Eu3+-Functionalized Covalent Organic Framework Hybrid Material as a Sensitive Turn-On Fluorescent Switch for Levofloxacin Monitoring in Serum and Urine

β-Cyclodextrin/carbon dots-grafted cellulose nanofibrils hydrogel for enhanced adsorption and fluorescence detection of levofloxacin

In this study, a novel hydrogel, β-cyclodextrin/carbon dots-grafted cellulose nanofibrils hydrogel (βCCH), was fabricated for removal and fluorescence determination of levofloxacin (LEV). A comprehensive analysis was performed to characterize its physicochemical properties. Batch adsorption experiments were conducted, revealing that βCCH reached a maximum adsorption capacity of 1376.9 mg/g, consistent with both Langmuir and pseudo-second-order models, suggesting that the adsorption process of LEV on βCCH was primarily driven by chemical adsorption. The removal efficiency of βCCH was 99.2 % under the fixed conditions (pH: 6, initial concentration: 20 mg/L, contact time: 300 min, temperature: 25 °C). The removal efficiency of βCCH for LEV still achieved 97.3 % after five adsorption-desorption cycles. By using βCCH as a fluorescent probe for LEV, a fast and sensitive method was established with linear ranges of 1-120 mg/L and 0.2-1.0 μg/L and a limit of detection (LOD) as low as 0.09 μg/L. The viability of βCCH was estimated based on the economic analysis of the synthesis process and the removal of LEV, demonstrating that βCCH was more cost-effective than commercial activated carbon. This study provides a novel approach for preparing a promising antibiotic detection and adsorption material with the advantages of stability, and cost-effectiveness.

Integrated Eu3+ loaded covalent organic framework with smartphone for ratiometric fluorescence detection of tetracycline

Developing rapid tetracycline sensing system is of great significance to monitor the illegal addition to drugs and pollution to food and ecosystem. By loading covalent organic frameworks (COFs) with Eu3+, a new hybridized material (COF@Eu3+) was prepared for tetracycline determination. Based on the Schiff base reaction, the COFs were by synthesized through solvent evaporation in 30 min at room temperature. Thereafter, Eu3+ was modified into COFs to develop the COF@Eu3+ sensing platform by adsorption and coordination. In presence of tetracycline, tetracycline can displace water molecules and coordinate with Eu3+ through the antenna effect. As a result, the red fluorescence of Eu3+ was enhanced by tetracycline with green fluorescence of COF as a reference. The developed ratiometric fluorescence sensor exhibits a linear range of 0.1-20 μM for detecting tetracycline with a detection limit of 30 nM. Integrated with a smartphone, the rapid tetracycline detection can be realized in situ, which is potential for high-throughput screening of tetracycline contaminated samples. Furthermore, the COF@Eu3+ fluorescence sensor has been successfully applied to the detection of tetracycline in traditional Chinese medicine compound preparation with satisfied recoveries. Therefore, a smartphone-assisted device was successfully developed based on Eu3+-functionalized COF, which is an attractive candidate for further applications of fluorescence sensing and visual detection.

A pH-regulated fluorescence covalent organic framework for quantitative water content detection in methanol

In this paper, we designed and synthesized a two-dimensional fluorescent covalent organic framework (TAPB-DMTP-COF) for the precise determination of H2O content in methanol. The COF was synthesized using two typical monomers by grinding method, which significantly reduced the synthesis time. By adjusting the pH value of the COF suspension to 4.0, the portion of the COF material structure is disrupted, thereby mitigating π-π stacking and resolving the aggregation-caused quenching (ACQ) effect. Consequently, the non-fluorescent TAPB-DMTP-COF exhibited blue-purple fluorescence emission in methanol. At the same time, it is observed that in the presence of H2O, there is a red shift in the maximum fluorescence emission peak of TAPB-DMTP-COF, which correlates with the H2O content within a specific range. Notably, this redshift demonstrates a linear relationship with H2O content from 4% to 80% in methanol. Our work presents novel insights for efficient analysis and detection of H2O content in methanol and could be used for H2O detection in other organic solvents.

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.

Metal-organic gels: recent advances in their classification, characterization, and application in the pharmaceutical field

Metal-organic gels (MOGs) are a type of functional soft substance with a three-dimensional (3D) network structure and solid-like rheological behavior, which are constructed by metal ions and bridging ligands formed under the driving force of coordination interactions or other non-covalent interactions. As the homologous substances of metal-organic frameworks (MOFs) and gels, they exhibit the potential advantages of high porosity, flexible structure, and adjustable mechanical properties, causing them to attract extensive research interest in the pharmaceutical field. For instance, MOGs are often used as excellent vehicles for intelligent drug delivery and programmable drug release to improve the clinical curative effect with reduced side effects. Also, MOGs are often applied as advanced biomedical materials for the repair and treatment of pathological tissue and sensitive detection of drugs or other molecules. However, despite the vigorous research on MOGs in recent years, there is no systematic summary of their applications in the pharmaceutical field to date. The present review systematically summarize the recent research progress on MOGs in the pharmaceutical field, including drug delivery systems, drug detection, pharmaceutical materials, and disease therapies. In addition, the formation principles and classification of MOGs are complemented and refined, and the techniques for the characterization of the structures/properties of MOGs are overviewed in this review.

A novel electrochemical sensing platform based on double-active-center polyimide covalent organic frameworks for sensitive analysis of levofloxacin

The development of a simple and sensitive electrochemical sensing platform for levofloxacin (LVF) analysis is of great significance to human health. In this work, a covalent organic framework (TP-COF) was in situ grown on the surface of Sn-MoC nanospheres with nanoflower-like morphology through a one-pot method to obtain the TP-COF@Sn-MoC composite. The prepared composite was used to modify a glassy carbon electrode (GCE) to realize the sensitive detection of levofloxacin. TP-COF was formed by polycondensation of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and pyromellitic dianhydride (PMDA), in which C = O and C = N groups served as double active centers for the recognition and electrocatalytic oxidation of the target molecule. Meanwhile, the introduction of Sn-MoC improved the conductivity of the electrode. The TP-COF@Sn-MoC composite produced a strong synergistic effect and showed a high electrocatalytic ability toward levofloxacin oxidation. The linear range of LVF was 0.6-1000 μM and the limit of detection (LOD) was 0.029 μM (S/N = 3). In addition, the sensor has been successfully applied for the analysis of LVF in human urine and blood serum samples with acceptable recovery rates, demonstrating that the sensor was promising in practical applications.

Lanthanide Functionalized Covalent Organic Frameworks Hybrid Materials for Luminescence Responsive Chemical Sensing

Covalent organic frameworks (COFs) possess several unique features of structural and functional chemistry, together with other modular photophysical performance, which make them candidates for luminescence responsive chemical sensing. Lanthanide (Ln3+ ) functionalized COFs hybrid materials still keep the parent COFs' virtues and also embody the abundant multiple luminescence response with both COFs and Ln3+ ions or other guest species. In this review, the summary is highlighted on the lanthanide functionalized COFs hybrid materials and their relevant systems for luminescence responsive chemical sensing. It is subdivided into five sections involving the three main topics. Firstly, the basic knowledges of COFs materials related to the luminescence responsive chemical sensing are introduced (including three sections), involving the chemistry, application and post-synthetic modification (PSM) of COFs, the luminescence and luminescence responsive chemical sensing, and the luminescence responsive chemical sensing of non-lanthanide functionalized COFs hybrids materials. Secondly, the systematic progresses are outlined on the lanthanide functionalized COFs hybrid materials in luminescence responsive chemical sensing, which is the emphasis for this review. Finally, the conclusion and prospect are given.

Ultrasensitive levofloxacin electrochemical biosensor based on semiconducting covalent organic framework/poly-L-cysteine/triangular Ag nanoplates modified glassy carbon electrode

A novel electrochemical biosensor with excellent performance was fabricated for levofloxacin (LEV) detection, which adopted triangular Ag nanoplates (Tri-AgNP) confined in a poly-L-cysteine (poly-L-Cys) film and a semiconducting covalent organic framework (COF) as the electrochemical sensing material. The developed electrochemical sensor revealed excellent analytical properties because of its good electrical conductivity, fast electron transfer, and abundant bioactive site. Based on this, a linear relationship between the LEV concentration and the peak current response at 0.92 V was obtained under the optimal experimental conditions by differential pulse voltammetry (DPV), with a wide linear range of 0.05 to 600 μM and a low limit of detection (LOD) of 0.0061 μM. The prepared sensor also realized sensitive and accurate determination of LEV in human serum and urine samples by standard addition method, with satisfactory recoveries (97.1 to 104%) and a low relative standard deviation of less than 4.6%. These results indicated that the novel ternary system has a promising application in the development of electrochemical signal probe and electrochemical biosensing platform.

Flumequine-mediated fluorescent zeolitic imidazolate framework functionalized by Eu3+ for sensitive and selective detection of UO22+, Ni2+ and Cu2+ in nuclear wastewater

Currently, antibiotics and heavy metal contaminants have posed a great threat for ecological security and human health. Herein, the lanthanide functionalized ZIF (named ZIF-90-PABA-Eu) is constructed by coordinating with Eu³⁺ via p-aminobenzoic acid intermediate. Due to the excellent fluorescence properties, the novel fluorescent probe can selectively monitor flumequine based on "turn on" mode. Furthermore, the obtained new material (named ZIF-90-PABA-Eu-Flu) can be used as "turn off" sensor for selective detection of both radioactive and nonradioactive heavy metal ions (UO₂²⁺, Ni²⁺ and Cu²⁺) which are the main component of nuclear industrial wastewater. ZIF-90-PABA-Eu-Flu shows ultra-short fluorescence response time (3 s) and ultra-low limit of detection (9.0 × 10^-3, 1.3 × 10^-2 and 6.1 × 10^-4 ppm) for three metal ions, which may be attributed to its good affinity with UO₂²⁺, Ni²⁺ and Cu²⁺. Moreover, principal component analysis (PCA) is applied to distinguish the three metal ions. Additionally, the possible sensing mechanism is investigated by the UV-vis spectra, luminescence lifetimes and theoretical calculation analysis. Based on these results, ZIF-90-PABA-Eu possesses promising potential in practical application and provides insight for the design of novel probes to continuously monitor flumequine, radioactive and nonradioactive heavy metal ions.

Multi-color fluorescence sensing platform for visual determination of norfloxacin based on a terbium (Ш) functionalized covalent organic framework

Sensitive and visual determination of fluoroquinolone antibiotics (FQs) is of great significance since their abuse and inappropriate handling can be problematic. Herein, we propose a lanthanide covalent organic framework fluorescence sensing system (Tb@COF-Ru) with visualization capability to determine the FQs level, where Tb@COF was employed as the sensing probe, while the red-emitting Ru(bpy)₃²⁺ serves as a constant red fluorescent background. With increasing norfloxacin concentration, the green fluorescence of Tb³⁺ is gradually enhanced, finally realizing the multicolor fluorescence change from red to green. With a smartphone for RGB analysis, visual monitoring and quantitative analysis were realized without any sophisticated instrument. Limits of detection for the fluorescence quantitative and visual mode for norfloxacin were 0.33 nM and 7.3 μM, respectively. This method was rapid (1 min) and visualized, providing a simple analysis of various food matrices (honey, milk, egg and beef) and water samples for trace FQs.

Detection of different chemical moieties in aqueous media by luminescent Europium as sensor

Detection of different chemical moieties especially trace metals is important for humans as well as water safety. In this review, different detectors synthesized by the combination of different ligands with luminescent europium complexes were discussed for the separation of metals and chemical moieties in aqueous media. These detectors displayed high sensitivity and selectivity. The limit-of-detection values were very low indicating that these detectors are best suitable for the sensing of chemical moieties and trace metals. These detectors’ luminescent changes could be noticed with the naked eye.

Highly stable β-ketoenamine-based covalent organic frameworks (COFs): synthesis and optoelectrical applications

Covalent organic frameworks (COFs) are one class of porous materials with permanent porosity and regular channels, and have a covalent bond structure. Due to their interesting characteristics, COFs have exhibited diverse potential applications in many fields. However, some applications require the frameworks to possess high structural stability, excellent crystallinity, and suitable pore size. COFs based on β-ketoenamine and imines are prepared through the irreversible enol-to-keto tautomerization. These materials have high crystallinity and exhibit high stability in boiling water, with strong resistance to acids and bases, resulting in various possible applications. In this review, we first summarize the preparation methods for COFs based on β-ketoenamine, in the form of powders, films and foams. Then, the effects of different synthetic methods on the crystallinity and pore structure of COFs based on β-ketoenamine are analyzed and compared. The relationship between structures and different applications including fluorescence sensors, energy storage, photocatalysis, electrocatalysis, batteries and proton conduction are carefully summarized. Finally, the potential applications, large-scale industrial preparation and challenges in the future are presented.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Covalent organic frameworks (COFs) are a class of organic crystalline porous materials discovered in the early 21st century that have become an attractive class of emerging materials due to their high crystallinity, intrinsic porosity, structural regularity, diverse functionality, design flexibility, and outstanding stability. However, many chemical and physical properties strongly depend on the presence of metal ions in materials for advanced applications, but metal-free COFs do not have these properties and are therefore excluded from such applications. Metalated COFs formed by combining COFs with metal ions, while retaining the advantages of COFs, have additional intriguing properties and applications, and have attracted considerable attention over the past decade. This review presents all aspects of metalated COFs, from synthetic strategies to various applications, in the hope of promoting the continued development of this young field.

Functionalized luminescent covalent organic frameworks hybrid material as smart nose for the diagnosis of Huanglongbing

Quantitative identification of several volatile organic compounds (VOCs) associated with the same disease provides a strong guarantee of the accurate analysis of the disease. Designing a single luminescent material to interact differently with multiple analytes can generate response patterns with remarkable diversity. Here, a highly green luminescent imine-based 2D COF (TtDFP) is designed and synthesized. TtDFP has ultrasensitive detection performance for trace water in organic solvent. Constructing a ratiometric fluorescence sensor can improve sensitivity for detecting analytes. To contrast the fluorescence signals of Eu³⁺ and COFs in sensing assays, a simple postsynthetic modification (PSM) method is used to introduce Eu³⁺ into TtDFP. The obtained red luminescent hybrid material Eu³⁺@TtDFP EVA film can be a fluorescent nose capable of "sniffing out" and quantifying VOCs (GA and PhA) associated with Huanglongbing (HLB, a devastating disease of citrus) at ppb levels. This work provides a technique of developing functionalized COF hybrid material to facilitate the distinction of various VOCs, which can also be extended to monitor the levels of other VOCs relevant to human health.

Ultra-sensitive detection of hydrogen peroxide and levofloxacin using a dual-functional fluorescent probe

Herein, a flower-shaped fluorescent probe was proposed for hydrogen peroxide (H₂O₂) and levofloxacin (LVF) sensing based on MoOx QDs@Co/Zn-MOFs with porous structure. Both MoOx QDs and Co/Zn-MOFs exhibited peroxidase-like properties, and the combination of them greatly aroused the synergistic catalytic capabilities between them. In o-Phenylenediamine (OPD)-H₂O₂ system, MoOx QDs@Co/Zn-MOFs efficiently catalyzed H₂O₂ to produce •OH and then oxidized OPD to its oxidation product (OxOPD). The OxOPD could not only emit blue fluorescence, but also inhibit the fluorescent intensity of MoOx QDs through fluorescence resonance energy transfer (FRET). Moreover, when introducing LVF into the system, the fluorescent intensities of MoOx QDs increased along with the aggregation of themselves while that of OxOPD remained unchanged, which was explained by the joint behavior of FRET and photo-induced electron transfer (PET) instead of the conventional aggregation-induced emission enhancement (AIEE). With these observation, the proposed probe was employed for H₂O₂ and LVF determination in biological samples with the limit of detection (LOD) of 32.60 pmol/L and 0.85 μmol/L, respectively, suggesting the method holds great promises for trace H₂O₂ and LVF monitoring in eco-environment.

Imine-Linked Covalent Organic Framework with a Naphthalene Moiety as a Sensitive Phosphate Ion Sensing

Due to the excellent ion-sensing potential of covalent organic frameworks (COFs), the new imine-linked conjugated COF (IC-COF) is synthesized through a water-based synthesis reaction between 1,5-diaminonaphthalene and 2,4,6-tris(4-formylphenoxy)-1,3,5-triazine to create a luminescence sensor. It is noteworthy that the green synthesized IC-COF shows excellent selectivity to phosphate ions (PO₄^3-) with a detection limit of 0.61 μM. The recyclability performance of IC-COF is high, indicating that it can be reused without a significant reduction in performance (5.2% decline after 5 cycles). Theoretical calculations using the density functional theory are performed on the IC-COF-PO₄^3- and IC-COF-Cu⁺ complexes to explore the sensing mechanism. The fluorescence quenching in the presence of PO₄^3- ions is attributed to the difference between PO₄^3- binding sites to the IC-COF compared to Cu⁺, which leads to the considerable change in the IC-COF absorption spectrum from 400 to 600 nm.

Covalent Organic Frameworks for Chemical and Biological Sensing

Covalent organic frameworks (COFs) are a class of crystalline porous organic polymers with polygonal porosity and highly ordered structures. The most prominent feature of the COFs is their excellent crystallinity and highly ordered modifiable one-dimensional pores. Since the first report of them in 2005, COFs with various structures were successfully synthesized and their applications in a wide range of fields including gas storage, pollution removal, catalysis, and optoelectronics explored. In the meantime, COFs also exhibited good performance in chemical and biological sensing, because their highly ordered modifiable pores allowed the selective adsorption of the analytes, and the interaction between the analytes and the COFs’ skeletons may lead to a detectable change in the optical or electrical properties of the COFs. In this review, we firstly demonstrate the basic principles of COFs-based chemical and biological sensing, then briefly summarize the applications of COFs in sensing some substances of practical value, including some gases, ions, organic compounds, and biomolecules. Finally, we discuss the trends and the challenges of COFs-based chemical and biological sensing.

Facile fabrication of Tb3+-functionalized COF mixed-matrix membrane as a highly sensitive platform for the sequential detection of oxolinic acid and nitrobenzene

A novel Tb³⁺-functionalized covalent organic framework-based polymer mixed-matrix membrane (Tb³⁺@COF MMM) has been successfully fabricated by incorporating the highly stable Tb³⁺@PI-COF as filler into polyvinylidene fluoride (PVDF) solution. Compared with pure COF membrane, MMM exhibits its good flexibility, processability and high detection sensitivity. The obtained Tb³⁺@COF-MMM (M) can be employed as a highly sensitive sensing platform for the sequential detection of oxolinic acid (OA) and nitrobenzene (NB) based on a "off-on-off" process. M has performed its great selectivity, high sensitivity, and low detection limit for detecting OA with "turn-on" mechanism. Moreover, owing to the good chemical stability and anti-interference of M sensor, it is prospective to efficiently detect residues of OA in serum or river water. After the detection of M-15 toward OA, the obtained fluorescent M-15/OA exhibits the rapid quenching, facile manipulation, cycling utility and low detection limits for sensing NB solution and vapor. This work has proposed a typical case of developing flexible Ln³⁺-functionalized COF-based polymer mixed-matrix membrane as a highly sensitive sensing platform for detecting OA and NB, simultaneously revealed the applied potentiality of M for monitoring animal health and environmental pollution.

Porous organic polymers as a platform for sensing applications

Sensing analysis is significantly important for human health and environmental safety, and has gained increasing concern. As a promising material, porous organic polymers (POPs) have drawn widespread attention due to the availability of plentiful building blocks and their tunable structures, porosity and functions. Moreover, the permanent porous nature could provide a micro-environment to interact with guest molecules, rendering POPs attractive for application in the sensing field. In this review, we give a comprehensive overview of POPs as a platform for sensing applications. POP-based sensors are mainly divided into five categories, including fluorescence turn-on sensors, fluorescence turn-off sensors, ratiometric fluorescent sensors, colorimetric sensors and chemiresistive sensors, and their various sensing applications in detecting explosives, metal ions, anions, small molecules, biological molecules, pH changes, enantiomers, latent fingerprints and thermosensation are summarized. The different structure-based POPs and their corresponding synthetic strategies as well as the related sensing mechanisms mainly including energy transfer, donor-acceptor electron transfer, absorption competition quenching and inner filter effect are also involved in the discussion. Finally, the future outlook and perspective are addressed briefly.

A hydrostable CuII coordination network prepared hydrothermally as a "turn-on" fluorescent sensor for S2- and a selective adsorbent for methylene blue

The effective monitoring of water pollution and further purification are pressing yet challenging issues for guaranteeing the health of human beings and the stabilization of ecological systems. For this purpose, the development of efficient sensing and adsorption materials as a result of supramolecular interactions, including coordination and H-bonding etc., have been attracting increasing attention. With the aid of a coordination-driven self-assembly strategy, a new nonporous 2D Cu^II coordination network, [Cu₂L(H₂O)₂]_n (donated as CuCP), based on H₄L, where H₄L = 4-(4-(3,5-di-carboxy-pyridin-4-yl)phenyl)pyridine-2,6-dicarboxylic acid, was afforded hydrothermally. Structural analysis indicated that CuCP featured a wrinkled network similar to the ancient Chinese folding screens and constructed by the fully deprotonated ligand L^4- with the coordination mode of bis(μ₂-η¹:η¹:η²) and penta-coordinated Cu²⁺, which could be further upgraded to a supramolecular 3D framework as a result of the synergism of multiple C-H⋯O hydrogen bonds. The hydrostability of CuCP could be maintained within a wide pH range from 2 to 12 as verified by PXRD determination, endowing it with potential environmental applications. Thanks to the combination of the soft Lewis acidity of Cu²⁺ and its large conjugated structure, CuCP could be used as a turn-on fluorescence sensor for S^2- and exhibited a different fluorescence response when Na₂S, (NH₄)₂S or H₂S were incorporated, even in actual water samples. The sensing mechanisms were disclosed in detail by the combination of experiments and density functional theory (DFT) calculations. Furthermore, CuCP was shown to be a selective and recoverable adsorbent with a maximum adsorption capacity of 379 mg g^-1 in 60 minutes for methylene blue (MB). The adsorption mechanism could be a combination of π⋯π stacking, n⋯π interaction, aggregation effects and Soft and Hard Acid-Base theory (HSAB). The results presented herein open up new perspectives for Cu^II species in environmental applications.

Eu3+-β-diketone functionalized covalent organic framework hybrid material as a sensitive and rapid response fluorescent sensor for glutaraldehyde

A covalent organic framework (named as TpDq) linked by β-ketoamine was prepared by imine condensation reaction with 1,3,5-triformylphloroglucinol (TFP) and 2,6-diaminoanthraquinone (DAAQ) as building blocks. Via employing a functionalized modification strategy, a new lanthanide complex Eu³⁺-β-diketone functionalized covalent organic framework hybrid material, Eu-TTA@TpDq (TTA = 2-thenoyltrifluoroacetone), has been synthesized. After post-synthetic modification (PSM), the shape and structure of the parent framework is well preserved and the modified material shows remarkable luminescence properties. Based on this, we designed it as a fluorescent probe and tried to use it to sense common aldehydes. The results indicate that Eu-TTA@TpDq exhibits a turn-off response toward glutaraldehyde which can distinguish from other common aldehydes. The fluorescent probe has the advantages of reusability, pH stability (4.50-8.52), fast luminescence response (<1 min) and low detection limit. The linear range of this method was 0-100 μM; the detection limit was 4.55 μM; the relative standard deviation was 2.16%. Furthermore, it has broad application prospect in both practical sensing of glutaraldehyde in water environment and simple detection of glutaraldehyde vapor. In addition, we preliminarily discussed the possible sensing mechanism.

The postsynthetic renaissance of luminescent lanthanide ions on crystalline porous organic framework materials

A series of crystalline porous organic framework materials (CPOFs), such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen bonded organic frameworks (HOFs) have received extensive attentions due to...

Luminescent Covalent Organic Frameworks for Biosensing and Bioimaging Applications

Luminescent covalent organic frameworks (LCOFs) have attracted significant attention due to their tunability of structures and photophysical properties at molecular level. LCOFs are built to highly ordered and periodic 2D or 3D framework structures through covalently assembling with various luminophore building blocks. Recently, the advantages of LCOFs including predesigned properties of structure, unique photoluminescence, hypotoxicity and good biocompatibility and tumor penetration, broaden their applications in biorelated fields, such as biosensing, bioimaging, and drug delivery. A specific review that analyses the advances of LCOFs in the field of biosensing and bioimaging is thus urged to emerge. Here the construction of LCOFs is reviewed first. The synthetic chemistry of LCOFs highlights the key role of chemical linkages, which not only concrete the building blocks but also affect the optical properties and even can act as the responsive sites for potential sensing applications. How to brighten LCOFs are clarified through description of structure managements. The ability to utilize the luminescence of LCOFs for applications in biosensing and bioimaging is discussed using state-of-the-art examples of varied practical goals. A prospect finally addresses opportunities and challenges the development of LCOFs facing from chemistry, physics to the applications, according to their current progress.

An imine-linked covalent organic framework for renewable and sensitive determination of antibiotic

Lanthanide-functionalized porous organic materials have been the promising candidates in the chemical and biological sensing. Considering the superior thermal and solvent stability of covalent organic frameworks (COFs), the development of lanthanide ions-functionalized COFs based sensing platform is meaningful, while remains to be a challenge. In this work, a new imine-linked COF which provides suitable coordination sites for Tb³⁺ was constructed via the Schiff base reaction between P-phenylenediamine (Pda) and 2,6-Diformylpyridine (Dfp). Benefiting from its high signal-to-noise, the COF@Tb shows excellent ability to determinate ciprofloxacin (CIP) with a detection limit of 3.01 nM. The measurement can maintain good stability in the presence of potential interference or in actual sample. Being washed with ethanol after each measurement, COF@Tb can be recycled for five times. This work provides a novel alternative strategy for efficient construction of lanthanide-grafted COFs and may promote the development of porous organic materials based chemical sensing.

Covalent organic frameworks as multifunctional materials for chemical detection

Sensitive and selective detection of chemical and biological analytes is critical in various scientific and technological fields. As an emerging class of multifunctional materials, covalent organic frameworks (COFs) with their unique properties of chemical modularity, large surface area, high stability, low density, and tunable pore sizes and functionalities, which together define their programmable properties, show promise in advancing chemical detection. This review demonstrates the recent progress in chemical detection where COFs constitute an integral component of the achieved function. This review highlights how the unique properties of COFs can be harnessed to develop different types of chemical detection systems based on the principles of chromism, luminescence, electrical transduction, chromatography, spectrometry, and others to achieve highly sensitive and selective detection of various analytes, ranging from gases, volatiles, ions, to biomolecules. The key parameters of detection performance for target analytes are summarized, compared, and analyzed from the perspective of the detection mechanism and structure-property-performance correlations of COFs. Conclusions summarize the current accomplishments and analyze the challenges and limitations that exist for chemical detection under different mechanisms. Perspectives on how future directions of research can advance the COF-based chemical detection through innovation in novel COF design and synthesis, progress in device fabrication, and exploration of novel modes of detection are also discussed.

Two chemically robust Cd(II)-frameworks for efficient sensing of levofloxacin, benzaldehyde, and Fe3+ ions

Two luminescent Cd(II)-organic frameworks [Cd₂(L1)(tdc)₂(H₂O)]_n (1) and [Cd(L2)_0.5(tdc)]_n (2) (L1 = 1,5-bis(1-(pyridine-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)pentane, L2 = 1,6-bis(1-(pyridine-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)hexane, and H₂tdc = 2,5-thiophenedicarboxylic acid) were hydrothermally synthesized and characterized. 1 displays a rare binodal (3,4)-connected 2D cem-d network, while 2 exhibits a 3D mog (moganite) framework. The two MOFs are highly thermally durable and water-stable in a wide pH range from 3 to 12. Interestingly, 1 and 2 represent the first reported examples of multi-responsive probes based on MOFs for selectively detecting levofloxacin, benzaldehyde, and Fe³⁺ ions with reusability. The luminescence sensing mechanisms of the two CPs were explored in detail.

Lanthanide upconversion and downshifting luminescence for biomolecules detection

Biomolecules play critical roles in biological activities and are closely related to various disease conditions. The reliable, selective and sensitive detection of biomolecules holds much promise for specific and rapid biosensing. In recent years, luminescent lanthanide probes have been widely used for monitoring the activity of biomolecules owing to their long luminescence lifetimes and line-like emission which allow time-resolved and ratiometric analyses. In this review article, we concentrate on recent advances in the detection of biomolecule activities based on lanthanide luminescent systems, including upconversion luminescent nanoparticles, lanthanide-metal organic frameworks, and lanthanide organic complexes. We also introduce the latest remarkable accomplishments of lanthanide probes in the design principles and sensing mechanisms, as well as the forthcoming challenges and perspectives for practical achievements.

pH-Regulated H4TCPE@Eu/AMP ICP Sensor Array and Its Fingerprinting on Test Papers: Toward Point-of-Use Systematic Analysis of Environmental Antibiotics

In this work, 1,1,2,2-tetra(4-carboxylphenyl)ethylene (H₄TCPE) was selected as the guest and incorporated into a Eu/AMP ICP host to establish a "lab-on-an-AIE@Ln/ICP" sensor array for identifying and sensing environmental antibiotics simultaneously. First, on the basis of a theoretical study of the antenna effect and reductive photoinduced charge transfer between the as-prepared H₄TCPE@Eu/AMP ICPs and antibiotics, respectively, the response from the sensitized time-resolved fluorescence of the host and the unique aggregation-induced emission (AIE) of the guest were selected as the main sensing elements for the sensor array. With the regulation of pH, the diverse fluorescence responses for antibiotics with either structural differences (flumequine, oxytetracycline, and sulfadiazine) or structural similarities (oxytetracycline, tetracycline, and doxycycline) were recorded and processed by principal component analysis; systematic analysis of environmental antibiotics was therefore realized. Encouraged by the superior anti-aggregation-caused quenching effect of H₄TCPE@Eu/AMP ICPs on the test strip, the distinct fluorescence color changes of the "lab-on-an-AIE@Ln/ICP" sensor array were further explored with the aid of smartphones. The fingerprinting pattern of the sensor array on test paper eventually holds great potential for the point-of-use systematic analysis of environmental antibiotics even in complicated real samples.

Covalent Organic Polymers and Frameworks for Fluorescence-Based Sensors

Following the advancements and diversification in synthetic strategies for porous covalent materials in the literature, the materials science community started to investigate the performance of covalent organic polymers (COPs) and covalent organic frameworks (COFs) in applications that require large surface areas for interaction with other molecules, chemical stability, and insolubility. Sensorics is an area where COPs and COFs have demonstrated immense potential and achieved high levels of sensitivity and selectivity on account of their tunable structures. In this review, we focus on those covalent polymeric systems that use fluorescence spectroscopy as a method of detection. After briefly reviewing the physical basis of fluorescence-based sensors, we delve into various kinds of analytes that have been explored with COPs and COFs, namely, heavy metal ions, explosives, biological molecules, amines, pH, volatile organic compounds and solvents, iodine, enantiomers, gases, and anions. Throughout this work, we discuss the mechanisms involved in each sensing application and aim to quantify the potency of the discussed sensors by providing limits of detection and quenching constants when available. This review concludes with a summary of the surveyed literature and raises a few concerns that should be addressed in the future development of COP and COF fluorescence-based sensors.

Fabricating Nanosheets and Ratiometric Detection of 5-Fluorouracil by Covalent Organic Framework Hybrid Material

Covalent organic framework (COF) nanosheets (NSs) are a new member in the family of two-dimensional (2D) nanomaterials that received increasing attention. The ability to prepare COF NSs with rapid acquisition is of great importance to explore their distinctive properties and potential applications. Herein, we elaborate design a new COF hybrid material EB-TFP:Eu(BTA)₄ as a sensing platform. In the process of ratiometric fluorescence detection of 5-fluorouracil (5FU), an anticancer drug, we realize the preparation of COF NSs. Interaction occurs between 5FU and COF hybrid material, where the interlayer π-π stacking of COF was weakened, benefiting the exfoliation of bulk COF to acquire 2D COF NSs. This strategy provides not only a sensitive and selective 5FU sensor but also a significant inspiration for engineering 2D COF NSs.

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

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

A turn-on fluorescence sensing strategy for rapid detection of flumequine in water environments using covalent-coordination functionalized MOFs

With high output and large use of antibiotics in the process of aquaculture, pollution caused by antibiotics in water environments is becoming a thorny problem, and its ecological risk has aroused widespread concern.

Two Co(ii)-based coordination polymers as multi-responsive luminescent sensors for the detection of levofloxacin, benzaldehyde and Fe3+ ions in water media

Two CPs display excellent sensitivity, selectivity and low limits of detection for detection of LEV, BZH and Fe3+ ions.

Conjugated Microporous Polymers Doped with Rare Earth Ions: Synthesis, Characterization and Energy Transfer

In order to study the energy transfer between the conjugated polymer and rare-earth ions, a series of conjugated microporous polymers (CMPs) CMP-COOH@M (M=Eu³⁺ , Tb³⁺ , La³⁺ , and Sm³⁺ ) with different kinds of rare-earth ions was synthesized, in which the conjugated networks can effectively improve the luminescence of rare-earth ions due to the effective energy transfer from the CMP network to the rare-earth ions centers. The absolute quantum yield of CMP-COOH (Φ_FL ) is 29.1 %, while the Φ_FL value of CMP-COOH@Eu, CMP-COOH@Tb, CMP-COOH@La, and CMP-COOH@Sm is 9.4, 8.6, 14.3, and 9.1 %, respectively. This result indicates that the quantum efficiency of CMPs network is 1/2-1/3 of the original one due to the coordination of rare earth ions, that is, rare-earth ions can be recognized as fine modulators to adjust the emission color of CMPs in a controlled manner through controlling the species of rare-earth ions.

Indicator Displacement Assay Inside Dye-Functionalized Covalent Organic Frameworks for Ultrasensitive Monitoring of Sialic Acid, an Ovarian Cancer Biomarker

Identifying biomolecules for disease diagnosis requires simple, accurate, and reliable analytical techniques. Multiple signal transduction pathways have promoted the development of various biological analysis systems. However, most systems are largely limited by a single mechanism or model analysis, which can easily lead to false-positive/negative results. Herein, we report a covalent organic framework (COF) (TpPa-1) functionalized with a dye (fluorescein sodium) and design this hybrid material (TpPa-1@Dye) to fabricate hydrogels for subsequent analysis with the indicator displacement assay (IDA) method. Selecting a suitable metal cation (Cr³⁺) for the preparation of hydrogels can reduce the background fluorescence, improve the detection sensitivity, and increase the corresponding sensing selectivity. The TpPa-1@Dye functions as an indicator in the IDA-in-COF system, and Cr³⁺ is a receptor of the analyte (sialic acid (SA), a biomarker for ovarian cancer diagnosis). Based on the above studies, the integrative logic operations (AND + IMP) are further established, it helps in elucidating the design rules of the IDA-in-COF approach. This work represents the first effort in designing IDA-in-COF luminescent sensors with an On-Off-On mechanism to determine biomarkers and provides a new approach for developing hybrid COF luminescent materials as analysis platforms for human health monitoring.

Quinolone Complexes with Lanthanide Ions: An Insight into their Analytical Applications and Biological Activity

Quinolones comprise a series of synthetic bactericidal agents with a broad spectrum of activity and good bioavailability. An important feature of these molecules is their capacity to bind metal ions in complexes with relevant biological and analytical applications. Interestingly, lanthanide ions possess extremely attractive properties that result from the behavior of the internal 4f electrons, behavior which is not lost upon ionization, nor after coordination. Subsequently, a more detailed discussion about metal complexes of quinolones with lanthanide ions in terms of chemical and biological properties is made. These complexes present a series of characteristics, such as narrow and highly structured emission bands; large gaps between absorption and emission wavelengths (Stokes shifts); and long excited-state lifetimes, which render them suitable for highly sensitive and selective analytical methods of quantitation. Moreover, quinolones have been widely prescribed in both human and animal treatments, which has led to an increase in their impact on the environment, and therefore to a growing interest in the development of new methods for their quantitative determination. Therefore, analytical applications for the quantitative determination of quinolones, lanthanide and miscellaneous ions and nucleic acids, along with other applications, are reviewed here.