Facile synthesis of dual-ligand terbium-organic gels as ratiometric fluorescence probes for efficient mercury detection

Development of a novel ICT-ESIPT-based NIR ratiometric fluorescent probe for specific detection of Hg2+ in the environment and living organisms

As a heavy metal contaminant, mercury ion (Hg2+) has caused great harm to environment and life. Mercury ions will migrate and transform in the environment and eventually accumulate in the human body, thus causing human poisoning. Therefore, it is of great significance to detect Hg2+ in the environment and living bodies. Based on this, we constructed an example of reactive near-infrared ratiometric fluorescent probe NIRPC-Hg based on the ICT-ESIPT mechanism. The probe could not only effectively overcome the effects of environmental changes, thus realizing the accurate detection of Hg2+ in the environment, but also possessed the advantages of large emission wavelength shift (130 nm red shift). In addition, the probe NIRPC-Hg was constructed with the classical recognition structure of Hg2+ and NIR fluorophore, which could detect Hg2+ sensitively with a low detection limit (9.21 nM). The satisfactory experimental results of environmental water samples proved that the probe had high application potential in the environment. At the same time, the probe NIRPC-Hg had the characteristics of smaller photo-toxicity and lower autofluorescence interference in the bioimaging applications, which could conveniently realize the sensitive detection of Hg2+ in cells and zebrafish. Therefore, the construction of probe NIRPC-Hg provided an effective tool to detect Hg2+ in the environment and living organisms.

Luminescent Lanthanide Infinite Coordination Polymers for Ratiometric Sensing Applications

Ratiometric lanthanide coordination polymers (Ln-CPs) are advanced materials that combine the unique optical properties of lanthanide ions (e.g., Eu3+, Tb3+, Ce3+) with the structural flexibility and tunability of coordination polymers. These materials are widely used in biological and chemical sensing, environmental monitoring, and medical diagnostics due to their narrow-band emission, long fluorescence lifetimes, and excellent resistance to photobleaching. This review focuses on the composition, sensing mechanisms, and applications of ratiometric Ln-CPs. The ratiometric fluorescence mechanism relies on two distinct emission bands, which provides a self-calibrating, reliable, and precise method for detection. The relative intensity ratio between these bands varies with the concentration of the target analyte, enabling real-time monitoring and minimizing environmental interference. This ratiometric approach is particularly suitable for detecting trace analytes and for use in complex environments where factors like background noise, temperature fluctuations, and light intensity variations may affect the results. Finally, we outline future research directions for improving the design and synthesis of ratiometric Ln-CPs, such as incorporating long-lifetime reference luminescent molecules, exploring near-infrared emission systems, and developing up-conversion or two-photon luminescent materials. Progress in these areas could significantly broaden the scope of ratiometric Ln-CP applications, especially in biosensing, environmental monitoring, and other advanced fields.

Design of aggregation-induced emission materials for biosensing of molecules and cells

In recent years, aggregation-induced emission (AIE) materials have gained significant attention and have been developed for various applications in different fields including biomedical research, chemical analysis, optoelectronic devices, materials science, and nanotechnology. AIE is a unique luminescence phenomenon, and AIEgens are fluorescent moieties with relatively twisted structures that can overcome the aggregation-caused quenching (ACQ) effect. Additionally, AIEgens offer advantages such as non-washing properties, deep tissue penetration, minimal damage to biological structures, high signal-to-noise ratio, and excellent photostability. Fluorescent probes with AIE characteristics exhibit high sensitivity, short response time, simple operation, real-time detection capability, high selectivity, and excellent biocompatibility. As a result, they have been widely applied in cellular imaging, luminescent sensing, detection of physiological abnormalities in the human body, as well as early diagnosis and treatment of diseases. This review provides a comprehensive summary and discussion of the progress over the past four years regarding the detection of metal ions, small chemical molecules, biomacromolecules, microbes, and cells based on AIE materials, along with discussing their potential applications and future development prospects.

Fluorescent Sensors Based on Lanthanide-Based Metal-Organic Frameworks via Devices and pH Response

In light of the escalating industrial and environmental pollution, there is a pressing need for the development of novel materials capable of swiftly detecting pollutants. Here, we report the synthesis of five lanthanide metal-organic frameworks sharing a common structure, prepared via a hydrothermal method and denoted as [Ln2(H2DHBDC)2(phen)(H2O)6]n (where CUST-888 corresponds to Tb, CUST-889 corresponds to Eu, CUST-890 corresponds to Gd, CUST-891 corresponds to Dy, and CUST-892 corresponds to Nd). Notably, CUST-888 and CUST-889 exhibit discernible visual alterations in response to acidic and alkaline conditions. To assess their practical utility, luminescent test strips and light-emitting diode lights based on CUST-888 and CUST-889 were devised, enabling the visual detection of luminescence color changes induced by Hg2+, Cr2O72-, tetracycline, and 2,4,6-trinitrophenol. Furthermore, highlighters derived from CUST-888 and CUST-889 were designed, showcasing robust stability, adjustable color, and substantial potential for application in the realm of anticounterfeiting.

Bimetallic Ag/Fe-MOG derived flake-like Ag2O/Fe2O3 p-n heterojunction for efficient photodegradation organic pollutants within a wide pH range

In this paper, we reported a facile and clean strategy to prepare the flake-like Ag2O/Fe2O3 bimetallic p-n heterojunction composites for photodegradation organic pollutants. The surface morphology, crystal structure, chemical composition and optical properties of Ag2O/Fe2O3 were characterized by SEM, high-resolution TEM images with EDX spectra, XRD, XPS, FT-IR and UV-vis DRS spectra respectively. The formation of Ag2O/Fe2O3 p-n heterojunction facilitated the interfacial transfer of electrons as well as the separation of charge carries. Hence, the as-synthesized Ag2O/Fe2O3-3 composites exhibited ultra-high photocatalytic activity. Under the experimental conditions of catalyst dosage of 0.4 mg mL-1 and irradiation time of 60 min, the degradation conversion rate of rhodamine B reached 96.1 %, which was 5.0 and 2.8 times of pure phase Ag2O and Fe2O3, respectively. Meanwhile, the degradation performance of Ag2O/Fe2O3-3 was not limited by pH, and it can achieve high degradation efficiency under 3-11. In addition, Ag2O/Fe2O3-3 also showed superb degradation ability for other common anionic dyes, cationic dyes and antibiotics. XPS and FT-IR spectra showed that Ag2O/Fe2O3-3 retained a carbon skeleton that facilitated electron transport and light absorption conversion. And the analyses of quenching experiment and EPR demonstrated •O2-, •OH and h+ were crucial reactive oxidant species contributing to the rapid organic pollutant degradation. This work provides new insights into obtaining p-n photocatalysts heterojunction with excellent catalytic activity for removing organic pollutants from wastewater.

An Encyclopedic Compendium on Chemosensing Supramolecular Metal-Organic Gels

Chemosensing, an interdisciplinary scientific domain, plays a pivotal role ranging from environmental monitoring to healthcare diagnostics and (inter)national security. Metal-organic gels (MOGs) are recognized for their stability, selectivity, and responsiveness, making them valuable for chemosensing applications. Researchers have explored the development of MOGs based on different metal ions and ligands, allowing for tailored properties and sensitivities, and have even demonstrated their applications as portable sensors such as paper-based test strips for practical use. Herein, several studies related to MOGs development and their applications in the chemosensing field via UV-visible or luminance along with electrochemical approach are presented. These papers explored MOGs as versatile materials with their use in sensing bio or environmental analytes. This review provides a foundational understanding of key concepts, methodologies, and recent advancements in this field, fostering the scientific community.

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.

Isolation of Sensing Units and Adsorption Groups Based on MOF-on-MOF Hierarchical Structure for Both Highly Sensitive Detection and Removal of Hg2

Bifunctional materials have attracted ongoing interest in the field of detection and removal of contaminants because of their integration of two functions, but they exhibit commonly exceptional performance in only one of these two aspects. The interaction between the two functional units of the bifunctional materials may compromise their sensing and adsorption abilities. Guided by the concept of domain building blocks (DBBs), a hierarchical metal-organic framework (MOF)-on-MOF hybrid was designed by growing gold nanoclusters (AuNCs)-embedded zeolitic imidazolate framework 8 (AuNCs/ZIF-8) on the surface of Zr-MOF (UiO-66-NH2) for the simultaneous detection and removal of Hg2+. In the hybrid, the amino groups (-NH2) and AuNCs─which were the adsorption groups and sensing units, respectively, were isolated from each other. Specifically, the adsorption groups (-NH2) were assembled in the inner UiO-66-NH2 layer, while the sensing units (AuNCs) were confined in the outer ZIF-8 layer. This hierarchical structure not only spatially hindered the electron transfer between these two units but also triggered the aggregation-induced emission of AuNCs because of the confinement of ZIF-8 on the AuNCs, thus changing the fluorescence of AuNCs from quenching to enhancement. The newly prepared UiO-66-NH2@AuNCs/ZIF-8 hybrid, as expected, showed an ultralow detection limit (0.42 ppb) and a high adsorption capacity (129.9 mg·g-1) for Hg2+. Overall, this work provides a feasible approach to improve the integrated performance of MOF-based composites based on DBBs.

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-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.

A novel luminol-coordinated silver(I) organic gel with self-enhanced chemiluminescence applied for uric acid detection

A novel silver(I)-based metal-organic gel (AgMOG) consisting of luminol as the ligand was synthesized by a facile strategy, which was found to exhibit self-enhancing chemiluminescence (CL) property. Based on this, a new AgMOG-K₂S₂O₈ CL system without additional catalyst was established. According to the results of CL spectra, electron spin resonance (ESR) spectra as well as the influence of radical scavengers to AgMOG-K₂S₂O₈ system, the possible CL mechanism of this system was discussed. In this CL system, AgMOG exhibited the dual properties of catalysis and luminescence. On the one hand, AgMOG can catalyze K₂S₂O₈ to produce SO₄^•-. The generated SO₄^•- can be converted to hydroxyl radical (OH^•) under alkaline condition, and further converted to other radical oxygen species (ROS, such as ¹O₂ and O₂^•-). Furthermore, the reaction between the K₂S₂O₈ and H₂O can form H₂O₂, which also can be catalyzed by AgMOG to produce ROS. On the other hand, the AgMOG can be oxidized by ROS to emit strong CL signal. Then, based on the quenching effect of uric acid (UA) to this CL system, a method for UA detection was established with a good linearity over the range from 0.08 to 10 µmol·L^-1. In this work, a new CL luminant with catalytic property was synthesized by a simple method, and a self-enhancing AgMOG-K₂S₂O₈ CL system was developed for the first time, providing a novel direction for the application of MOG in the CL field.

Colorimetric method transforms into highly sensitive homogeneous voltammetric sensing strategy for mercury ion based on mercury-stimulated Ti3C2Tx MXene nanoribbons@gold nanozyme activity

Nanozymes were emerged as the next generation of enzyme-mimics which exhibit great applications in various fields, but there is rarely report in the electrochemical detection of heavy metal ions. In this work, Ti₃C₂T_x MXene nanoribbons@gold (Ti₃C₂T_x MNR@Au) nanohybrid was prepared firstly via a simple self-reduction process and its nanozyme activity was studied. The results showed the peroxidase-like activity of bare Ti₃C₂T_x MNR@Au is extremely weak, while in the presence of Hg²⁺, the related nanozyme activity is stimulated and improved remarkably, which can easily catalyze oxidation of several colorless substrates (e.g., o-phenylenediamine) to form colored products. Interestingly, the product of o-phenylenediamine exhibits a strong reduction current which is considerably sensitive to the Hg²⁺ concentration. Based on this phenomenon, an innovative and highly sensitive homogeneous voltammetric (HVC) sensing strategy was then proposed to detect Hg²⁺ via transforming the colorimetric method into electrochemistry since it can exhibit several unique advantages (e.g., rapid responsiveness, high sensitivity and quantificational). Compared to the conventional electrochemical sensing methods for Hg²⁺, the designed HVC strategy can avoid the modification processes of electrode coupled with enhanced sensing performances. Therefore, we expect the as-proposed nanozyme-based HVC sensing strategy provides a new development direction for detecting Hg²⁺ and other heavy metals.

Highly fluorescent hydroxyl groups functionalized graphitic carbon nitride for ultrasensitive and selective determination of mercury ions in water and fish samples

Heavy metal ion pollution is always a serious problem worldwide. Therefore, monitoring heavy metal ions in environmental water is a crucial and difficult step to ensure the safety of people and the environment. A mercury ion (Hg2+) fluorescence probe with excellent sensitivity and selectivity is described here. The functionalized graphitic carbon nitride nanosheets (T/G-C3N4) fluorescence probe was fabricated using melamine as a precursor by the pyrolysis technique, followed by a rapid KOH heat treatment method for 2 min. The chemical structure and morphology of the T/G-C3N4 probe were characterized using multiple analytical techniques including UV–Vis, SEM, XPS, XRD, and fluorometer spectroscopy. Geometry optimization of T/G-C3N4 as a modified probe was performed to assess its stability and interaction ability with Hg(II) via using the density function approach. The T/G-C3N4 probe showed a linear response based on quenching over the range 0–1.25 × 103 nM Hg(II); the detection limit was 27 nM. The remarkable sensitivity of T/G-C3N4 towards the Hg2+ ions was explained by the intense coordination and fast chelation kinetics of Hg2+ with the NH2, CN, C=N, and OH groups of T/G-C3N4 nanoprobe. The T/G-C3N4 probe demonstrates exceptional selectivity for Hg2+ ions among other metal ions including (Na+, Ag+, Mg2+, Fe2+, Fe3+, Co2+, Ni2+, Cd2+, K+, Ca2+, Cu2+, Pb2+, Mn2+ and Hg2+) and over a broad pH range (6–10), together with remarkable long-term fluorescence stability in water (> 30 days) and minimal toxicity. T/G-C3N4 was used to detect and quantify Hg2+ ions in tuna and mackerel fish and the results compared to ICP-AES. The results obtained offer a new simple and green technique for the design of multifunctional fluorescent probe appropriate for environmental applications.

Graphical Abstract

Ratio fluorescence sensor based on CD/Cu-MOFs for detection of Hg2

Trace detection of toxic heavy metals is a very important and difficult problem in several areas: convenience, sensitivity, and reliability. Herein, we develop an innovative fluorescence resonance energy transfer (FRET)-based ratio fluorescence sensor for the detection of heavy metal mercury ion (H g ²⁺). The sensing platform is composed of coumarin derivatives (CDs) and a copper metal-organic framework (Cu-MOF) named CD/Cu-MOF. The constructed CD/Cu-MOFs ratio fluorescence sensor exhibits dual emission peaks at 430 and 505 nm under the single excitation wavelength of 330 nm. With the addition of H g ²⁺, the fluorescence intensity of the system at 430 nm gradually increased, and the fluorescence intensity at 505 nm remained stable, resulting in a change in the fluorescence ratio. There is a good logarithmic relationship between the H g ²⁺ concentration in the range from 2×10^-8 to 0.001 nM and the ratio of the fluorescence emission intensity of the system (F ₄₃₀/F ₅₀₅) (R ²=0.9901), and its calculated detection limit is 3.76×10^-9 n M. In addition, the CD/Cu-MOFs ratio fluorescence sensor has achieved a good recovery rate of standard addition in the actual food sample recovery experiment, which provides an effective method for the detection of H g ²⁺ in food samples.

The synthesis of carbon dots by folic acid and utilized as sustainable probe and paper sensor for Hg2+ sensing and cellular imaging

In this work, the blue emission carbon dots (FA-CDs) are synthesized by one-pot solvothermal method by using folic acid as precursor. The FA-CDs emitted bright emission at 445 nm when excited at 360 nm with the QY of 31.2 %. The FA-CDs exhibit sensitive quenching response to Hg²⁺ with variable concentrations systematically, which determined FA-CDs can be employed as fluorescent probe, with a reliable linear relationship between fluorescence intensity and Hg²⁺ concentration, and a limit of detection (LOD) of 1.29 nM. Notably, the quenched FA-CDs can be recovered by using EDTA saturated solution with the emission comparable to initial in succession. The FA-CDs based paper sensor can be explored with similar detection performance, and it can also be restored by EDTA saturated solution. Both the restored CDs and paper sensor can be reused in the next turn for detecting Hg²⁺, which allowed the FA-CDs and their paper sensor can be serviced as sustainable probe for Hg²⁺ detection. The visual LOD of paper sensor can be determined at 0.1 μM, notably, the paper sensor can be reused at least 3 times with good performance, which is beneficial to environmental protection and saving resources. Possess excellent water solubility and non-toxic properties, the cellular imaging of FA-CDs was evaluated with excellent quality fluorescent image results. The FA-CDs provide a promising convenient fluorescent probe for multi-application in detection and imaging.