and sensitivity of Fe₃O₄-MWCNTs@Hemin, the proposed fluorescence method was used to analyze complex biological blood samples with a satisfactory result. It demonstrated the significant potential for developing effective and dependable fluorescent analytical platforms for preserving human health.

Advance Progress on Luminescent Sensing of Nitroaromatics by Crystalline Lanthanide-Organic Complexes

Water environment pollution is becoming an increasingly serious issue due to industrial pollutants with the rapid development of modern industry. Among many pollutants, the toxic and explosive nitroaromatics are used extensively in the chemical industry, resulting in environmental pollution of soil and groundwater. Therefore, the detection of nitroaromatics is of great significance to environmental monitoring, citizen life and homeland security. Lanthanide-organic complexes with controllable structural features and excellent optical performance have been rationally designed and successfully prepared and used as lanthanide-based sensors for the detection of nitroaromatics. This review will focus on crystalline luminescent lanthanide-organic sensing materials with different dimensional structures, including the 0D discrete structure, 1D and 2D coordination polymers and the 3D framework. Large numbers of studies have shown that several nitroaromatics could be detected by crystalline lanthanide-organic-complex-based sensors, for instance, nitrobenzene (NB), nitrophenol (4-NP or 2-NP), trinitrophenol (TNP) and so on. The various fluorescence detection mechanisms were summarized and sorted out in the review, which might help researchers or readers to comprehensively understand the mechanism of the fluorescence detection of nitroaromatics and provide a theoretical basis for the rational design of new crystalline lanthanide-organic complex-based sensors.

SCSC Transformation and Post-Synthesis Modification of MOFs with Proton Conduction and Ratiometric Fluorescence-Sensing Properties

The modification of metal-organic framework (MOF) materials to facilitate their practical applications is an extremely challenging and meaningful topic. In this work, two stepwise modification strategies for MOFs were conducted. First, we have demonstrated a single-crystal-to-single-crystal (SCSC) transformation from a microporous three-dimensional (3D) MOF to a two-dimensional (2D) coordination polymer (CP). The centrosymmetric [Cd(3-bpdb)(MeO-ip)]_n (1) transforms into a chiral [Cd₂(3-bpdb)(MeO-ip)₂(CH₃OH)₂]_n (2), which is triggered by the reaction time with methanol that acts as a structure-directing agent. The conversion relationship of 1 to 2 at different reaction times was studied in detail. Density functional theory (DFT) calculations clearly state that the irreversible formation of 2 is thermodynamically favorable. Intriguingly, 2 exhibits good proton conduction of 1.34 × 10^-3 S cm^-1 under 363 K and 98% relative humidity (RH) due to unique H-bond network characteristics. To the best of our knowledge, there are very few cases of 3D to 2D SCSC transformation stimulated by reaction time. The results have important implications for understanding the SCSC transformation mechanism and synthetic chemistry. On the other hand, the lanthanide³⁺-functionalized hybrids (Ln³⁺-MOF), Ln³⁺@1, were continuously prepared by incorporating luminescent Ln³⁺ ions into the structure of 1 through encapsulating post-synthesis modification (PSM). Tb³⁺@1 exhibits double emission in water and shows visual ratiometric fluorescence behavior for sensing glutamic acid (Glu), tryptophan (Trp), and Al³⁺, which is more reliable and accurate than single emission. Our work may not only provide new insights into the multiple modification of MOF materials but also promote the practical application of such materials.

A ratiometric luminescence sensing platform based on lanthanide-based silica nanoparticles for selective and sensitive detection of Fe3+ and Cu2+ ions

Detection of Fe(III) and Cu(II) in water is highly desirable because their abnormal levels can cause serious harm to human health and environmental safety. In this work, a ratiometric luminescence sensing platform based on lanthanide-based silica nanoparticles was constructed for the detection of Fe³⁺ and Cu²⁺ ions. The terbium-silica nanoparticles (named SiO₂@Tb) with dual-emission signals were successfully prepared by grafting Tb³⁺ ions onto trimellitic anhydride (TMA) functionalized silica nanospheres. It can serve as a ratiometric fluorescent probe for the detection of Fe³⁺ and Cu²⁺ ions in water with the green emission of Tb³⁺ ions as a response signal and the blue emission of silica nanospheres as the reference signal. Significantly, an easy-to-differentiate color change for visual detection was also realized. SiO₂@Tb shows high sensitivity even in very low concentration regions towards the sensing of Fe³⁺ and Cu²⁺ with low detection limits of 0.75 μM and 0.91 μM, respectively. Moreover, the mechanism for the luminescence quenching of SiO₂@Tb was systematically investigated, and was attributed to the synergetic effect of the absorption competition quenching (ACQ) mechanism and cation exchange. This study demonstrates that SiO₂@Tb can be employed as a promising fluorescent probe for the detection of Fe³⁺ and Cu²⁺ ions, and the combination of lanthanide ions with silica nanoparticles is an effective strategy to construct a ratiometric fluorescent sensing platform for the determination of analytes in environmental detection.

A novel ratiometric fluorescence probe for the detection of copper (II) and silver(I) based on assembling dye-doped silica core-shell nanoparticles with gold nanoclusters

A creatively designed and constructed a multifunctional ratiometric fluorescence probe is reported by assembling glutathione (GSH)-protected gold nanoclusters (AuNCs) with fluorescein-doped mesoporous silica nanoparticle (FS) for the detection of Cu²⁺ and Ag⁺ ions, which could eliminate most interferences by self-calibration. Under the excitation at 450 nm, the fluorescence connected with AuNCs can rapidly respond by quenching or enhancement, respectively, for Cu²⁺ and Ag⁺ ions, while the fluorescein isothiocyante (FITC) fluorescence served as reference with negligible change. The fluorescence intensity ratio showed good linear relationships with Cu²⁺ and Ag⁺ concentrations in the range 0.5-10 μM and 0.1-8 μM, respectively. The detection limits were as low as 140 nM and 60 nM for Cu²⁺ and Ag⁺ ions, respectively. The color change induced by fluorescent intensity ratio variation could also be employed for visual discrimination. The AuNC-embedded FS (FS-Au) nanoprobe was successfully used for Cu²⁺ and Ag⁺ ion determination in drinking water and intracellular Cu²⁺ imaging, which exhibits promising prospects in cost-effective and rapid determination of both Cu²⁺ and Ag⁺ with good sensitivity and selectivity.